Organisms Respond to changes in the In/Ex Environments

Question 1

What is a stimulus?

Answer 1

A change in the internal / external environment

Question 2

What is the function of the co-ordinator?

Answer 2

Formulates a suitable response to a stimulus

Question 3

What is the function of a receptor?

Answer 3

It detects a stimulus

Question 4

What is the function of an effector?

Answer 4

Produces a response to a stimulus

Question 5

What is taxis?

Answer 5

A directional response to a stimulus. The organisms will move directly towards or away from the stimulus

Question 6

What is kinesis?

Answer 6

A non-directional response to a stimulus. The rate of movement is affected by the intensity of the stimulus i.e move faster / slower or turn more / less frequently.

Question 7

What is Tropism?

Answer 7

Growth Response to a stimulus that occurs in flowering plants

Question 8

What are the 2 types of Tropism?

Answer 8

• Phototropism - Response to light

* Gravitropism – Response to Gravity

Question 9

State 2 features of a reflex action

Answer 9

• Rapid

- Automatic responses

Question 10

What is the normal 7 stage Reflex arc pathway?

Answer 10

1) Stimulus
2) Receptor
3) Sensory neurone
4) Connector neurone
5) Motor neurone
6) Effector
7) Response

Question 11

Where does the sensory neurone come from and go to?

Answer 11

From receptor to spinal cord

Question 12

Where is the Connector neurone located?

Answer 12

Within Spinal Cord

Question 13

Where does the Motor Neurone come from and go to?

Answer 13

From Spinal Cord to Effector

Question 14

What is the CNS (Central Nervous system) made up of?

Answer 14

Brain + Spinal Cord

Question 15

What is the function of Dendrites?

Answer 15

Synapse to / with connector neurones

Question 16

What is the function of axon?

Answer 16

Very long and it conveys nerve impulses from spinal cord to effector

Question 17

Structure & Function of Myelin Sheath?

Answer 17

Made from Schwann cells wrapped around the axon. Forms a fatty layer around the axon + increases speed of transmission of the nerve impulses.

Question 18

What are the Nodes of Ranvier?

Answer 18

Gaps between Schwann cells where ions can move between the cell and tissue fluid

Question 19

How is a resting potential of -70mV maintained?

Answer 19

• Active transport (needing ATP + Protein carriers), 3Na+ are pumped out for every 2K+ pumped in.
• Facilitated diffusion – K+ diffuse rapidly out of the cell as the membrane is more permeable to K+. Na+ can only diffuse back slowly as membrane is less permeable to Na+.
• Results in tissue fluid outside having more positive ions than inside (negative electrical charge inside than outside) so the membrane is polarised and an electrochemical gradient has been established

Question 20

Explain the process of depolarisation (graph line sharply increases?

Answer 20

• Membrane becomes more permeable to Na+ ions
• This is due to the Sodium Volted Gated Channels open
• Sodium ions diffuse into the axon

Question 21

What is the Threshold Value usually?

Answer 21

-40mV

Question 22

Explain the process of Repolarisation?

Answer 22

• Membrane becomes more permeable to K+ ions
• This is due to the potassium ion Volted Gated Channels open
• Potassium ions diffuse into the axon

Question 23

Explain the process of Hyperpolarisation?

Answer 23

• Potential difference may overshoot the resting potential
• So Potassium Volted Gated Channels close
• Sodium/Potassium pump restores the resting potential

Question 24

What is a Nerve Impulse?

Answer 24

The depolarisation of one part of the neurone which sets off the depolarisation of the next section along the entire neurone

Question 25

What is a Refractory Period?

Answer 25

The time while the membrane is unable to respond to another depolarisation

Question 26

State 3 factors affecting the speed of conduction

Answer 26

* Myelin Sheath * Axon Diameter * Temperature

Question 27

What is the gap between 2 neurones where synaptic transmission occurs?

Answer 27

Synaptic cleft

Question 28

How is information conveyed during synaptic transmission?

Answer 28

This is via diffusion of a neurotransmitter

Question 29

In cholinergic neurones, what is the neurotransmitter?

Answer 29

Acetylcholine

Question 30

In Adrenergic neurones, what is the neurotransmitter?

Answer 30

Noradrenaline

Question 31

Explain the 6 events at a synapse?

Answer 31

1) Action Potential arrives at synaptic knob, increasing the permeability of the presynaptic membrane to Calcium ions (Ca2+ channels open) allowing calcium ions to diffuse in 2) Ca2+ make synaptic vesicles move towards and fuse with the presynaptic membrane. Acetylcholine released into synaptic cleft via exocytosis 3) Acetylcholine diffuses across cleft and binds to complementary shaped receptor on the postsynaptic membrane. This causes sodium ion channels to open and sodium ions diffuse in 4) Depolarisation of the postsynaptic membrane takes place; Action Potential started 5) Enzyme, actylcholinesterase, hydrolyses acetylcholine into acetate + chlorine which shuts Na+ channels 6) Products diffuse back across cleft, reabsorbed, resynthesised using ATP into acetylcholine and repackaged into vesicles This is an excitatory synapse

Question 32

What is an excitatory synapse?

Answer 32

An action potential is initiated at the postsynaptic membrane

Question 33

What is meant by an inhibitory synapse?

Answer 33

This is when an action potential is NOT initiated at the postsynaptic membrane. Instead K+ channels open and the membrane becomes hyperpolarised.

Question 34

What is the function of the synapse?

Answer 34

* Transmit info between neurones | * Pass impulses in one direction (unidirectionality)

Question 35

Why can impulses only go in one direction?

Answer 35

This is because neurotransmitters can only be released from the presynaptic membrane and receptors are only found on the postsynaptic membrane

Question 36

What is Temporal Summation?

Answer 36

Several Action Potentials arrive in rapid succession at 1 synaptic knob, a high frequency of impulses = Intense Stimulus. The effect is additive and leads to above threshold = depolarisation at the postsynaptic membrane

Question 37

What is Spatial Summation?

Answer 37

2 or more Action Potentials arrive at one synapse from different presynaptic neurones at the same time. The effect is additive leading to an above threshold depolarisation at the postsynaptic membrane.

Question 38

What is the structure of a Neuromuscular Junction?

Answer 38

* Synapse between Motor Neurone & Muscle Fibre (Muscle cell) * Postsynaptic membrane is the Sarcolemma (muscle fibre membrane) * Muscle Fibre contains Sarcoplasm (cytoplasm) and bundles of Myofibrils

Question 39

What is the structure & Function of Myofibrils?

Answer 39

They consist of protein filaments which are involved in Muscle Contraction (More later)

Question 40

What is the structure of the Sarcolemma?

Answer 40

Folded deeply into muscle fibre forming extensive network of T-tubules

Question 41

What does the Sarcoplasmic Reticulum contain?

Answer 41

Calcium ions

Question 42

What is the neurotransmitter at the neuromuscular junction?

Answer 42

Acetylcholine

Question 43

Where is the action potential initiated at the neuromuscular junction?

Answer 43

Sarcolemma so the muscle contracts