Respiration (A Level only) (AQA A Level Biology)

Describe the mechanism by which ATP is formed in the mitochondria.

Mitochondrial diseases in humans cause their mitochondria to malfunction. Individuals that suffer from mitochondrial disease are only able to endure intense exercise for a short period of time. Explain why this is.

Lab technicians wanted to investigate ATP production in a preparation of isolated mitochondria. They suspended mitochondria in an isotonic solution and added ADP, phosphate and a respiratory substrate. Oxygen was supplied throughout the preparation. 

Suggest and explain why glucose would not be a good choice for the respiratory substrate in this experiment.

Explain why the solution used was isotonic.

Figure 1 below shows the respirometer apparatus used by a teacher for measuring the rate of oxygen consumption of seeds during aerobic respiration. 

Figure 1

For the first 12 minutes, the tap attached to tube 1 was left open and the syringe from tube 2 was taken away. Suggest two reasons why this was done.

A temperature of 25°C was used during the experiment. A student suggested using a temperature of 30°C, explain why the teacher didn’t do this.

After 12 minutes, the tap connected to tube 1 was closed and the syringe was attached to tube 2. Every 60 seconds, the syringe plunger was moved to make the levels in the U-tube identical. The reading on the volume scale of the syringe was then recorded. The results are shown in Table 1 below.

Table 1

Predict which tube the coloured liquid in the tubing moved towards during the experiment. Justify your answer.

The mass of the seeds was 1.8 g. Using the information provided in Table 1, calculate the rate of oxygen consumption in cm³ g^–1 hour^–1 by the seeds. Show your working.

Researchers measured the rate of CO₂ production by three groups of insects of the same species at 15 °C, 25 °C and 35 °C. The mean mass of each group of insects was also recorded. Their results can be seen in Table 1 below.

Table 1

Complete the Table 1 above and sketch a graph of your values against temperature. Calculate rates to 3.s.f.

The internal body temperature of the insects was largely determined by the temperature of the container they were kept in. At each of the temperatures, the researchers recorded the rate of CO₂ release by individual insects over time. Figure 1 below shows the results for three insects kept at different temperatures.

Figure 1

Using your knowledge of insects gas exchange systems, explain the peaks seen in the rate of CO₂ excretion.

Suggest a method for calculating the total amount of CO₂ released at 35 °C during the recording period.

Describe and explain the effect of temperature on the rate of CO₂ release.

Lab technicians investigated the impact of regular exercise on the skeletal muscle fibres of guinea pigs.  The muscle fibres of exercised guinea pigs (who had 8 weeks of regular exercise) were compared with those of non-exercised guinea pigs. The muscle fibres from both sets of guinea pigs were stained with a specific chemical to show up succinic acid dehydrogenase activity. The darker and more intense the stain, the greater the succinic acid dehydrogenase activity. Figure 1 shows a set of results that they obtained.

Figure 1

Succinic acid dehydrogenase is an important enzyme that is used during the Krebs cycle. 

Suggest two reasons for the difference in the staining seen between the muscle fibres of the exercised guinea pigs vs the non-exercised guinea pigs.

Lab technicians decided to investigate the endurance capabilities of the different guine pigs. They had the guinea pigs carry out prolonged exercise and compared the length of time that the exercised guinea pigs and non-exercised guinea pigs could continue for. The exercised guinea pigs were able to exercise for a significantly longer time than the non-exercised guinea pigs. Explain why.

The lab technicians determined the mean diameter of muscle fibres in exercised guinea pigs by using an optical microscope to examine sections of muscle tissue. The circular area (πr² ) of a single field of view was 1.5 mm². The diameter of this area was equal to the diameter of 10 muscle fibres. Use this information to calculate the mean diameter in μm (micrometres) of a single muscle fibre in this sample of tissue.

The scientists also compared the diameter of samples of muscle fibres taken from male and female guinea pigs. The results are shown in Figure 2 below.

Figure 2

Describe two differences between the two samples of muscle fibres.

A researcher investigated the use of a new carbohydrate source (substance L) for the production of ethanol as biofuel. She wanted to find the optimum length of time to leave a mixture of yeast and substance L to produce ethanol. They set up an airtight container containing yeast and substance L.  The oxygen, carbon dioxide and ethanol concentrations were measured over 10 hours. The results of this experiment are shown in Figure 1 below.

Figure 1

The researcher used a sealed container that was airtight. Give three reasons why the container had to be airtight.

Explain the relationship seen between the concentration of oxygen and the concentration of carbon dioxide between 0 and 2.5 hours.

A student concluded that the yeast started to respire anaerobically when the oxygen concentration fell below a certain concentration. Suggest at what time in the experiment this occurred. Justify your answer.

A biofuel company wanted to know how long they should let the reaction go on for when commercially producing ethanol for biofuels using substance L . Use Figure 1 to suggest a length of time (to the nearest hour). Justify your answer.

