· Web viewThe diagram shows apparatus used to measure the oxygen uptake of snails that live...

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A-level Biology (7401/7402)Section 5 Practical Skills

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Q1. S The diagram shows apparatus used to measure the oxygen uptake of snails that live on the seashore. The apparatus was kept at a constant temperature.

(a) (i) Explain the purpose of the strip of filter paper in the potassium hydroxide solution.

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(ii) The level of liquid in the right-hand side of the manometer went down during the experiment. Explain why.

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(iii) What measurements are needed to calculate the rate of oxygen uptake by the snails in mm3 g–1 h–1?

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(b) Two experiments were carried out using the apparatus shown in the diagram.

1 The oxygen uptake of batches of 10 seashore snails kept in moist air was measured at temperatures between 5 °C and 35 °C.

2 Experiment 1 was repeated but with batches of 10 seashore snails covered by aerated seawater.

The experiments were repeated several times and means and standard deviations calculated. The results are shown in the table. The values given are means plus or minus one standard deviation.

Temperature / °COxygen uptake of

snails kept in moistair / mm3 g–1 h–1

Oxygen uptake ofsnails kept in

seawater / mm3 g–1 h–1

5 35 ± 2 28 ± 8

10 34 ± 6 32 ± 3

15 36 ± 3 35 ± 3

20 86 ± 8 52 ± 10

25 141 ± 13 96 ± 15

30 132 ± 14 108 ± 9

35 120 ± 16 79 ± 21

(i) Describe one similarity and one difference between the pattern of mean oxygen uptake of the snails kept in moist air and those covered by seawater.

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(ii) Explain why valid conclusions cannot be drawn about the trends in oxygen uptake at temperatures of 25 °C and above.

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(Total 10 marks)

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Q2.In some countries, pigs are reared in intensive units in which the temperature is controlled. Agriculturalscientists investigated the effect of temperature on pig growth and on the efficiency with which the pigsconverted food to biomass.

(a) (i) In the investigation, the scientists used pigs of the same breed, with similar genotypes.Explain why.

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(ii) The pigs were allowed to eat as much food as they wanted.How could this have decreased the reliability of any conclusions drawn from theinvestigation?

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The table shows the results of this investigation.

Temperature / °C Mean growth rate /kg per day

Efficiency of conversion offood to biomass /%

0 0.54 19

10 0.80 42

20 0.85 48

30 0.45 37

35 0.31 37

(b) (i) Describe the effect of temperature on mean growth rate.

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(ii) A student concluded from these data that the mean growth rate of the pigs was fastest at 20 °C.Do you agree with this conclusion? Explain your answer.

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(c) (i) Pigs can survive at temperatures above 35 °C. Use the data to suggest why scientists did notcarry out any investigations at temperatures higher than 35 °C.

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(ii) The efficiency of conversion of food to biomass is lower at 0 °C than it is at 20 °C.Suggest an explanation for the lower efficiency.

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(d) Pigs require a mixture of fibre and protein in their food. The greater the ratio of fibre to protein, the lessthe food costs.

Scientists took five large groups of pigs. They fed each group a different high-fibre food. Each of the foods contained fibre from different plant species, but they all had the same energy content. The scientists fed a control group of pigs a low-fibre food with the same energy content. After 10 days, the scientists comparedthe masses of the pigs fed on high-fibre food to those fed on low-fibre food.

The graph shows the results of the investigation. The bars represent ±2 standard errors of the mean.

A farmer saw these results and concluded that he should replace his pigs’ usual food with food B.Evaluate this conclusion.

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(Total 15 marks)

Q3. Gas exchange in an aquatic plant was investigated by placing shoots in tubes containing bromothymol blue indicator solution. Bromothymol blue indicator is yellow below pH 6, green between pH 6.1 and 7.5, and blue at pH 7.6 and above. Into each of four tubes, A, B, C and D, 10 cm3 of bromothymol blue solution were placed. Each tube was closed with a bung and left for 10 minutes. Similar-sized shoots of an aquatic plant were then placed into each of tubes A, B and C. The tubes were treated as shown in the diagram.

