Response to Stimuli

Question 1

Describe how a Pacinian corpuscle works

Answer 1

During resting potential sodium channels are too narrow to allow sodium ions through;
When pressure is applied, membrane stretches;
Sodium ion channels open;
Sodium ions enter causing depolarisation of membrane;
Causing generator potential which creates an action potential

Question 2

Describe how increased sympathetic stimulation increases cardiac output.

Answer 2

Increased stimulation of SAN;
Increase in heart rate;
Increase in stroke volume

Question 3

Describe how rod cells act as transducers of energy.

Answer 3

Convert light energy to electrical energy;

Light energy causes change in rhodopsin

Question 4

Describe how the Pacinian acts as a transducer of energy.

Answer 4

Converts mechanical energy to electrical energy

Question 5

The diameter of the pupil is reduced in bright light. Describe the part played by the autonomic nervous system in reducing the diameter.

Answer 5

Bright light stimulates impulses from eye to brain;
Parasympathetic system;
Stimulates contraction of circular muscles

Question 6

Earthworms move away from light. Why does this increase their chances of survival?

Answer 6

Leads them into the soil;

So they can conserve water, find food and avoid predators.

Question 7

Explain how a Pacinian corpuscle produces a generator potential in response to external pressure.

Answer 7

Stretches membrane;
Sodium ion channels open;
Sodium ions enter causing depolarisation

Question 8

Explain how retinal convergence enables a person to see in dimly lit conditions.

Answer 8

Action potentials or generator potentials from several receptors sent to single synapse;
Sufficient neurotransmitter released;
Action potential more likely to be generated in this neurone

Question 9

Explain how stimulation of chemoreceptors during exercise results in a change in heart rate.

Answer 9

Increase in carbon dioxide from respiration;
Decrease in blood pH detected by chemoreceptors;
More impulses to medulla;
More impulses from medulla along sympathetic nerve;
To SAN, increasing heart rate

Question 10

Explain how stimulation of pressure receptors during exercise results in a change in heart rate.

Answer 10

When blood pressure is higher than normal, they send an impulse to the medulla;
Fewer impulses from medulla along parasympathetic nerve;
To SAN, decreasing heart rate;
When blood pressure is lower than normal, they send an impulse to the medulla;
More impulses from medulla along sympathetic nerve;
To SAN, increasing heart rate

Question 11

Explain the effect of the parasympathetic division of the autonomic nervous system on cardiac output.

Answer 11

Decreases activity of SA node;

Decreases rate of contraction of heart muscle

Question 12

Explain the importance of reflex actions.

Answer 12

Avoids damage to tissues;

Helps escape from predators

Question 13

Explain the trichromatic theory of colour vision.

Answer 13

three types of cones;

each sensitive to different wavelength

Question 14

Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness.

Answer 14

rhodopsin broken down by light;

time for resynthesis;

Question 15

The heart muscle is myogenic. What does this mean?

Answer 15

The muscle contraction originates from within the heart muscle itself

Question 16

Increased intensity of exercise leads to an increased heart rate. Explain how.

Answer 16

Carbon dioxide detected by chemoreceptors;
Changes to heart rate controlled by medulla;
More impulses to SAN

Question 17

In humans, both sympathetic and parasympathetic divisions of the autonomic nervous system influence the secretion of saliva. When food is in the mouth, increased
parasympathetic stimulation of the salivary glands results in increased secretion of saliva. Explain the benefit of increased sympathetic stimulation of the salivary glands
once the food has been swallowed.

Answer 17

Will reduce secretion of saliva;

And prevent unnecessary expenditure of energy

Question 18

The iris of the eye contains antagonistic muscles which control the diameter of the pupil. Use your knowledge of the iris muscles to explain what is meant by antagonistic
muscle action.

Answer 18

radial and circular muscles in iris;
opposing action = antagonistic;
radial contraction increases pupil diameter / circular contraction
reduces (or vice versa for iris).

Question 19

A person looks at two spots of blue ink on a piece of white paper in bright light. The two spots are close together. Under these conditions, the person can clearly see two blue, circular spots.
Explain how rays of light from a spot are made to form a distinct circular image on the retina.

Answer 19

Correct reference to refraction;
By cornea and/or lens;
Shape of lens changes

Question 20

Neurones of type A are found in the autonomic nervous system. The autonomic nervous system consists of the sympathetic division and the parasympathetic division.
Suggest the effect that stimulation by neurones of the sympathetic division would have on the diameter of arterioles leading to skeletal muscle. Explain your answer.

