response to stimuli and nervous coordination

Question 1

What is taxes

Answer 1

A taxis is a simple response in which direction of movement of the organism is determined by the direction of the stimulus
movement of the whole organism toward(positive) or away (negative) from the stimulus

Question 2

what is phototaxis

Answer 2

the movement of simple photosynthesising organisms towards/ away from light

Question 3

what is chemotaxis

Answer 3

the movement towards or away from a high concentration or a particular substance. This enables bacteria to move toward food source or away from toxic compounds

Question 4

what is kinesis

Answer 4

a form of response in which an organism doesn’t move toward or away from a stimulus. The response is related to the intensity of the stimulus and involves a change in the rate of movement and turning of the organism.

Question 5

what is a tropism

Answer 5

A tropism is a growth movement of part of a plant in response to a directional stimulus. Positive or negative depending on wether they bend toward or away from the stimulus

Question 6

Do plant shoots grow toward or away from the light

Answer 6

toward (positive phototropism) so their leaves can absorb light for photosynthesis

Question 7

Do plant roots grow toward or away from light

Answer 7

away from light (negative phototropism) and toward gravity (positive geotropism). This increases the probability that roots will grow into the soil to absorb water and mineral ions

Question 8

what is auxin amd what does it do ?

Answer 8

auxin is a plant growth factor which stimulates plant growth. It’s produced in the growing religions of a plant e.g roots and shoots.

Question 9

How does auxin effect phototropism

Answer 9

Cells in the shoot top produce IAA which diffuses down the shoot stimulating upward growth (elongated cells)
If the shoot is exposed to a unidirectional light stimulus the light causes movement of IAA from illuminated side to shaded side
The greater concentration on the shaded side causes greater elongation causing the shoot to bend toward the light

Question 10

How does auxin effect the roots

Answer 10

High auxin concentration inhibits growth on the lower side so the root grows downwards.

Question 11

what does the endocrine system do

Answer 11

releases hormones( chemical messengers) that travel in the bloodstream to a target cells. The response is slow, long lasting and widespread

Question 12

What are the 2 mechanisms by which hormones act on cells

Answer 12

peptide hormones- cannot pass through the cell membrane. The have a specific tertiary structure which is complementary to that of a protein receptors in the cells membrane so they bind activating enzyme activity.
steroid hormones- can rapidly pass through the cell membrane as they are lipid soluble

Question 13

what is the role of a sensory neurone

Answer 13

sensory neurones posses receptors which a stimulated by a specific stimulus. An impulse is then transmitted along a sensory neurone to the CNS

Question 14

What is the role of the motor neurone

Answer 14

transmits impulses to the appropriate effector either a muscle or a gland

Question 15

What is the role of the relay neurone

Answer 15

act as a link between the sensory and motor neurone and are stimulated in the CNS

Question 16

How are the 3 neurones involved in the reflex arc

Answer 16

The receptor detects the stimulus and transmits an impulse along the sensory to the brain/ spinal cord. The sensory neurone synapses with a relay which passes the impulse to the motor. Impulses are transmitted along the motor neurone to the effector( e.g muscle)

Question 17

What is depolarisation

Answer 17

This is when a receptor is stimulated above threshold and an action potential is generated transmitting a nerve impulse, the potential across the axon membrane changed from a negative INSIDE value of -70mv to a positive 40mv.

Question 18

What does depolarisation result from

Answer 18

an increase in the permeability of the axon membrane to sodium ions as sodium channels/gates are open. The sodium ions diffuse down a concentration gradient causing more sodium chanels to open further increasing the permeability

Question 19

What is repolerisation

Answer 19

After the membrane is fully depolarised the sodium channels close and the potassium channels open to allow potassium out of the axon. Becasue they are positively charged it makes the inside less positive

Question 20

How does the sodium potassium pump restore the resting potential

Answer 20

actively removes the sodium ions that have entered during depolarisation and returns the potassium ions back to the axon

Question 21

How is the resting potential maintained

Answer 21

1. The membrane is more permeable to the loss of potassium ions than the intake of sodium ions. This is due more potassium channels being open resulting in a net loss of positively charged ions from the axon
2. The sodium potassium pimp actively removes sodium and potassium in with use of ATP

Question 22

what is the refractory period

Answer 22

The time required for the redistribution of ions that have moved during the action potential.
Results in seperate discrete impulse

Question 23

How does temperature affect the speed of a nerve impulse

Answer 23

Will increase the speed of transmission upto a certain point. Increase in diffusion of ions and enzyme activity particularly in respiration which provided ATP for active transport but the S-P pump

Question 24

How does axon diameter effect the speed of transmission

Answer 24

The greater the diameter of an axon the faster the speed of conductance

Question 25

How does myelination effect the speed of an impulse

Answer 25

insulated the neurone and increases the speed of transmission as the action potential jumps from one node of ranvier to the next (where depolarisation occurs) this is called saltatory conduction

Question 26

What are rods useful for

Answer 26

for vision at low light intensity (dark) they possess high visual sensitivity

Question 27

what are cones useful for

Answer 27

important for good discrimination of detail they have high visual acuity and enable colour vision

Question 28

Why do rods have high visual sensitivity

Answer 28

Several rods synapse with one bipolar neurone, in dim light the stimulation of several rods next to each other has an addictive effect in the bipolar neurone and impulses are transmitted to the brain. Enables threshold to be reached.

Question 29

Why do cones have low visual sensitivity

Answer 29

cones have a 1:1 relationship with a bipolar neurone so do not generate impulses along the neurone at low light

Question 30

why do cones have high visual acuity

Answer 30

They only synapse with 1 bipolar neurone therefore for each cone stimulated a set of impulses is transmitted to the brain providing maximum acuity because each part of the image is detected by a different cruel so there is no blurring

Question 31

why do cones have high visual acuity

Answer 31

They only synapse with 1 bipolar neurone therefore for each cone stimulated a set of impulses is transmitted to the brain providing maximum acuity because each part of the image is detected by a different cruel so there is no blurring

Question 32

why do rods have low visual acuity

Answer 32

they share a bipolar neurone, several rods may be stimulated but only one neurone is stimulated so the brain only receives one set of impulses.

Question 33

why do rods have low visual acuity

Answer 33

they share a bipolar neurone, several rods may be stimulated but only one neurone is stimulated so the brain only receives one set of impulses.

Question 34

Describe the mechanism of synaptic transmission

Answer 34

1. arrival of action potential at synaptic knob cause’s depolarisation of presynaptic membrane.
2. This stimulates the opening of calcium ion channels causing Ca to move into synaptic knob via facilitated diffusion
3. synaptic vesicles fuse with the presynaptic membrane and break open
   4.neurotransmitter diffuse across the synaptic cleft
4. attached to specific protein receptor on the post synaptic membrane
5. attachment stimulates entry of Na which pride EPSP excitatory potentials
6. As more neurotransmitters attach and Na enters EPSP build up leading tp depolarisation of postsynaotic neurone