High School Biology Experiments

Experiments

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Table of Contents

Module 1- ................................................................................................................................................ 2

1. Effect of Temperature on enzyme activity- .................................................................................... 2

2. Effect of pH on enzyme activity - .................................................................................................... 4

3. Effect of substrate concentration on enzyme activity- ................................................................... 6

4. Effect of dissolved CO2 on pH of water- ......................................................................................... 8

5. Investigating blood cells- .............................................................................................................. 10

6. Conducting tissues- Xylem and phloem- ....................................................................................... 12

7. Dissection of Kidney- ..................................................................................................................... 14

8. Water Conservation in plants- ...................................................................................................... 16

Module 2- .............................................................................................................................................. 18

1. Model of Natural Selection- .......................................................................................................... 18

2. Model of meiosis- ......................................................................................................................... 20

3. Effect of environment on phenotype- .......................................................................................... 21

4. Model for polypeptide synthesis- ................................................................................................. 23

Module 3- .............................................................................................................................................. 25

1. Identify microbes in water- ........................................................................................................... 25

2. Model of Pasteur’s experiment to identify the role of microbes in decay- .................................. 27

3. Plant Diseases- .............................................................................................................................. 29

Module 4- .............................................................................................................................................. 31

1. Model of DNA- .............................................................................................................................. 31

2. Linkage- ......................................................................................................................................... 34

Experiments

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Module 1-

1. Effect of Temperature on enzyme activity-

Aim- To investigate the effect of temperature on the activity of an enzyme (Rennin). Hypothesis- the optimum temperature for the enzyme, Rennin, works best at 37 degrees (i.e. body temperature), as it is found within the stomach of an organism. Materials- Beakers (250mL), hot plate, test Tubes (3), rennin Solution, stopwatch, measuring cylinder, thermometer, test tube rack, milk. Variables-

Independent variable: temperature of the water bath. This temperature is constantly

changed throughout the experiment to test its effect on rennin. The temperatures used

were 0 c, 20 c, 40 c, 60 c and 80 c and were measured using a thermometer.

Dependent variable: enzyme activity or rate of reaction, measured as average time it takes

for milk to curdle. The time it took for the milk to curdle was measured using a stopwatch.

Controlled variables: Amount of milk placed into each of the test tubes (5mL), the amount and concentration of rennin used (1ml), the time the test tubes were left in the water bath (5min) and the same amount and type of milk. Risk assessment/safety procedures-

1. The milk and the enzyme may be contaminated and shouldn’t be consumed. Neither

the milk nor the enzyme was consumed and safety gloves and lab coat was worn

when handling them.

2. Glassware is fragile and if broken, can cause cuts. The glassware was placed in the

centre of the table and handled carefully to avoid breakages.

3. A hot plate/water bath was used which can cause burns. Care was taken while

handling the hot water bath, didn’t touch with bare skin and kept objects away.

Method-

1. Rennin solution was obtained.

2. A water bath was prepared at 40 degrees in a 250ml beaker using a hot plate.

3. 5ml of milk were placed into two test tubes labelled A (experimental) and B (control)

and 1ml of Rennin solution to the test tube labelled C.

4. The 3 test tubes were placed in the water bath and were left for 5 minutes.

5. The contents of test tube C were poured into test tube A and the stopwatch was

started.

6. Every minute or so, the test tubes were examined by gently tilting them and it was

made sure they were not shaken.

Experiments

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7. The time taken for clotting to occur in both test tubes was recorded.

8. The above steps were recorded at temperatures of 0 degrees (using ice cubes to

keep constant temperature), 20degrees (tap water), 60degrees and 80degrees (using

hot plate).

9. The entire experiment was repeated several times and the average results were

calculated.

Results-

Conclusion-

Enzymes function at an optimum temperature. In this investigation, Rennin works best at 37

degrees. A very high temperature, such as 80 degrees, denatures the enzyme, whereas a

very low temperature, such as 0 degrees, slows down enzyme reaction.

Experiments

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2. Effect of pH on enzyme activity -

Aim- to investigate the effect of pH on the activity of catalase. Hypothesis- the enzyme catalase works best at an optimum pH of approximately 7 (neutral). This is because catalase is found in many living organisms that require oxygen and their internal pH is neutral. In this experiment the best pH is 7.5. Materials- Citric acid buffer solutions of pH 4.4, 5.2, 6.5, 7.5 and 9, Hydrogen peroxide

solution, potato, 10ml and 100ml measuring cylinders, stopwatch, stand and clamp, water

bucket, cork borer, large test tube, rubber stopper and delivery tube, scalpel, hand gloves,

safety Glasses.