They were then placed at equal distances from a 60 watt lamp and left for one hour.

The table shows the initial and final colours of the indicator in the four tubes.

Tube Treatment Initial colour of indicator

Colour of indicator after one hour

A Uncovered Green Blue

B Covered with black paper Green Yellow

C Covered with muslin Green Green

D Uncovered Green Green

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(a) Explain the results for

tube A;

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tube B;

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tube C.

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(b) (i) Explain how the results from tube D help to confirm that the explanations for the other tubes are valid.

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(ii) Explain why all the tubes were placed the same distance from the lamp.

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(Total 6 marks)

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Q4. The percentage of light absorbed by an aquatic plant was measured when it was exposed to different wavelengths. The rate of photosynthesis was also measured at each wavelength of light. The results are shown in the graph.

(a) Describe and explain the relationship between light absorption and the rate of photosynthesis for the wavelengths of light between 410 nm and 500 nm.

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(b) Give one dependent variable you could measure in order to determine the rate of photosynthesis in an aquatic plant.

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(c) Use the graph to identify the range of wavelengths of light that would be green in colour.

Give a reason for your answer.

Wavelengths ................... to ................... nm

Reason ........................................................................................................

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(d) A suspension of chloroplasts was isolated from an aquatic plant and a reagent was added. The reagent is blue when oxidised and is colourless when reduced.

(i) The suspension of chloroplasts in blue reagent was exposed to sunlight. The blue colour disappeared. Use your knowledge of the light-dependent reactions of photosynthesis to explain why.

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(ii) Another suspension of chloroplasts was set up as before. Small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why.

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(Total 9 marks)

Q5. Detritivorous insects feed on the dead remains of plants. Some students estimated the numbers of detritivorous insects at two different sites in an ecosystem. They also obtained data about the net primary production of the sites to see if this influenced the numbers of insects present. Net primary production is a measure of plant biomass formed per year. The results are shown in the table.

Site Number of insectsper m2

Net primary production /g m–2 y–1

A 316 1440

B 90 550 (a) Explain how the students could use the mark-release-recapture technique to estimate the numbers of insects.

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(b) The students used the chi-squared (χ2) test to test the hypothesis that there was no significant difference between the numbers of insects per square metre at sites A and B. The value they obtained was 125.8. They checked this value in χ2 tables.

(i) How many degrees of freedom should they check against?

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(ii) What level of probability is normally used to judge whether a difference is statistically significant?

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(iii) The value of χ2 for the 0.001 level of probability for this number of degrees of freedom is 10.8. What does the value obtained by the students suggest about the difference in numbers of the insects per square metre between the two sites?

Explain your answer.

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(c) (i) Explain why the net primary production of an area does not represent the total amount of plant biomass formed per year by photosynthesis.

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(ii) Suggest how the difference in net primary production of sites A and B might explain the difference in the number of insects between the sites.

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(Total 11 marks)

Q6. Ions of metals such as zinc often pollute rivers. The effect of zinc ions on gas exchange and respiration in fish was investigated. Fish were kept in tanks of water in a laboratory.

The fish in one group (X) had a solution of a zinc compound injected directly into their blood and were then put in a tank of zinc-free water. A second group (Y) was not injected but had the solution of the zinc compound added to the water in the tank.

The partial pressure of oxygen in the blood of both groups of fish was then monitored. The results are shown in the graph.

(a) During this investigation, the water temperature in the tanks was kept constant. Explain why changes in the water temperature might lead to the results of the investigation being unreliable.

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(b) The results from the two groups were compared using a statistical test.

(i) Suggest a null hypothesis that could be tested.

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(ii) Explain why it is important to use a statistical test in analysing the results of this investigation.

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(c) Two suggestions were made to explain the results shown in the graph.

A Zinc ions reduce the rate at which oxygen is taken up from the water and passes into the blood.

B Zinc ions reduce the ability of haemoglobin to transport oxygen.

