Required Practicals 7 - 12

Question 1

RP7 - What is the purpose of chromatography?

Answer 1

To separate different components in a sample.

Question 2

RP7 - State the factors affecting the rate of migration of different pigments.

Answer 2

Solubility
Mass
Affinity to the paper

Question 3

RP7 - What is the formula of the RF value?

Answer 3

Distance moved by pigment / Distance moved by solvent

Question 4

RP7 - What is the purpose of finding the RF value of a pigment?

Answer 4

Experimental RF value can be compared to a standard value in a database to identify the pigment.
The standard value should be measured using the same paper and solvent.

Question 5

RP7 - Outline the procedure of using chromatography to separate photosynthetic pigments.

Answer 5

1. Draw a horizontal pencil line 1cm above the bottom of the filter paper.
2. Add some acetone and use the mortar and pestle to grind up the leaf sample
   and release the pigments.
3. Use a capillary tube to transfer the pigment onto the pencil line.
4. Suspend the paper in the solvent so that the level of the liquid does not lie
   above the pencil line and leave the paper until the solvent has run up the
   paper to near the top.
5. Remove the paper from the solvent and draw a pencil line marking where the
   solvent moved up to.
6. Calculate the Rf value for each spot.

Question 6

RP7 - State the hazards and precautions in this practical.

Answer 6

Solvents are irritant and flammable.
Keep away from naked flames, wear eye protection and avoid contact with skin.
Leaf extract may be a biohazard.
Wash hands after use.

Question 7

RP8 - What is the function of dehydrogenase in chloroplasts?

Answer 7

It catalyses the acceptance of electrons by NADP in the light dependent reactions.

Question 8

RP8 - What is the purpose of DCPIP?

Answer 8

It is a redox indicator dye and acts as an alternate electron acceptor instead of NADP. It turns from blue to colourless when reduced.

Question 9

RP8 - Why is the plant extract chilled in an ice-water bath?

Answer 9

To lower the activity of enzymes to prevent them from breaking down the
chloroplasts.

Question 10

RP8 - How is the control set up?

Answer 10

Fill a cuvette with chloroplast extract and distilled water.

Question 11

RP8 - How is light intensity controlled?

Answer 11

Adjust the distance of the lamp from the set up.
Perform the practical in a dark room so that the only light source is the lamp.

Question 12

RP8 - What is the function of the muslin cloth?

Answer 12

To filter out any debris in the ground leaf mixture but allowing chloroplasts to pass through.

Question 13

RP8 - Why are the stalks of leaves removed before grinding?

Answer 13

The stalks do not contain many chloroplasts.

Question 14

RP8 - Outline the procedure of investigating the effect oflight intensity, after chloroplast extract has been obtained.

Answer 14

1. Set the colorimeter to the red filter. Zero using a cuvette containing
   chloroplast extract and distilled water.
2. Place test tube in the rack 30cm from light source and add DCPIP.
   Immediately take a sample and add to cuvette. Measure the absorbance of
   the sample.
3. Take a sample and measure its absorbance every 2 minutes for 10 minutes.
4. Repeat for different distances from lamp up to 100 cm.

Question 15

RP9 - What is the function of methylene blue in this practical?

Answer 15

It is a redox dye and acts as an alternate electron acceptor of the electrons transferred during ATP synthesis.
It turns from blue to colourless, indicating the end point.

Question 16

RP9 - Outline the procedure to investigate the effect of temperature on the rate of respiration of yeast.

Answer 16

1. Set up a water bath at 35°C.
2. Add equal volumes of the yeast and glucose solution to three test tubes.
   Place test tubes in the water bath and leave them to equilibrate for 10 minutes.
3. Add 2 cm3
   of methylene blue to the test tubes and start the timer. Shake for 10 seconds and place test tube back in water bath. Record how long it takes for the methylene blue to turn colourless for each test tube.
4. Repeat the experiment using temperatures of 40°C, 50°C, 60°C and 70°C.

Question 17

RP9 - How are the results used to calculate the rate of respiration at each temperature?

Answer 17

Rate = 1 / time taken for methylene blue to decolourise

Question 18

RP9 - Why does the yeast solution need to be buffered?

Answer 18

To maintain a constant pH so that the enzymes are functioning at their optimum pH.

Question 19

RP9 - What is the effect of temperature on the rate of respiration?

Answer 19

As temperature increases, the rate of respiration increases to an optimum. This is because the rate of enzyme activity increases.
Beyond the optimum, enzyme activity decreases as enzymes denature with high temperature.

Question 20

RP10 - How can a choice chamber be used to measure the favourable environment of a small organism?

