## Posts Tagged ‘A-level’

### Compression Of Cast Iron Experiment

Wednesday, July 2nd, 2008

## Introduction

This is an 'A' Level Design & Technology project. At the time when this was done this project was worth 15% of the marks. It helped me get an A grade in 1998. The whole project is reproduced here for your reference. The only parts of the project not shown are the photographs and the graph.

 This is a real A-Level project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned.

## Aims

This is an experiment to see if cast iron shears at an angle of 45° and also to check if the cast iron samples breaks at pressure at which books say it should break.

## Planning Strategy

I plan to alter the compressive apparatus first to measure the force at which the cast iron samples sheared. I will then work out what size of cast iron sample the apparatus can take before making the individual samples. If I make the samples first then I could end up with 10 samples which were unsuitable for the apparatus.

The book 'S.G. Iron Properties And Applications' puts the average pressure at which cast iron shears at 98kg/mm². The maximum load that the compressive rig will produce is 350kg/mm². The maximum area of the cast iron samples can therefore be worked out.

Maximum area of cast iron samples = Maximum Compressive load ÷ Average Pressure at which iron breaks.

350kg ÷ 98kg/mm² = 3.57mm²

The maximum diameter of the samples is then worked out.

The maximum diameter that each cast iron piece can be is 2.13mm. I shall therefore make all the samples with a diameter of 2mm.

Once I have made and tested the apparatus I will make the samples. I will make them all out of the same long piece of cast iron so that the samples would be uniform. I will make them one after another so that they can be as similar as possible. If I make a few first and some more a few weeks later then small changes in the lathe settings could cause irregularities in the samples which would lead to an unfair test.

In order to make sure that the samples are all tested in the same environmental conditions I plan to do all the compressive tests in the same one hour period if possible.

## Cast Iron

Iron is a widely used metal in industry. It is fairly soft but is often alloyed to form Steel which is very hard. Iron is made in a blast furnace by the reduction of iron ore by carbon monoxide. The carbon monoxide gas comes from the burning of coke.

Iron Oxide (Iron Ore) + Carbon Monoxide ----> Iron + Carbon Dioxide

Limestone is added to remove some of the iron's impurities and then it is ready to be cast into `pigs` so it can be used in the iron industry. This pig iron is melted again and the correct amounts of other elements are added to make it into cast iron.

Cast Iron contains the following:

• Carbon 3.0-4.0%
• Silicon 1.0-3.0%
• Manganese 0.5-1.0%
• Sulphur under 0.1%
• Phosphorus under 1.0%

It is often used to make frames, engine blocks and surface plates.

## What I will be Doing

Many identical cylinders will be compressed using a compression apparatus. The compressive force is provided by a car jack. By looking at the gauge I will be able to measure the compressive pressure at which each of the samples shears. The average of these results will be taken to find the iron's compressive strength. By looking at all the samples I will be able to see if cast iron does shear at an angle of 45° when enough compressive force is added to it.

According to the book S.G. Iron propities and applications the compressive strength of iron is 94-102kg/mm².

## Safety

When the tests are carried out the compressive rig will have a shield around it to prevent any of the iron from being propelled across the room when it breaks. As a lot of force is going to be applied to the samples they could easily explode into many fragments which could be very dangerous. I will also be wearing safety glasses to protect my eyes and ensuring that there is no one near the apparatus when the tests are being carried out.

## To make the iron cylinders

 I took a square piece of cast iron and cut it into a long rectangle with ends of 10mm by 10mm.
 I put this rectangular section into a lathe and made it into a cylinder with a diameter of 9mm.

From this I cut 10 equal length pieces each 15mm long. The top 5mm of each cylinder was cut using the lathe to have a diameter of 2mm as below. The measurements of the diameter were taken using a micrometer screw gauge.

Above you can see the dimensions of each cast iron piece. To ensure accuracy all the blocks had to be identical or as near to identical as it is possible to get.

The larger 9mm diameter base is left to give the cylinder stability when it is in the compressor. Each of the samples is put in the compressive rig and an increasing load is applied to each piece until it breaks. The diagram below shows the compressive rig.

 As the car jack is pumped up it applies a pressure to the iron. The Picture on the left shows the compressor before the pressure is applied, the picture to the right is what is looks like afterwards.

The pressure can be read off from the gauge which is connected to the car jack.

In order to measure the pressure at which the cast iron shears it was necessary to add a slave needle to the gauge which will tell us the pressure reached before the Iron snapped. In order for the needle to be put in I had to completely dismantle the gauge which is shown above and cut out a small cylinder of brass to lengthen the gauge shaft. A hole was drilled into the end of the brass cylinder so that it could be press fitted over the original shaft. The main needle was silver soldered onto the brass shaft.

 A slave needle was cut out of steel and was put onto the extended shaft so that it could move freely. A short length of brass wire was cut and silver soldered onto the slave needle 40mm from the end as shown to the left so that as the main needle moved it would push the slave needle with it. The needle was slightly curved downwards so that it would 'stick' at the point where it was pushed to by the main needle.

## Results

I carried out the above experiment and I obtained the following results.

 Test Number Pressure at which Cast Iron Sheared (Kg) Pressure at which Cast Iron Sheared (Kg/mm²) 1 310 98.68 2 320 101.86 3 315 100.27 4 300 95.5 5 315 100.27 6 295 93.9 7 300 95.5 8 310 98.68 9 300 95.5 10 305 97.08 Average 97.72

These results are to the nearest 5kg due to the scale on the gauge. The pressure needed to break the sample per mm² is worked out by.

Pressure/mm² = Pressure at which iron sheared / (Π x r²)

These results were then plotted in a scatter graph showing the pressure at which each sample broke.

## Conclusion

These results are very close to what would be expected S.G Iron Properties And Applications said that the compressive strength of iron is 94-102kg/mm² and all but one of my results are in-between the boundaries. The average is 97.72kg/mm² which lies roughly between the two values. By looking at the samples 8 out of the 10 samples showed a shear of 45°. Two of the samples had just been broken up totally and showed no angle but this was probably due to a weakness in the metal or the sample being incorrectly placed in the compressor. The 45° angle can be seen in the photograph below. The angle on the picture appears to be slightly different to 45° but this is because the sample was not quite at 90° to the camera. The angle on the sample is 45°.

The reason that iron break at an angle of 45° is due to the structure of the atoms in the material. They are arranged in a way so that if enough pressure is applied the atoms will slide past each other at 45°.

## Limitations

1. The tests were not all carried out on the same day so the temperature for the tests could have varied. A change in temperature can make the metal expand or contract and so lead to irregularities in the sizes of the samples.
2. The lathe does not cut the metal smoothly, it leaves many small grooves and scratches in the metal which can cause it to be weak in places and so alter the load at which the sample would break. This could also account for the reason that two of the sample totally broke up when put under pressure instead of splitting at a 45° angle.
3. The samples may have had sand or gas inclusions which may make them irregular and so reduce the accuracy of the tests.
4. The scale on the gauge is only to the nearest 5kg so readings more accurate than to the nearest 5kg can not be taken.

## Improvements / Extension Work

1. Instead of testing each sample individually a special rack could have been built to compress all the samples at once. However the pressure needed to compress 10 samples may have been to great to achieve. The shattered samples may also intermix unless they were somehow kept separate.
2. The compressive rig could have been improved if a small pit was drilled into it the same diameter as the base of the iron samples as this would ensure that the samples are standing straight in the rack and do not fall over. This would ensure that the anvil comes straight down on the sample each time to ensure that all the tests are consistent.
3. Different sizes of cast iron could have been used as by using samples with larger diameters it would be easier to see the 45° angle.
4. Test could be done to see if the way that that the pressure applied to the iron affects it's compressive strength. In this experiment the pressure was applied gradually but if the pressure was applied very suddenly the results could be quite different. In order to do this a weight could be dropped from a fixed height which would apply a very sudden pressure to the samples.

## Sources

1. SG Iron Properties & Applications
2. Materials For The Engineering Technician - R.A. Higgins

### Extrusion of plastic investigation

Tuesday, July 1st, 2008

## Introduction

This is a 'A' Level Design & Technology project. At the time when this was done this project was worth 15% of the marks. It helped me get an A grade in 1998. The whole project is reproduced here for your reference. In is an investigation into the method of making extruded plastic floor skirtings. The name of the company has been changed to CompanyX. The name of the product range has been changed to the Purple range. All the names of the people in the company trees have been errased.

 This is a real A-Level project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned.

## Contents

I went to CompanyX Extrusions to follow the design process of their recently launched Purple range of floor skirting. I went there to examine what had happened from the original idea to the designing, producing, selling and marketing of the finished product.

## Planning Strategy

I will be going to CompanyX for one afternoon a week for 10 weeks. I plan to spend three afternoons at the extrusion site, two afternoons in the Sales office, two at the marketing department and two afternoons at the storage and packaging department.

By splitting my time up so that I spend different afternoons in the different departments I will be able to see how the company operates as a whole and so get an idea of how the various parts of CompanyX interconnect. I will prepare questions in advance so that I can find out as much information as I need on every visit. I will talk to several people on each visit, hopefully the manager in charge of the section and one of the ordinary employees in the section. This way I will be able to get information on how the area is operated by the management and also how the ordinary employees work in the section. From this I should be able to obtain a balanced view of how CompanyX operates. I will take notes whilst I am at CompanyX and write them up when I got home to ensure that the information is fresh in my memory. From these notes I will be able to prepare a report on the extrusion of the Purple range of floor skirtings.

## The Company

CompanyX makes extruded plastic parts. Most of their products are used in the building industry for stairs and for carpets. The parts are made at K---- Street and then sent to their C---- Street factory where they are packaged and distributed.

CompanyX operates on a three shift rotating pattern from Monday's to Friday. The shifts are from 6.00am - 2.00pm, 2.00pm - 10.00pm and 10.00pm to 6.00am.

CompanyX has it's own tool room, quality control laboratory, die cleaning store and a material recycling facility.

One of their newest products is the Purple range of floor skirting. It consists of a plastic skirting board with the pattern already printed onto it. This makes it easier for the architects and decorators to match the skirting to the decorations. It is also easier because normally a pattern has to be separately applied to the skirting but there is no need for this with the Purple range.

CompanyX do not stock large quantities of each of their products. If a certain product is ordered they just produce a new batch. They are able to do this as each product has a quick turnaround. The product can be quickly made then a few hours later that extruder can be making a totally different product. They have 12 extruders so they can make many different products simultaneously.

Like all of CompanyX's other products the Purple range is made using extrusion. This is where soft plastic is forced through a die to make the right shape

## The Sales Team

The sales team is responsible for collecting the orders from customers and passing them on to the manufacturing department. It provides a service from Monday to Friday. The area managers from the sales team will install their products for customers and also give advice on which product is most suitable for them.

## Marketing Department

The marketing department provides marketing for all the CompanyX products. It is responsible for producing product literature, samples, market research, corporate hospitality and exhibitions to promote it's products.

CompanyX have their own design and printing facilities for any promotional literature.

## Quality Control Department

Some of the bigger CompanyX customers have included the Ministry of Defence and the National Health Service, they have insisted on checking their suppliers such as CompanyX to make sure that the goods being supplied are of good quality. CompanyX therefore had to ensure that they had good quality control procedures in place to satisfy their customers. CompanyX Extrusions have kept their quality standards high and because of this they have obtained the BS 5750 certificate. This certificate confirms to their customers that they have good quality control procedures in place.