Variables-

Independent variable: pH buffer solution.

Dependent variable: the rate of reaction (volume of water displaced).

Controlled variables: Size of potato cylinders, amount of buffer solution, time of reaction,

volume of hydrogen peroxide and substrate concentration.

Risk Assessment/Safety Procedures-

1. Citric acid is corrosive therefore it can cause burns or irritations. Hand gloves are to

be worn to prevent any contact from citric acid buffer solution. Safety Glasses are to

be worn to prevent splashes in the eyes.

2. Hydrogen peroxide is an irritant and an oxidising agent (highly flammable). Hand

gloves and safety glasses are to be worn to prevent contact with skin/eyes. It is to be

kept away from any flames.

3. Glassware is fragile and if broken, can cause cuts. The glassware was placed in the

centre of the table and handled carefully to avoid breakages.

Method-

1. The apparatus was set up as shown below-

Experiments

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2. A cylinder of potato 5cm long was cut using a cork borer. It was then cut into 10, ½ cm

lengths and placed in the test tube.

3. 5ml of pH 4.4 buffer solution was added and the pH was recorded.

4. 5ml of hydrogen peroxide was added and the rubber stopper was immediately inserted

and the stopwatch was started.

5. The volume of oxygen collected in the measuring cylinder was recorded every minute

for 5 minutes.

6. The experiment was repeated using a different pH buffer solution and fresh potato.

7. The experiment was repeated using the different pH buffer solutions and the hydrogen

peroxide only. No potato was added and this acted as the CONTROL EXPERIMENT.

8. The steps 1-7 were repeated for each pH and the average results for each pH value was

calculated.

Conclusion-

Enzymes work best at an optimum pH and if this range is exceeded dramatically ( such as

with pH 4.4 or 9) the enzyme will become denatured and the rate of reaction will eventually

stop. The experiment proved that catalase works best at pH 7.5 as the greatest volume of

oxygen as produced (8ml).

Experiments

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3. Effect of substrate concentration on enzyme activity-

Aim- to investigate the effect of substrate concentration on enzyme activity. Hypothesis- As the substrate concentration increases the rate of enzyme activity will

increase up to a point. This is because each substrate molecule occupies an active site and

these active sites will eventually be fully occupied so the rate of enzyme activity will

increase up to the optimum and then continue to occur at the optimum.

Materials- 20mL hydrogen peroxide, distilled water, 5 test tubes and test tube rack, 10ml

pipette, cork borer, fresh potato, labelling pen or labels, ruler in cm and mm, stopwatch.

Variables-

Independent variable: substrate concentration: 0%, 25%, 50%, 75% and 100% of hydrogen

peroxide.

Dependent variable: rate of reaction (measured as height of oxygen bubbles produced).

Controlled variable: Size of potato cylinders, type of potato, total volume of solution

(substrate) and time for the reaction (5minutes).

Risk assessment/safety procedures-

1. Hydrogen peroxide is an oxidising agent and toxic if ingested. Do not put it near a

flame and don’t ingest it. Wear safety glasses to prevent it entering the eyes if

splashes occur. It is also highly corrosive. Wear gloves, lab coat and safety glasses to

avoid contact with skin and eyes. Wash area with cold running water if it comes in

contact wit skin or eyes.

2. Glassware can cause cuts if broken. Glassware must be kept in the centre of the

bench. If broken it should be disposed of carefully with a dust pan.

3. Scalpel is very sharp and can cause cuts. While passing the scalpel it must be done

carefully and must be pointed downwards, away from the body. If cut, wash, apply

pressure and apply first aid.

Method-

1. 5 test tubes labelled 1-5 were set up.

2. The volumes of hydrogen peroxide and distilled water were pipette into each test

tube as shown below.

Test tube 1 2 3 4 5

mL H2O2 0 2.5 5 7.5 10

mL Distilled water 10 7.5 5 2.5 0

% of H2O2 0 25 50 75 100

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3. The contents of each test tube were mixed and the level of liquid was marked in

each test tube, using the felt tip pen.

4. Prepared five cylinders of potato using a cork borer and each were cut into 6 equal

pieces.

5. Placed a set of 6 potatoes was placed into each test tube and quickly started the

stopwatch.

6. After 5 minutes for each test tube, the height of the oxygen bubbles produced was

marked and measured using a ruler, and the results were recorded in a table.

7. The experiment was repeated 5 times and the average results for each test tube

were calculated. NOTE- test tube 1 acted as a control (has no substrate).