Describe the formation of acetyl coenzyme A in the link reaction.

One of the steps of the Krebs cycle is outlined below:

Fumarate is the first substrate to bind with the enzyme fumarase. Explain how fumarate enables the water to then bind to the enzyme.

The Krebs cycle, which takes place in the mitochondrial matrix, releases hydrogen ions. These hydrogen ions provide a source of energy for the synthesis of ATP, using coenzymes and carrier proteins in the inner membrane of the mitochondrion. 

Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP.

Another step of the Krebs cycle converts isocitrate to α-ketoglutarate. In this step, NAD is reduced to reduced NAD. 

Use your knowledge of redox reactions in biology to suggest a name for the enzyme that catalyses this step. Give a reason for your choice.  

A researcher used the apparatus shown in Figure 1 to measure the rate of respiration in yeast. The researcher placed the flask in a water bath with the bung open (so that the yeast culture reached a constant temperature), before adding the alkaline pyrogallol, inserting the bung and starting the investigation.

Figure 1

When the researcher inserted the bung and began the experiment, the coloured liquid initially moved to the right. After a period of time, the coloured liquid slowed, stopped and reversed its direction, moving to the left. 

Use Figure 1 and your knowledge of respiration to explain these observations.  

When the coloured liquid moved to the left, the researcher measured that the coloured liquid moved 1.8 cm in 16 hours. The internal diameter of the capillary tubing was 1.3 mm.

The volume of the capillary tubing is given by r² l, where l = length.

Calculate the rate of gas production in mm³ hr^–1. Show your working and give your answer to an appropriate number of significant figures. 

Figure 2 shows a population growth curve of yeast cells cultured in a laboratory experiment. 

Figure 2

Explain the events that occur in the stationary phase.  

A brewer wished to cultivate a fresh strain of yeast for a trial batch of a new beer. He required a minimum of 3 billion yeast cells from his laboratory culture.  Using the formula below, calculate the number of cells he would have to introduce into the culture for his culture to be ready in 24 hours. Assume ideal growth conditions and a growth rate of 0.6 for this strain of yeast.  Give your answer to 2 significant figures. 

P_t = P₀ e^rt

P_t = the population after a certain time

P₀ = the population at the start

e = 2.718 (a constant)

r = growth rate over the time period t

t = time period (in hours) 

Dugongs are aquatic mammals. Dugongs use lungs as organs of gas exchange so they do not breathe when they are under water during a dive.

Figure 1 shows changes in oxygen and lactate concentration in the blood of a dugong before, during and after a dive.

Figure 1

Calculate the percentage change in lactate level in the dugong’s blood in the five minute period following the end of its dive. 

Referring to Figure 1, explain why the concentration of oxygen in the dugong’s blood fell during the dive. 

After 50 minutes, the dugong’s blood lactate began to fall. Explain why. 

During a dive, a dugong reduces the supply of blood to its diaphragm. Suggest one advantage to the dugong of conserving blood supply to the diaphragm during a dive.

A student measured the rate of aerobic respiration of a beetle using the experimental set-up shown in Figure 1.

Figure 1

The student closed the tap. After sixty minutes the drop of coloured liquid had moved to the left. Explain why the drop of coloured liquid moved to the left.

In order to calculate the aerobic respiration rate, state the measurements that the student would need to have taken. Suitable units of respiration rate are mm³ of oxygen g^–1 h^–1.

A researcher added a respiratory inhibitor to isolated mitochondria and observed the following changes:  

• Oxygen uptake remained unchanged

• Production of ATP decreased

• The temperature increased

The respiratory inhibitor is known to prevent the establishment and maintenance of a proton gradient across mitochondrial membranes. 

Using this information, and your own knowledge, explain how the inhibitor caused these observation

When ATP is formed in oxidative phosphorylation, it takes approximately 31 kJ mol^-1 of energy to condense ADP with P_i . Deduce the amount of energy required to perform the following conversion. Give a reason for your answer. 

adenosine monophosphate + inorganic phosphate → adenosine diphosphate

      (AMP)                              (P_i)                                  (ADP)

Explain why oxygen is referred to as the ‘terminal electron acceptor’ in the process of aerobic respiration. 

Molecules other than carbohydrates are, under certain circumstances, used as respiratory substrates. 

Name two main groups of molecules that are used in this way and describe how their catabolic products join the main pathways of respiration.  

Pieces of cut parsnip were placed in a solution containing potassium ions (K⁺). Air with differing concentrations of oxygen was bubbled through the solution and the rates of respiration and uptake of potassium were measured. The results are shown in Table 1.

Table 1

Describe and explain the relationship between oxygen concentration and the two dependent variables shown in Table 1.

Describe the production of ATP in aerobic respiration.