## The Beginning

In 1995 CompanyX noticed that a German company was importing decorative floor skirtings into the country. CompanyX decided to make their own version of it. This was to be different to all their other products as this was the first decorative skirting that they had ever tried to design. They contracted an outside company to do some research into floor skirtings. From this research they had a rough idea of the sort of product they wanted to make. It had to be attractive and functional and be easy to fix onto the wall. There was no formal design process for this product. The design team just made freehand sketches until they came up with a shape that was pleasing to the eye.

CompanyX then had to work out how to get a decorative effect onto the skirting. They got an outside company to try laminating the plastics with the patterns but this proved too costly and it only worked with hard plastics.

They found an English company which had had a lot of success with laminating plastics for small children's toys such as 'Pogs'. CompanyX consulted them and found out that they put their patterns on the toys using heat transferred plastic foils. An American company designed a variety of patterns for them and sold them the finished foils in 170m long rolls.

## The Manufacturing Process

The actual plastic used for the Purple range is PVCP. They buy it in bags of small pellets. These are only about 5mm long to ensure that they can be melted down easily. The pellets are also produced by extrusion. Soft hot plastic is forced through a die containing many circular holes by an extruder. Pellets are cut by a rotating blade which is on the end of the die. There are around 300 colours of plastic pellets available that are made in this way.

When CompanyX get an order in for an existing product they can very quickly set up all the machines ready to make that product. The most important part in the extruders is the compressive screws which push the plastic through the dies.

## Extrusion Of The Purple Range

To force the plastic through the die they use compressive screws which rotate slowly at about 30 RPM. As they rotate the plastic moves along them. These screws heat the plastic to make it soft. As the plastic moves along the screw it gets compressed due to the thread of the screws getting closer together. The diameter of the screws also decreases so by the time the plastic has reached the end it is very compressed and flows easily through the die.

Each screw is around 1.5m long and is made up of a steel core. The screws used for soft plastics are single screws which have a much shallower thread than those used for harder plastics as they do not need to apply as much force to the softer plastics. The screws for hard plastics are twin screws which have two screws next to each other which rotate in opposite directions.

Twin Screw

The compressive screw is housed in a barrel and it is an exact fit to ensure that plastic cannot work it's way back along the barrel. Four metal Micre Bands are placed around the barrel. These bands heat the compressive tube up to around 160 -170 ºC which is sufficient to make the plastic soft and workable.

Soft Plastic Screw

The screws consist of four separate zones.

At the thickest end is the Feed-Zone. This is where the plastic pellets drop onto the screws. These pellets are fed into the machine by a hopper which lets the PVCP pellets freely fall onto the screw by gravity. CompanyX also do extrusions with harder plastics, in these machines the pellets are fed onto the screws by a pump.

The hoppers on the extruders are kept continuously filled by a simple suction pump which sucks the pellets from a feeding funnel at the bottom of the machine into the hopper at the top of the machine. This makes it much easier to keep the extruders full of pellets as if they did not have these pumps in place someone would have to climb up about 2 metres of stairs to fill the hopper.

Hopper

After the Feed-Zone the thread of the screw starts to get closer together and so compresses the plastic. This is know as the Compressive Zone. In this zone the amount that the plastic is compressed depends on the type of plastic. Soft plastics such as used in the Purple range are only slightly compressed as they are soft enough to be easily extruded without the extra pressure. The harder plastics are put under a lot of pressure to get the soft enough to go through the die.

The third zone is the Decompressive Zone. This is only present in the screws that are used to extrude hard plastics. In the extrusion process of hard plastics bubbles may build up in the plastic as it is pushed along the screw. If these are not got rid of then this could ruin a whole batch of products. The Decompressive Zone is the area where the bubbles are got rid of. Here the thread of the screw gets wider and so releases the pressure that the plastic was under. The barrel in this area has many small holes in it's surface. The area around this part of the barrel is also under a vacuum which sucks all the air out of the barrel. The plastic is not sucked out as it is not molten enough to get out at this point. It is also no longer under pressure so it will not be forced out of the holes.

In soft plastics, air bubbles are simple able to leave the barrel by flowing up the screw. They therefore do not need a Decompressive zone. Instead at several points along the screw they have jagged edges known as mixers which simply mix the plastic as it passes through them. These mixers make sure that the plastic is of an even composition and make sure that any air is not trapped in the plastic.

The final area of the screw is the Metering Zone. Here the plastic is once again put under pressure as the diameter of the screw narrows to it's smallest point. The plastic is compressed heavily so that it will be able to flow out of the die easily.

## The Die

The dies are custom made by CompanyX for whichever product they are making at the time. They are around 300mm long and have a diameter of about 200mm. In order to function properly they must be at a temperature of about 140 - 150 ºC. If they were fitted cold onto the extruders then it would take about two hours to heat up to the correct temperature which is not acceptable as it is costing CompanyX around £35 per hour to keep their extruders functioning. A few hours before the dies are needed they are taken out of the die room and put in a pre heater which heats them up. When they are needed they are wheeled onto the factory floor and fitted onto the extruder. It then only takes about 25 -30 minutes for them to settle at the right temperature. This period of time is known as the settling down period. This pre heating technique allows CompanyX to get the maximum possible use out of each of their extruders.

Once the plastic has passed through the compressive screw it is soft and is at the right temperature to be extruded. However it is also spinning and so it's motion needs to be altered from spinning round to go straight onto the die. This is achieved by having a breaker plate in-between the screw and the die. This is a metal cylinder around 50mm long which has many small holes in it. When the plastic reaches the cylinder it is forced to go through the holes and so passes in a straight line towards the die.

A range of dies that CompanyX can use

The soft plastic goes through the die and is now in the correct shape. It is still molten so it has to be kept in the right shape and cooled down quickly. The plastic passes through a series of toast racks if it is a soft plastic or calibrators if it is a hard plastic. These toast racks or calibrators are exactly the same shape as the original die and so allow the plastic to keep it's shape while it is cooled down.

The hot plastic is drenched in cold water as it passes through these toast racks and the area between each toast rack is under water so the plastic can cool down as quickly as possible.

The calibrators of the hard plastics are almost identical to the toast racks of the hard plastics except that as the plastic passes through the calibrator it is pulled through a vacuum. The calibrators have many small tubes in them that suck the plastic onto them. This helps to make the surface of the plastic as smooth as possible. If there was a tiny scratch in the die then this mark could be passed onto all the plastic that passes through it but the Calibrators help to get rid of these scratches by sucking the plastic into the shape that it is meant to be.

The extruder plastic passing through the toast racks
and being sprayed with water to cool it down

As the plastic passes out of the row of toast racks it is blasted with a jet of pressurised air which blows any water droplets off it. This is very important as any water on the plastic could cause bubbles to form under the decorative foil when it is applied which would result in that batch of products being scrapped.

As the plastic is pushed out of the extruder by the screws it is also pulled off by a separately controlled Haul-Off which consists of two belts which pull the plastic between it. The two machines are separately controlled so this can create problems for the plastic. If it is pulled out much faster than it is being pushed out by the extruder then the plastic will stretch and end up being much thinner than it is supposed to be. If it is pushed out faster than the haul off is pulling it out then it could end up too thick or it could even end up buckling.

A Haul Off

This can be put to use if the size of the plastic needs adjusting slightly. If they find that the plastic coming out of the machine is too thin they simply slow down the haul off slightly and if the plastic is coming off slightly too thick then they speed up the haul off.

## Decorative Foils

As the plastic skirting passes out of the haul off is goes through the foil heat transfer machine. The plastic passes through a cloth to make sure that it is totally dry. The foil which is slightly too big is rolled onto the plastic and heat is applied to the area where it needs to stick to the skirting. The foil is applied under tension to ensure that it does not buckle or have any bubbles in it. The excess foil is pulled away by another roller leaving just the skirting with the decorative pattern on it.

Foil Transfer Machine

Once through the foil transfer machine, a protective plastic film is rolled onto the plastic. The soft plastics are then rolled into rolls by a mechanical roller. Hard plastics cannot be rolled and are therefore cut into lengths of about 2-3 metres by the haul off before being tipped into boxes.

## Cutting The Finished Product

The haul off has a counting mechanism built into it so that once a set amount of plastic has passed through, it guillotines the plastic if it is a soft plastic. The haul offs which are used with hard plastics use a saw to cut the plastic to the correct length.

Guillotine

## Fitting The Purple Range

When used in the UK the finished product is designed to be glued onto the walls by using a solvent-based glue. The product is not flat and has a gap but CompanyX recommend applying a lot of glue so that the gap is totally filled. The method of fixing the skirting to the walls is slightly different in the rest of Europe where due to EEC regulations they cannot use solvent based glues. Here a strong form of double sided sticky tape must be used.

## Quality Control

Samples are regularly taken of the products as they come off the extruders. Each product has a specification sheet which details the acceptable error limit. If any of the plastic does not conform to the standards then that batch is scrapped.

The sizes of the plastic are checked with an electronic micrometer. The samples are then taken to a testing room. Here they are cooled to freezing point and a 1kg weight is dropped on the sample from a height of 1m to test the strength of the plastic.

A hand held scanner known as a spectrometer checks the colour of the plastic to make sure it is exactly right. CompanyX buy in their plastic in the colour they want them so if something is wrong with the colour they have to go to the plastic manufactures to find out what is wrong with the colour.

CompanyX make sure that the foil stays on the plastic by using the selotape test. For this a fixed length of ordinary selotape is stuck onto the sample and the ripped off. To pass this test none of the foil should come off with the selotape.

An abrasive test is done to test the strength of the sample. An abrasive wheel is lowered onto the sample with a fixed amount of pressure and is allowed to rotate 200 times. Only a certain amount of plastic is allowed to come off in this test.

To see how the sample ages CompanyX place it in an oven at 60°C. One day in this oven ages the sample by 16 days so they were able to make sure that it could survive for a year easily in less than a month. The Purple range is designed to last five years so that after five years they hope that the companies will have to order a new batch of the product to replace the old skirting.

If a sample fails any of these tests then the whole batch is scrapped. The soft plastics can be sold back to the plastic manufacturers who melt them down and make new plastic pellets out of them but hard plastic have to be sold onto a scrap merchant for a loss.

## On Site Testing

Once the product had passed all these quality control targets it was decided to give it a real life test. In April 1996 CompanyX installed the product at F---- School in M---- and in D---- Hospital. CompanyX installed the skirting in areas such as the canteen in F---- School where they knew it would get a lot of wear. After six months they went back to these places to check the progress of the skirtings. CompanyX found that the product had worn well so they decided to launch it in November 1996.

## Marketing

The marketing department was involved from the start of the manufacture of the Purple range. They had to conduct a survey to find out if there was a need for the product and also to find out what architects might want from a wall skirting. CompanyX pay 'Focus Groups' consisting of architects, designers and distributors to have an open discussion on what they would like to see out of a product. They found that the Purple range would have a good market in modern office buildings and in private hospitals. Once they had found that there was a market for it they could start planning the marketing whilst the production team made the product.

The Purple range is different from most other products as it is "Architect Specified" which means that if an architect is designing a building he may put in that the building is to use Perspective's wall skirtings. As CompanyX are the only people to make this product it means that if they can convince the architects to add this skirting to their designs then they are guaranteed some sales.

