Topic 2 exam questions

Question 1

Describe the mechanism of breathing that causes air to enter the lungs. (3)

Answer 1

1. Diaphragm (muscles) contract and diaphragm flattens/pulled down;
2. External intercostal muscles contract and ribcage pulled up/out;
3. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric pressure);

Question 2

Describe how gas exchange occurs in single-celled organisms and explain why this method cannot be used by large, multicellular organisms. (3)

Answer 2

1. Diffusion (across the cell surface membrane);
2. Large organisms have small(er) sa : vol ratio
3. Diffusion pathway would be too long
   OR
   (Rate of) Diffusion too slow;

Question 3

Give two reasons why glucose uptake by muscle cells increases significantly during exercise.
Explain your answers.

Answer 3

1. Increased respiration;
2. To provide more ATP for muscle contraction;
3. (More glucose being used so) concentration gradient for glucose
   OR
   Increased numbers of glucose transporter proteins in the membrane;
4. (Glucose enters by) facilitated diffusion;

Question 4

Name the type of blood vessel that controls blood flow to muscles and explain how these blood vessels change blood flow during exercise.

Answer 4

1. Arteriole;
2. (Circular/smooth) muscle relaxes;
3. Vasodilation increases blood flow
   OR
   Widens/dilates (lumen of) blood vessel so increases blood flow;

Question 5

Describe the hydrolysis reactions involved in the digestion of triglycerides. (2)

Answer 5

1. Breaking of ester bonds;
2. By addition of water;

Question 6

Describe two other functions of bile salts. (2)

Answer 6

1. Emulsify lipids/fats;
2. Increases surface area (of lipid/fat) for (increased) lipase activity;
3. Form micelles;

Question 7

Describe how natural selection may have led to all mammals in a population producing CEL.(4)

Answer 7

1. Mutation results in (a new) allele;
2. Those with the (new) allele able to digest milk/triglycerides;
3. Individuals with CEL/allele more likely to (survive and) reproduce;
4. Directional selection;
5. Increase in frequency of (this) allele in population;

Question 8

Suggest how they collected data to give a reliable mean for these variables. (2)

Answer 8

1. Random samples;
2. Large sample size;

Question 9

One of these fish spends most of its time not moving, waiting to catch passing prey. The other species is very active, hunting mobile prey.

Suggest which of the species in Table 1 is the very active fish species.

Explain your answer. (2)

Answer 9

(Trachurus trachurus) – no mark

1. More oxygen uptake/diffusion
   OR
   More gas exchange;
2. More energy/ATP from respiration;