Conclusion-

As the substrate concentration increases the rate of enzyme activity increases up to a

certain point i.e. as the substrate increased from 0-100%, the rate of reaction also increased

as shown by the average height of oxygen bubbles produced. However, if the experiment

continues with the concentrated hydrogen peroxide (100%), the reaction will proceed at the

maximum rate. This is because once all the active sites of the enzymes are occupied the rate

of reaction ceases to increase but will proceed at the maximum rate.

Experiments

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4. Effect of dissolved CO2 on pH of water-

Aim- to investigate the effect of dissolved carbon dioxide on the pH of water.

Hypothesis- as the concentration of dissolved CO2 in the water increases the pH of the water

will decrease. This is because when carbon dioxide dissolves in water it forms carbonic acid.

This dissociates to form hydrogen ions and bicarbonate ions. This increase in hydrogen

lowers the pH of the water. Carbonic Acid ---> hydrogen + bicarbonate.

Materials- 50mL distilled water, beaker (100mL), pH probe and data logger connected to

computer, straw, stopwatch, pH chart.

Variables-

Independent variable: dissolved CO2 concentration in the water.

Dependent variable: pH of the water.

Controlled variables: volume of distilled water (50ml), time CO2 was exhaled into the water

(60sec) and amount of UI used (10drops).


1. Glassware can cause cuts if broken. Glassware must be kept in the centre of the

bench. If broken it should be disposed of carefully with a dust pan.

2. Universal indicator is toxic and splashing may occur resulting in substances entering

the eye. Safety glasses must be worn to prevent splashing into the eyes when

blowing into the water with UI.

Method-

1. 50ml of distilled water was measured with a measuring cylinder and added into a

100ml beaker.

2. A pH probe was inserted into the beaker and it was connected to a data logger which

was connected to a computer.

3. Using a straw, Carbon dioxide was exhaled into the beaker for 60seconds, using a

stopwatch that was started simultaneously with the blowing of the straw. Changes in

the pH as the Carbon dioxide dissolved into the water were measured by the pH

probe, read by the data logger, and recorded by the computer in the form of a

graph, which was then printed out on a pH chart.

4. The experiment was repeated several times and the average results were calculated

(increases reliability).

5. As a control experiment the experiment was repeated several times without exhaling

into the beaker. This proved that any change in the pH of the water were a result of

dissolved CO2.

Experiments

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Results-

pH of water- pH probe and data logger- quantitative data

Conclusion-

In conclusion an increase in the concentration of dissolved carbon dioxide in water results in

a decrease in the pH of the water. This was observed in the graph produced by the data

logger and computer (refer to results).

Experiments

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5. Investigating blood cells-

Aim- To estimate the size of red and white blood cells

Materials- prepared slide of human blood smear, light microscope, labelled diagrams of human blood cell types, graph with 1mm grid.


1. When using the microscope, if care is not taken the slide and the objective lens can

break and pieces can cause cuts. Only lower the objective lenses while looking from

the side of the microscope. While looking through the eyepiece the lenses must only

be moved upwards to prevent them from crashing onto the slide and breaking the

lenses and slide.

2. There is a risk of infection if blood smears are prepared in the lab. Only a prepared

slide of human blood smear is used. This reduces chances of infection.

Method-

1. A light microscope was set up.

2. A microscope slide with a mini-grid was placed on the platform and it was focused

under the HP objective lenses.

3. The diameter of the field of view was measured and the value was recorded.

4. A prepared slide was observed under high power.

5. The slide was moved so that a row of red blood cells were lined up across the

diameter.

6. A row was selected so that it didn’t include too many side on red blood cells. The

number of red blood cells across the diameter was estimated.

7. The number of red blood cells was divided by the diameter to estimate their size.

8. The number of white blood cells that could fit across the diameter was estimated

and the diameter was divided by the number of white blood cells to estimate their

size.

9. Steps 1-8 were repeat with different slides and the average was taken to minimise

any errors to increase the reliability.

Experiments

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Results a-

1- Diameter of low power= 4.2mm= 4200micrometres

2- Diameter of high power= DLP X LPM÷HPM=420micrometres

3- No of RBC at HP=71 RBC across diameter

4- 70 cells=420 micrometres 1 cell= x x =6micrometres

5- Scaled diagram - scale= 1cm=2micrometres

6- Diagram of red blood cell-

Results b-

White Blood cell

25cells=420micrometres

1cell=16.8 micrometres

Scale

1cm=4micrometres

Experiments

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6. Conducting tissues- Xylem and phloem-

Aim- To draw transverse and longitudinal sections of xylem and phloem tissue.