The marketing department have the job of making the product known to the industry and the architects. They produce single A4 information sheets that are sent to approximately 5500 distributors and architects which costs them £3700. They also produced more expensive material such as brochures, sample boxes, and 'clapper board' sample cases which are given to serious potential customers. As their sample boxes cost £5 and 'clapper board' sample cases cost £10 they can't afford to give them out to everybody. They had to organise a launch day to which many customers were invited. They also got news of the range into about 20 of the trade journals for which they pay up to £90 for having a photo printed in the editorial.

It costs around £250,000 for them to research and promote a product but it is essential as people can't buy a product if they don't know about it.

## Sales

The sales department is divided into 12 areas, each dealing with a specific area of the country. Each sales person is responsible for all the distributors in his or her area only. CompanyX sell their products to 80-100 main distributors around the country. They prefer not to deal with the builders directly and if they do ring up they are referred to their nearest distributor. The diagram below shows this relationship between CompanyX and it's contractors.

Distributors buy CompanyX goods because they have the largest range of products in the floor and stair edging business. The have an 80% market share in the UK. A lot of their competitors can sell the goods more cheaply than CompanyX, but the greater range of products that CompanyX sell ensures that they should be able to keep their lead in the UK markets for the foreseeable future.

When an order is telephoned in the sales person can quickly call up the details of any of their products or customers from a database. With having the sales people only responsible for a certain area of the country the sales people can quickly get to know the customers and so are able to deal with their orders more efficiently. Once the order has been taken it is sent by an internal network to the factory where the products can either be fetched from the warehouse or a new batch can be made.

CompanyX then store the products till they can be sent to the customer. They have regular delivery of the products throughout the country ranging from every other day for the London area to only once a week for Scotland.

The sales people also are responsible for dealing with any problems or queries that the customers may have about the range of products.

## Conclusion

The Purple range of floor skirtings was launched on the 11th November 1996. I visited them up to June 1997 and only a small amount of The Purple range had been sold. They initially produced a small batch which was worth several thousand pounds but did not sell any of it. This floor skirting now has to be scrapped because the protective plastic on the product starts to deteriorate after six months.

There lack of sales is partly because they have many other products to sell and market so the Purple range gets left out in favour of CompanyX's older but more marketable products. If they do want to sell it they need to have a more effective marketing strategy to make sure that all the architects know about it. It will only be bought if the architects specify a CompanyX floor skirting in their plans so they need to send samples and information out to the architects so that they know what the product is. They have sent samples to distributors but they will not but it unless architects start wanting the Purple range in their designs.

As having a decorative floor skirting is only cosmetic to a building the architects or builders would probably prefer to use the cheaper plain floor skirting in order to cut costs. Therefore it will only be bought for buildings where there is extra money to spend on making the interior look better.

It is also only designed to last 3-4 years which is a factor which will turn a lot of people off this product. People do not want to have to change their floor skirtings every few years, they want them to last for a long time. CompanyX naturally would like companies to buy a new batch of the Purple range every 3-4 years but many of these companies are much more likely to want a harder wearing alternative that needs a lot less maintenance.

They however are not too worried by the lack of orders because with products such as this it usually takes a few years before the orders start to come in. The Purple range is a good idea for a floor skirting and in use looks much more attractive that the usual plain floor skirtings so it is certain to become quite popular in the next few years.

### How The Population Of Yeast Changes Over A Number Of Days

Friday, June 6th, 2008

# A Level Biology Project

## Aims

This is an experiment to examine how the population of yeast alters over a number of days.

## Background Information

Yeast is a single celled fungus. It reproduces asexually by budding. It respires anaerobically.

Formula: Yeast + Carbohydrate ------------> Alcohol + Carbon Dioxide

## Apparatus Needed For The Experiments

1. Yeast
2. Cider
4. Muslin
5. Haemocytometer
6. Colorimeter
7. Pipette
8. Pipette Filler

## Method

I am planning to use two methods to measure how the population of yeast changes over time. Method 1 uses a haemocytometer whilst method 2 uses a colorimeter to measure the number of yeast cells each day.

A haemocytometer is a microscope slide which has an etched grid on it. It consists of a 1mm² square known as a A square which is divided into 25 B squares which have an area of 0.04mm². These B squares are each divided into 16 C squares which have an area of 0.0025mm².

A colorimeter is a machine that is used to see how much light can pass through a liquid. It shows how much light is being transmitted through a sample of liquid. As the number of cells gets higher, less light will be transmitted through the sample. Special thin walled test tubes are used in the colorimeter so that they do not affect the amount of light passing through the sample.

To prepare the yeast solution do the following steps.

1. Measure out 50cm³ of cider into a conical flask using a measuring flask. Cider is used to provide food for the yeast to grow in.

2. Using a 1cm³ pipette carefully measure out 1mm³ of yeast suspension and add it to the conical flask containing the cider.

3. Mix the solution and then put a muslin cloth over the top of the conical flask which should be held in place using an elastic band.

4. Put this conical flask in an oven pre heated to 40ºC. The change in yeast population can then be measured by using a haemocytometer and by using a colorimeter.

The Haemocytometer Test

1. First set up the microscope, place the cover slip on the haemocytometer slide between the two grooves and put the slide on the microscope.

2. A drop of yeast solution should be taken from the conical flask using a dropper pipette and put next to the cover slip. The yeast solution will be drawn under the cover slip by capillary reaction.

3. Focus the microscope so that you can see the smallest type C squares.

4. Count the number of yeast cells that you can see in 10 randomly picked squares. Note down all these results in a table such as the one below.

 Test Number 1 2 3 4 5 6 7 8 9 10 Average Day 1 Day 2 Day 3 Day 4 Day 5 Day 6

This haemocytometer test should be repeated daily for about two weeks. The results in the table can then be plotted into a graph.

The Colorimeter Test

The number of cells can be measured by with a colorimeter using the following method.

1. Calibrate the colorimeter by pouring 3cm³ of plain cider into a colorimeter test tube and placing the test tube into the colorimeter. Adjust the colorimeter so that with the plain cider it is showing 100% light transmission. Take the plain cider test tube out of the machine.

2. Take the conical flask containing the yeast solution out of the oven. Using a pipette measure out 3cm³ of the yeast solution into a clean colorimeter test tube.

3. Place this test tube into the colorimeter into the machine and note down the value of light transmission into a table such as the one below.

 Day 1 2 3 4 5 6 7 8 9 10 Colorimeter Reading

4. Pour the yeast solution back into the conical flask. Put the muslin back on the flask and return it to the 40ºC oven.

Both the haemocytometer and the colorimeter method of measuring the change in yeast cell population should be repeated at daily intervals for roughly two weeks.

A graph of Cell Numbers against time can then be plotted using the data. To convert the colorimeter readings to numbers of cells a calibration chart should be used.

## Predictions

I predict that as the number of days goes up the number of yeast cells in the solution will go up. This will continue for a number of days until the rate starts to slow down and eventually it will stop going up as no new cells are being produced.

The rate will go up over time because the yeast cells reproduce asexually which means that they are able to reproduce very quickly. They also have the perfect conditions for reproducing. They are being kept at a temperature of 40ºC which is very near to their optimum living temperature. They have lots of food from the cider and they have a lot of space to reproduce in. The rate will slow down after a while because the yeast will start killing itself off with the alcohol which it produces as part of it's respiratory process. This is known as a negative feedback reaction.

## Results

The Experiments - started to carry out the above experiments but after a few days decided to give up on the haemocytometer test because it was too time consuming. I carried out the colorimeter readings as written above and the results can be seen below. In order to get the number of yeast cells produced I am using a calibration curve so that by using the percentage transmission results the number of cells per mm² can be read off it.

I carried out the above experiment and these results were obtained. To make the colorimeter test as accurate as possible as well as my own results I used six other peoples sets of results and then took the average of each days results to work out how many yeast cells there are per mm² using the calibration curve.

A graph of the log of the cell numbers against time was plotted. A log graph is used because the increase in the number of cells per mm² over the 11 days is so big that it would not be practical to have a graph with numbers that large on it. This graph shows the total cell numbers both living and dead.

## Interpretation

The number of cells increased as the time went by as I had predicted. It increased as a fairly steady rate which can be seen on the Log graph. The population is able to increase at this rapid rate due to it's asexual reproduction. When the yeast cell is ready to reproduce a bud starts to grow out from it’s cell membrane which gets bigger and bigger until it is big enough to break off and become a new yeast cell. This is shown in the diagram below. [not reproduced]

These two yeast cells are then able to reproduce making four cells then eight then sixteen and so on. The yeast cells have plenty of space to grow in and lots of food from the cider. They are also being kept at 40ºC which is close to their optimum temperature for living. The number of cells does not keep doubling in this way. This is because the cells start to die through natural death and they are also killed by the alcohol which the yeast produce as part of their natural respiration process.

From day 3 to 4 the Log number increases from 6.87 to 6.95 which is an increase in cell numbers from 7413102 to 8912509. This is an increase of 20% for one day. From days 8 to 9 the Log goes up from 7.22 to 7.30 which is an increase in cell numbers from 16595869 to 19952623 which is an increase of 20% for one day. This shows that the rate of increase up to day nine is very steady.

After day nine the rate of population increase starts to slow down which is shown by the decreasing gradient on the graph. From day 10 to 11 the Log goes up from 7.37 to 7.41 which shows an increase in cell numbers from 23442288 to 25703958 which is an increase of 9.6% for one day. This is a fairly large drop in the expansion of the population of yeast. The rate of increase from day 10 to 11 is half that of the increase from day 3 to 4.

The rate has started to decrease by 9 and 10 because the yeast is starting to be killed off by the alcohol. This alcohol is produced as a by-product to the yeast's respiring. The alcohol poisons the yeast which causes it to die. This is known as a negative feedback reaction. The increase in yeast cells numbers leads to less space for them to reproduce so they are having to compete for space. The cells which don't have enough space will soon die. The yeast cells may also be running out of carbohydrates from the cider so this could lead them to die. The increase in alcohol and the lack of space starts to kill the cells off and so after 9 to 10 days the rate of increase in cell numbers slows down. If the experiment was continued for a few more days then I would expect the rate to stop as by then all the yeast cells would be dead.

The graph plotted of cell numbers does refer to the total number of cells both living and dead. If just the number of living cells was counted then the number of cells would start by rising at a slow rate as reproduction is only just beginning (Lag Phase). The numbers of yeast cells would then rise at a very fast rate before levelling off (Log Phase). By the time C is reached the alcohol levels have built up so the birth rate is equal to the death rate causing the population to remain constant. After D the numbers would then start dropping as the yeast cells die from lack of space and alcohol poisoning. This is known as the death phase. The theoretical curve is shown below. [not reproduced]

A - B Lag Phase
B - C Log Phase
C - D Stationary
D - E Death Phase

## Limitations

To help make this experiment more accurate, I used seven sets of results and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example:

a) It is also impossible to precisely measure out the amounts of Yeast or cider when making the solution. As the scale on the pipettes shows the volume to the nearest mm³ the volume of the solutions that I used should be correct to the nearest mm³.

b) It is also impossible to perfectly calibrate the colorimeter corectly each time. This slight variation could lead to some minor innacuracies in the results. The colorimeter was used because the haemocytometer method was taking too long to do.

c) The experiment was not carried out at the same time each day which could lead to uneven gaps between measurements.

d) The oven temperature may not have remained constant all the time causing the rate of reproduction to alter as the oven temperature changed.

## Anomolies

The plotted results on the graph produce a straight line of best fit to begin with which then goes into a curve of slightly decreasing gradient. It is a very smooth graph so no anomalies are present.

