Questions I got wrong P4

Question 1

Explain the rise and fall in membrane potential during an action potential (4)

Answer 1

1. (Increased permeability to sodium ions as) sodium (ion) channels/gates open;
2. Sodium ions diffuse in and cause depolarisation / inside (of neurone) becomes less negative / becomes positive / increase in membrane potential;
3. (Decreased permeability of sodium ions and increased permeability of potassium ions as) sodium (ion) channels/gates close and potassium (ion) channels/gates open;
4. Potassium ions diffuse out and cause repolarisation/ inside (of neurone) becomes less positive / more negative / decrease in membrane potential;

Question 2

The refractory period causes action potentials to move in one direction only. Why. (2)

Answer 2

1. Action potential can only pass to the next region that is polarised/at resting potential;
2. (Action potential cannot pass backwards as) membrane not permeable to sodium ions / sodium (ion) channels/gates are closed/unresponsive to another stimulus;

Question 3

Describe the role of restriction endonuclease and DNA ligase enzymes in process of inserting a gene into a plasmid. (4)

Answer 3

1. Restriction enzyme cuts (bacterial) chromosome to remove (PETase) gene;
2. Cuts (PETase) gene and plasmid with the same restriction endonuclease;
3. Creates complementary sticky ends/(overhanging) ends with complementary single strands;
4. DNA ligase to anneal/join the plasmid and (PETase) gene
   OR
   DNA ligase forms phosphodiester bonds between the plasmid and (PETase) gene;

Question 4

Each beetle spends more time in a control area than area with a chemical. Scientists conclude this is a kinesis response. Describe observations of the beetle’s movement that would support this. (2)

Answer 4

1. Beetles will move slower in the control area;
2. They will turn less frequently in the control area;

Question 5

Explain how siRNA could inhibit the expression of a gene and slow the onset of cancer (3)

Answer 5

1. siRNA bind to mRNA (produced from target gene(s);
2. (Gene not expressed so) protein not produced
   OR
   mRNA is broken down (into fragments);
3. Leads to increased cell death/apoptosis of tumour cells so reduces volume of the tumour (compared to control) / reduces the growth of tumour;

Question 6

Describe two ways the appearance of the sarcomeres would change when a muscle fibre contracts (2)

Answer 6

1. Length of the sarcomere decreases;
2. Length of the H zone decreases;
3. Length of the I band decreases;
4. Z-lines move closer together;

Question 7

Explain how a reduction in the effect of calcium ions might lower the force of contraction (3)

Answer 7

1. Less tropomyosin moves away from the binding sites on actin;
2. Less (actinomyosin) cross bridges form;
3. Less activation of ATPase so less movement of actin over myosin;

Question 8

Explain how an increase in the concentration of carbon dioxide in the blood causes an increase in heart rate (3)

Answer 8

1. Chemoreceptors in aorta/carotid arteries detect increase in carbon dioxide concentration;
2. Action potentials/nerve impulses to medulla/cardio acceleratory centre;
3. Increased frequency of action potentials/nerve impulses along cardiac nerve/sympathetic nerve fibres;

Question 9

Describe how resting potential is maintained (2)

Answer 9

1. Sodium ions actively removed/pumped out (by sodium-potassium pumps);
2. Potassium ions diffuse (out) more rapidly (than sodium ions in)/membrane more permeable to potassium ions (than sodium ions);

Question 10

Explain how the Pacinian corpuscle allows an organism to distinguish between different levels of pressure (2)

Answer 10

1. Greater pressure results in greater deformation of
   layers/membranes/lamellae in the pacinian corpuscle/more sodium channels open;
2. Greater pressure produces a higher frequency of action potentials/impulses;

Question 11

State how a shortened muscle is returned to its non-contracted length (1)

Answer 11

Antagonistic muscle contracts

Question 12

Describe how filaments move during muscle contraction (5)

Answer 12

• Tropomyosin moves from binding sites by Ca2+ ions
• Myosin head binds to actin
• Breakdown of ATP provides energy to move myosin head
• Myosin head moves and pulls actin past
• Binding of ATP releases myosin head from actin
• Myosin head returns to normal position

Question 13

Describe how insulin reduces the conc. of glucose in human blood (3)

Answer 13

• Insulin binds to specific receptors on liver cells
• Increase in no. of glucose channel proteins in membrane
• Increase uptake of glucose by facilitated diffusion
• Conversion of glucose to glycogen

Question 14

Why is a logarithmic scale used?

Answer 14

Large range of concentrations;