Homeostatis and Response

Question 1

What is homeostasis?

Answer 1

Homeostasis is the regulation of the conditions inside your body (and cells) to maintain a stable internal environment, in response to internal and external changes

Question 2

Give examples of conditions maintained by homeostasis in the body (3)

Answer 2

● Blood glucose concentration
● Body temperature
● Water levels

Question 3

What two types of responses are used in body control systems?

Answer 3

Nervous and chemical

Question 4

What three components do all control systems have?

Answer 4

● Receptors
● Coordination centres
● Effectors

Question 5

What is the function of a receptor?

Answer 5

Receptors detect changes in the
environment (stimuli).

Question 6

What is the function of a coordination centre?

Answer 6

Coordination centres obtain and process information from receptors.

Question 7

What is the function of an effector?

Answer 7

Effectors (muscles or glands) bring about responses to stimuli

Question 8

What is the function of the nervous system?

Answer 8

The nervous system allows the body to react to its surroundings and coordinate an appropriate response.

Question 9

How does a stimulus lead to a response being carried out by the body?

Answer 9

● Stimulus is converted into an electrical impulse by the receptors.

● The electrical impulse passes along sensory neurones to the central nervous system (CNS).

● The CNS coordinates an appropriate response and an
electrical impulse is sent along motor neurones to the effector, which carries out the response.

Question 10

What sequence of events describes how the nervous system works?

Answer 10

Stimulus → receptor → coordinator →effector → response

Question 11

What is a reflex action?

Answer 11

A reflex action is an automatic and rapid response which does not involve any conscious input from the brain.

Question 12

Why are reflex actions important?

Answer 12

Reflex actions aid survival by preventing harm to the body.

Question 13

Describe how a reflex action occurs via a reflex arc

Answer 13

● The stimulus is detected by a receptor.

● An electrical impulse passes along a sensory neurone to the spinal cord
(part of the CNS).

● At a synapse between a sensory neurone and a relay neurone, a
chemical diffuses across the gap and stimulates a new impulse which
passes along the relay neurone.

● The same process occurs at a synapse between a relay neurone and a motor neurone.

● At the effector, an appropriate response is carried out.

Question 14

What is the difference between a reflex pathway and a conscious pathway?

Answer 14

Within a reflex pathway, the coordination centre is a relay neurone found in the spinal cord/unconscious parts of the brain.

In a conscious pathway, the coordination centre is in the conscious part of the brain.

Question 15

What is the function of the cerebral cortex? C-4

Answer 15

C - controls consciousness,
intelligence, memory and
language.

Question 16

What is the function of the cerebellum? (C-1)

Answer 16

A - controls muscular coordination

Question 17

What is the function of the medulla? (C-1/2)

Answer 17

B - controls unconscious activities eg. breathing, heart rate

Question 18

Why is the investigation and treatment of the brain difficult? (4)

Answer 18

● The brain is a complex and delicate organ.

● The brain is easily damaged and destroyed.

● Certain membranes prevent drugs from reaching the brain.

● The exact function of each part of the brain is not known.

Question 19

What methods are used by scientists to determine brain function? (3)

Answer 19

● Studying patients with brain damage
● Electrical stimulation of the brain
● MRI scans

Question 20

What stimuli are the receptors of the eye sensitive to?

Answer 20

Light intensity and colour

Question 21

What are the two main functions of structures found within the eye?

Answer 21

● Focusing on near or distant objects - accommodation.

● Adaptation to dim light.

Question 22

Describe the structure and function of the retina

Answer 22

F - The retina is a light-sensitive
layer found at the back of the eye.

Light stimulates the retinal cells,
resulting in impulses being sent
to the brain.

Question 23

Describe the structure and function of the optic nerve

Answer 23

G - The optic nerve connects
the eye and the brain.

It carries impulses to the brain so that an image can be visualised.

Question 24

Describe the structure and function of the sclera

Answer 24

H - The sclera is the tough outer layer of the eye which protects its internal
structures.