## Extension Work

This experiment could be improved in a number of ways. It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.

The test should be carried out at the same time each day to ensure that the length of time between each measurement is the same.

A test that could differentiate between living and dead cells would be very useful because then just the numbers of living cells could be counted. This would tell us how the population of living cells alters over time rather than at the moment where we can only find out how the total number of cells changed over time.

Different sources of carbohydrate apart from cider could be used to see if this affects the rate that the yeast numbers increase.

Different sized flasks could be used as this could increase or decrease competition between the yeast cells depending on the size. This would tell us how big a factor the competition between the cells is.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.

### The Effect Of Substrate Concentration On The Activity Of The Enzyme Catalase

Thursday, June 5th, 2008

# A Level Biology Project

## Aims

This is an experiment to examine how the concentration of the substrate hydrogen peroxide affects the rate of reaction of the enzyme catalase.

## Introduction

This is an A-level biology project. It helped me get an A grade for biology many years ago. The whole project is reproduced here for your reference.

## Background Information

Enzymes such as Catalase are protein molecules which are found in living cells. They are used to speed up specific reactions in the cells. They are all very specific as each enzyme just performs one particular reaction.

Catalase is an enzyme found in food such as potato and liver. It is used for removing Hydrogen Peroxide from the cells. Hydrogen Peroxide is the poisonous by-product of metabolism. Catalase speeds up the decomposition of Hydrogen Peroxide into water and oxygen as shown in the equations below.

### Formula:

```                       Catalase
Hydrogen Peroxide---------------------->Water + Oxygen
Catalase
2H2O2------------------->2H2O+O2
```

It is able to speed up the decomposition of Hydrogen Peroxide because the shape of it's active site matches the shape of the Hydrogen Peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction.

## Apparatus Needed For The Experiments

1. Gas Syringe
2. Metal Stand
3. Yeast Catalase
4. Hydrogen Peroxide
5. Test Tubes
6. Beakers
7. Test Tube Rack
8. Stop Watch
9. Pipette
10. Pipette Filler
11. Tap Water

## Method

To test out how the concentration of hydrogen peroxide affects the rate of reaction first set up the apparatus below.

[Aparatus picture not reproduced]

1. Add 2cm3 of yeast to one test tube. Add 4cm3 of hydrogen peroxide solution at a concentration of 20% to the other test tube. Use a pipette to measure out the volumes. It is very important to accurately measure the amounts of Hydrogen Peroxide, Yeast and water to ensure a fair test.

2. Pour the hydrogen peroxide solution into the test tube containing the yeast and immediately put the gas syringe bung on the end of the test tube, at the same time start the stopwatch.

3. Bubbles should start to rise up the tube and the gas syringe will move outwards, as soon as the gas syringe passes the 30cm3 mark stop the stopwatch and note the elapsed time down to the nearest 1/10th of a second.

4. Repeat the experiment with hydrogen peroxide concentrations of 16%, 12%, 10%, 8%, 4% and 0%. The 0% concentration of hydrogen peroxide solution is done as a control solution to show that at 0% concentration no reaction occurs. The different concentrations of Hydrogen Peroxide are made by adding tap water to the 20% Hydrogen Peroxide in the correct amounts. The table below shows what amounts of Hydrogen Peroxide and water are needed to make the solutions.

 Concentration Of Hydrogen Peroxide Volume Of Hydrogen Peroxide (cm3) Volume Of Water (cm3) 20% 4 0 16% 3.2 0.8 12% 2.4 1.6 10% 2 2 8% 1.6 2.4 4% 0.8 3.2 0% 0 4

5. Repeat all the tests at least three times so that an average can be obtained. Repeating the experiments several times will help to produce better and more accurate results as any inaccuracies in one experiment should be compensated for by the other experiments. Note all the results in a table such as the one below.

 Hydrogen Peroxide Concentration 0% 4% 8% 10% 12% 16% 20% Time Taken (Test 1) Time Taken (Test 2) Time Taken (Test 3) Average of the Tests Rate

The rate can then be worked out by

Rate=30/Average Time

This gives the rate in cm3 of oxygen produced per second, this is because I am timing how long it takes to produce 30cm3 of oxygen. From these results a graph can be plotted with concentration on the x-axis and time taken on the y-axis.

I am using yeast catalase as opposed to catalase from apples, potatoes or liver because it is easier to get the desired amount of yeast catalase by simply measuring it off. To obtain catalase from a substance such as potato would involve crushing it and with that method you would never be sure of the concentration of the catalase. If the catalase was used up then another potato would have to be crushed and this could produce catalase of a totally different concentration which would lead to inaccuracies in the experiment making this an unfair test.

To ensure this is a fair test all the variables except for the concentration of Hydrogen Peroxide must be kept the same for all the experiments. Variables that must not be altered include:-

Temperature, yeast concentration, type of yeast, batch of yeast, volume of yeast, volume of hydrogen peroxide, air pressure and humidity.

When measuring the volumes of Hydrogen Peroxide, Yeast and Water the measurement should be taken by looking at the scale at an angle of 90 degrees to it to avoid any parallax error.

## Predictions

I predict that as the substrate concentration increases, the rate of reaction will go up at a directly proportional rate until the solution becomes saturated with the substrate hydrogen peroxide. When this saturation point is reached, then adding extra substrate will make no difference.

The rate steadily increases when more substrate is added because more of the active sites of the enzyme are being used which results in more reactions so the required amount of oxygen is made more quickly. Once the amount of substrate molecules added exceeds the number of active sites available then the rate of reaction will no longer go up. This is because the maximum number of reactions are being done at once so any extra substrate molecules have to wait until some of the active sites become available.

## Results

I carried out the above experiment and these results were obtained.

 Hydrogen Peroxide Concentration 0% 4% 8% 10% 12% 16% 20% Time Taken (Test 1) 47.3 18.4 17.3 14.5 10.6 9.7 Time Taken (Test 2) 43.3 19 16.7 14.9 11.2 10 Time Taken (Test 3) 52.2 17.2 18.5 11.2 8.6 7.8 Average of the Tests 47.6 18.2 17.5 13.5 10.1 9.2 Rate=30/Average (Cm3/second) 0 0.63 1.65 1.71 2.22 2.97 3.26

All the times are in seconds. The average results are all written down to one decimal place because although the stopwatch gives results to two decimal places it is impossible to get accurate times to two decimal places due to the fact that our reaction times are not fast enough to stop the stopwatch precisely. I then worked out the rates of the reactions with the equation

Rate=30/Average Time

From these rates I was able to plot a graph of the rate of reaction against concentration of Hydrogen Peroxide.

## Interpretation

When the concentration of Hydrogen Peroxide is increased, the rate of reaction increases at a directly proportional rate until the concentration of Hydrogen Peroxide reaches about 16%. If you double the concentration of Hydrogen Peroxide then the rate of reaction doubles as well. When the concentration is doubled from 8-16% the rate goes up from 1.65-2.97 Cm3 Oxygen produced per second, which is an increase of 1.8 times. I would expect the rate to increase two times if the Hydrogen Peroxide concentration is increased two times because there are twice as many substrate molecules which can join onto the enzymes active sites. The reason that the number is less than two times could be put down to the fact that at 16% the Enzyme's active sites may already be close to being saturated with Hydrogen Peroxide. There may also be some experimental error which causes the inaccuracies.

After 16% the increase in the rate of reaction slows down. This is shown by the gradient of the graph going down. At this point virtually all the active sites are occupied so the active sites are said to be saturated with Hydrogen Peroxide. Increasing the Hydrogen Peroxide Concentration after the point of saturation has been reached will not cause the rate of reaction to go up any more. All the active sites are being used so any extra Hydrogen Peroxide molecules will have to wait until an active site becomes available.

The theoretical maximum rate of reaction is when all the sites are being used but in reality this theoretical maximum is never reached due to the fact that not all the active sites are being used all the time. The substrate molecules need time to join onto the enzyme and to leave it so the maximum rate achieved is always slightly below the theoretical maximum. The time taken to fit into and leave the active site is the limiting factor in the rate of reaction.

The diagram below shows what happens.

[not reproduced]

## Limitations

To help make this experiment more accurate, I repeated it three times and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables except for the concentration of Hydrogen Peroxide the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example:

a) There is a slight delay between pouring the Hydrogen Peroxide into the yeast, putting the bung on and starting the stopwatch. This will slightly affect all the results but as I carried out all the three steps in the same way for all the experiments it should not make any difference to the overall result.

b) It is also impossible to precisely measure out the amounts of Hydrogen Peroxide, Yeast and Water each time. As the scale on the pipettes shows the volume to the nearest mm3 the volume of the solutions that I used should be correct to the nearest mm3. The volume of gas in the test tube to start with is slightly affected by the amount which the bung is pushed down each time, if the bung is pushed down further then the volume in the tube will be less so the 30cm3 of gas is reached faster.

c) Due to the fairly slow speed of our reactions it is only possible to measure the time of the reaction to the nearest 0.1 second even though the stopwatch shows the measurements to the nearest 0.01 second.

## Anomolies

The plotted results on the graph produce a straight line of best fit to begin with which then goes into a curve of steadily decreasing gradient. The only anomalies are the results at 8% and 10%. The result at 8% is slightly above the line of best fit and the 10% result is slightly below it. This is probably due to an experimental error involving one of the factors mentioned above.

## Extension Work

This experiment could be improved in a number of ways. It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.

Using more concentrations of Hydrogen Peroxide would have produced a better looking graph and I would have liked to use concentrations higher than 20% to extend the graph so that the maximum possible rate of reaction could be reached.

The problem of the delay between pouring in the Hydrogen Peroxide, bunging the test tube and starting the stopwatch could have been limited by getting another person to start the stopwatch when the hydrogen peroxide was poured into the tube.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.

### Investigation Into The Blowfly Larvae’s Response To Light

Wednesday, June 4th, 2008

# A Level Biology Project

## Aims

I plan to investigate how blowfly larvae react to light.

## Introduction

This is an A-level biology project. It helped me get an A grade for biology many years ago. The whole project is reproduced here for your reference.

## Background Information

The way in which animals respond to external factors is known as behaviour. As animals become bigger their behaviour becomes more complex. This is because larger animals tend to have a more complex nervous and hormonal system. Two of the types of behaviour are called taxis and kinesis.

Taxis is a movement whose direction is determined by the direction of the stimulus. Some animals may move towards certain stimuli such as the smell of food. Others may move away from a stimuli such as excessive heat.

Kinesis is a behaviour pattern in which the animal changes it’s rate of movement in relation to the intensity of the stimulus. For instance if an animal is used to living in a humid environment then it’s activity will increase in a non-humid environment, this will help them to find a new humid environment as quickly as possible.

## Apparatus Needed For The Experiments

1. 20 Blowfly larvae
2. Perspex Tray and lid
3. Lamp
4. Stopwatch
5. Ruler
6. Felt tip
7. Paper
8. Petri dish

## Method

I am planning to use the following method for my experiment.

1. The apparatus is set up as shown in the picture below.

Diagram Of The Apparatus [not reproduced]

2. A piece of marked paper (an example of which is shown below) is put in the plastic dish. Each of the positive and negative sectors should have angles of 120° and each of the neutral sectors should have an angle of 60°. The end marked “positive” is positioned nearest to the light.

3. The plastic tray should be 10cm away from the front of the lamp. The lamp should be shining at a shallow angle along the tray.

4. A pencil is spun to find a random direction. The maggot is then placed in the centre of the plastic dish facing in the direction of the pencil.

