B7. Co-ordination and response

Question 1

What is the ‘CNS’?

Answer 1

Stands for ‘Central Nervous System’;

Brain and spinal cord, which have role of coordination

Question 2

What is the ‘PNS’?

Answer 2

Stands for ‘Peripheral Nervous System’; nerves, which connect all parts of the body to the CNS

Question 3

Describe the human nervous system in terms of the central nervous (brain and spinal cord as areas of coordination) and the peripheral nervous system, which together serve to coordinate & regulate body functions.

Answer 3

 Sense organs are linked to the PNS; they contain groups of receptor cells;
 When exposed to a stimulus they generate an electrical impulse, which passes along peripheral nerves to the CNS, triggering a response.
 Peripheral nerves contain sensory and motor neurons;
 Sensory neurons transmit nerve impulses from sense organs to the central nervous system;
 Motor neurons transmit nerve impulses from the CNS to effectors (muscles or glands)
 Neurons are covered with a myelin sheath, which insulates them to make transmission of the impulse more efficient;
 Relay neurons pick up messages fromother neurons and pass them on to other neurons.
 The cytoplasm (mainly axon and dendron) is elongated to transmit the impulse for long distances.

Question 4

Define ‘reflex action’

Answer 4

A reflex action is a fast, automatic response to a stimulis.

Question 5

Describe the sequence of events of then reflex action.

Answer 5

Stimulus (sharp pin in finger) -> Receptor (pain receptors in skin) -> Coordination (spinal cord) -> Effector (biceps muscle) -> Response (biceps muscle contracts, hand is withdrawn from pin)

Question 6

What is ‘blind spot’?

Answer 6

Part of the retina in front of the optic nerve that lacks rods or cones.

Question 7

What is ‘optic nerve’?

Answer 7

Transmits electrical impulses from the retina to the brain.

Question 8

What is ‘sclera’?

Answer 8

A tough, white layer that protects the eyeball.

Question 9

What is ‘choroid’?

Answer 9

Produces a black pigment to prevent reflection of light inside the eye.

Question 10

What is ‘retina’?

Answer 10

A light sensitive layer made of rods and cones.

Question 11

What is ‘cornea’?

Answer 11

A transparent layer at the front of the eye that refracts the light entering to help to focus it.

Question 12

What is ‘iris’?

Answer 12

A coloured ring of circular and radial muscle that controls the size of the pupil

Question 13

What is ‘lens’?

Answer 13

A transparent, convex, flexible, jelly-like structure that refracts light to focus it.

Question 14

What are ‘rods’?

Answer 14

Sensitive to dim light, do not respond to colour.

Question 15

What are ‘cones’?

Answer 15

Function when the light is bright, able to distinguish between different colours of light.

Question 16

What happens in bright light?

Answer 16

• Circular muscles contract
• Radial muscles relax
• Pupil constricts

Question 17

What happens in dim light?

Answer 17

• Circular muscles relax
• Radial muscles contract
• Pupil dilates

Question 18

What happens to the eye when looking at a distant object?

Answer 18

• Ciliary muscles relax
• Lens become thin
• Suspensory ligaments pulled tight

Question 19

What happens to the eye when looking a near object?

Answer 19

• Ciliary muscles contract
• Suspensory ligaments slacken
• Lens get fatter

Question 20

Define ‘hormone’

Answer 20

A chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver.

Question 21

State the role of the hormone adrenaline in the chemical control of metabolic activity, including increasing the blood glucose concentration and pulse rate.

Answer 21

• Secreted by adrenal glands located above each kidney
• Helps us to cope with danger by increasing the heart rate
• Thus supplying oxygen to brain and muscles more quickly, this increase the rate of metabolic activity and gives more energy for fighting or running away
• The blood vessels in skin and digestive system contract so that they carry very little blood
• Causes the liver to release glucose into the blood

Question 22

Examples of situations in which adrenaline secretion increases.

Answer 22

• A man holding a gun to your head

- Examination

Question 23

What is ‘stimuli’?

Answer 23

Change in environment, detected by receptor cells.

Question 24

What is ‘nerve impulse’?

Answer 24

An electrical signal that passes along neurones (nerve cells).