Materials- Light microscope, coverslip, beaker of water, watch glass, celery stem, eosin dye

solution, scalpel, probe, dropper, slides, cover slips, prepared slides of a plant stem both

longitudinal and transverse sections.






lenses and slide.


carefully and must be pointed downwards, away from the body.

Method-

1. A light microscope was setup.

2. A celery stem that had been left in eosin dye for 24 hours was obtained. Excess dye

was washed off with water.

3. The thinnest section possible was cut from the stem using a scalpel. Both

longitudinal and transverse sections were cut.

4. The cut sections were placed in a glass of water.

5. The thinnest sections were placed on microscope slides in a drop of water and were

covered with cover slips.

6. The longitudinal and transverse sections were observed under the microscope, firstly

under low power than high power.

7. The xylem and phloem cells were identified in longitudinal and transverse sections.

8. Observed the prepared slides of the plant stems that had been stained to show

different tissues were observed.

9. Large labelled diagrams were made displaying the L.S and T.S of both xylem and

phloem and a diagram of the transverse section of the stem was made.

Experiments

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Results-

Conclusion-

The structure of Xylem is different to the structure of phloem. Xylem is composed of large

vessels, whose walls are thickened and strengthened by lignin. Xylem also contains hard

fibre cells, which adds support to the tissue. Xylem is dead and conducts water. Phloem

comprises supporting fibre cells, and two special cell types: sieve tubes and companion cells.

Unlike xylem, phloem tissue is alive and is the tissue for translocation.

Experiments

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7. Dissection of Kidney-

Aim- To examine the external and internal structure of a kidney and to relate structure to

function

Materials- Sheep kidney (with fat possible), dissecting tray, scalpel, forceps, scissors, hand

gloves, microscope and slides and/or photographs of the cellular structure of the kidney,

model of a kidney and/or other visual resources.






lenses and slide.



Method-

1. The fat was carefully removed from around the kidney.

2. The three tubes entering and leaving the kidney were identified (as the renal artery,

renal vein and ureter) and separated.

3. The kidney was cut in half lengthwise and the three tubes were left intact on one

side of the dissection.

4. The internal appearance of the kidney was observed and the cortex, medulla and

pelvis were identified.

5. The dissected kidney was disposed of correctly. The instruments, bench and hands

were washed thoroughly.

6. A slide of the microscopic structure of kidney tissue was examined. The Bowman’s

capsule, nephron tubules and collecting ducts were examined.

Experiments

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Results-

Conclusion-

The purpose of the kidney is to filter out metabolic wastes and maintain a balance in water,

salts and pH. The adaptation which gives the kidney its function is the many structures it

contains; glomerulus, nephrons, Loop of Henle, ect. There are approximately 800000 to

1000000 nephrons inside the kidney.

Experiments

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8. Water Conservation in plants-

Aim- To investigate structural features of various leaves that assist in conservation of water

Materials- Leaves from the following plants: banksias, casuarinas, eucalypt, geranium,

hakea, pigface, microscope slides, microscopes, hand lens/magnifying glasses, scalpel,

dropper.


1. Some plants may be toxic and there is a risk of allergic reaction to plant/soil. Gloves

should be used to protect the hands from contact with the soil.

2. The scalpel is very sharp and can cause cuts. While passing the scalpel it must be

done carefully and must be pointed downwards, away from the body.





lenses and slide.

4. Pot plants can fall of the bench and cause injuries. The pot plants must be left in the

centre of the bench to prevent them from falling off the bench.

Method-

1. A variety of leaves was collected from different species as listed in the materials.

2. The shape of the leaf was observed and compared with the Surface Area: Volume

ratio.

3. The orientation of the leaves was observed and any vertically hanging leaves were

noted.

4. A hand lens was used to observe the leaves for the presence of fine hairs.

5. A drop of water was placed on each leaf surface (upper and lower) to see if it had a

waxy cuticle.

6. A leaf was cut from the pigface and the cut surface was run across a microscope slide

to investigate any water storage in fleshy tissue.

7. Thin cross-sections of the various leaf surfaces were prepared and a light microscope

was used to see if stomates were present on the upper or lower surface and if the

stomates were sunken.

8. The water conservation features and how they reduce water loss, along with

examples of plants with the feature were recorded in a table.

Experiments

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Results-

FEATURE HOW IT REDUCES WATER LOSS EXAMPLES OF PLANT WITH

FEATURE

Vertically hanging leaves

- Leaves hung vertically - Reduce the surface area expose to the sun - Less water evaporates.