5. The dish’s cover is placed on the tray.

6. As soon as the maggot’s head leaves the paper’s inner circle the stopwatch is started. The position of the maggot’s head is then marked with a small ‘a’ on the plastic cover every 5 seconds until the maggot leaves the outer circle.

7. The maggot is taken out of the tray and placed in a spare petri dish so that it is not used again. This is because a maggot that has already been used may react differently if it is used again as it’s behaviour may be affected by it’s previous experience in the tray.

8. The distance between each ‘a’ is measured and noted down in a table such as the one below. The sector (positive, negative or neutral) that the maggot left the outer sector is noted in the table. The distance between each of the points and the front of the lamp is then measured and noted in another similar table.

 Time Experiment 5 10 15 20 25 Sector 1 2 3

The rate in cm/second for each 5 second interval is then worked out with the following equation

Speed=Distance / Time

and put into a table such as the one above.

8. A new sheet of paper is then placed in the perspex tray with the ‘positive’ end pointing towards the light. This is to make sure that the maggot’s behaviour is not affected by following the trails of the other maggots. The experiment is then repeated another 19 times.

Using the results I plan to plot a graph of distance from the lamp against speed. This will allow me to se how the speed of the maggot alters as it’s distance from the lamp changes.

The Chi² test will be used to see if the differences in the maggot’s direction of movement are significant.

I will use the following method to do the Chi² test. The Observed value is the number of maggots that crossed each sector. The expected value is the number of maggots that I would expect to cross each sector according to the null hypothesis.

 Direction Observed Expected O - E (O - E)² (O - E)² / E Positive Negative Neutral Total:

If the total of the three “(O - E)² / E” values is bigger than 3.84 then I can be 95% confident that there is a significant difference between the results.

In order to make this experiment as accurate as possible a number of steps must be taken.

• The experiment should be carried out in darkness with only the light from the bench lamp reaching the plastic tray. All the rooms light should be turned off and the window’s blinds should be closed.
• Each maggot should only be used once to ensure that their behaviour is not affected by their previous experience in the perspex tray.
• A fresh sheet of paper is used each time to ensure that the maggots can not follow the trails of any previous maggots.
• The lamp should be at the same height and distance away from the tray for each experiment.
• The distance should be measured from the front of the lamp to the plastic tray.
• Each maggot should be positioned on the paper facing a random direction to ensure that it does not just move in a straight line in the direction that it is positioned.
• When marking the position of the maggot the head of the mark should be placed at the maggots head to ensure consistency throughout the experiment. The eye should be directly above the maggot to avoid parallax error when putting the mark on the perspex.

Although taking these steps will make the experiment more accurate, it’s accuracy is still limited by several factors.

• The accuracy of each measurement is limited to the nearest 0.5 mm the ruler is graduated in mm.
• It is impossible to manage to mark the positions exactly every 5 seconds. Some of the time intervals may be slightly bigger than others.

## Predictions

I predict that the maggots will move away from the light source. This is because bright lights could kill them from exposure to ultra violet radiation, or by drying the maggots out.

If the maggots move away from the light then they will avoid the harmful ultra violet light and will avoid drying out. Staying in a darker area will make the maggots less visible to predators which will increase their chances of survival. If they move away from the light then their movement pattern is called negative phototaxis.

I predict that their movements will be faster if they are nearer to the light. By moving faster when they are near the light they will be able to get away from the light quickly. Once they are a reasonable distance away I predict that they will slow down as they are no longer in danger of being killed by overexposure to the light.

If the maggots were to stay in the sunlight then there is a chance that they could dry out and so die.

Null Hypothesis As their is the same angle for each of the three sectors (positive, negative and neutral) an equal amount of maggots should leave each sector.

33.3% of maggots should leave by the positive sector.
33.3% of maggots should leave by the negative sector.
33.3% of maggots should leave by the neutral sector.

The Experiment - The experiment was carried out as stated in the plan. As the maggots moved fairly quickly I had to use 2 second intervals between each mark instead of 5 second intervals.

## Results

These are the results from my experiments.

## Interpretation

I will analyse the results for the experiment. As I predicted the maggots moved away from the light as soon as they were placed in the plastic container. The maggot’s behaviour is therefore negative phototaxis. 15 of the maggots left the outer circle through the negative sector, showing that the maggots move away from the light. The Chi² test for the experiment is shown below.

 Direction Observed Expected O - E (O - E)² (O - E)² / E Positive 1 6.67 -5.67 32.11 4.82 Negative 15 6.67 8.33 69.44 10.42 Neutral 4 6.67 -2.67 7.11 1.07 Total: 16.3

As the total is bigger than 3.84 I can be 95% sure that there is a significant difference between these and the results as predicted in the null hypothesis. I can therefore reject the null hypothesis. Maggots will move away from the light in an experiment such as this. For example maggot 17 heads away from the light at a speed of 1.3cm/s. By the time it has crossed the outer sector it has slowed down to 1.1cm/s. 15 of the 20 maggots display similar behaviour and move away from the light and exit the circle by the negative sector.

They have light stimuli on either side of their head. By moving their head they can detect where the stimuli is coming from. If the maggot detects that the light is stronger on the left hand side of it’s head then it will turn right so that it is moving away from the light. If the light is stronger on the right hand side of it’s head then it will turn left. This helps the maggot to move away from the light. If the light intensity is the same on both sides of it’s head then it will head in a straight line.

This could explain why maggot 18 headed towards the light. When it was placed in the tray it may have been pointing towards the light so it was receiving equal light on both stimuli. It therefore moved forwards in a straight line towards the light. It did speed up as it got closer to the light as it must have been trying to get away from the light as quickly as possible. As the light was of equal strength on both sides of it’s head it was unable to tell that it was heading towards the light.

By looking at the graph of the speed of movement against the distance from the lamp it can be seen that the majority of the lines move downwards and to the right. This shows that as the maggots get further away from the light their speed decreases. This maggots may therefore be showing photokinesis. More experiments would need to be done to confirm this. Kinesis is a reaction to the intensity of the stimulus and not the direction so photokinesis could be tested by using a light whose brightness can be altered.

Many of the maggots moved slowly during their first few seconds in the tray. This is probably due to them getting their bearings and working out where the light is coming from before moving off in the opposite direction.

Secondary Data

Here is some secondary data which I will use to compare with the data that I obtained.

By carrying out the Chi² test this data produces similar results to my own.

 Direction Observed Expected O - E (O - E)² (O - E)² / E Positive 0 3.33 -3.33 11.11 3.33 Negative 9 3.33 5.67 32.11 9.63 Neutral 1 3.33 -2.33 5.44 1.63 Total: 14.6

These results confirm that we can be 95% sure that the difference in direction is significant.

By looking at the data and the graph it can be seen that 9 of the 10 maggots head away from light. 7 of them slow down as they get further away from the light. None of the maggots head towards the light. This data produces the same conclusion as my data and confirms that my results are correct.

The maggots show negative phototaxis behaviour. The maggots use the sensors on either side of their head to work out where the light is coming from. They then turn away from the light and head towards the dark to get away from the light. They do this to avoid the harmful ultra violet light which can harm them. By performing this negative phototaxis behaviour the maggots can increase their chance of survival.

## Limitations

The accuracy of this experiment is limited by a number of factors.

a) It was impossible to get rid of all background light as other similar experiments were being carried out in the same room.

b) The accuracy of each measurement is limited to the nearest 0.5 mm the ruler’s are graduated in mm.

c) I had no way of knowing how old the maggots were. The maggot’s response may alter with age which could explain why some maggots did not show the expected response.

d) As the bench lamp was only 10cm away from the perspex tray it may have caused a heating effect on the tray. The maggot’s may therefore have reacted to the heat as well as the light. This could have been prevented by placing the lamp further away.

## Extension Work

This experiment could be improved in a number of ways.

1) It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.

2) Each person should have carried out their experiments in a different room to cut out all background light.

3) A perspex screen could have been placed between the light and the perspex tray to reduce any heating effect the light may have on the maggots.

4) Different ages of maggots could have been tested to see if the maggots response to the stimuli varies with age.

5) Different intensities of light could be used to see if the maggots react differently from one light intensity to another.

6) Different colours of light could be used to see if this has an effect on the maggots.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.

### Factors Affecting The Rate Of Photosynthesis

Tuesday, June 3rd, 2008

# A Level Biology Project

## Aims

I plan to investigate how different factors affect the rate of photosynthesis. I will be changing the levels of light and CO2 and then measuring the photosynthetic rate.

## Introduction

This is a A-level biology project. It helped me get an A grade for biology many years ago. The whole project is reproduced here for your reference.

## Background Information

The rate of photosynthesis is affected by a number of factors including light levels, temperature, availability of water, and availability of nutrients. If the conditions that the plant needs are improved the rate of photosynthesis should increase.

The maximum rate of photosynthesis will be constrained by a limiting factor. This factor will prevent the rate of photosynthesis from rising above a certain level even if other conditions needed for photosynthesis are improved. This limiting factor will control the maximum possible rate of the photosynthetic reaction.

For instance, increasing the temperature from 10ºC to 20ºC could double the rate of photosynthesis as the plant's enzymes will be closer to their optimum working temperature. As the temperature is increased, molecules in the cells will be moving at a faster rate due to kinetic theory. If the temperature is raised above a certain level, the rate of photosynthesis will drop as the plant's enzymes are denatured. They will therefore be more likely to join onto the enzymes and react.

The amount of water available to the plant will affect the rate of photosynthesis. If the plant does not have enough water, the plant's stomata will shut and the plant will be deprived of CO². It is difficult in normal lab conditions to prove that water directly affects photosynthesis unless a heavy isotope is used to trace the path of water.

Chlorophyll is needed for photosynthesis. This can be proved by studying a variegated leaf. It is however very difficult to study how different levels of chlorophyll in the plant will affect it's photosynthesis rate. This is because in a variegated leaf the cells either contain chlorophyll or they don't.

Carbon dioxide concentration will directly affect the rate of photosynthesis as it is used in the photosynthesis reaction. It is also easy to change the amount of carbon dioxide that the plant receives.

Light is also directly used in the photosynthesis reaction and is easy to change in normal lab conditions. Carbon Dioxide and Light are the factors that I will change in the experiment as they are easy to change and measure.

## Apparatus Needed For The Experiments

1. Elodea
2. 20mm² syringe
3. Capillary tubing
4. Stand
5. Stopwatch
6. Ruler
7. NaHCO³ Solution
8. Bench lamp
9. Distilled water

## Method

I could measure the decrease in the substances needed for photosynthesis, such as how much the amount of CO2 decreases over time. This is however difficult in normal lab conditions. I will instead measure how one of the products of photosynthesis (oxygen) increases over time. I am planning to use the following method for my experiment.

