Homeostasis and Response

Question 1

What is homeostasis?

Answer 1

The regulation of the conditions inside your body to maintain a stable internal environment, in response to changes in both internal and external conditions.

Question 2

How does the negative feedback system counteract a excessively high level of a substance.

Answer 2

The receptor detects a stimulus - level is too high. The coordination centre receives and processes the information from the receptor, then organises a response. The effector produces a response, which counteracts the change and restores the optimum level - the level decreases.

Question 3

What is a stimulus?

Answer 3

A change in the environment.

Question 4

Describe the reflex arc.

Answer 4

Stimulus → Receptor → Sensory Neurones → A relay neurone in the Central Nervous System (a coordination centre) → Motor Neurones → Effectors (e.g. muscles or glands)

Question 5

What is a synapse?

Answer 5

The connection between two neurones.

Question 6

How are signals/impulses transferred through a synapse?

Answer 6

The nerve signal is transferred by chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the next neurone.

Question 7

What is the cerebral cortex responsible for?

Answer 7

It’s responsible for things like consciousnesses, intelligence, memory and language.

Question 8

What is the cerebellum responsible for?

Answer 8

Responsible for muscle coordination.

Question 9

What is the medulla responsible for?

Answer 9

Controls unconscious activities like breathing and your heartbeat.

Question 10

What is the sclera?

Answer 10

The tough, supporting wall of the eye.

Question 11

What is the cornea?

Answer 11

The transparent outer layer found at the front of the eye. It refracts light into the eye.

Question 12

What is the iris?

Answer 12

The iris contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye.

Question 13

What is the function of the lens?

Answer 13

The lens focuses the light onto the retina (which contains receptor cells sensitive to light intensity and colour).

Question 14

What controls the shape of the lens?

Answer 14

The ciliary muscles and suspensory ligaments.

Question 15

What is the function of the optic nerve?

Answer 15

The optic nerve caries impulses from the receptors on the retina to the brain.

Question 16

What happens to the eye in response to very bright light?

Answer 16

When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. This reduces the amount of light that can enter the eye. The opposite process happens in dim light.

Question 17

What happens in the eye when focusing on near objects?

Answer 17

The ciliary muscles contract, which slackens the suspensory ligaments. The lens becomes fat (more curved). This increases the amount by which it refracts light. The opposite happens when focusing at distant objects.

Question 18

Describe hyperopia (long-sightedness)

Answer 18

Lens: Doesn’t refract the light enough or the eyeball is too short.
Image: The images of near objects are brought into focus behind the retina.
Lens used: Convex

Question 19

Describe myopia (short-sightedness)

Answer 19

Lens: Refracts the light too much or the eyeball is too long.
Image: The images of distant objects are brought into focus in front of the retina.
Lens used: Concave

Question 20

What are treatments for vision defects and their advantages and disadvantages?

Answer 20

Contact lenses - lightweight, almost invisible, more convenient than glasses for activities like sports. Hard lenses are less comfortable but have a lower chance of infection than soft lenses.

Laser eye surgery - Laser used to vaporise tissue, changing the shape of the cornea. Risk of complications.

Replacement lens surgery - Used to treat hyperopia. More effective but higher risks than laser eye surgery.

Question 21

What coordination centre is used for keeping the core body temperature constant?

Answer 21

The thermoregulatory centre in the brain.

Question 22

How does your body react hot temperatures?

Answer 22

Sweat is produced by sweat glands and evaporates from the skin. The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin (vasodilation).

Question 23

How does your body react to cold temperatures?

Answer 23

Hairs stand up to trap an insulating layer of air. Blood vessels supplying skin capillaries constrict to close off the skin’s blood supply (vasoconstriction). When you’re cold you shiver. This needs respiration, which transfers some energy to warm the body.

Question 24

What endocrine glands are a part of the endocrine system?

Answer 24

The pituitary gland, thyroid, adrenal gland, pancreas, ovaries and testes.