Eucalypts

Waxy cuticle - Reduces water loss as cuticle prevents evaporation - Reflects radiation from sun, reducing heat gain.

Saltbush, Eucalypts

Photosynthetic stems - Reduces surface area exposed to sun and water loss.

Casuarina

Needle-like leaves - Reduce surface area and water loss. Casuarina, Hakea, Acacia

Water storage in fleshy tissues

-Water is stored in trunk, leaves or roots. Pigface

Sunken stomates - Stomates lay in cavity in leaf which results in humid air being concentrated above stomata which reduces water loss.

Hakeas

Hairy leaves - Reduces air movement - Increases humidity over stomates, preventing transpiration and water loss.

Conclusion-

A plant that is adapted to an arid environment is called a xerophyte. Many xerophytes have

specialised tissues for storing water e.g. cacti. Others may have thin narrow leaves or even

spikes for minimising water loss. Xerophyte leaves often have abundant stomata to

maximise gas exchange during periods in which water is unavailable, and the stomata are

recessed in depressions, which are covered in fine hairs to help trap moisture in the air.

Experiments

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Module 2-

1. Model of Natural Selection-

Aim- to observe natural selection by means of a model.

Hypothesis- The green coloured toothpicks would be the least likely to be picked on the

grass, the red toothpicks would be the least likely to be picked on the red background and

the same for yellow.

Materials- 60 coloured toothpicks (20 green, 20 red, 20 yellow), different coloured

backgrounds.

Variables-

Independent: background.

Dependent: number and colour of toothpicks found.

Controlled: total number of toothpicks of each colour (20), time given for predators to pick

toothpicks (15 sec), total area of background surface (3m by 3m) and same predators.


1. Toothpicks have sharp, pointed ends- care must be taken whilst picking up

toothpicks to prevent pointed ends causing injuries to hands.

Method-

1. Measure out a 3m by 3m area on the grass surface. Mark the corners of the square

with wooden pegs and the sides of the area with strings.

2. Obtain 60 toothpicks (20 green, 20 red and 20 yellow).

3. Work in groups of 3 whereby one member will be the scatterer, the other two will be

predators.

4. Ask the ‘predators’ to look away and then scatter the toothpicks over the marked

area.

5. Allow the predators 15 seconds to find as many toothpicks as they can.

6. Count the number of each colour of toothpick found and record in table.

7. Repeat the above steps 5 times to see if similar results are obtained. If similar results

are obtained the results are reliable. Calculate the average of the repeats as the final

results to make any errors insignificant.

8. The experiment is valid because only one variable is tested at a time.

Experiments

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Results-

Limitations-

1. It doesn’t take into account other factors that may affect the survival of an individual

in a population e.g. disease.

2. It assumes equal numbers of individuals are born each year whereas in natural

population numbers vary.

3. Oversimplifies natural selection in terms of time it takes to occur.

Advantages-

1. Simulates process of natural selection.

2. It shows that organisms with favourable characteristics have higher chance of

survival and reproduction than organisms without the characteristic.

3. It can be improved by repeating the experiment on a larger number of backgrounds and comparing the results to see if similar results are obtained.

Conclusion-

Green toothpicks were least chosen in the green background. This models natural selection

as it shows that green camouflage would be a “favourable characteristic,” and over time,

there would be greater numbers of green toothpicks in the population. This also applies to

the yellow toothpicks on the yellow background and the red toothpicks on the red

background.

Experiments

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2. Model of meiosis-

Aim- to develop a model to illustrate meiosis.

Materials- 2 different coloured dough (green and yellow).

Method-

1. Obtained two different colours of play dough e.g. green and yellow. Different colours

were used to represent maternal and paternal chromosomes within the homologous

pairs of chromosomes.

2. The green dough was rolled into two strips of equal length to represent replicated

chromosomes.

3. The two strips were joined by pressing near the middle to indicate the position of the

centromere. The green chromosome represents the paternal chromosome.

4. The above steps (2-3) were repeated with yellow dough to construct the maternal

chromosome.

5. The above steps (2-4) were repeated to construct another pair of homologous

chromosomes.

6. The homologous chromosomes were paired up in a line at the equator to show the

two tetrads at the first meiotic division.

7. Crossing Over was shown by swapping the ends of the two innermost chromatids in

the tetrad.

8. The chromosomes were moved through the steps of first and second meiotic division

to show the production of haploid gametes.

9. The homologous chromosomes were rearranged at the equator to show another

possible arrangement of homologous chromosomes at the first division. This is to

represent random segregation.

Limitations-

1. Oversimplifies the process of meiosis as only two pairs of chromosomes were shown

where in reality the number would have been much larger.