1. The apparatus is set up as below with the syringe full of the 0.01M solution of NaHCO3 solution. Two marks 10cm apart are made on the capillary tubing.
2. The syringe is placed 0.05m away from the lamp.
3. Using the syringe plunger the meniscus of the NaHCO3 is set so that it is level with the first mark.
4. A stopwatch is then started. The meniscus should gradually move down the capillary tube as the elodea produces oxygen as a by-product of photosynthesis. As the oxygen is produced it increases the pressure in the syringe and so the meniscus is pushed down the tube.
5. When the meniscus reaches the level of the bottom mark the stopwatch should be stopped and the time should be noted in a table such as the one below.
 Molarity of NaHCO3 Light Intensity 1/d² (m) 0.00 (Distilled water) 0.01 0.02 0.05 0.07 0.1 400 278 204 156 100 25 11 4

The light intensities have been worked out using the following equation

Light Intensity = 1 / Distance² (m)

6. Using the same piece of elodea and the same distance between the lamp and the syringe the experiment (steps 1 to 5) should be repeated for the other concentration of NaHCO3.
7. The experiment (steps 1 to 6) should then be repeated at each different distance between the syringe and the light for all the NaHCO3 concentrations. The remaining distances are 0.05m, 0.06m, 0.07m, 0.08m, 0.1m, 0.2m, 0.3m, and 0.5m.
8. The entire experiment should then be repeated three times in order to obtain more accurate data and to get rid of any anomalies that may occur in a single experiment.

Measuring the volume of oxygen is more accurate than counting the number of bubbles produced as each bubble could be a different size. In order to make this experiment as accurate as possible a number of steps must be taken.

• The experiment should be carried out in darkness with only the light from the bench lamp reaching the elodea.
• The same piece of elodea should be used each time in order to make sure that each experiment is being carried out with the same leaf surface area.
• The amount of NaHCO3 solution should be the same for each experiment. 20mm² should be used each time.
• The lamp should be at the same height for each experiment. It should be level with the syringe each time.
• The distance should be measured from the front of the lamp to the syringe. Although taking these steps will make the experiment more accurate, it's accuracy is still limited by several factors.
• Some of the oxygen will be used for photosynthesis by the plant.
• Some of the oxygen will dissolve into the water.

From these recorded times I will work out the rate of the reaction using the following equation.

Rate Of the Reaction = 1 / Time (s)

Using these rates I plan to plot a graph of the rate of reaction against light intensity.

## Predictions

### Light

I predict that if the light intensity increases the rate of the reaction will increase at a proportional rate until a certain level is reached, the rate of increases will then go down. Eventually a level will be reached where increasing the light intensity will have no more effect on the rate of reaction as there is some other limiting factor.

Light is needed for photosynthesis in plants. When chloroplasts in the leaf's cell are exposed to light they synthesise ATP from ADP. Oxygen is produced as a by-product of the photosynthesis reaction. Therefore increasing the concentration of light will increase the amount of ATP being synthesised from ADP and so more oxygen will be released as a by product.

### NaHCO3

I predict that as the concentration of NaHCO3 increases the rate of the reaction will increase at a proportional rate. Eventually increasing the NaHCO3 concentration more will have no effect as other limiting factors will be limiting the rate of photosynthesis. Carbon dioxide is needed for the photosynthesis reaction. It is used to make the organic products of photosynthesis. If the elodea is able to absorb more CO2 then the rate of photosynthesis will increase as the plant is able to make more of the organic compounds. The plant is given CO2 in the form of NaHCO3.

## Results

Pooled results from the group were used. They were taken over a 2 day period.

 Molarity of NaHCO3 Light Intensity 1/d² (m) 0.00 (Distilled water) 0.01 0.02 0.05 0.07 0.1 400 3571 1666 1099 523 200 243 278 1670 5183 988 600 375 262 204 4998 4485 1175 1005 473 351 156 5590 2300 1770 1445 621 550 100 9990 3150 2900 2552 1224 645 25 4762 3984 2850 1640 1408 11 5945 4348 3780 2830 2564 4 16480 11904 5196 6578 3226

Using these results I worked out the rate

Rate Of the Reaction = 1 / Time(s) x 1000

The rate was multiplied by 1000 to make the numbers easier to handle.

 Molarity of NaHCO3 Light Intensity 1/d² (m) 0.00 (Distilled water) 0.01 0.02 0.05 0.07 0.1 400 0.28 0.60 0.91 1.91 5.00 4.12 278 0.60 0.19 1.01 1.67 2.67 3.82 204 0.20 0.22 0.85 1.00 2.11 2.85 156 0.18 0.43 0.56 0.69 1.61 1.82 100 0.10 0.32 0.34 0.39 0.82 1.55 25 0.21 0.25 0.35 0.61 0.71 11 0.17 0.23 0.26 0.35 0.39 4 0.06 0.08 0.19 0.15 0.31

A graph of the rate of reaction against light intensity was drawn. It shows how the amount of CO2 and light affect the rate of photosynthesis. Lines of best fit were drawn for each CO2 concentration to make up for any inaccuracy in any individual result. The line of best fit gives a good picture of how the overall rate of reaction is affected by the light and CO2.

## Interpretation

I will analyse the results for how the amount of light and CO2 affects the rate of photosynthesis.

My prediction that the rate of photosynthesis would go up if the light intensity and NaHCO3 levels were increased proved correct. As the elodea absorbed the light and CO2 it produced oxygen gas which increased the pressure in the syringe. This pushed the air bubble in the capillary tube down. The chloroplasts produce ATP and reduce NADP to NADPH2 when exposed to light. It is at this stage of the reaction that oxygen is produced as a waste product.

As predicted when the light intensity increases so does the rate of photosynthesis. I predicted that a level would be reached where increasing the light intensity would have no more effect on the rate of reaction as there would be some other limiting factor which limits the rate of the reaction. The rate increases at a steady rate as the light intensity increases until near the end of each line where the rate of increase decreases. This is either because the photosynthesis reaction has reached it's maximum rate of reaction or another factor is limiting the rate. As 6 different CO2 concentrations were used I can see that the first five reactions are not occurring at their maximum rate as there is the 0.1M NaHCO3 rest which is occurring at a faster rate then the other 5. The photosynthesis reactions of the other five test must therefore be limited by the concentration of CO2 to the plant.

As predicted when the NaHCO3 concentration is increased the plant in able to get more CO2 which causes the rate of reaction to go up. I predicted that once the NaHCO3 had been raised above a certain level increasing the rate further would have no effect as there would be other limiting factors limiting the rate of the reaction. As the NaHCO3 concentration in the water was increased the rate of photosynthesis was able to go up. The plant therefore made more oxygen as a waste product. At a NaHCO3 concentration of 0.1M once the light intensity gets above 300 the rate of reaction slows down very quickly. This could be because photosynthesis is occurring at it's maximum possible rate or because another limiting factor is limiting the rate of reaction.

### Distilled Water

With the distilled water the rate of reaction went up from 0.1 to 0.4 when the light intensity was increased from 100 to 400. This is a 4 times rise which is quite large. The curve on the graph does however level out quite soon showing that the rate is being limited by the lack of NaHCO3 in the water.

### 0.01M NaHCO3

At a light intensity of 4 the rate is 0.06 but this rises to 0.6 when the light intensity is brought up to 400. The curve is very shallow and levels off towards a light intensity of 350 - 400.

### 0.02M NaHCO3

The amount of NaHCO3 is double that of the 0.01M NaHCO3 experiment. The rate also finishes off twice that of the 0.01M experiment. This would surgest that there was a directly proportional relationship between the amount of NaHCO3 and the rate of reaction.

### 0.05M NaHCO3

The curve for the 0.05M NaHCO3 is steeper than the previous curves. The rate rises to 1.9 at a light intensity of 400.

### 0.07M NaHCO3

The 0.07M NaHCO3 test produces a line which is steeper than all the previous curves. The plant is using the extra CO2 to photosynthesise more. As the plant has more CO2 the limiting factor caused by the lack of CO2 is reduced. This test did produce a big anomaly. The rate for a light intensity of 400 is 5. By following the line of best fit I can see that this result should be more like 3.5. The elodea for this test was very close to the light source. It is possible that it had been left here for a while which caused the lamp to heat the elodea up. This would have increased the rate of reaction of the plant's enzymes which would have increased the photosynthesis rate.

### 0.1M NaHCO3

The 0.1M NaHCO3 produced the steepest line. Near the end of the line it looks as if the rate of reaction is hit by another limiting factor. The line goes up steadily but then between a light intensity of 300 and 400 levels off very quickly. This would surgest that at a 0.1M NaHCO3 is sufficient for the plant to photosynthesise at it's maximum rate with it's current environmental conditions. Increasing the NaHCO3 concentration after this level would therefore have no effect unless the next limiting factor was removed.

The fact that the curve levels off so quickly indicates that there is another limiting factor limiting the photosynthesis. It could be temperature. These tests are being carried out at room temperature so the temperature would have to be raised another 15ºC before the enzymes in the plant's cells were at their optimum working temperature. More tests could be done by using water that was at a higher temperature to see what effect this would have on the photosynthesis rate. It is however impossible to raise the plant's temperature without affect other factors. For instance the actual amount of oxygen released by the plant is slightly more than the readings would surgest as some of the oxygen would dissolve into the water. At a higher temperature less oxygen would be able to dissolve into the water so the readings for the photosynthesis rate could be artificially increased.

It is also possible that the photosynthetic reactions in the plant are occurring at their maximum possible rate and so can not be increased any more.

The light is probably not a limiting factor as all but one of the curves level off before the maximum light intensity of 400 is reached. The maximum light intensity that the plants can handle is therefore just below 400.

Water will not be a limiting factor as the plants are living in water. They therefore have no stomata and absorb all their CO2 by diffusion through the leaves.

## Limitations

The accuracy of this experiment is limited by a number of factors.

1. Some of the oxygen give off is used for respiration by the plant.
2. Some of the oxygen dissolved into the water.
3. Some was used by small invertebrates that were found living within the pieces of elodea.
4. The higher light intensities should be quite accurate but the smaller light intensities would be less accurate because the light spreads out. the elodea will also get background light from other experiments.
5. The lights are also a source of heat which will affect the experiments with only a small distance between the light and the syringe. this heating could affect the results.
6. Using the same piece of elodea for each experiment was impractical as the elodea's photosynthesis rate decreased over time. By using a different piece of elodea for each experiment did create the problem of it being impossible for each piece to have the same surface area.
7. As the tests took place over a two day period there will be some inaccuracy caused by factors such as temperature. There was no practical way for the long tests to be kept at a totally constant temperature for the two day period and they will probably have cooled down at night and then warmed up in the day leading to a slight inaccuracy.

## Extension Work

This experiment could be improved in a number of ways.

1. It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.
2. Each person should have done their experiments in a different room to cut out all background light.
3. All the experiments should be done sequentially.
4. A perspex screen could have been placed between the light and the syringe to reduce any heating effect that the light may have.
5. The experiment could have been carried out with higher NaHCO3 to see if increasing the concentration would increase the rate of photosynthesis, or if a concentration of 0.1M NaHCO3 produces the maximum rate of photosynthetic reaction.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.

### Surface Area / Volume Ratio Biology Experiment

Monday, June 2nd, 2008

# A Level Biology Project

## Aims

This is an experiment to examine how the Surface Area / Volume Ratio affects the rate of diffusion in substrates and how this relates to the size and shape of living organisms.

## Introduction

This is an A-level biology project. It helped me get an A grade for biology many years ago. The whole project is reproduced here for your reference.

## Background Information

The surface area to volume ratio in living organisms is very important. Nutrients and oxygen need to diffuse through the cell membrane and into the cells. Most cells are no longer than 1mm in diameter because small cells enable nutrients and oxygen to diffuse into the cell quickly and allow waste to diffuse out of the cell quickly. If the cells were any bigger than this then it would take too long for the nutrients and oxygen to diffuse into the cell so the cell would probably not survive.

Single celled organisms can survive as they have a large enough surface area to allow all the oxygen and nutrients they need to diffuse through. Larger multi celled organisms need specialist organs to respire such as lungs or gills.

