Respiration (CIE A Level Biology)

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

Fig. 1

For the first 12 minutes the tap attached to tube 1 was left open and the syringe from tube 2 was removed.

Suggest two reasons why this was done.

A temperature of 25^°C was used during the experiment. One of the students suggested using a temperature of 35^°C.

Explain why the teacher did not 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 U-tube moves 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 and give your answer to two decimal places.

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

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

Explain the reason for this.

Fig. 1 below shows a mitochondrion.

Fig. 1

Identify the structures labelled A and B in the diagram.

Some forms of mitochondrial dysfunction result in mitochondria that lack fully formed cristae as shown in Fig. 2 below.

Suggest, with a reason, the effect of this on the production of ATP.

Fig. 3 below shows glycolysis.

Fig. 3

State the net production of ATP and reduced NAD during glycolysis.

The Krebs cycle, which takes place in the mitochondrial matrix, releases hydrogen ions. These hydrogen ions, together with coenzymes, provide energy for the synthesis of ATP.

Describe the role of coenzymes in the synthesis of ATP.

Explain why the link reaction is described as an oxidative decarboxylation reaction.

Fig.1 below shows the Krebs cycle.

Fig. 1

Identify the number of carbon atoms (e.g. 1C) in the compounds at each stage of the Krebs cycle (A to D).

Reduced NAD and FAD are produced throughout the stages of respiration. 

Table 1

Complete Table 1 above to show how many molecules of reduced NAD and FAD are produced at each stage per molecule of glucose.

Fig. 1 outlines some of the steps of glycolysis.

Fig. 1

State the precise location of glycolysis in the cell.

[1]

(ii)

With reference to Fig.1:

• State the steps where phosphorylation occurs

• State the step where oxidation occurs

• Name the type of reaction by which ATP is made during step 5.

[3]

Some cancer cells have different metabolic requirements from normal cells. These cancer cells obtain most of their ATP from glycolysis, even if oxygen is available.

State how the glucose and oxygen requirements of these cancer cells differ from normal cells.

The link reaction and Krebs cycle take place in the mitochondrion. The main stages of the link reaction and Krebs cycle are listed in Table 1.

They are not listed in the correct order.

Table 1 

Complete Table 2 to show the correct order of the stages.

Three of the stages have been done for you.

Table 2

Outline the role of NAD in respiration in aerobic conditions.

Carbon dioxide is removed from compounds in the link reaction and Krebs cycle by decarboxylation.

(i)

State the total number of molecules of carbon dioxide removed in the link reaction and Krebs cycle for each molecule of glucose respired.

[1]

(ii)

In a mammal, carbon dioxide diffuses from cells into the blood to be transported to the lungs.

Suggest why carbon dioxide is transported in the blood mainly as hydrogen carbonate ions and not as carbonic acid.

A researcher investigated the use of a new carbohydrate source (substance L) for use in the production of ethanol as biofuel. They wanted to find the optimum time period for which for a mixture of yeast and substance L should be left in order to maximise the efficiency of ethanol production.

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 Fig.1 below.

Fig. 1

Give three reasons why the container had to be airtight. 

Describe and 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 level.

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 Fig.1 to suggest a length of time (to the nearest hour). Justify your answer.

Compare and contrast aerobic respiration and anaerobic respiration.

Extreme rainfall and flooding can create major problems when growing crops. As water levels rise, fields can become waterlogged and crops become submerged underwater.

Suggest how waterlogged conditions may negatively impact the growth of crops.

A species of rice plant, Oryza sativa, possesses adaptations that maximise aerobic respiration in flooded fields, e.g. it demonstrates an increased rate of upward growth which allows the leaves to remain above the waterline.

Fig.1 below shows a cross-section of an Oryza sativa stem, taken near the tip.

Fig. 1

Using Fig.1, explain one other adaptation present in the stems of Oryza sativa that aids aerobic respiration in flooded fields.

Describe how some species of rice plant are adapted to maximise anaerobic respiration.

(ii)

It is common practice for farmers to grow rice in paddies (intentionally flooded fields).

