Aerobic respiration

In the following passage, the numbered spaces can be filled with biological terms.

Write the correct biological term beside each number below that matches the space in the passage.

The equation for the aerobic respiration of glucose is:

Six carbon dioxide molecules are produced from each glucose molecule.

Use your knowledge of the link reaction and Krebs cycle to explain why.

An inhibitor of the electron transfer chain was added to aerobically respiring yeast cells.

As aerobic respiration was inhibited, the following changes occurred:

• oxygen uptake decreased

• ATP production decreased

• ethanol was produced.

Explain the changes in the yeast cells following the addition of the inhibitor.

Oxygen uptake decreased

ATP production decreased

Ethanol was produced

Describe binary fission in bacteria.

Microbiologists investigated the effect of two temperatures on the population growth of a species of bacterium.

They grew separate bacterial cultures in identical nutrient media at 20 °C and 24 °C for 8 hours.

Figure 1 shows the estimated final population size of each culture.

The bacterial population at 24 °C is larger than that at 20 °C

Calculate this difference as a percentage increase.

The actual number of bacteria can be calculated from the log₁₀ value by using the 10^x button on your calculator.

Give your answer to the nearest whole number.

Show your working.

Percentage increase =

Bedaquiline is a drug that inhibits ATP synthase in mycobacteria by stopping hydrogen ion (proton) movement.

Explain how bedaquiline can kill these bacteria.

A student investigated the effect of temperature on the rate of aerobic respiration in woodlice.

Figure 1 shows the apparatus they used.

The student altered the temperature of the water bath and measured how far the drop of coloured liquid moved every minute for 5 minutes.

Other than those stated, suggest two variables the student should have kept constant in this investigation.

Describe how the student used the apparatus in Figure 1 to reset the drop of coloured liquid back to the right-hand end of the tubing.

The student also set up a control experiment.

Suggest a suitable control experiment and explain why it was necessary.

Control experiment

Figure 2 shows the student’s results at 25 °C

The mass of the woodlice in the tube was 3.78 g

Use Figure 1 (on page 4) and Figure 2 to calculate the mean rate of oxygen uptake

The formula for the volume of the capillary tubing is πr²l.

Use π = 3.14 in your calculation.

Show your working and give your answer to 2 decimal places.

ATP is essential for muscle contraction (line 1).

Describe the roles of ATP in muscle contraction.

Calculate how long maximum exercise would last if ATP was not resynthesised (lines 3–4).

Describe and explain how taking creatine supplements (lines 5–6) and ‘carbohydrate loading’ (lines 6–7) can improve performance of different types of muscle fibres during different types of exercise.

Suggest and explain how GLUT4 and CD36 transport proteins (lines 10–11) are beneficial during exercise.

An increase in muscle activity causes an increase in heart rate (lines 12–14).

Describe and explain how.

A student investigated the effect of different sugars on the rate of respiration in yeast. Yeast normally respires glucose.

Figure 2 shows the method she used for her first experiment.

Other than those stated, suggest two variables the student needed to keep constant in her investigation.

Figure 3 shows the result she obtained for yeast in glucose solution.

Use Figure 2 and Figure 3 to calculate the rate of carbon dioxide production in mm s^–1 for yeast in glucose solution.

Give your answer in standard form and to 2 significant figures.

Show your working.

The student repeated the experiment using yeast in maltose solution. She found the rate of carbon dioxide production was slower than with yeast in glucose solution. Suggest why.

A student used the apparatus shown in Figure 1 to measure the rate of aerobic respiration of seeds for 48 hours.

During the 48 hours, the coloured liquid moved to the left.

Explain why.

Apart from time, give two measurements the student would have to make to determine the rate of aerobic respiration of these seeds in cm³ hour^–1

The student used the same apparatus to determine the volume of carbon dioxide the seeds produced during 48 hours.

Give the change the student would need to make to the contents of the apparatus and describe how he could calculate the volume of carbon dioxide produced.

The student calculated that during the 48 hours, 6.2 × 10^–4 cm³ of oxygen was absorbed by 40 g of seeds.

Calculate the oxygen uptake in cm³ g^–1 hour^–1

Describe the process of glycolysis.

Malonate inhibits a reaction in the Krebs cycle.

Explain why malonate would decrease the uptake of oxygen in a respiring cell.

Explain how a resting potential is maintained across the axon membrane in a neurone.

Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon.

A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.

Explain why.

Read the following passage.

North American black bears can hibernate for up to 7 months without food or water. The bears survive using the fat stores in their bodies. The bears build up the fat stores during the summer. During hibernation, the heart rate of black bears decreases from a summer mean of 55 beats per minute to 14 beats per minute. Their metabolic rate falls by 75%. 5

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation. Uncoupling proteins are found in the inner mitochondrial membrane and act as proton channels during chemiosmosis. However, these proton channels do not generate ATP.

