Response to Stimuli

Question 1

Stimulus

Answer 1

A detectable change in the internal or external environment of an organism that produces a response in the organism

Question 2

How does the ability to respond to stimuli increase the chances of survival?

Answer 2

There is a selection pressure favouring organisms with more appropriate responses.

Question 3

A Taxis

Answer 3

A simple response whose direction is determined by the direction of the stimulus. They can either move towards or away from stimulus, positive or negative.

Question 4

Kinesis

Answer 4

Organism doesn’t move towards or away from stimulus but moves more rapidly with changing direction the more unfavourable the stimulus is.

Question 5

What are kinesis designed for?

Answer 5

To bring the organism back into favourable conditions. Important when a stimulus is less directional eg. humidity and temperature.

Question 6

Tropism

Answer 6

A growth movement of part of a plant in response to a directional stimulus.

Question 7

What are the components of the peripheral nervous system?

Answer 7

Sensory neurones and motor neurones.

Question 8

What are the components of the motor nervous system?

Answer 8

Voluntary nervous system and autonomic nervous system.

Question 9

The spinal cord

Answer 9

Column of nervous tissue that runs along the back and lies inside the vertebral column for protection. Pairs of nerves emerge at intervals along the spinal cord.

Question 10

Reflex

Answer 10

Involuntary response to a sensory stimulus.

Question 11

Advantage of reflex arcs

Answer 11

1. Involuntary -> don’t require decision making powers of the brain, leaving it free to carry out more complex responses
2. Protect the body from harmful stimuli (from birth)
3. Fast, neurone pathway is short with very few synapses. Important in withdrawal reflexes.

Question 12

What are the components of the autonomic nervous system?

Answer 12

The sympathetic nervous system -> stimulates effectors. The parasympathetic nervous system -> inhibits effectors.

Question 13

What part of the brain regulates changes to heart rate?

Answer 13

Medulla Oblongata

Question 14

What are the two connecting centres of the medulla oblongata?

Answer 14

1. Centre that increases heart rate -> SAN

2. Centre that decreases heart rate -> SAN

Question 15

Where are chemoreceptors found?

Answer 15

The wall of the carotid arteries.

Question 16

Chemoreceptors

Answer 16

Sensitive to changes in the pH of the blood that result from changes in CO2 conc.

Question 17

Outline the process of control by chemoreceptors.

Answer 17

1. When blood has a higher than normal conc. of CO2, pH is lowered
2. Chemoreceptors in the wall of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in medulla oblongata that increases heart rate
3. Centre increases frequency of impulses with the sympathetic nervous system to SAN which increases heart rate
4. Increased blood flow causes more CO2 to be removed by lungs so CO2 levels return to normal
5. pH rises to normal and chemoreceptors in wall of carotid arteries and aorta reduce frequency of nerve impulses to medulla oblongata
6. Medulla reduces the frequency of impulses to SAN, decreasing heart rate

Question 18

How do pressure receptors react when blood pressure is higher than normal?

Answer 18

They transmit a nervous impulse to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses through the parasympathetic nervous system to the SAN of the heart, which decreases the heart rate.

Question 19

How do pressure receptors react when blood pressure is lower than normal?

Answer 19

They transmit a nervous impulse to the centre in the medulla oblongata that increases heart rate. This centre sends impulses through the sympathetic nervous system to SAN, increasing heart rate.

Question 20

Features of the Pacinian corpuscle

Answer 20

1. Specific to mechanical pressure

2. Produces a generator potential by acting as a transducer

Question 21

Receptors

Answer 21

Convert the energy of the stimulus into a nervous impulse known as a generator potential

Question 22

What type of sodium channel does the Pacinian corpuscle have?

Answer 22

Stretch-mediated sodium channel

Question 23

Outline the function in a Pacinian Corpuscle

Answer 23

1. At resting potential, the stretch-mediated sodium channels of the membrane are closed
2. When pressure is applied to the Pacinian corpuscle, it changes shape and the membrane around its neurone becomes stretched
3. This allows the sodium channels to open and sodium ion diffuse into the neurone
4. The influx of sodium ions causes depolarisation, producing a generator potential
5. The generator potential creates an action potential that passes along the neurone to the the CNS.

Question 24

How do rod and cone cells transduce?

Answer 24

Convert light energy into the electrical energy of a nerve impulse.

Question 25

Why do rod cells only produce black and white images?

Answer 25

Can’t distinguish different wavelengths of light.

Question 26

How do rod cells respond to light of very low intensity?

Answer 26

Many rod cells share a single sensory neurone. A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells to which they are attached. Greater chance that threshold value will be exceeded as a number of rod cells are attached to a single bipolar cell.

Question 27

How do rod cells create a generator potential?

Answer 27

Rhodopsin, the pigment in the rod cells must be broken down. Low-intensity light is sufficient to cause this breakdown.

Question 28

Why do rod cells have low visual acuity?

Answer 28

Many rod cells are linked to a single bipolar cell so light received rod cells sharing the same neurone will only generate a single impulse regardless of how many neurones are stimulated.

Question 29

How do cone cells allow us to perceive images in full colour?

Answer 29

3 different types of cone cells each responding to a different wavelength of light. Proportion of each type that’s stimulated allows us to see in full colour.

Question 30

Why do cone cells only respond to high light intensity?

Answer 30

Each cone cell often has their own separate bipolar cell connected to a sensory neurone so stimulation of several cone cells can’t combine to help exceed threshold value.

Question 31

How do cone cells create a generator potential?

Answer 31

Iodopsin, requires a higher light intensity for its breakdown to create a generator potential.

Question 32

Why do cone cells have a high visual acuity?

Answer 32

Each cone cell has its own connection a single bipolar cell so if two adjacent cone cells are stimulated the brain receives 2 separate impulses and can distinguish between 2 separate sources of light.

Question 33

How are rod cells and cone cells distributed on the retina?

Answer 33

Cone cells -> fovea, retina opposite the pupil

Conc. of cone cells diminishes further away from fovea. Rod cells are found at the peripheries of retina.

Question 34

Are there more rod cells or cone cells?

Answer 34

More rod cells.