Response to Stimuli

Question 1

What is the benefit of responding to stimuli?

Answer 1

Animals:

• Move away from harmful stimuli
• Maintain internal environment at optimum

Plants:

• Growth towards favourable conditions

Question 2

What are the two ways of communication within animals?

Answer 2

1. Nervous - electrical impulses
2. Hormonal - hormones

Question 3

Compare nervous and hormonal communication

Answer 3

Nervous:

• Localised
• Short-lived
• Rapid

Hormonal:

• Widespread
• Long-lasting
• Slow

Question 4

What are chemical mediators?

Answer 4

Chemicals secreted by cells which result in a cellular response

Question 5

What is the receptor for pressure in the skin?

Answer 5

Pacinian Corpuscle

Question 6

How is pressure detected?

Answer 6

1. Pressure opens stretch-mediated sodium channels
2. Na⁺ ions diffuse into the neurone
3. If the generator potential reaches threshold, an action potential is induced

Question 7

What are the receptors for light?

Answer 7

Rod cells

Cone cells

Question 8

What is the fovea?

Answer 8

The place on the retina where most of the cones are concentrated.

Question 9

What is the arrangement of the connections between rod/cone cells and bipolar cells?

Answer 9

One cone per bipolar cell

Multiple rods per bipolar cell

Question 10

Compare the two types of photoreceptor in the eye

Answer 10

Rod cells:

• Monochromatic
• Very sensitive to light
• Poor visual acuity

Cone cells:

• Trichromatic
• Less sensitive to light
• High visual acuity

Question 11

What are the pigments found in the photoreceptors?

Answer 11

Rods: rhodopsin

Cones: iodopsin

Question 12

What is the structure of the nervous system?

Answer 12

Question 13

What are reflexes?

What is their purpose?

Answer 13

A response made without a conscious decision

Aid survival by rapidly avoiding harmful stimuli

Question 14

Define: Taxis

Answer 14

Directional response to a stimulus

Question 15

Define: Kinesis

Answer 15

Non-directional response to a stimulus:

More unpleasant stimuli result in increased movement

Question 16

What region of the brain regulates heart rate?

Answer 16

Medulla

Question 17

What receptors detect blood pressure?

Answer 17

Baroreceptors in the aorta/vena cava

Question 18

What do chemoreceptors in the aorta and carotid artery detect?

Answer 18

O₂/CO₂/pH

Question 19

What happens when blood pressure/O₂ levels are too high?

Answer 19

1. Detected by the relevant receptor which sends impulses to the medulla
2. Medulla sends more impulses down parasympathetic neurones to the SAN
3. Heart rate decreases

Question 20

What happens when blood pressure/O2 levels are too low?

Answer 20

1. Detected by the relevant receptor, sends impulses to the medulla
2. Medulla sends more impulses down sympathetic neurones to the SAN
3. Heart rate increases

Question 21

Define: Tropism

Answer 21

Growth regulation by plants in response to a directional stimulus

Question 22

By what means to plants respond to stimuli?

Answer 22

Using growth factors such as auxins

Question 23

What is the IAA and what is it’s role in plants?

Answer 23

Indoacetic Acid is an auxin which:

• Stimulates cell elongation in shoots
• Inhibits cell elongation in roots