Summary Pearson Edexcel Biology Paper 5 Processes: Pt 2

BIOLOGY PAPER 5 PROCESSES: PART 2

CONTENTS:

- Topic 8

- 8A: How A Response Is Generated By Effectors 3

- 8A: Resting Potential Mechanisms 3

- 8A: Action Potential: ONLY AT THE NODES OF RANVIER 3

- 8A: How Impulses Are Transmitted Across The Synaptic Cleft By
Diffusion of Neurotransmitters 3-4

- 8A: Synaptic Transmission For ACh 4

- 8A: Effects of Drugs On The Nervous System 4-5

- 8A: How Sensory Receptors Work 5

- 8A: How Rods Work 5-6

- 8A: Habituation 6

- 8B: Spinal Reflexes 6

- 8B: Cranial Reflexes: AKA. Pupil Reflex 6-7

- 8B: How Auxins Work 7

- 8B: Role of Gibberellins in Seed Germination 7-8

- 8B: Reversible Reactions of Pr & Pfr: CONTROLS FLOWERING 8

- 8B: Using Phytochrome As A Transcription Factor: Using Green
Fluorescent Protein 8

- 8C: Producing Recombinant DNA 8-9

- 8C: Making An Artificial Copy of A Desired Gene 9

- 8C: Identifying Transferred Organisms: Replica Plating 9

- 8C: Harvesting Human Insulin from GM Bacteria 9-10

- 8C: Making Transgenic Plants 10

,- 8C: Making Transgenic Animals 10

- 8C: Using A DNA Microarray 10-11

,TOPIC 8:

8A: How A Response Is Generated By Effectors:

1. The stimulus is detected by a receptor
2. Impulses are sent along the sensory neurone; to the CNS; along the relay
neurone & along the motor neurone
3. Impulses are received by the effector which makes it relax/contract


8A: Resting Potential Mechanisms:

1. The Na⁺/K⁺ pump creates concentration gradients across the membrane
2. K⁺ diffuses out & down the K⁺ concentration gradient
- Makes the outside of the membrane POSITIVE & the inside NEGATIVE

3. The electrical gradient pulls K⁺ back into the cell
4. At -70mV potential difference, the 2 gradients counteract each other & there is
no net movement of K⁺


8A: Action Potential: ONLY AT THE NODES OF RANVIER:

1. Voltage-dependent Na⁺ channels open
- Na⁺ flows into the axon- depolarising the membrane

2. Voltage-dependent Na⁺ channels close
3. Voltage dependent K⁺ channels open
- K⁺ leaves the axon- repolarising the membrane

4. Na⁺ is pumped out
5. The membrane is hyperpolarised
6. Voltage-dependent K⁺ channels close
- K⁺ diffuse back into the axon
- This recreates the resting potential


8A: How Impulses Are Transmitted Across The Synaptic Cleft By Diffusion of
Neurotransmitters:

1. Action potential arrives & depolarises the presynaptic membrane
2. Ca²⁺ channel proteins open
- Ca²⁺ diffuses in

, 3. Causes synaptic vesicles to move to presynaptic membrane
4. Some of these vesicles fuse with the presynaptic membrane & releases the
transmitter substance into the synaptic cleft
5. The molecules diffuse across the gap & attached to specific protein receptor sites
on Na⁺ channels of the postsynaptic membrane
- Causes Na⁺ channels to open
- Na⁺ flows into nerve fibres
- Causes a change in potential difference across the
membrane & an EPSP is set up

THE MOVEMENT OF NEGATIVE IONS INWARDS RESULTS IN AN IPSP BEING SET UP

6. Once the transmitter has had its effect, it’s destroyed by enzymes in the
synaptic cleft


8A: Synaptic Transmission For ACh:

1. Action potential arrives & depolarises the presynaptic membrane
2. Ca²⁺ channels proteins open
- Ca²⁺ diffuses in

3. Presynaptic vesicles fuse with the membrane & ACh is released
4. ACh diffuses across the synaptic cleft
5. ACh binds to receptor proteins that open & allows Na⁺ to diffuse through
6. Postsynaptic membrane is depolarised
7. ACh is broken down into acetate & choline by acetylcholinesterase
8. Choline is recycled into ACh


8A: Effects of Drugs On The Nervous System:

INCREASING THE RESPONSE:

1. Increases the AMOUNT of neurotransmitter synthesised
2. Increases the RELEASE of neurotransmitters from vesicles at the presynaptic
membrane
3. Increases the EFFECT of the normal neurotransmitter
4. Prevents the DEGRADATION of the neurotransmitter by enzymes
5. Prevents the REUPTAKE into the presynaptic knob

DECREASING THE RESPONSE:

1. Blocks the SYNTHESIS of neurotransmitters