2. Behaviour of genes is not shown e.g. genes aren’t shown on the chromosomes.

Benefits/Strengths-

1. Two different colours enable maternal and paternal chromosomes to be

distinguished.

2. The model illustrates the behaviour of chromosomes during crossing over.

3. The model shows that the movement of chromatids during meiosis 2 is at 90 to the

movement of homologous chromosomes at meiosis 1.

4. The model also shows the production of haploid gametes from diploid cells.

Experiments

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3. Effect of environment on phenotype-

Aim- to investigate the effect of one environmental factor on the phenotype of pea plants.

Materials- 20 pots, packet of genetically identical pea seeds (tall), potting mix, measuring

cylinder, ruler, measuring tape, gloves, safety glasses.

Variables-

Independent variable: amount of light the plant is exposed to.

Dependent variable: height of the pea plants.

Controlled variables: temperature, time for growth, type of soil, size of pot, amount of

water given.


1. Composts/potting mix contain microbes including bacteria and fungi. Avoid contact

with eyes and skin by wearing hand gloves and lab coat.

2. Inhalation of dust may irritate nose/throat/lungs. Avoid breathing in dust.

Method-

1. Firstly, the twenty pots were filled to the same level with potting mix, using ruler to

mark the level.

2. Then 5 pea seeds were put into each pot at equal depth, using a ruler to measure

depth.

3. The pots were then watered (10mL using measuring cylinder) and the potting mix

was moistened. 10 of the pots were placed on the window sill and the other 10 in a

dark cupboard, all of them for 2 weeks.

4. The pots were watered with the same amount of water each day (10mL).

5. The heights of the plants were recorded each day and any other differences such as

colour were noted.

6. The heights of the plants were measured using a measuring tape and results were

recorded each day. Any other differences such as colour were also noted.

7. The average height for the plants grown in both dark and light was calculated.

Experiments

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Results-

Discussion/conclusion-

1. Compare growth of pea plants in light and dark- In the light the pea plants reached an

average height of 32.3cm whereas in the dark the plants reached an average height of

38.8cm. The peas grew taller in the dark. The pea plants grown in the dark also

appeared yellow in colour indicating a lack of the pigment chlorophyll.

2. How has the availability of light affected the growth i.e. how has the environmental

factor affected the phenotype- In terms of height all the pea plants had genetically

identical information (tall gene). With identical conditions all the seeds would be

expected to grow to the same height. There was differences observed after 2 weeks

and this was because of the environment. All variables were controlled except for the

amount of light the plants received. Therefore we can conclude that the lack of light

has resulted in pea plants growing taller than they do in the presence of light.

Environment + Genotype = Phenotype

3. Comment on the reliability of the data and any sources of error- It was observed that

not all the seeds germinated at the same time. Also not all the seeds germinated.

However, 10 pots each containing 5 seeds were placed in light and 10 in dark. These

repeat trials increase the reliability of the data.

Experiments

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4. Model for polypeptide synthesis-

Aim- to develop a model to illustrate polypeptide synthesis

Materials- blue, red, green, white, and yellow plastic pegs, wool of three different colours,

paper, cardboard, marking pen, sticky tape.

Method-

Transcription in the nucleus-

1. Construct a double stranded DNA molecule as shown in the diagram below. Use blue

pegs to represent adenine, red pegs to represent thymine, green pegs to represent

guanine and yellow pegs to represent cytosine.

2. Use the sequence ATG AAA CTC on one of the strands and clip the complementary

‘base’ pegs on to these to form a double stranded molecule.

3. Now, ‘unzip’ the DNA by unclipping all the pegs, leaving two single stranded

molecules.

4. ‘Copy’ your original strand by again clipping complementary bases on, but this time

match adenine with a white Uracil peg.

5. Thread wool of a different colour through the holes in these pegs to represent a

strand of messenger RNA.

Translation on the ribosome-

6. To represent tRNA molecules, use another colour of wool again and thread it

through appropriately coloured pegs to represent the triplets CUC AAA and AUG.

7. On each of your three tRNA molecules attach a cardboard label with the amino acid

names glutamic acid, phenylalanine and tyrosine respectively.

8. Unclip your messenger RNA molecule from the original DNA strand and attach the 3

tRNA molecules to it according to the sequence of bases present.

9. Attach the amino acids together with sticky tape and remove all pegs and wool. You

should be left with a sequence of amino acids that represent a portion of a

polypeptide.

Experiments

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Benefits of the model-

This model showed that DNA contained the code needed for polypeptide synthesis.