Which of these suggestions is the more likely? Explain the evidence from the graph that supports your answer.

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(d) During the investigation, the pH of the blood was also monitored. It decreased in group Y. Suggest an explanation for this decrease in pH.

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(e) Leaves were collected from sycamore trees growing in a polluted wood and the concentration of some metal ions in samples of these leaves was measured. Woodlice were then fed with the leaves. After 20 weeks, the concentration of the ions in the bodies of the woodlice was measured. Some of the results are shown in the table.

Concentration of ions / µg g–1

Copper Cadmium Zinc Lead

Leaves 52 26 1430 908

Woodlice 1130 525 1370 132

(i) Which of the elements shown in the table is concentrated most by the woodlice? Use suitable calculations to support your answer.

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(ii) Suggest what happens to most of the lead ions in the leaves eaten by the woodlice.

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(iii) Explain the difference in the copper ion concentration between the leaves and the woodlice.

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(f) Yorkshire fog is a species of grass. Two varieties of Yorkshire fog were studied. One variety was tolerant to arsenic, while the other variety was not. In a series of investigations, it was found that

• Arsenic-tolerant plants grow in soil which contains a high concentration of arsenic.

• Arsenic-tolerant plants growing in soil containing high concentrations of arsenic and phosphorus-containing compounds have very low concentrations of arsenic in their cells. They also have low concentrations of phosphates in their cells. Arsenic and phosphorus are chemically similar.

• Plants that are not tolerant to arsenic grow poorly on soil which has a high concentration of both arsenic and phosphorus-containing compounds.

• Tolerance to arsenic in Yorkshire fog is caused by a single gene with the allele, a, for tolerance recessive to the allele, A, for non-tolerance.

(i) What caused the allele for tolerance to first arise?

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(ii) Give two functions of phosphates in plant cells.

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(iii) Arsenic-tolerant Yorkshire fog plants are very rare in areas with low concentrations of arsenic in the soil, even where the soil has a high concentration of phosphate. Explain why they are unable to compete in these conditions with plants that are not tolerant to arsenic.

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(Total 20 marks)

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Q7. A scientist investigated the uptake of radioactively labelled carbon dioxide in chloroplasts. She used three tubes, each containing different components of chloroplasts. She measured the uptake of carbon dioxide in each of these tubes.Her results are shown in the table.

Tube Contents of tube Uptake of radioactively labelled CO2 /

counts per minute

A Stroma and grana 96 000

B Stroma, ATP and reduced NADP 97 000

C Stroma 4 000

(a) Name the substance which combines with carbon dioxide in a chloroplast.

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(b) Explain why the results in tube B are similar to those in tube A.

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(c) Use the information in the table to predict the uptake of radioactively labelled carbon dioxide if tube A was placed in the dark. Explain your answer.

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(d) Use your knowledge of the light-independent reaction to explain why the uptake of carbon dioxide in tube C was less than the uptake in tube B.

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(e) DCMU is used as a weed killer. It inhibits electron transfer during photosynthesis. The addition of DCMU to tube A decreased the uptake of carbon dioxide. Explain why.

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(Total 8 marks)

Q8.A student investigated the effect of different wavelengths of light on the rate of photosynthesis. She used the apparatus shown in Figure 1.

Figure 1

(a) What measurements should the student have taken to determine the rate of photosynthesis?

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(b) Other than temperature and pH, give two factors which should be kept constant during this investigation.

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(c) The student did not use a buffer to maintain the pH of the solution. Explain what would happen to the pH of the solution during this investigation.

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(2)

(d) Figure 2 shows the student’s results.

Figure 2

Suggest and explain why the rate of photosynthesis was low between 525 nm and 575 nm wavelengths of light.

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(Total 7 marks)

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Q9.Plants have pigments that absorb light energy for photosynthesis. These pigments include two types of chlorophyll and a group of pigments known as carotenoids. Different species of plant contain different amounts of these pigments. The pigments that each plant species has are adaptations to where and how they live; their ecological niche.