## Apparatus Needed For The Experiments

1. Beakers
2. Gelatin blocks containing cresol red dye
3. 0.1M Hydrochloric acid
4. Stop Watch
5. Scalpel
6. Tile
7. Safety glasses

## Method

1. A block of gelatin which has been dyed with cresol red dye should be cut into blocks of the following sizes (mm).

5 x 5 x 5
10 x 10 x 10
15 x 15 x 15
20 x 20 x 20
10 x 10 x 2
10 x 10 x 10 (Triangle)
10 x 15 x 5
20 x 5 x 5

The triangle is of the following dimensions. [not reproduced]

The rest of the blocks are just plain cubes or rectangular blocks.

Cresol red dye is an acid / alkali indicator dye. In the alkali conditions of the gelatin it is red or purple but when it gets exposed to acid it turns a light yellow colour.

Gelatin is used for these tests as it is permeable and so it acts like a cell. It is easy to cut into the required sizes and the hydrochloric acid can diffuse at an even rate through it.

I am not using any blocks bigger than 20 x 20 x 20 as a preliminary test found that it was only practical to use blocks of 20mm³ or less as anything bigger than this would take longer than the amount of time that we have to do the experiment.

2. A small beaker was filled with 100cm³ of 0.1 molar Hydrochloric acid. This is a sufficient volume of acid to ensure that all the block sizes are fully covered in acid when dropped into the beaker.

3. One of the blocks is dropped into this beaker and the time for all the red dye to disappear is noted in a table such as the one below.

 Dimensions (mm) Surface Area Volume (mm³) Surface Area / Volume Ratio Test 1 Test 2 Test 3 Average Time

4. This test should be repeated for all the sizes of blocks three times to ensure a fair test. Fresh acid should be used for each block to ensure that this does not affect the experiment’s results.

5. The surface area / volume ratio and an average of the results can then be worked out. A graph of Time against Surface Area to Volume Ratio can then be plotted. From this graph we will be able to see how the surface area affects the time taken for the hydrochloric acid to penetrate to the centre of the cube.

## Predictions

I predict that as the Surface Area / Volume Ratio increases the time taken for the hydrochloric acid to penetrate to the centre of the cube will go down. This is because a small block has a large amount of surface area compared to it’s volume so the hydrochloric acid will have a large surface area to diffuse through. A larger block has a smaller amount of surface area in relation to it’s size so it should take longer for the hydrochloric acid to diffuse into the centre of the cube. The actual rate of the hydrochloric acid diffusing through the gelatin should be the same for all the blocks but when the surface area / volume ratio goes up it will take less time for the hydrochloric acid to reach the centre of the cube.

## Results

I carried out the above experiment and these results were obtained.

 Dimensions (mm) Surface Area Volume (mm³) Surface Area / Volume Ratio Test 1 Test 2 Test 3 Average Time 5 x 5 x 5 150 125 1.2:1 7.02 6.57 4.53 6.16 10 x 10 x 10 600 1,000 0.6:1 10.3 23.25 15.33 16.28 15 x 15 x 15 1,350 3,375 0.4:1 29.55 30.22 23.45 28.01 20 x 20 x 20 2,400 8,000 0.3:1 53.4 32.44 58.56 48.3 10 x 10 x 2 280 200 1.4:1 0.26 0.37 1.58 1.01 10 x 15 x 5 550 750 0.73:1 7.2 10.23 10.47 9.3 20 x 5 x 5 450 500 0.9:1 3.18 2.58 4.09 3.29 10 x 10 x 10 (Triangle) 441.42 500 0.88:1 9.58 3.34 5.25 6.19

The Surface area to Volume ratio is calculated by

Surface Area To Volume Ratio = Surface Area / Volume

From these rates I was able to plot a graph of the Surface Area to Volume Ratio against time.

## Interpretation

In all the blocks of gelatin the rate of penetration of the hydrochloric acid from each side would have been the same but all the blocks take different amounts of time to clear because they are different sizes. As the blocks get bigger it takes longer for the hydrochloric acid to diffuse through all the block and so clear the dye. It takes longer to reach the centre of the cube even though the rate of diffusion is the same for all the cubes.

As the volume of the blocks goes up the Surface Area / Volume ratio goes down. The larger blocks have a smaller proportion of surface area than the smaller blocks. The smallest block has 1.4mm² of surface area for every 1mm³ of volume. The largest block only has 0.3mm² of surface area for each 1mm³ of volume. This means that the hydrochloric acid is able to diffuse to the centre of the smallest block much faster than the largest block. The acid took 48 minutes to diffuse to the centre of the largest block but only 1 minute in the smallest block. A living cell would not survive if it had to wait 48 minutes for oxygen to diffuse through it so living cells need to be very small.

When the surface area to volume ratio goes down it takes longer for the hydrochloric acid to diffuse into the cube but if the ratio goes up then the hydrochloric acid diffuses more quickly into the block of gelatin. Some shapes have a larger surface area to volume ratio so the shape of the object can have an effect on the rate of diffusion.

It is important that cells have a large surface area to volume ratio so that they can get enough nutrients into the cell. They can increase their surface area by flattening and becoming longer or by having a rough surface with lots of folds of cell membrane known as villi. [picture not reproduced]

The villi vastly increase the surface area of the cell whereas the cell which is round only has a small surface area in relation to it’s volume. Both cells above have an volume of 1cm³. The cell on the left has a surface area of 3cm² but the cell on the right with villi has a surface area of 10cm². The cell membrane is made up of a lipid bi-layer with many proteins integrated into it. [picture not reproduced]

Oxygen can diffuse easily through the membrane and Carbon Dioxide and other waste products can easily dissolve out. The concentration of oxygen in the cell is always lower than outside the cell which causes the oxygen to diffuse in. Gases will always dissolve from an area of high to low pressure. The concentration of carbon dioxide outside the cell is lower than the concentration in the cell so the carbon dioxide will always dissolve out of the cell.

Single celled organisms such as amoebas have a large surface area to volume ratio because they are so small. They are able to get all the oxygen and nutrients they need by diffusion through the cell membrane.

Larger organisms such as mammals have a relatively small surface area compared to their volume so they need special systems such as the lungs in order to get enough oxygen. Surface area to volume ratio is very important in lungs where a large amount of oxygen has to get into the lungs. The lungs have a very large surface area because they contain millions of sacs called alveoli which allow oxygen to diffuse into the bloodstream. By having millions of these alveoli the lungs are able to cram a very large surface area into a small space. This surface area is sufficient for all the oxygen we need to diffuse through it and to let the carbon dioxide out.

By increasing the surface area the rate of diffusion will go up.

## Precautions

a) All the gelatin used should be taken from the same block to ensure that all the blocks are made up of the same materials.

b) All the tests should be done at room temperature to ensure that the blocks of gelatin do not melt.

c) The same volume of acid should be used for all the tests to ensure that the rate of diffusion can not be affected by the pressure of a larger volume of acid.

d) Safety glasses should be worn to protect your eyes from the hydrochloric acid.

## Limitations

To help make this experiment more accurate, I repeated it three times for each block size and then used the average of all the results to plot a graph with a line of best fit. I tried to keep all the variables except for the size of the gelatin blocks the same for all the experiments. However, in reality it is impossible to keep all the variables precisely the same. For example:

a) It is also impossible to precisely measure the size of gelatin block each time. I measured the sizes to the nearest mm so the sizes of block that I used should be correct to the nearest mm.

b) When the gelatin blocks are dropped into the beakers the base of the block comes into contact with the bottom of the beaker which reduces the surface area of the block that comes into contact with the hydrochloric acid.

c) The results will be slightly inaccurate as the moment when the gelatin block has lost all it’s dye is a matter of opinion and not something that can be measured precisely.

d) Due to the fairly slow speed of our reactions it is only possible to measure the time of the reaction to the nearest 0.1 second even though the stopwatch shows the measurements to the nearest 0.01 second.

## Anomolies

The graph produced shows a smooth curve with a decreasing gradient as the surface area to volume ratio goes up. The only anomaly is the result for the 5 x 5 x 5 block. The result here is higher than the curve of best fit for the graph. The results for the 5 x 5 x 5 block ranged from 4.53 to 7.02 seconds with an average of 6.15 seconds. The line of best fit for the graph suggests that the average should be around 3 seconds. The anomalous result was probably due to experimental error as a result of this being the first block size that I used in the experiment. The most likely explanation is that I was unsure of how to judge when all the dye had disappeared and as a result delayed pressing the stop button of the stop watch. As the experiment progressed with the other block sizes I probably got better at making this judgement.

## Extension Work

This experiment could be improved in a number of ways.

1) It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.

2) Using more shapes and sizes of gelatin block would have produced a better looking graph.

3) Variables that might affect the rate of diffusion could be investigated. The rate of diffusion may also be affected by temperature, strength of acid and volume of acid

4) The block could be suspended in the hydrochloric acid so than none of it’s surfaces are in contact with the wall of the beaker. A small cradle could be used to suspend the blocks in the acid which would mean that all six sides of the cube should be in contact with the acid. This would ensure that diffusion could occur evenly through all the sides of the cube.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.

### Effects Of Varying Environmental Conditions On The Rate Of Transpiration In Leafy Shoots

Sunday, June 1st, 2008

# A Level Biology Project

## Aims

I plan to investigate how environmental conditions affect the transpiration of plants.

## Introduction

This is an A-level biology project. It helped me get an A grade for biology many years ago. The whole project is reproduced here for your reference.

## Background Information

The Sun provides the energy to turn the water in the plants into a vapour causing it to evaporate into the leave’s internal air spaces before diffusing out of the stomata into the air. This is known as transpiration. As the water evaporates out of the top of the plant it creates a suction on the column of water below it in the xylem. The upwards force on the column of water created by transpiration and the downwards force due to gravity created a tension in the column of water.

As the upwards pull is greater than the downwards pull the column of water moves up the xylem. Cohesion tension theory tells us that it is the evaporation of water from the leaves which causes the upwards movement of water. The water molecules have a high cohesion as they are polar and so are electrically attracted to each other. They are held together by hydrogen bonds. The column of water does not tend to break as it has a very high tensile strength from the bonds.

The water is able to evaporate out of the leaf as the leaf has a high water potential and the air has a low water potential so the water molecules pass down the concentration gradient from the spongy and palisade mesophyll cells into the leave’s internal air spaces before diffusing out into the air.

Transpiration is needed to keep the cells of the spongy and palisade mesophyll cells moist as this allows carbon dioxide to dissolve before diffusing into the cells for photosynthesis. The stomata open in the day to let carbon dioxide diffuse in, and to let oxygen diffuse out as part of photosynthesis. At night photosynthesis is unable to take place due to the absence of light so the stomata are closed to reduce water loss.

Light causes potassium ions to be pumped into the guard cells which lowers their water potential and so water diffuses into the guard cells causing them to go turgid and so open. At night potassium moves out of the guard cells into the surrounding cells so the water diffuses out of the guard cells causing them to close.

In hot climates the water loss by transpiration can exceed the water uptake from the roots which causes the plants to suffer from water stress. To combat this ABA is produced by the plant which causes the rapid pumping of potassium ions out of the guard cells which closes them and so reduces the water loss by transpiration.

## Apparatus Needed For The Experiments

1. Privet shoot (used as it has many big leaves)
2. Capillary tubing (1.13mm Diameter)
3. Bowl of water
4. Stand
5. Stopwatch
6. Ruler
7. Vaseline

## Method

For this experiment a simple potometer will be made to measure the rate of water uptake from the plant. The potometer is the easiest way of measuring this and is quite accurate as well. The experiment is limited by the fact that the potometer measures the total water uptake and not just the transpiration rate.