This model illustrated how mRNA is made using information in DNA and how the

information on mRNA is used to assemble amino acids.

This model illustrates the movement of the ribosome along the mRNA so that amino

acids could be formed.

It illustrates complementary base pairing in the two strands and complementary

base pairing between codons and anti-codons.

Limitations-

It oversimplifies the process f polypeptide synthesis as the enzymes involved are not

shown.

This model only shows 3 amino acids being assembled whereas in reality a

polypeptide chain may have 300-400 amino acids joined together.

Experiments

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Module 3-

1. Identify microbes in water-

Aim- to examine a range of microorganisms found in water.

Materials- 4 sterile nutrient agar plates, sticky tape, marking pens, water samples from a

variety of sources (pond/river water, tap water and distilled water), methylated spirits, 3

sterile pipettes.

Method-

1. Sterilise the workbench area with methylated spirits.

2. Collect 4 petri dishes that contain nutrient agar.

3. Leave one plate unexposed, seal with sticky tape and label as control.

4. For each water sample place 0.5ml onto agar plate using a sterile pipette. Close the

lid gently and rock the water sample so that it spreads evenly over the entire plate.

5. Seal with sticky tape and label correctly.

6. Incubate all the plates for 3 days at 30 degrees Celsius.

7. Record results in table, identify, count and record number of colonies and types of

microorganisms in water.

Variables-

Independent variable: source of water.

Dependent variable: number of colonies/type of bacteria grown.

Controlled variables: time allowed for bacteria to grow (3days), temperature of incubation

(30 Degrees Celsius) and amount of water pipette into agar pate (0.5ml).


1. All microbes when grown in large numbers are potentially harmful therefore certain

precautions must be taken. All equipment should be placed in disinfectant after use.

2. Re-used items should be disinfected or autoclaved (pressure cooker).

3. Plastic equipment including used agar plates should be disinfected and autoclaved

before disposal.

4. Hands should be washed and dried before leaving.

5. Agar plates should never be opened after experiment has been setup as they may

contain pathogens.

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Results-

Conclusion-

Large numbers of microbes were found in the pond water, whereas no microbes were found

in the distilled water. Sterile techniques are needed to prevent contamination from other

sources such as hands, air etc.

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2. Model of Pasteur’s experiment to identify the role of microbes in decay-

Aim- to repeat Pasteur’s experiment concerning spontaneous generation of life.

Materials- 2 x 250ml conical flasks, clear broth (e.g. peptone dissolved in water or clear soup

or beef sock that has been added to boiling water and filtered), clear plastic tubing, rubber

stopper/ glass tube insert, hot plate.

Variables-

Independent Variable: presence or absence of coiled tubing.

Dependent variable: extent of contamination, observed as “cloudiness” in the broth.

Controlled variables: same volume of broth (100ml), same time for experiment (7days),

same room temperature, same time for experiment (7 days), same type of nutrient broth.

NOTE: Open flask is control, coiled tubing is experimental- must state in method.


1. Care should be taken when heating the broth as steam burns. Stay away from the

boiling broth when steam is being released.

2. Spitting broth can enter eyes and cause injury. Wear safety goggles to protect eyes

from spitting broth.

3. Care should be taken when handling hot plate and the hot flasks. Keep clear of hot

plate and hot flasks and don’t touch with bare skin to avoid burns. Only handle them

once they have cooled.

Method-

1. Prepare a fresh, clear broth and place 100ml of the broth in each of the two conical

flasks (labelled A and B).

2. Place the rubber stopper with coiled rubber tubing on flask B (experimental flask).

Leave flask A open (control flask).

3. Gently boil the flasks on a hot plate for 5 minutes. Ensure that steam is escaping

from both containers. Take care as steam burns can be worse than hot water burns.

4. Allow the flasks to cool. Place them in a tray and leave them for 10 days.

5. Examine the broth in each flask. Look for the appearance of “cloudiness” in the

broth. This is indicative of the presence of microbes.

6. Record your observations.

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Results-

The broth in the conical flask with the rubber stopper and coiled tubing remained clear and

there was no evidence of any contamination. The broth in the open conical flask turned

cloudy suggesting microbes had entered and contaminated the broth.

Microbes in the air were able to enter through the open neck of the flask and cause

contamination. In the flask which had the coiled plastic tubing (resembling swan necked

flask) the microbes got trapped in the coil therefore there was no contamination. This

investigation models Pasteur’s famous experiment. It shows that the microbes are present

in the air and when they enter the nutrient broth they cause decay. This experiment

disproves the theory of spontaneous generation.