Question 25

What are ‘receptor cells’?

Answer 25

Cells that are sensitive to stimuli.

Question 26

What are ‘effector cells’?

Answer 26

Cells that carry out responses to certain stimuli.

Question 27

What is a ‘response’?

Answer 27

A reaction of a organism to a specific stimulus.

Question 28

Describe the pathway of nerve impulses of voluntary actions.

Answer 28

Stimulus -> Receptor -> Spinal cord -> Brain -> Effector -> Response

Question 29

Describe the pathway of nerve impulses of involuntary actions (reflexes).

Answer 29

Stimulus -> Receptor -> Coordinator -> Effector -> Response

Question 30

What is the ‘coordinator’?

Answer 30

Part of the CNS that connects information from stimulus to effector.

Question 31

What are ‘sense organs’?

Answer 31

Group of receptor cells responding to specific stimuli.

Question 32

Define ‘phototropism’.

Answer 32

A response in which a plant grows towards or away from the direction from which light is coming.

Question 33

Define ‘geotropism’

Answer 33

A response in which a plant grows towards or away from gravity.

Question 34

What are ‘auxins’?

Answer 34

Plant hormones that control growth. Synthetic auxins are used as weedkillers by making the weeds grow too fast.

Question 35

Explain the effect of auxin to a plant’s growth in terms of geotropism.

Answer 35

• If a shoot is placed horizontally in the absence of light, auxins accumulate on the lower side of the shoot, due to gravity;
• This makes the cells on the lower side grow more quickly than on the upper side, so the shoot bends upwards - negative geotropism;
• If a shoot is placed horizontally in the absence of light, auxins accumulate on the lower side of the root, due to gravity;
• Thus the cells on the lower side grow more slowly than those on the upper side, so the root bends downwards - positive geotropism

Question 36

Explain the effect of auxin to a plant’s growth in terms of phototropism.

Answer 36

• When a shoot is exposed to light from one side, auxins produced from the shoot tip towards the shaded side of the shoot;
• Cells on shaded side stimulated to absorb more water than those on the light side;
• Thus unequal growth causes the stem to bend towards light; positive phototropism
• If a root is exposed to light in the absence of gravity, auxins produced by the root tip moves towards the shaded side of the root;
• Cells on the shaded side are stimulaed to absorb less water than those on the light side;
• Thus unequal growth causes the root to bend away from the light; negative phototropism

Question 37

Define ‘homeostasis’.

Answer 37

The maintenance of a constant internal environment.

Question 38

What happens to the body in cold environment?

Answer 38

• Shivering - muscles in some parts of the body contract and relax very quickly. This produces heat and is called shivering.
• Metabolism may increase
• Hair stands up - this produces ‘goose flesh’ and traps a thicker layer of warm air next to the skin, acting as an insulator.
• Vasoconstriction - the arterioles that supply the skin blood capillaries becomes narrower, thus less blood flows in them and thus less heat is lost to the air by radiation.

Question 39

What happens to the body in hot environment?

Answer 39

• Hair lies flat - no insulation
• Vasodilation - the arterioles that supply the skin blood capillaries gets dilated, thus more blood flows through them and thus heat is readily lost from the blood into the air by radiation;
• Sweating - sweat gland secretes sweat on the surface of the skin, which evaporates, taking heat from the skin with it, thus cooling the body
• Metabolism slows down

Question 40

Explain negative feedback.

Answer 40

Acts to ensure that the actual temperature is as close to the pre-set temperature as possile.

Question 41

Describe the role of insulin in controlling blood glucose levels.

Answer 41

• When blood glucose levels are high, then insulin is secreted by pancreas.
• Insulin passes in the bloodstream then to the liver;
• Insulin stimulates the liver to absorb glucose;
• Insulin converts glucose to glycogen;
• Insulin also increases the rate of respiration; so more blood glucose is absorbed by cells and used up, to reduce blood glucose levels.

Question 42

Describe the role of glucagon in controlling blood glucose levels.

Answer 42

• When blood glucose levels drop below normal, glucagon is secreted by the pancreas;
• Glucagon passes in the bloodstream and then to the liver;
• Glucagon converts glycogen to glucose in the liver
• Glucose is then released into the bloodstream