Chapter 14 Response to Stimuli

Question 1

What is a stimulus?

Answer 1

A detectable change in the environment.

Question 2

What is Taxes?

Answer 2

A simple response in organisms in which an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus.

Question 3

What taxis do earthworms show?

Answer 3

Negative phototaxis, so they move away from light. They move towards dark environments such as in the soil to help them avoid dehydration, predators and to locate food.

Question 4

What is Kinesis?

Answer 4

When an organism changes the speed of movement and the rate it changes direction.

Question 5

What is a tropism?

Answer 5

Term given to when plants respond via growth, to stimuli.

Question 6

Name a plant growth factor

Answer 6

IAA (indoleacetic acid)

Question 7

What is the nervous system made up of?

Answer 7

Peripheral and the central nervous system.

Question 8

What is the peripheral nervous system made up of?

Answer 8

Receptors, sensory and motor neurones.

Question 9

What is the CNS made up of?

Answer 9

Brain and the spine

Question 10

What are types of receptor cells?

Answer 10

Pacinian corpuscle
Rods
Cones

Question 11

What does the pacinian corpuscle do?

Answer 11

Responds to pressure changes.

Question 12

Where can you find pacinian corpuscle receptors?

Answer 12

Deep in the skin, mainly in fingers and feet.

Question 13

What is the pacinian corpuscle made up of?

Answer 13

A single sensory neurone wrapped with layers of tissues separated by gel.
The sensory neurone in the pacinian corpuscle has special channel proteins in its plasma membrane.

Question 14

What are stretch mediated sodium channels and how do they work?

Answer 14

Plasma membranes contain channel proteins which allows ion transportation and the membranes surrounding the sensory neurones have stretch mediated sodium channels.
These channels open and allow Na+ ions to enter the sensory neurone only when they are stretched and deformed.

Question 15

How do rod cells process images?

Answer 15

In black and white

Question 16

Explain the process of rod cells creating a generator potential

Answer 16

Pigment of rhodopsin must be broken down by light energy
There is enough energy from low intensity light to cause the breakdown
Enough pigment has to be broken down for the threshold to be met in the bipolar cell

Question 17

Why can rod cells function at low light intensities?

Answer 17

The threshold can be reached in low light as so many rod cells are connected to a single bipolar cell (summation).

Question 18

What pigment do cone cells contain?

Answer 18

Iodopsin.

Question 19

Why do cone cells have high visual acuity?

Answer 19

Since there is only one cone cell connected to a bipolar cell.
This allows the brain to distinguish between separate sources of light.

Question 20

Why can’t we see colour in the dark?

Answer 20

Cone cells can only respond to high light intensity

Question 21

Exercise causes an increase in heart rate.
Describe the role of receptors and of the nervous system in this process.

Answer 21

1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall
   in pH
   OR
   Baro / pressure receptors detect rise in blood pressure;
2. Send impulses to cardiac centre / medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for chemoreceptors / CO2)
   OR
   By parasympathetic (nervous system for baro / pressure
   receptors / blood pressure);

Question 22

When the heart beats, both ventricles contract at the same time.
Explain how this is coordinated in the heart after initiation of the heartbeat
by the SAN.
(2 marks)

Answer 22

1. Electrical activity only through Bundle of His / AVN;
2. Wave of electrical activity passes over / through both ventricles at the
   same time;

Question 23

The fovea of the eye of an eagle has a high density of cones. An eagle
focuses the image of its prey onto the fovea.
Explain how the fovea enables an eagle to see its prey in detail.
Do not refer to colour vision in your answer. (3 marks)

Answer 23

1. High (visual) acuity;
2. (Each) cone is connected to a single neurone;
   Accept no retinal convergence.
   Accept ‘bipolar/nerve cell’ for neurone.
3. (Cones send) separate (sets of) impulses to brain;