Coordination and response

Question 1

What is some of a plants response to a stimuli

Answer 1

Geotropism- the shots grow away from gravity and the roots grow towards gravity

Phototropism- The shoot grows towards the sunlight and the roots grow away from the light

Auxin- The plant hormone that results in more elongation of shoot cells but less elongation of root cells

Question 2

What is positive phototropism in shoots

Answer 2

Auxin is produced by the tip and diffuses down the shaded side, causing the cells in the shade to elongate. This
means the shoot bends towards the light.

Question 3

What is negative phototropism in roots

Answer 3

Auxin is produced which gathers on the shaded side, causing the cells here to elongate less. This means that the
roots grow away from the light

Question 4

What is negative geotropism in roots

Answer 4

Auxin is produced by the tip which travels to the lower side due to gravity, causing the cells here to elongate more,
meaning that the shoot bends up, away from gravity.

Question 4

What is positive geotropism in roots

Answer 4

Auxin is produced which gathers on the lowest side, causing the cells here to elongate less. This means that the roots
grow downwards.

Question 5

Explain the nervous system

Answer 5

Organisms are Able to Respond to Changes in Environment (Stimuli) for Survival
The Nervous System allows the Body to Respond to Changes in the Environment and is Coordinated by the Brain
The central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves
stimulation of receptors in the sense organs sends electrical impulses along nerves into and out of the central
nervous system, resulting in rapid responses
Organisms can also have Reflexes which are Fast Involuntary Actions that Protect their Body from Damage

Question 6

What is a receptor

Answer 6

Specialised cells that detect change in the environment eg sensory neurons in the finger will detect heat

Question 7

What is a stimuli

Answer 7

change in environment

Question 8

What is an effector

Answer 8

Part of the body that produces the response muscles in the fingers contract to pull the finger away from heat

Question 9

Explain the reflex arc

Answer 9

a stimulus is present (e.g. heat from a hot object, pressure from a sharp object)
- a receptor detects the change (e.g. skin receptors detect heat)
- a sensory neurone passes electrical nerve impulses from the receptor towards the relay neurone in the
spinal cord
- Chemical neurotransmitters are released and diffuse across the synapses between the sensory and relay
neurone
- The electrical impulse travels through the relay neurone towards the motor neurone
- Chemical neurotransmitters are released and diffuse across the synapses between the relay and motor
neurone
- The electrical impulse travels through the motor neurone, towards the effector
- The effector carries out a response, e.g. a muscle contracts to pull your hand away

Question 10

Explain what synapses

Answer 10

he electrical impulse travels along the first axon (of the first neurone, known as the presynaptic neurone)
This triggers the end of the presynaptic neurone to release chemical messengers called neurotransmitters from vesicles
These vesicles fuse with the presynaptic membrane, releasing their contents into the synaptic cleft
The neurotransmitters diffuse across the synaptic cleft and bind with receptor molecules on the membrane of the second neurone (known as the postsynaptic membrane)
This stimulates the second neurone to generate an electrical impulse (which then travels down the second axon)
The neurotransmitters are then destroyed to prevent continued stimulation of the second neurone (otherwise the neurotransmitters would cause repeated impulses to be sent)
Synapses ensure that impulses only travel in one direction, avoiding the confusion that would be caused within the nervous system if impulses were able to travel in both directions

Question 11

Explain the iris reflex

Answer 11

In bright light – circular muscles contract, radial muscles relax and the pupil constricts to become narrower. This is
important to prevent damage from bright light hitting the retina.

In dim light – circular muscles relax, radial muscles contract and the pupil dilates to become wider. This is important
to allow enough light to the retina to see

Question 12

What is accommodation

Answer 12

On near objects – ciliary muscles contract, suspensory ligaments slacken, the lens becomes fatter, increasing the
amount of light refracted.

On distant objects – Ciliary muscles relax, suspensory ligament tightens, the lens becomes thinner, decreasing the
refraction of light.

Question 13

What are hormones

Answer 13

Hormones are chemical messengers released by glands in to the blood where they are carried to target cells to result
in a change.

Question 14

What is the difference between hormones and nerves

Answer 14

Hormones are slower than electrical impulses,
Hormones act for a longer time than nerves.
Hormones are more general than nerves which act on a precise area.

Question 15

What is homeostasis

Answer 15

Homeostasis is maintaining a constant internal environment, for example, water balance and temperature

Question 16

What does the body do when its too hot

Answer 16

Too hot
- Increased sweat production by sweat glands, which evaporates at the skin to remove heat
- Arterioles at the skin surface dilate (vasodilation), increasing blood flow to the surface, increasing the
amount of heat that radiates to the surroundings
- Hairs on skin lie flat to remove any insulation

Question 17

What does the body do when its too cold

Answer 17

too cold
- Arterioles at the skin surface constrict (vasoconstriction), decreasing blood flow to the surface, decreasing
the amount of heat that radiates to the surroundings
- Muscles contract to shiver, increasing respiration which releases heat from body cells to warm the body
- Hairs stand on end to trap air which insulates the body