3.6.1 Stimuli

Question 1

What’s a stimulus

Answer 1

Change in internal or external environment of an organism, leads to a response

Question 2

Why do organisms respond to stimuli

Answer 2

Increases chance of survival

Question 3

What’s a receptor

Answer 3

Detects stimuli, each receptor is specific to a type of stimulus

Question 4

What’s a coordinator

Answer 4

Links receptors and effectors, formulates a suitable response to a stimulus

Question 5

What’s an effector

Answer 5

Produces a response

Question 6

What’s are two types of response

Answer 6

Hormonal
Nervous system

Question 7

What’s the sequence of a response to stimuli

Answer 7

Stimulus, receptor, coordinator, effector, response

Question 8

Three types of simple responses to stimuli

Answer 8

Taxis
Kinesis
Tropism (plants)

Question 9

What’s taxis

Answer 9

Organism responds directly to stimulus by moving towards (a favourable) or away from (an unfavourable) stimulus

eg earthworks move away from light

Question 10

What’s kinesis

Answer 10

Organism changes the rate at which it moves/ rate it changes direction

In favourable conditions organisms turn lots to stay In that environment
In unfavourable conditions organisms turn less to help them move into a new favourable environment

Question 11

What’s the central nervous system (CNS)

Answer 11

Brain and spinal cord

Question 12

What’s the peripheral nervous system (PNS) and which nerves do they contain

Answer 12

Pairs of nerves that originate from the brain or spinal cord

Sensory neurones, carry nerve impulses from receptors towards the central nervous system

Motor neurones, carry nerve impulses from CNS to effectors

Question 13

Two types of motor nervous system

Answer 13

Voluntary nervous system, nerve impulses are carried to body muscle, under conscious control

Autonomic nervous system, nerve impulses carried to glands/smooth muscle/Cardiac muscle, subconscious

Question 14

What’s a reflex arc

Answer 14

The pathway of neurones involved in a reflex

Question 15

What’s a reflex

Answer 15

A rapid and automatic response to a stimulus

Question 16

Stages of a reflex arc

Answer 16

Stimulus eg heat from an object
Receptor eg Receptors on skin generates a nerve impulse in the sensory neurone
Sensory neurone, passes nerve impulse to spinal cord
Coordinator (relay neurone), connects sensory neurone to motor neurone in spinal cord
Motor neurone, carries nerve impulses from spinal cord to an effector eg muscle
Effector eg muscle in upper arm contracts
Response eg hand pulled away from hot object

Question 17

Why is a reflex arc important

Answer 17

Involuntary, response is always the same
Protect body from harm, effective from birth
Fast, neurone pathway has one or two synapses, response is also automatic

Question 18

What’s phototropism

Answer 18

Response of shoots to light

Question 19

What’s gravitropism

Answer 19

The response of roots to gravity

Question 20

What are specific growth factors

Answer 20

Regulate growth of shoots/roots in response to directional stimuli

Question 21

Explain phototropism in plants

Answer 21

IAA evenly distributed through plant, Light causes movement of IAA to shaded side of plant, higher conc of IAA on dark side of shoot, cells on this side elongate more than the other side, shoot too bends towards light

Question 22

Explain gravitropism in plants

Answer 22

IAA evenly distributed through roots, greater conc of IAA on lower side of root, IAA in roots inhibits elongation of cells on lower side, roots bend downwards towards gravity

Question 23

What types of tropisms effect shoots and roots

Answer 23

Both tropisms effect both shoots and roots, IAA always inhibits cell elongation in roots

Question 24

How does IAA elongate cells

Answer 24

H+ ions are actively transported from the cytoplasm into the cell wall, cells become more plastic allowing it to elongate