PAPER 2

Question 1

Describe and explain how temperature affects rate of photosynthesis

Answer 1

1) - as temp ^ , rate ^
- enzymes e.g rubisco gains KE
- more e-s complexes form

2) - Above an optimum temperature, rate decreases
-enzymes denature
- fewer e-s complexes form

Question 2

Describe and explain how light intensity affects the rate of photosynthesis

Answer 2

1) - as light intensity ^ , rate ^
- LDR increases so more ATP and NADPH
- LIR increases as more GP reduced to TP and more TP regenerates RuBP

2) - above a certain light intensity, rate stops increasing
- another factor is limiting

Question 3

Describe and explain how CO2 concentration affects rate of photosynthesis

Answer 3

1) - As CO2 concentration increase, rate ^
- LIR increased
- as more CO2 combines with RuBP to form GP
- more GP reduced to TP
- more TP is converted to useful organic substances and more RuBP is regenerated
2) above a certain CO2 concentration rate stops ^
- another factor is limiting

Question 4

Describe control of heart rate by SAN

Answer 4

Sinoatrial node (SAN) acts as pacemaker → releases regular waves of electrical activity across atria
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Causing atria to contract simultaneously
2 Non-conducting tissue between atria / ventricles prevents impulse passing directly to ventricles
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Preventing immediate contraction of ventricles
3 Waves of electrical activity reach atrioventricular node (AVN) which delays impulse
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Allowing atria to fully contract and empty before ventricles contract
4 AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex
where it branches into Purkyne tissue
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Causing ventricles to contract simultaneously from the base up

Question 5

Explain how a resting potential is established across the axon in a neurone

Answer 5

Na+/K+pump actively transports:
(3) Na+ out of axon AND (2) K+ into axon

Creating an electrochemical gradient:
Higher K+conc. inside AND higher Na+conc. outside

Differential membrane permeability:
More permeable to K+
→ move out by facilitated diffusion

Less permeable to Na+ (closed channels)

Question 6

Describe the all or nothing principle

Answer 6

For an action potential to be produced, depolarisation must exceed threshold potential
Action potentials produced are always same magnitude / size / peak at same potential

Bigger stimuli instead increase frequency of action pot

Question 7

Describe the all or nothing principle

Answer 7

For an action potential to be produced, depolarisation must exceed threshold potential

Action potentials produced are always same magnitude / size / peak at same potential

Question 8

Explain how changes in membrane permeability lead to depolarisation and the generation of an action potential

Answer 8

Stimulus - Na+ channels open - membrane permeability to Na+ increases
- Na+ diffuse into axon down electrochemical gradient ( depolarisation occurs as positive ions going in )

depolarisation - if threshold is reached then AP is generated
- more voltage gated Na+ channels open
- greater influx of Na+, potential rises to +40mv

repolarisation - v-gated Na+ channels close, v-gated k+ channels open, K+ diffuses out

** hyperpolarisation**
K+ channels are slow to close so there is a slight overshoot - too many K+ diffuse out

resting potential
- restored by Na+/K+ pump (original ion distribution) -65mv

repolarisation - if th