Discuss the benefit of growing rice plants in these conditions.

The West Indian manatee, Trichechus manatus, is a large, aquatic mammal found in the warm coastal waters of the Caribbean. They mainly feed on sea grass and other aquatic plants, meaning that they need spend extended periods of time underwater.

Fig. 1 shows an image of a West Indian manatee.

CC BY 2.0, via Flickr

Fig. 1

During feeding there is an increase in the lactate concentration of manatee blood.

Explain this increased lactate concentration.

Fig. 2 shows changes in lactate concentration in the blood of a manatee before, during and after a feeding dive.

Fig. 2

Calculate the percentage change in the lactate concentration between 10 and 15 minutes after the dive was completed.

Show your calculations.

Explain the change in lactate concentration calculated in part (b).

Manatees prefer to live in warm waters around coastlines and in rivers. If they are exposed to extremely cold water for prolonged periods of time they develop a condition called 'cold water stress syndrome', which may be fatal.

With reference to respiration, suggest why cold water stress syndrome may be fatal to manatees.

Fig. 1 below shows a species of ground squirrel, a group of mammals that measure around 25 cm in length. Ground squirrels are known to spend winter months undergoing alternate periods of torpor and wakefulness; during torpor levels of physiological activity decrease significantly, and body temperature and metabolism are much lower than usual.

CC BY-SA 2.0, via Flickr

Fig. 1

Use the information provided to suggest why it is beneficial for ground squirrels to enter torpor during winter months.

Scientists have hypothesised that one factor involved in inducing torpor in ground squirrels is cellular levels of hydrogen sulfide (H₂S). One study measured the levels of H₂S in the liver cells of ground squirrels during the summer, during torpor, and during the periods of wakefulness that occurred between periods of torpor. Their results are shown in Fig. 2. Error bars show standard deviation.

Fig. 2

A research assistant viewed Fig. 2 and concluded that increased levels of H₂S caused torpor in ground squirrels.

Discuss the research assistant's conclusion.

Fig. 3 below shows the effects of low concentrations of H₂S (A) and high concentrations of H₂S (B) on events taking place on the inner mitochondrial membrane. Note that numerals I-IV denote a series of protein complexes.

Fig. 3

Use information in Fig. 3 to suggest and explain how low levels of H₂S could affect respiration rate. 

[4]

(ii)

Use Fig. 3 to suggest how high levels of H₂S might result in torpor in ground squirrels.

[3]

Changes in levels of H₂S is one of several cellular events that scientists believe could be responsible for induction of torpor in ground squirrels.

Another mechanism is the post-translational modification of some mitochondrial proteins. 

Give one example of a type of molecule that might be produced by the modification of a protein after translation.

[1]

(ii)

Identify the location in which post-translational modification might occur within a cell.

[1]

Fig. 1 below illustrates two different respiration pathways within an animal cell.

Fig. 1

The Warburg effect is a change that occurs in the metabolism of tumour cells that results in a 70-fold increase in lactate production, regardless of oxygen availability.

Other than an increase in lactate production, describe the metabolic changes that will be occurring in cells where the Warburg effect is taking place.

[3]

(ii)

Suggest why this could be considered a surprising change to occur inside tumour cells.

[2]

The Warburg effect can also be seen in immune cells that are in the vicinity of tumour cells. These immune cells demonstrate lower than normal activity levels.

Suggest why immune cells that are close to tumour cells may demonstrate lower than normal activity levels.

Fig. 2 shows the effect of a treatment that targets cell metabolism on cancer cells. The error bars indicate standard deviation.

Fig. 2

Describe the effect of the treatment on cancer cells.

[2]

State what can be concluded about the effect of the treatment on cancer cell metabolism.

[1]

Drugs that target cell metabolism can act on different cellular processes.

Suggest how drugs that target the following cellular mechanisms might affect respiration in tumour cells:

Activity of lactate dehydrogenase, the enzyme that is involved in the conversion of pyruvate to lactate.

[1]

(ii)

The function of GLUT4 glucose transporter proteins.

[1]