Experiments

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3. Plant Diseases-

Aim- To examine plant shoots and leaves and gather information/ evidence of plant

pathogens, including insect pests, viruses or fungi.

Materials- leaves/stem from various plants, hand lens, scalpel.




2. Some plants may be toxic and there is a risk of allergic reactions to the plant. Hand

gloves must be worn to prevent any contact with the plants or allergens on plant.

3. Pests on plant may bite. Wear hand gloves to prevent contact.

Results/observations-

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Experiments

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Module 4-

1. Model of DNA-

Aim- to construct a model of DNA, identify the different components of a nucleotide and

understand the way in which bases pair up with each other.

Materials- polystyrene block, blue tack, two pieces if wire 60cm long, 42 pieces of Macaroni,

42 pipe cleaners (4 different colours), retort clamp and stand, food colouring, wooden

dowel, plasticine (play dough).

Method-

1. Obtained red food colour in a 50ml beaker.

2. Placed play dough at one of the open ends of the macaroni.

3. Dunked the macaroni in food colour to dye only half of the macaroni. The coloured

half represents the sugar and the uncoloured half represents the phosphate.

4. Placed the macaroni on paper with the play dough end facing down and sticking to

the paper in order to dry.

5. Obtained 4 different colours of pipe cleaners to represent bases: red to represent

adenine, yellow to represent thymine, blue to represent guanine and pink to

represent cytosine.

6. Cut 8cm of the pipe cleaners. Twist 2cm from one end of the pipe cleaners

(complementary bases) together e.g. red with yellow and blue with pink.

7. Inserted the other end of the pipe cleaners into the coloured ends (sugar) of the

macaroni. Ensured that the pipe cleaners were 8cm in length between the

macaronis- the same distance between the two wires in the polystyrene. The

macaronis coloured ends were assembled to show the anti-parallel nature of the

complementary nucleotides.

8. Attached a block of polystyrene on the base of a clap stand using sticky tape.

9. Inserted two pieces of wire into the polystyrene 8cm apart.

10. Threaded two macaronis of the assembled complementary nucleotides into the two

wires.

11. Completed the DNA by threading 10 complementary base nucleotides onto the

wires. There are 10 complementary bases in one turn of the DNA helix.

12. Attached the free ends of the wires to a wooden dowel and twisted the dowel to

show a turn of the double stranded molecule.

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Experiments

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Advantages of the model-

Helps to visualise the 3D structure of a DNA i.e. the double helix structure of the

DNA.

It shows the complementary base pairing (A-T and C-G) represented by red-yellow

and blue-pink pairing.

It shows that DNA molecule is the same width throughout i.e. purine always pairs

with a pyrimidine.

It shows 2 polynucleotide chains or strands running in opposite directions (anti

parallel).

Shows basic arrangement of molecules in a nucleotide (phosphate-uncoloured part

of macaroni, sugar-coloured part of macaroni and a nitrogenous base-pipe

cleaners).

Limitations-

Hydrogen bond between bases is not shown.

Size of bases weren’t to scale.

Phosphodiester bond between phosphate and sugar of adjacent nucleotides is not

shown.

The protein histones, cores around which DNA molecule winds are not shown.

In actual molecule sugars and phosphates are connected by actual chemical bond

but in the model they are represented together as a single piece of macaroni half

dyed.

Conclusion-

Describe structure of DNA and nucleotides.

Experiments

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2. Linkage-

Aim- To develop a model to illustrate linkage.

Materials- pipe cleaners, rubber bands (4 different colours, 2 of each).

Method-

A heterozygote (GgDd) cell containing a pair of chromosomes with linked genes

(genes G and D are linked) was modelled.

1. Cut 4 pieces of pipe cleaners, each 10cm in length.

2. Twist two pipe cleaners together to represent 2 chromatids joined together at

centromere in a chromosome. Repeat this for the other two pieces of pipe cleaners.

3. Attach 2 different coloured rubber bands (green for G, yellow for g, red for D, blue

for d), 4cm apart on each of the chromatids on the 2 chromosomes. The same

colours on sister chromatids were used to represent identical genes. The rubber

bands represent alleles and the 2 rubber bands on the same chromatids means

linked genes.

4. The homologous pair of chromosomes was moved through the stages of meiosis and

the combinations of genes in the gametes were recorded.

5. Crossing over was modelled by cutting and rejoining pipe cleaners at the cross over

point. This was done at various positions to see the effects of linked genes being

close together or further apart. Meiosis was also modelled without crossing over and

with 2 pairs of chromosomes with non-linked genes.

Experiments

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Experiments

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Experiments

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High School Biology Experiments