Figure 1 shows the absorption of light of different wavelengths by chlorophyll a, chlorophyll b and carotenoids.

Figure 1

A scientist investigated the energy in light of different wavelengths reaching the ground in a forest. She measured the energy in

• direct sunlight• sunlight that had passed through the leaves of trees.

Figure 2 shows her results.

Figure 2

Beech trees have two types of leaves called sun leaves and shade leaves. Sun leaves grow on branches exposed to direct sunlight, shade leaves grow on branches exposed to light that has passed through leaves. An ecologist collected sun leaves and shade leaves from beech trees and determined the mean mass of each photosynthetic pigment in both types of leaf. His results are shown in Figure 3.

Figure 3

Photosynthetic pigment Mean mass of each pigment per m2 of leaf

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area / μg (± standard deviation)

Sun leaves Shade leaves

Chlorophyll a 299.3 (± 2.1) 288.9 (± 0.1)

Chlorophyll b 90.7 (± 2.1) 111.1 (± 0.1)

Carotenoids 0.10 (± 0.01) 0.07 (± 0.01)

(a) It is an advantage to beech trees to produce more chlorophyll b in the shade leaves.

Suggest and explain why.

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(b) There are two hypotheses about the advantage to plants of producing carotenoids.

Hypothesis 1

Carotenoids help shade leaves to absorb more light of wavelengths 480 nm to 520nm for photosynthesis.

Hypothesis 2

Carotenoids prevent damage to chlorophyll from very bright light.

(i) Which hypothesis do the data provided on the resource sheet support?

Explain your answer.

Hypothesis ....................................

Explanation ............................................................................................

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(ii) Suggest one other piece of experimental evidence you would need in order to be more confident about drawing your conclusion in (b)(i).

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(Total 5 marks)

Q10.The figure below shows the apparatus used for measuring the rate of oxygen consumption in aerobic respiration by seeds.

(a) For the first 10 minutes, the tap attached to tube A was left open and the syringe from tube B was removed.

Suggest three reasons why the apparatus was left for 10 minutes.

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(b) Suggest and explain why the chosen temperature was 20 °C for this experiment.

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After 10 minutes, the tap attached to tube A was closed and the syringe was attached to tube B. Every minute, the syringe plunger was moved until the levels in the U-tube were the same. The reading on the syringe volume scale was then recorded.

The results are shown in the table below.

Time / minutes Reading on syringe volume scale / cm3

0 0.84

1 0.81

2 0.79

3 0.76

4 0.73

5 0.70

6 0.68

7 0.66

8 0.63

9 0.62

10 0.58

(c) During the experiment, the coloured liquid in the tubing moved towards tube B.Explain what caused this.

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(d) The mass of the seeds was 1.6 g. Use the information in the table above to calculate the rate of oxygen consumption in cm3 g–1 hour–1 by the seeds.

Show your working.

Rate = .................................................................................. cm3 g–1 hour–1

(2)(Total 10 marks)

Q11.A student investigated the rate of anaerobic respiration in yeast. She put 5 g of yeast into a glucose solution and placed this mixture in the apparatus shown in the figure below.She then recorded the total volume of gas collected every 10 minutes for 1 hour.

(a) Explain why a layer of oil is required in this investigation.

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(b) The student’s results are shown in the following table.

Time / minutes Total volume of gascollected / cm3

10 0.3

20 0.9

30 1.9

40 3.1

50 5.0

60 5.2

(i) Calculate the rate of gas production in cm3 g–1 min–1 during the first 40 minutes of this investigation. Show your working.

Answer = ................... cm3 g–1 min–1

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(ii) Suggest why the rate of gas production decreased between 50 and 60 minutes.

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(iii) Yeast can also respire aerobically. The student repeated the investigation with a fresh sample of yeast in glucose solution, but without the oil. All other conditions remained the same.Explain what would happen to the volume of gas in the syringe if the yeast were only respiring aerobically.

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(2)

(c) Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. Explain why.

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(Total 8 marks)

· Web viewThe diagram shows apparatus used to measure the oxygen uptake of snails that live...

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