Answer 20

By setting up chambers in different quadrants with different environmental conditions: dark + dry, dark + damp, light + dry, light + damp
Organisms will move to the quadrant they find favourable

Question 21

RP10 - What factors must be controlled when repeating the experiment?

Answer 21

Number of animals
Environmental conditions
Time allowed for animals to choose

Question 22

RP10 - Which statistical test is used to analyse the results of this practical and why?

Answer 22

Chi squared test. It compares the expected and observed values, and tests if there is a significant difference.

Question 23

RP10 - What is the conclusion drawn if the calculated value is greater than the critical value?

Answer 23

Null hypothesis is rejected.
Less than 5% probability that the difference is due to chance alone.
There is a statistically significant difference between the expected and observed values.

Question 24

RP10 - What do animals do when they are in unfavourable environments?

Answer 24

They move faster and change direction more frequently to increase their chances of survival.

Question 25

RP10 - State the hazard and precaution involved in this practical.

Answer 25

The live organisms used are a biohazard. Wash hands after handling.

Question 26

RP11 - How can Benedict’s solution be used to measure the concentration of glucose in a solution?

Answer 26

Use a colorimeter to measure the absorbance of a series of solutions of known concentrations to create a calibration curve. Compare the absorbance of an unknown sample to the calibration curve

Question 27

RP11 - What is a serial dilution?

Answer 27

A dilution where successive concentrations increase/decrease in a logarithmic fashion

Question 28

RP11 - Outline the procedure of this practical.

Answer 28

1. Make a serial dilution of glucose, ranging from 0 to 10 mmol dm-3
2. Place 2 cm3
   of each of the unknown samples in separate boiling tubes.
3. Add 2 cm3
   of Benedict’s solution to all boiling tubes.
4. Place boiling tubes in a water bath at 90°C for four minutes.
5. Zero the colorimeter using a cuvette with distilled water and set to red filter.
6. Place known samples into cuvette and measure the absorbance of each using the colorimeter.
7. Make a calibration curve.
8. Measure the absorbance of the unknown samples using the colorimeter. Use the calibration curve to determine glucose concentrations.

Question 29

RP11 - What are the axes in a calibration curve?

Answer 29

Absorbance against glucose concentration.

Question 30

RP11 - What would a high glucose concentration in urine
suggest?

Answer 30

It may suggest diabetes. Lack of insulin leads to high blood glucose concentration, hence high concentration in the glomerular filtrate, so not all glucose can be reabsorbed in the proximal convoluted tubule.

Question 31

RP11 - State the hazards and precautions of this practical.

Answer 31

Benedict’s solution is an irritant, wear eye protection, avoid contact with skin.
Handle the hot water bath with care.

Question 32

RP11 - How can you increase the accuracy of the estimate of the unknown glucose solution?

Answer 32

Increase the number of concentrations (at smaller intervals) for the calibration
curve within the range of concentrations that the unknown solution belongs in.

Question 33

RP12 - List 3 abiotic factors.

Answer 33

Light intensity Humidity
Temperature Wind speed
Water supply Day length
Nutrient supply Rainfall

Question 34

RP12 - List 3 biotic factors.

Answer 34

Competition for resources
Predation
Disease

Question 35

RP12 - How is percentage cover calculated?

Answer 35

Use a quadrat with squares. Count how many squares the required species is present in.

Only count a square if more than half of the square is covered.

Calculate the percentage of squares the species is present in.

Question 36

RP12 - Outline the procedure to this practical.

Answer 36

1. Choose an area to take samples from. Use a random number generator to
   generate 10 sets of random coordinates.
2. Use two tape measures to create a set of axes off which coordinates can be
   read.
3. Place the quadrat at each of the coordinates, placing the bottom left corner on
   the coordinate every time.
4. Record the percentage cover for the chosen species.
5. At each coordinate, a measure of the independent variable should be taken.
   Eg. record light intensity using a photometer at each location

Question 37

RP12 - How can the results be used to determine the
relationship between the chosen factor and the
percentage cover?

Answer 37

Use a statistical test eg. Pearson’s linear correlation, Spearman’s rank

Question 38

RP12 - Why should a random number generator be used?

Answer 38

To avoid bias in random sampling.

Question 39

RP12 - State the formula for the mark-release-recapture
method.

Answer 39

Population size = no. in 1st sample x no.in 2nd sample /
no. marked in 2nd sample

Question 40

RP12 - State the assumptions when using the mark-release-recapture method.

Answer 40

No births, deaths or immigrations.
Random mixing of marked individuals with population.
Marking does not affect behaviour of individuals or make them more vulnerable to predators.