Wrongly answered exam questions P2

Question 1

Explain why the speed of transmission of impulses is faster along a
myelinated axon than along a non-myelinated axon.

Answer 1

1. Myelination provides (electrical) insulation;
   Reject thermal insulation.
   Accept description of (electrical) insulation.
2. (In myelinated) saltatory (conduction)
   OR
   (In myelinated) depolarisation at nodes (of Ranvier);
3. In non-myelinated depolarisation occurs along whole/length (of axon);
   Accept action potentials for depolarisation

Question 2

Describe and explain how three features of the cells in the proximal convoluted tubule allow the rapid absorption of glucose in the blood

Answer 2

1. Microvilli provide a large surface area/ folded cell surface membrane provides a large surface area
2. Many channel/carrier proteins for facilitated diffusion
3. Many carrier proteins for active transport
4. Many channel/carrier proteins for co-transport
5. Many mitochondria produce ATP/ many mitochondria for active transport
   Many ribosomes to produce carrier/channel proteins

Question 3

Give three reasons for the low efficency of energy transfer from secondary consumers to tertiary consumers in an ecosytem

Answer 3

1. Heat loss from respiration
2. Food not digested or not all eaten
3. Excretion

Question 4

Describe and explain how succession occurs

Answer 4

1. (Colonisation by) pioneer species;
2. Pioneers/species/organisms change the
   environment/habitat/conditions/factors;
3. (Environment becomes) less hostile FOR NEW SPECIES
   (Environment becomes) less suitable for
   previous species;
4. Change/increase in diversity/biodiversity;
5. (To) climax community;

Question 5

Describe how ultrafiltration occurs in a glomerulus.

Answer 5

1. High blood/hydrostatic pressure;
   Ignore references to afferent and efferent arterioles
   Ignore ‘increasing/higher blood pressure’ as does not
   necessarily mean high
2. Two named small substances pass out eg water, glucose,
   ions, urea;
   Accept correct named ions
   Accept mineral ions/minerals
   Accept amino acids/small proteins
   Ignore references to molecules not filtered
3. (Through small) gaps/pores/fenestrations in (capillary)
   endothelium;
   Accept epithelium for endothelium
4. (And) through (capillary) basement membrane;

Question 6

What happens when there is a thicker medulla in the kidneys?

Answer 6

1. Thicker medulla means a longer loop (of Henle);
2. (The longer the loop of Henle means) increase in sodium ion
   concentration (in medulla)

Question 7

Why is a respirometer left for 10 minutes before collecting data?

Answer 7

1. Equilibrium reached;
2. Allow for expansion/pressure change in
   apparatus;
3. Allow respiration rate of seeds to stabilise;

Question 8

Describe the roles of calcium ions and ATP in the contraction of a myofibril.

Answer 8

1. Calcium ions diffuse into myofibrils from
   (sarcoplasmic) reticulum;
2. (Calcium ions) cause movement of tropomyosin
   (on actin);
3. (This movement causes) exposure of the
   binding sites on the actin;
4. Myosin heads attach to binding sites on actin;
5. Hydrolysis of ATP (on myosin heads) causes
   myosin heads to bend;
6. (Bending) pulling actin molecules;
7. Attachment of a new ATP molecule to each
   myosin head causes myosin heads to detach
   (from actin sites);

Question 9

Why should the scientist use ch-squared?

Answer 9

Observed and expected results. It is categorical data.