Answer 20

Dilates;

More blood to muscles

Question 21

As well as pulling the finger away, the gardener also feels pain caused by the thorn. Explain how she becomes aware of the pain.

Answer 21

impulses to brain;
sensory areas (in brain);
processing by association area

Question 22

Explain what the results of cutting the sympathetic and parasympathetic nerves demonstrate about the control of resting heart rate.

Answer 22

Resting heart rate controlled by both divisions;
Heart rate changes when parasympathetic/sympathetic nerve cut;
Larger change in heart rate when parasympathetic nerve is cut

Question 23

Reflexes are described as being rapid, automatic responses. Use the information in the diagram to explain those features of a reflex arc which result in the response being rapid and automatic.

Answer 23

Rapid because only involves three neurones;
Automatic because same pathway used each time;
no thinking involved

Question 24

Rod cells allow us to see objects in dim lights. Explain how the connections of rod cells to neurones in the retina make this possible.

Answer 24

Several rods have connections with one neurone;
Generator potentials exceed the threshold;
Individual generator potentials do not exceed the threshold

Question 25

Using your knowledge of tropism, describe how plants’ growth is adapted for survival.

Answer 25

Plant shoots grow towards light (positive phototropism) so that their leaves can capture more light for photosynthesis;
Plant roots grow away from light (negative phototropism) and towards gravity (positive geotropism) so that their roots will grow into the soil, where they are better able to absorb water and nutrients

Question 26

What are the two systems by which receptors communicate to effectors?

Answer 26

Hormones;

The nervous system

Question 27

What is a kinesis?

Answer 27

Random movements in response to a stimulus;

From an unfavourable environment to a favourable one

Question 28

What is a reflex?

Answer 28

A rapid response to a stimulus;

Which is involuntary

Question 29

What is a stimulus?

Answer 29

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

Question 30

What is a stretch-mediated sodium channel?

Answer 30

Changes its permeability to sodium when it is stretched

Question 31

What is a taxis?

Answer 31

A directional response to a stimulus;

From an unfavourable environment to a favourable one

Question 32

What is a tropism?

Answer 32

A growth movement of part of a plant;

In response to a directional stimulus

Question 33

What is meant by visual acuity?

Answer 33

Ability to distinguish between small objects.

Question 34

What is the function of the autonomic nervous system?

Answer 34

Controls the involuntary activities of internal muscles and glands

Question 35

What role do motor neurones play?

Answer 35

Carry nerve impulses away from the central nervous system to effectors

Question 36

What role do sensory neurones play?

Answer 36

Carry nerve impulses from receptors towards the central nervous system

Question 37

Explain how the change in the ability of the lens to become more convex affects the ability to focus clearly as people get older.

Answer 37

More convex the lens, the greater the refraction;
High refraction needed for near vision;
Lens becomes less elastic with age;
Hence difficulty in focusing on close objects

Question 38

When you place your hand on a hot object, your involuntary response is to pull your hand away.
Describe the reflex arc which coordinates this process.

Answer 38

Temperature receptors in skin detect the stimulus (heat from the object);
This creates a nerve impulse in a sensory neurone;
Sensory neurone passes the nerve impulse to the spinal cord;
Intermediate neurone links the sensory neurone to a motor neurone in the spinal cord;
Motor neurone carries the nerve impulse from the spinal cord to an effector;
The effector is the muscle in the arm which contracts to remove hand

Question 39

Why are more cone cells found at the fovea?

Answer 39

Fovea receives the highest intensity of light;

Cone cells only respond to high intensity of light

Question 40

Why can rod cells not detect colours?

Answer 40

Cannot distinguish different wavelengths of light

Question 41

Why can rod cells respond to a very low intensity of light?

Answer 41

Many rod cells share a single neurone;
Therefore the threshold value is exceeded;
Low intensity is sufficient to break down rhodopsin, creating generator potential

Question 42

Why do brightly coloured objects appear grey in dim light?

Answer 42

Only rod cells stimulated by dim light;

Rod cells cannot distinguish between different wavelengths of light

Question 43

Why do cone cells only respond to a high intensity of light?

Answer 43

Each cone cell connected to a single neurone;
So cannot combine to help exceed the threshold value and create a generator potential;
Iodopsin requires high light intensity for its break down to create a generator potential

Question 44

Why do cones have high visual acuity?

Answer 44

Each cone cell connected to a single neurone;
So each that are stimulated will generate an impulse;
So can distinguish between the separate sources of light

Question 45

Why do rods have low visual acuity?

Answer 45

Many rod cells share a single neurone;
Only generate a single impulse;
So cannot distinguish between the separate sources of light