Biology IGCSE - Coordination and Response

What is the name given to groups of cells that detect external stimuli?

Receptors

Give two examples of cells

Rod and cone cells in the eye

What is the name given to groups of cells that bring about a response to stimuli?

Effectors

Give two examples of groups of cells

Muscle cells and cells in glands

Name the three main types of neurone

Sensory, relay, motor

What does the CNS consist of?

Brain and spinal cord

What does the CNS do?

Coordinates the response

What is the process of a response?

Stimulus-receptor-coordinator-effector-response

Why is it important that organisms respond to changes in their environment?

Increase their chances of survival

What is a reflex?

An automatic response to certain stimuli

Why have reflexes?

They can reduce the chances of being injured

What is the gap between the sensory neurone and the relay neurone in the CNS called?

A synapse

What is the process of a reflex (arc)?

stimulus-receptor-sensory neurone-relay neurone-motor neurone-effector-response

What does the conjunctiva do?

Lubricates and protects the surface of the eye

What does the cornea do?

Refracts light into the eye

What does the iris do?

Controls how much light enters the eye by controlling the diameter of the pupil

What does the lens do?

Focuses light onto the retina

What types of cells are sensitive to light?

Rod cells

What types of cells are sensitive to colours?

Cone cells

What does the optic nerve do?

Carries impulses from receptors to brain

What is a hormone?

A chemical 'messenger'

How are hormones transported around the body?

In the blood plasma

Where are hormones produced?

In glands

Describe ADH (source, purpose, effect)

Produced in pituitary gland

Controls water content

Increases permeability of collecting duct in kidneys

Describe adrenaline (source, purpose, effect)

Produced in adrenal glands

Readies body for 'fight or flight' response

Increases heart rate, blood flow to muscles and blood sugar level

Describe insulin (source, purpose, effect)

Produced in pancreas

Helps control blood sugar level

Stimulates liver to turn glucose into glycogen

Describe testosterone (source, purpose, effect)

Produced in testes

Main male sex hormone

Promotes male secondary sexual characteristics

Describe progesterone (source, purpose, effect)

Produced in ovaries

Supports pregnancy

Maintains uterus lining

Describe oestrogen (source, purpose, effect)

Produced in ovaries

Main female sex hormone

Controls menstrual cycle and promotes female secondary sexual characteristics

Describe a nervous response (speed, effect, area)

Very fast message

Short effect

Precise area

Describe a hormonal response (speed, effect, area)

Slower message

Long-lasting effect

General area

What is homeostasis?

The maintenance of a constant internal environment

Why do conditions in the body need to be kept constant?

So that cells can function properly

What does homeostasis involve maintaining? (2 things)

Water content

Body temperature

In what ways is water lost from the body? (3 things)

Through skin as sweat

Via lungs in breath

Via kidneys as uring

On a hot day, what is any urine produced like? (3 things)

Small in volume, dark in colour, concentrated

On a cold day, what is any urine produced like? (3 things)

Large in volume, light in colour, diluted

What is the optimum temperature for enzymes?

37 degrees C

How does the brain maintain body temperature?

Receives messages from receptors in skin

The CNS activates necessary effectors

Do large organisms have big or small surface area to volume ratio? What effect does this have on the maintenance of body temperature?

Small, prevents them from losing gaining or losing heat quickly

What is the name of the plant growth hormones?

Auxins

What parts of the plant do they effect?

The tips of roots and shoots

What effect does auxin have? (2 things)

Stimulates cell elongation

Promotes growth in shoot, inhibits growth in root

Are shoots positively or negatively phototrophic?

Positively

What happens when shoot tips are exposed to light? (2 steps)

Auxin accumulates on shaded side

Cells on shaded side elongate faster, bending shoot towards the light

Are shoots positively or negatively geotrophic?

Negatively

What happens when a shoot grows horizontally? (2 things)

Auxin accumulates on underside of tip

Lower side grows faster, bending shoot upwards

Are roots positively or negatively geotrophic?

Positively

What happens when roots grow horizontally? (2 things)

Auxin accumulates on the lower side

In roots, auxin inhibits growth, so cells on top grow faster, bending root downwards