Stimulus and Response

Question 1

What is a kinesis?

Answer 1

Non-directional response to a stimulus, results in a changed rate of movement to keep the organism in a more favourable environment.

Question 2

What is a stimulus?

Answer 2

A change in the internal or external environment.

Question 3

Describe the basic order of a reflex arc.

Answer 3

Stimulus
Receptors
CNS
Effectors
Response

Question 4

Give an example of a reflex arc after touching a hot surface.

Answer 4

S - touch hot surface
R - thermoreceptors in skin detect temperature change, tasks it impulse along sensory neurone to the CNS
C - relay neurone transmits an impulse to the motor neurone
E - bicep receives impulse, contracts.
R - hand pulls away.

Question 5

How does the heart control an increase in blood pressure?

Answer 5

Baroreceptors in aortic/carotid bodies detect high pressure, and the sensory neurone transmits an impulse to the medulla, which transmits an impulse along the parasympathetic neurones. These secrets acetylcholine, which binds to receptors on SAN and slows the heart rate, reducing b.p.

Question 6

What type of receptor is a Pacinian Corpuscle, and what does it detect?

Answer 6

A mechanoreceptor, detects pressure and vibrations.

Question 7

Describe the structure of a Pacinian Corpuscle.

Answer 7

A naked end of a sensory neurone (sensory nerve ending) wrapped in many layers of lamellae.

Question 8

How does a Pacinian corpuscle respond to a pressure stimulus?

Answer 8

PC Stimulated
Lamellae deformed, press of SNE
Deforms stretch mediated sodium channels in sensory neurone cell membrane.
Sodium ion channels open, ions diffuse into cell, creating generator potential.
If the potential reaches the threshold, an impulse is transmitted,

Question 9

What does the PC demonstrate?

Answer 9

That receptors only respond to specific stimuli.

Question 10

What is the difference in the sensitivity of rods and cones, and why?

Answer 10

Many rod cells are connected to a single neurone, so many weak generator potentials combine to reach the threshold and trigger an action potential. Cones are each individually connected to a single neurone, so a greater amount of light per cell is required to generate an action potential.

Question 11

What is the difference in visual acuity between rods and cones, and why?

Answer 11

Rods give low acuity as many rods are connected to the same neurone. Light from two objects close together can’t be distinguished.
Cones give a high acuity as each cone is connected to one neurone, so two separate action potentials are generated from two cones. Easier to distinguish between separate points.

Question 12

How are rods and cones differently distributed in the retina?

Answer 12

Rods lie mainly in the peripheral parts of the retina, cones are packed together in the fovea,

Question 13

What is a taxis?

Answer 13

A directional response to a stimulus.

Question 14

What is a gland?

Answer 14

A group of cells that are specialised to secrete a useful substance e,g. Hormone. Pancreas secretes insulin for example.

Question 15

What is a hormone?

Answer 15

A protein or steroid that acts as a chemical messenger.

Question 16

Outline the four differences between hormonal and nervous response.

Answer 16

Electrical impulse carried by neurones vs hormones carried in blood
Fast response vs slow response
Localised effect vs widespread effect
Short term effect vs long term effect

Question 17

What do histamines and prostaglandins do?

Answer 17

Histamine - stored in mast cells/basophils. Released in responded to injury or infection. Increases capillary permeability so more cells from immune system can move out of the blood to the infected area.
Prostaglandins - involved in inflammation, fever, blood clotting, and blood pressure regulation.

Question 18

How do nerve cells stimulate target cells?

Answer 18

By secreting chemical neurotransmitters directly onto them.

Question 19

What is a tropism?

Answer 19

A response by a plant to a directional stimulus. This maintains the roots and shoots of a flowering plant in a favourable environment.

Question 20

What is a growth factor?

Answer 20

A chemical that speeds up or slows down plant growth.

Question 21

Where are auxins produced, and why will a shoot stop growing if the tip is cut off? What effect do they have on growth in roots and shoots.

Answer 21

Produced in the tip of shoots (diffuse to where they are needed) if the tip of a shoot is removed, all the auxin is removed (as it is in the tip), so growth stops. Inhibit root growth, stimulate shoot growth.

Question 22

What is IAA, and why is it important?

Answer 22

Indoleacetic acid, an important auxin, produced in the tips of shoots in flowering plants. Diffuses / actively transports over short distances, and via the phloem over long distances. Different parts of the plant have different amounts of IAA, so there is uneven growth of the plant. It will move to the shaded parts of shoots, so the shoot bends towards light.