In the mountains of North America, when winter changes into spring, the coat 10 colour of snowshoe hares changes from white to brown. Climatic changes have caused the snow to melt earlier. This has reduced the survival rate of snowshoe hares in these habitats. The change in coat colour occurs when new fur replaces old fur. This is called moulting. Recent research has shown that snowshoe hares within a population moult at different times. Moulting at 15 different times could be a major factor in ensuring the survival of snowshoe hare populations.

Use the information in the passage and your own knowledge to answer the following questions.

Black bears can hibernate for up to 7 months without food or water (lines 12).

Suggest and explain how.

During hibernation, the heart rate and the metabolic rate of black bears decrease

Use your knowledge of the nervous control of heart rate to describe how these are linked.

In many mammals, ‘uncoupling proteins’ help to maintain a constant body temperature during hibernation (lines 67).

Suggest and explain how.

Climatic change has reduced the survival rate of snowshoe hares in mountain habitats

Suggest and explain how.

Snowshoe hares within a population moult at different times (line 15).

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats.

Describe the advantage of the Bohr effect during intense exercise.

A cyclist completed a fitness test on an exercise bike. The intensity of the exercise was increased every 10 seconds. The test finished when he was unable to cycle any further. The partial pressure of oxygen (pO₂) and of carbon dioxide (pCO₂) in air breathed out was measured.

Figure 3 shows the results of the cyclist’s fitness test.

Ventilatory threshold (VT) is a measure of the point when anaerobic respiration increases because aerobic respiration alone can no longer maintain muscle contraction.

VT can be identified as the first point when there is an increase in pO₂ breathed out, without an equivalent increase in pCO₂ breathed out.

Use Figure 3 to determine the time after the exercise started when the cyclist reached VT.

Calculate the ratio of pO₂ to pCO₂ in breathed-out air at this time.

Show your working.

An increase in the intensity of exercise produces an increase in the volume of carbon dioxide produced.

However, Figure 3 shows that the pCO₂ in air breathed out did not show a large increase during the exercise.

Suggest one physiological change that would cause this result. Explain how the physiological change would allow for the removal of the increase in the volume of carbon dioxide produced.

Physiological change

When muscle fibres have very low concentrations of ATP, they may get ATP in the

following ways.

• AMPK (an enzyme) oxidises fatty acids.

• Phosphocreatine donates phosphate to ADP in anaerobic conditions.

Figure 4 shows how these chemicals work.

At more than 80% of maximum muscle effort, ATP can only be made for a limited time.

Use Figure 4 to suggest one reason why.

Tick () the correct box.

GW1516 is a performance-enhancing drug. GW1516 activates AMPK and develops slow muscle fibres at rest.

Use Figure 4 to justify why professional athletes are not allowed to take GW1516.

Do not include details of chemiosmotic theory in your answer.

EPO is another performance-enhancing drug. It can increase the haematocrit (the percentage of red blood cells in blood).

A heart attack is caused by a lack of glucose and oxygen being delivered to cardiac muscle via the coronary arteries. The overuse of EPO can increase the risk of a heart attack.

Suggest how.

The normal haematocrit for human males is 47(±5)%. For professional male cyclists, the maximum haematocrit allowed is 50%.

A student suggested that professional male cyclists should be allowed to use EPO until their haematocrit is 50%.

Give two reasons why this suggestion is not valid.

Section B

one question.

You are advised to spend no more than 45 minutes on this section.

Explain why the student removed the shoot tip from each seedling.

Explain why the student added glucose solution to each Petri dish.

Explain why the lids were kept on the Petri dishes.

Describe and explain the results shown in Table 1 and suggest how the results might have differed if lengths of root had been used.

The student produced the different concentrations of IAA using a stock 1 g dm^–3 solution of IAA (1 g dm^–3 = 1 part per thousand) and distilled water.

Complete Table 2 with the volumes of stock IAA solution and distilled water required to produce 40cm³ of 10 ppm (parts per million) IAA solution.

Scientists investigated the effect of a decrease in pH on muscle contraction. The scientists did the investigation with four different preparations of isolated muscle tissue: A, B, C and D.

A - mouse muscle fibres at typical pH of mouse muscle tissue (control 1).

B - mouse muscle fibres at 0.5 pH units below typical pH.

C - rabbit muscle fibres at typical pH of rabbit muscle tissue (control 2).

D - rabbit muscle fibres at 0.5 pH units below typical pH.

They measured the force of muscle contraction of the muscle fibres at 12 °C, 22 °C and 32 °C

Figure 3 shows the results the scientists obtained for B and D compared with the appropriate control.

A student looked at the results and concluded that a decrease in pH does cause a decrease in the force of muscle contraction.

Use Figure 3 to evaluate this conclusion.

Another group of scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues.

Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues.

Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction.

In muscles, pyruvate is converted to lactate during prolonged exercise.

Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration.

Yeast cells can respire aerobically or anaerobically. A student used the apparatus shown in Figure 3 to measure the rate of respiration in yeast.

She:

• positioned the flask in a water bath so that the yeast culture reached a constant temperature

• then left the apparatus for one hour before starting her investigation.

Suggest one reason why it was important that the student left the apparatus for one hour after the yeast culture reached a constant temperature.

During her investigation, the coloured liquid moved to the right.

Explain why it moved to the right.

The student found that the coloured liquid moved 1.5 cm in 24 hours. The diameter of the lumen (hole) of the capillary tubing was 1 mm.

πr 2 π The volume of a capillary tubing is given by , where is 3.14 and = length.

Calculate the volume of gas produced in cm³ hour¹. Show your working.

Figure 4 shows a typical population growth curve for yeast under laboratory conditions.

Explain why a log scale is used to record the number of cells.

Many yeast cells die during the death phase.

Suggest one reason why.

The following equation can be used to make predictions of the growth in the population of yeast cells under ideal laboratory conditions.

X_t the population after a certain time

t time period in hours over which r applies

A population of 2000 yeast cells was left for 10 hours. The value for the growth rate was 0.5

Assuming no yeast cells died, calculate the predicted size of the population after 10 hours. Show your working.

In women, the first division of meiosis produces one daughter cell that has almost all of the cytoplasm. The other daughter cell consists of a nucleus surrounded by a very small amount of cytoplasm and a cell-surface membrane. This very small daughter cell is called a polar body. Polar bodies do not usually divide. The same process occurs in the second division of meiosis, resulting in one egg cell and two polar bodies.

The diagram in Figure 3 shows the formation of an egg cell and two polar bodies during meiosis. It also shows what happens to one pair of homologous chromosomes. This pair carries two alleles of gene A.

Complete Figure 3 by putting A or a in the boxes. One box has been completed for you with A.

combination of alleles on the chromosome in the first polar body in Figure 3.

A scientist measured the diameter of a polar body and the diameter of the nucleus inside it. The diameter of the polar body was 10.4 µm and the diameter of the nucleus was 7.0 µm. The density of mitochondria in the cytoplasm of the polar body (outside of the nucleus) was 0.08 mitochondria per µm³.

Calculate the number of mitochondria in the polar body. You should assume polar bodies and nuclei are spherical.

The formula for the volume of a sphere is πr³ where π = 3.14

Show your working.

Mitochondrial diseases are caused by faulty mitochondria. All of a person’s mitochondria are inherited from their mother via the egg cell. An egg cell contains

One proposed treatment to prevent passing on faulty mitochondria involves

• removing the nucleus from an egg cell donated by a woman with healthy mitochondria

• replacing this nucleus with the contents of the polar body from a woman whose egg cells are affected by mitochondrial disease.

Suggest how this treatment prevents inheritance of mitochondrial diseases.

If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

Suggest and explain one reason why.

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Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

AMP-activated protein kinase (AMPK) is an enzyme that regulates a number of cellular processes. Exercise leads to activation of AMPK.

Figure 1 shows one effect of activation of AMPK during exercise.

CPT1 is a channel protein that transports fatty acids into mitochondria.

Using Figure 1, explain the benefit of activation of AMPK during exercise.

Scientists investigated the effect of regular exercise on skeletal muscle fibres in mice. The scientists compared the muscle fibres of mice after six weeks of regular exercise (trained mice) with those of mice that had not exercised (control mice). The scientists stained the muscle fibres from both sets of mice to show succinic acid dehydrogenase activity. The darker the stain the greater the succinic acid dehydrogenase activity.

Figure 3 shows a typical set of results they obtained.

Succinic acid dehydrogenase is an enzyme used in the Krebs cycle.

Suggest one reason for the difference in the staining between the muscle fibres of the control mice and the trained mice.

The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice.

Explain why.

The scientists determined the mean diameter of muscle fibres in trained mice using an optical microscope to examine sections of muscle tissue. The circular area (πr of one field of view was 1.25 mm². The diameter of this area was equal to the diameter of 15 muscle fibres.

Using this information, calculate the mean diameter in µm (micrometres) of muscle fibres in this section of tissue.

The scientists also compared the diameter of samples of muscle fibres taken from young mice and adult mice.

Some of their results are shown in Figure 4.

Describe two differences between these samples of muscle fibres.

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.

Describe how.

The presynaptic knob contains actin filaments and myosin molecules.

The myosin molecules can attach to mitochondria and move them towards the presynaptic membrane, as shown in Figure 1.

Use your knowledge of how myosin and actin interact to suggest how the myosin molecule moves the mitochondrion towards the presynaptic membrane.

Do not include the roles of calcium ions and tropomyosin in your answer.

This movement of mitochondria happens when nerve impulses arrive at the synapse.

Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse.