Experiments Page 1 of 37 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
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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.
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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.
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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-
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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).
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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.
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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).
Risk assessment/safety procedures-
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.
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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).
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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.
Risk assessment/safety procedures-
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.
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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
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6. Conducting tissues- Xylem and phloem-
Aim- To draw transverse and longitudinal sections of xylem and phloem tissue.