Muscles

Question 1

The diagram below shows part of a muscle fibre. (1)

The label that shows a sarcomere is

A B C D

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Answer 1

C (1)

Question 2

When a muscle contracts, the length of a sarcomere (1)

A becomes zero B decreases C increases D stays the same

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Answer 2

B (decreases) (1)

Question 3

In the diagram below, tropomyosin is found in (1)

A B C D

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Answer 3

C (1)

Question 4

The sarcoplasmic reticulum releases ions that bind to troponin. These ions are (1)

A calcium B phosphate C potassium D sodium

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Answer 4

A (calcium) (1)

Question 5

The thin filament in a muscle fibre is (1)

A actin B ATP C ATPase D myosin

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Answer 5

A (actin) (1)

Question 6

Slow twitch muscle fibres have (1)

A less myoglobin than fast twitch fibres B more myoglobin than fast twitch fibres C no myoglobin D the same quantity of myoglobin as fast twitch fibres

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Answer 6

B (more myoglobin than fast twitch fibres) (1)

Question 7

Explain why tendons need to be inelastic. (3)

[2014/01 WBI05/01]

Answer 7

Tendons are inelastic to ensure when muscle contracts, all the force is transferred to the bone (1) which allows the bone to move (1) as tendons attach the muscle to the bone (1).

Question 8

Some animals, such as spiders, bite and inject venom into their prey. The venom affects the transmission of nerve impulses and paralyses the prey. In an investigation, scientists estimated the toxicity of the venom by measuring the dose that can kill 50% of prey after injection. This dose is called the LD₅₀. The graph below shows the relationship between the percentage of prey killed and the dose of venom A and venom B.

(i) Use the information in the graph to compare the toxicity of venom A and venom B. (2)
(ii) Place a cross in the box next to the independent variable in this investigation. (1)

A dose of venom B mass of the prey C percentage of prey killed D toxicity of the venom

[2015/01 WBI05/01]

Answer 8

(i) Comparing A and B, the dose of venom requires for A to have the same percentage of prey killed for B is always lower which means that venom A is more toxic (1). For example, 13.5 mg kg^-1 is required to have 100% of prey killed for B, whereas only 10 mg kg^-1 for A (1).
(ii) A (dose of venom) (1)

Question 9

The venom from L. mactans (black widow spider) causes constant impulses to be sent along motor neurones. This results in cramps (constant muscle contractions), a symptom of a black widow spider bite.

Suggest how constant impulses along motor neurones cause cramps. (4)

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Answer 9

Constant impulses mean more acetylcholine would be triggered, which causes the muscle fibre to depolarise, and a wave of depolarisation travels along the sarcoplasmic reticulum. This causes more (1) calcium ions (1) to be released into the muscle fibre from the sarcoplasmic reticulum (1). The calcium ions would then bind to troponin (1) which changes the shape of troponin which allows the tropomyosin (1) to move which exposes the binding sites on the actin filaments. The calcium ions also allow the myosin head to return to its original position where it joined with ADP and inorganic phosphate. The myosin head then attaches to the binding site on the actin filament and forms a cross bridge. ADP and inorganic phosphate are then released from the myosin head which causes a shape change in the myosin head. As the myosin head bends forward, it moves the actin filament towards the myosin filament which shortens the sarcomere, causing the muscle to contract. Muscle contraction happens more frequently due to the increase in calcium ions present.