I am planning to use the following method for my experiment.

1. A privet shoot is cut under water in a large bowl about 1 inch up the stem. This should remove any blockages that are within the xylem when the shoot was originally cut. In order to stop the xylem vessels from being crushed when the shoot is cut, it should be cut diagonally with a razor blade. The end of the privet shoot should be left in the bowl of water that it was cut in order to prevent any air bubbles getting into the system.

2. The capillary tube should be completely filled with water by submerging it into the same bowl as the privet shoot.

3. The capillary tube should be attached to the shoot underwater being careful to make sure that there are no air bubbles in the tube.

4. The joins between the capillary tube and the shoot should be sealed with Vaseline to make sure that the system is water tight.

5. Making sure that the open end of the capillary tube remains underwater the plant can be raised out of the water and clamped above the bowl of water in an upright position.

6. The whole system should now be full of water and completely air tight. As the plant transpires it will pull water up through the tubing. This apparatus will measure the total water uptake.

7. Allow the apparatus to equilibrate for about 5 minutes. As this is the control experiment the leaves should be exposed to the maximum possible light intensity by using a bench lamp. There should also be no wind in the area that the experiment is taking place.

8. Introduce an air bubble to the system by holding the apparatus out of the water until a bubble forms.

9. Measure how far the bubble has risen up the capillary tube every thirty seconds for five minutes. When measuring the distances your eye should be at a 90º angle from the bottom of the bubble. This way parallax error can be avoided when looking at the scale on the ruler. You also must measure from the same point of bubble every time in order to ensure consistency in the measurement taking. I am planning to take all my measurements from the bottom of the bubble. The distances travelled should be noted.

Diagram Of The Potometer [not reproduced]

The test should be repeated 5 or 6 more times so that an accurate average of the rate of water uptake can be obtained. After each experiment the tubing can be refilled with water by placing the end of the tube underwater and squeezing it to force the air bubble out of the tube.

10. The air temperature of the room should also be noted. This test will give the rate of transpiration under normal inside conditions. These set of results are a control set of results against which the other results can be compared.

It is very important that the whole apparatus is air tight as if any bubbles of air were to get into the xylem then transpiration would not occur. This is because any air bubble would break the continuous column of water which is usually present in the xylem and so the water molecules below the air bubble would not feel the upwards pull from the above water molecules. The xylem would soon fill with air in a process called cavitation. The plant is cut under water an inch up it’s stem in order to get rid of the bottom part of the xylem which may have an air bubble in it. Doing this makes sure that the shoot which will be used in the experiment has water in it’s xylem.

The experiment can then be repeated but this time changing the following environmental conditions.

### Wind

To measure how wind affects transpiration a hairdryer or fan that blows cold air can be used to blow the leaves. The fan has to be fairly close to the leaves but not so close that it will buffet the leaves as this may cause the stomata to close.

### Humidity

The shoot will be enclosed in a transparent plastic bag. The humidity will soon increase as the water vapour which has been transpired will not be able to leave the bag and so will stay around the plant thereby increasing the humidity.

### Light

The windows will be covered and the lights dimmed to make the conditions darker.

### Surface Area

The surface area of the leaves of the plant can be reduced by vasolining the leaves on the top and especially to the bottom side of the leaf. The bottom side of the leaf is where the stomata are so this is where most of the water loss in the plant occurs. Applying Vaseline to the bottom surface of the leaf will block the stomata and so water vapour will be unable to leave the leaf through this leaf. The effect that this has on the rate of transpiration can be measured. The surface area of the leaf that has just been vaselined can be measured by drawing around the leaf on some graph paper. The surface area can be worked out by counting the squares. This vaselining technique can be used on more and more leaves till all the plant’s leaves are vaselined.

Each experiment should be replicated several times in order to obtain more accurate data and to get rid of any anomalies that may occur in a single experiment. I will note the results in a table for each 30 second period in all the experiments.

From these recorded distances I will work out the rate of water uptake for each 30 second period for all the experiments. Using these rates I plan to plot several graphs of the rate of water uptake against the time for various environmental conditions. I shall plot the results for the same environmental factors on the same graph so that the effect that these environmental factors has on the rate can easily be compared.

I shall also work out the volume of water taken up per minute. This can be worked out with the following equation.

Volume Of Water Uptake = p x Radius Of The Capillary Tube² x Distance Travelled

## Predictions

I predict that if the wind is increased the rate of transpiration will increase. In the control test where there will be no wind a band a water vapour will be able to form in the air spaces of the leaf and around it as water transpires out. This will reduce the water potential gradient between inside the leaf and the air so the rate of transpiration will be reduced. If air is blown across the leaves by the wind or in the case of this experiment a hairdryer, this band of water vapour will be blown away and further water vapour will not be able to accumulate. This will lead to an increase in the water potential gradient between the inside of the leaf and the air and so the rate at which water transpires into the air will increase.

I predict that if the surface area of the plant’s leaves available for transpiration is halved then the rate of transpiration will be halved. This is because the plant loses almost all it’s water through it’s leaves so if it loses the ability to transpire through half of it’s leaves then the plant will only lose half as much water through transpiration. The amount of surface area that the plant has should be directly proportional to the rate of transpiration.

## Results

Secondary results that were taken in January 1998 under controlled conditions were provided. The environmental conditions were measured with electronic probes. These results showed the distance that the air bubble had travelled up the capillary tube over a period of 4 minutes.

Using these results I worked out the rate of travel up the capillary tube for all the experiments. I also averaged the duplicated experiments to give me an average set of results for experiments 14 and 15, and also an average of experiments 11 and 12. I averaged experiments 1, 2 and 9 to produce control data for the rate of travel up the capillary tube against which the other results can be compared.

The sheet of secondary results is shown on the next page. The results table with my extra calculations for the rates of uptake and the averages of the duplicated experiments are shown on the page after that. [not reproduced]

Graphs of the rate of uptake against time were drawn by me for the surface area of the leaves and the wind speed.

## Interpretation

I will analyse the results for the surface area experiments and the wind speed experiments.

### Surface Area

The graph shows that as the surface area goes down, the rate of transpiration goes down. This would seem to prove my prediction. When the surface area of the plant’s leaves available for transpiration is reduced, the rate of transpiration is also reduced. When the surface area of the leaves is reduced from 5058mm² to 2773mm² (which is a decrease of 46%), the rate of transpiration decreases 50% which would seem to suggest a directly proportional relationship between the surface area and the rate of transpiration. However, when the surface area is reduced by 76% from (2773mm² to 659mm²) the rate of water uptake only reduces by 33%. This would suggest that perhaps the rate of transpiration is reducing at a directly proportional rate but that the rest of the water is being used for photosynthesis. When the plant had a large surface area only a small percentage of water was lost due to photosynthesis. When the plant’s surface area for transpiration was reduced the effect of photosynthesis on the water loss was a lot more noticeable.

Photosynthesis was able to continue because the leaves were still on the plant and receiving light, they must have had enough carbon dioxide left in the photosynthesising cells for photosynthesis to continue after the stomata had been blocked by the vasoline. If the plant had been left for a longer period of time then the carbon dioxide levels in the photosynthesising cells would have dropped and so the rate of photosynthesis would also have reduced.

The main anomaly with this graph is that it shows the control results, (surface area of 5997mm²) with a slower rate of water uptake than the experiment where the plant had a leaf surface area of 5058mm².

By looking at the provided raw data sheet it can be seen that the first two control experiments with a surface area of 5997mm² (1 and 2) would give an average rate of 0.9cm/minute which would make the rate higher than the experiment where the surface area was 5058mm². However it is the third control experiment (number 9) which drags the average rate down to below that of the experiment with less surface area. I believe the reason the rate for control experiment 9 being significantly lower than experiment 1 and 2 is due to experiment 9 being done straight after experiment 8 where the light level was reduced to 21%. This reduced light level will have slowed down the rate of transpiration to the extent that it had not had time to recover when experiment 9 (the third control experiment) was started. The reduced light level would have caused the stomata to close which would have resulted in less water being able to transpire out of the stomata. Therefore experiment 9 produced a lower average than that of 1 and 2.

### Wind

Wind moving past the leaves caused a large increase in the rate of water uptake. When there was no wind in the control experiments the average rate of water uptake was 0.85cm/minute. When the wind was added at 0.98m/s, the transpiration rate increased to1.1cm/minute, (an increase of 23%).

As I predicted, increasing the wind increases the water uptake rate. Increasing the wind speed to 1.1m/second further increased the transpiration rate to 1.13cm/second. The rate was much slower in the control test because in the absence of wind, a band of water vapour was able to form in the internal air spaces of the leaf and around the leaf as the water vapour transpired out. This reduced the water potential gradient between the spongy and palisade mesophyll cells inside the leaf and the air so the rate of transpiration was reduced. When air was blown across the leaves by the hairdryer, this band of water vapour was blown away and further water vapour was not be able to accumulate. This led to an increase in the water potential gradient between the spongy and palisade mesophyll cells inside the leaf and the air and so the rate of transpiration into the air increased.

## Limitations

a) The experiment measures the total water uptake which includes water used by the plant as well as the water lost through transpiration. Though most of the water (90 - 99%) is lost through transpiration, a small amount is used by the plant for photosynthesis and so this experiment is not able to tell us the exact rate of transpiration.

b) It is often difficult to change just one environmental condition without changing another. For example the lamps used to give the leaves the maximum possible light intensity in the experiment will also have the effect of slightly heating up the leaves. This could cause the rate of transpiration to go up.

c) These experiments were carried out one after another without leaving enough time for the plant to equilibrate after each experiment. For example, after the light intensity had been reduced to 21% in experiment 8, not enough time was allowed after it for the plants transpiration rate to rise to it’s normal level. Therefore, experiment 9 which was a control experiment produced a significantly lower average rate than the control experiments 1 and 2.

d) There was a general deterioration in the results as the experiments went on. As the experiments were carried out the water would have warmed up to room temperature. This will have caused bubbles to form in the xylem as the air started to dissolve out of it. These air bubbles could have caused a loss of cohesion tension in the leaves, which may have lead to cavitation in the xylem. This cavitation would have reduced the number of working xylem in the stem and could account for the reduced rated of uptake in later experiments.

## Extension Work

This experiment could be improved in a number of ways.

1) It could be repeated more times to help get rid of any anomalies. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.

2) More time should have been allowed between experiments to allow the plant to fully equilibrate before the next experiment was started. This would have reduced the number of anomalies caused by the sudden exposure of the plant to completely different conditions when the previous effects of the last experiment’s conditions had not had time to wear off.

3) The water used in the bowl could have been allowed to warm up to room temperature before the experiment began. This would have stopped the air in the water from dissolving out and leading to cavitation in the xylem vessels.

4) A different method of carrying out the experiment could have been devised that would measure the rate of transpiration instead of the total water uptake.

### Disclaimer

This is a real A-level school project and as such is intended for educational or research purposes only. Extracts of this project must not be included in any projects that you submit for marking. Doing this could lead to being disqualified from all the subjects that you are taking. You have been warned. If you want more help with doing your biology practicals then have a look at 'Advanced Level Practical Work for Biology' by Sally Morgan. If you want more detailed biology information then I'd recommend the book 'Advanced Biology' by M. Kent.