Respiration, Muscles and the Internal EnvironmentEdexcel International A Level Biology: Topic test

1. 1
   Cyanide is a poison that stops the last carrier in the mitochondrial electron transport chain from passing electrons to oxygen. A person who has swallowed cyanide rapidly becomes very ill, and a blood test shows a high concentration of lactate.

   (a)

   What is the immediate effect of cyanide on a mitochondrion?

   [1 mark]

   • AThe proton gradient increases, so ATP synthase makes more ATP
   • BThe proton gradient across the inner membrane cannot be maintained, so ATP synthesis by oxidative phosphorylation falls
   • COxygen is converted to carbon dioxide instead of water
   • DSubstrate-level phosphorylation in the Krebs cycle replaces all of the lost ATP production

   (b)

   Which process in the mitochondrial matrix soon slows down in the poisoned cells because its reduced coenzymes cannot be reoxidised?

   [1 mark]

   • AGlycolysis
   • BThe hydrolysis of ATP
   • CThe synthesis of glycogen
   • DThe Krebs cycle

   (c)

   Explain why the person's blood contains a high concentration of lactate.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A footballer kicks a ball. The quadriceps muscle at the front of her thigh contracts to extend her knee, and the hamstring muscle at the back of her thigh flexes it.

   (a)

   Which statement about the structures at the knee joint is correct?

   [1 mark]

   • AA tendon joins muscle to bone, and a ligament joins bone to bone
   • BA tendon joins bone to bone, and a ligament joins muscle to bone
   • CTendons and ligaments both join muscle to bone
   • DTendons join muscle to muscle, and ligaments join bone to muscle

   (b)

   When the quadriceps contracts to extend the knee, what happens to the hamstring?

   [1 mark]

   • AIt also contracts, which makes the leg extend more forcefully
   • BIt contracts so that the leg flexes at the same time
   • CIt relaxes, because the two muscles are an antagonistic pair
   • DIt stays unchanged because only the quadriceps is attached to the bones of the leg

   (c)

   Explain why skeletal muscles are arranged in antagonistic pairs.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A mutation in a person's skeletal muscle fibres results in a form of troponin that cannot bind calcium ions. The rest of the contractile machinery is normal, and nerve impulses reach the muscle fibres normally.

   (a)

   Explain why the muscle fibres cannot contract when nerve impulses stimulate them.

   [3 marks]

   (b)

   Describe how, in a normal muscle fibre, myosin and ATP cause the filaments to slide once the binding sites on actin are exposed.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A healthy volunteer drank 1.0 dm³ of pure water within 10 minutes. Over the next two hours his urine output rose to about ten times its normal rate, and the urine was very dilute. Tests on his urine before and after drinking showed that it contained no glucose and no protein.

   (a)

   Explain how the body responds to the water load so that the water potential of the blood plasma returns to normal.

   [6 marks]

   (b)

   Explain why the urine of a healthy person contains no glucose and no protein.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A baker works for several hours beside a large oven in a hot kitchen, and her core body temperature starts to rise above its set point.

   (a)

   Which statement describes negative feedback?

   [1 mark]

   • AA change in a variable is detected and the effectors amplify the change
   • BThe set point is permanently raised by the response
   • CA change in a variable is detected, and the effectors act to reverse the change and restore the set point
   • DReceptors send impulses only when the variable is exactly at the set point

   (b)

   Which statement describes positive feedback?

   [1 mark]

   • AThe response increases the original change, moving the variable further from its starting value
   • BThe response reverses the change, returning the variable to the set point
   • CThe response stops as soon as the change is detected
   • DThe effectors act before any change has taken place

   (c)

   Explain how the hypothalamus brings about a decrease in the baker's core body temperature.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   Oestrogen is a steroid hormone that makes the cells lining the uterus grow. These cells contain oestrogen receptor proteins, but skin cells do not.

   (a)

   Oestrogen can enter its target cells because

   [1 mark]

   • Ait is a peptide that enters through a receptor protein in the cell surface membrane
   • Bit is taken in by endocytosis in vesicles
   • Cit binds to a receptor in the cell surface membrane, which then enters the nucleus
   • Dit is lipid-soluble and diffuses through the phospholipid bilayer

   (b)

   Inside a target cell, the oestrogen-receptor complex

   [1 mark]

   • Aleaves the cell to bind to receptors on neighbouring cells
   • Bacts as a transcription factor that binds to DNA and switches on particular genes
   • Ctriggers a second messenger cascade at the cell surface membrane
   • Dbinds to ribosomes and makes proteins directly

   (c)

   Explain why oestrogen affects the cells lining the uterus but not skin cells.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A patient with high blood pressure takes a drug that blocks the receptors for adrenaline on the cells of the sinoatrial node (SAN). Before the treatment, her resting heart rate was 72 beats per minute and her stroke volume was 70 cm³. After the treatment, her resting heart rate was 60 beats per minute and her stroke volume was unchanged.

   (a)

   Calculate the percentage decrease in the patient's resting cardiac output caused by the treatment.

   [3 marks]

   (b)

   Explain how adrenaline and the cardiovascular control centre in the medulla oblongata increase the heart rate of a healthy person during exercise.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A woman has a damaged atrioventricular node (AVN). Her electrocardiogram (ECG) shows that her atria contract 75 times per minute, but her ventricles contract only 35 times per minute and not in step with the atria. A doctor fits an artificial pacemaker. Heart muscle cells contain many mitochondria and respire aerobically almost all of the time.

   (a)

   Describe how the heartbeat is normally coordinated in a healthy heart, and explain why damage to the AVN produces these ECG results.

   [6 marks]

   (b)

   Explain why heart muscle cells rely on aerobic respiration, and describe how oxidative phosphorylation makes ATP.

   [6 marks]

   Total for question 8: 12 marks

End of questions