Stimuli and Response

Question 1

define stimuli

Answer 1

• changes in the environment (either external or internal) that produces a response in an organism

Question 2

what are the three types of neurones and their function

Answer 2

• sensory neurones - posses receptors which are stimulated by a specific stimulus.
• motor neurones - transmit impulses to the appropriate effector (muscle or gland)
• relay neurones- act as a link between sensory and motor neurones ( also called intermediate or coordinator neurones)

Question 3

what is a reflex

Answer 3

• a rapid automatic response to a stimulus

Question 4

describe the reflex arc

Answer 4

• receptors detect the stimulus and transmit impulses along the sensory neurone to the brain/spinal cord
• sensory neurone synapses with relay neurone which passes impulses to the motor neurone
• impulses are then transmitted along the motor neurone to the effector

Question 5

what are the advantages of reflexes

Answer 5

• they are innate
• automatic rapid response preventing damage to tissues
• increases the chance of escaping from predators
• important in detecting changes so homeostasis can be achieved

Question 6

describe the nervous system

Answer 6

• rapid , short-lived and localised

Question 7

define taxis

Answer 7

• the direction of the stimulus affects the direction of movement of the organism

Question 8

define kineses

Answer 8

• the intensity of the stimulus affects the rate of turning or movement of the organism

Question 9

define tropism

Answer 9

• the growth of part of a plant in response to a directional stimulus

Question 10

describe how IAA affects growth in shoots

Answer 10

• IAA is negatively phototropic meaning it gathers on the shaded part of the plant
• in the shoots, high concentrations of IAA stimulates cell elongation and so there is greater elongation of the cells in the shaded part of the shoot therefore bending the shoot towards the light

Question 11

describe how IAA affects growth in roots

Answer 11

• IAA gathers at the lower side of the roots
• in the roots, high concentrations of IAA inhibit cell elongation and so there is less elongation of the cells on the lower side of the root therefore bending the root downwards