Question 25

Describe the structure and function of the cornea

Answer 25

A - The cornea is the curved transparent layer at the front of the eye. It lets light into the eye and allows light to be focused onto the retina.

Question 26

Describe the structure and function of the iris

Answer 26

B - The iris is a muscle which controls the size of the pupil by contracting or relaxing. This allows the eye to adjust to bright and dim lighting

Question 27

Describe the structure and function of the ciliary muscles and suspensory ligaments

Answer 27

The ciliary muscles (C) and suspensory ligaments (E) hold the lens in place and control its shape.

Question 28

Describe how the iris alters the size of the pupil in both bright and dim light

Answer 28

● Bright light: circular muscles contract and radial muscles relax - makes pupil smaller to avoid retinal damage. ● Dim light: circular muscles relax and radial muscles contract - makes pupil larger so more light can enter the eye.

Question 29

What is accommodation?

Answer 29

Accommodation is the alteration of the lens’ shape in order to focus on near or distant objects.

Question 30

How does the eye focus on a nearby object? (3)

Answer 30

● Ciliary muscles contract. ● Suspensory ligaments loosen. ● Lens becomes thicker and more curved - light rays are refracted strongly.

Question 31

How does the eye focus on a far away object? (3)

Answer 31

● Ciliary muscles relax ● Suspensory ligaments tighten ● Lens becomes thinner - light rays are refracted weakly

Question 32

What is myopia?

Answer 32

Myopia (short-sightedness) usually occurs when the lens of the eye is too curved. As a result, light is focused in front of the retina so images appear blurry.

Question 33

How can myopia be treated?

Answer 33

Myopia can be treated using glasses with a concave lense, which spreads out light rays so they can be focused on the retina.

Question 34

What is hyperopia?

Answer 34

Hyperopia (long-sightedness) usually occurs when the lens of the eye is too flat. As a result, light is focused behind the retina so images appear out of focus.

Question 35

How can hyperopia be treated?

Answer 35

Hyperopia can be treated using glasses with a convex lense, which brings the light rays together so they can be focused on the retina

Question 36

What are the two types of contact lenses?

Answer 36

Contact lenses are lenses that are placed on the eye. There are two types: ● Hard - rigid material, last a long time, must be kept sterile. ● Soft - flexible material, last for a shorter time, more comfortable

Question 37

What is laser eye surgery?

Answer 37

Laser eye surgery is the use of lasers to fix visual defects in adults. To treat myopia, lasers reduce the thickness of the cornea so light is refracted less strongly. To treat hyperopia, lasers alter the curvature of the cornea so that light is refracted correctly.

Question 38

How can replacement lenses be used to treat visual defects?

Answer 38

A replacement lens can either implanted into the eye (along with the natural lens) or it may replace the natural lens altogether. Risks of lens replacement include retinal damage, cataracts and infections

Question 39

What are the risks of lens replacement? (3)

Answer 39

Risks of lens replacement include retinal damage, cataracts and infections

Question 40

Where is body temperature controlled in the body?

Answer 40

Body temperature is controlled by the thermoregulatory centre in the hypothalamus of the brain.

Question 41

How is temperature monitored by the body? (2)

Answer 41

● Thermoregulatory centre has receptors sensitive to blood temperature. ● Skin has receptors sensitive to skin temperature - sends impulses to thermoregulatory centre.

Question 42

What physiological changes occur when the body temperature is too high? (2)

Answer 42

● Vasodilation - blood vessels near the surface of the skin dilate - more heat is radiated away. ● Sweating - evaporation of water takes away heat energy from the surface of the skin.

Question 43

What physiological changes occur when the body temperature is too low? (3)

Answer 43

● Vasoconstriction - blood vessels near the surface of the skin constrict - less heat radiated away. ● Shivering - respiration allows muscles to contract. It is an exothermic process, so heat energy is released. ● Sweating stops