14.1 Response to stimuli

Question 1

stimulus

Answer 1

detectable change in internal or external environment of an organism that leads to a response in the organism

Question 1

stimuli selection pressure

Answer 1

organism that have better ability to respond to stimuli survive and reproduce, passing on their alleles

Question 2

receptors

Answer 2

detect stimuli
specific to one type of stimulus

Question 3

co-ordinator

Answer 3

formulates suitable response
can occur at molecular level or involve large organ e.g. brain

nervous system or hormonal communication

Question 4

response sequence

Answer 4

stimulus -> response -> co-ordinator -> effector -> response

Question 5

taxis

Answer 5

simple response whose direction is determined by direction of the stimulus

Question 6

positive taxis

Answer 6

move towards favourable stimulus

Question 7

negative taxis

Answer 7

move away from unfavourable stimulus

Question 8

kinesis

Answer 8

form of response which changes the speed at which it moves and the rate at which it changes direction

Question 9

rate of turning increases

Answer 9

when organisms crosses sharp division from favourable into unfavourable environment

raises chances of turning back into favourable

Question 10

rate of turning decrease with sharp turns

Answer 10

when organism is deep into unfavourable environment

moves long straight lines

brings organism into new favourable region

Question 11

tropism

Answer 11

growth of plant in response to directional stimulus

Question 12

positive phototropism

Answer 12

plant shoots grow toward light

plant roots grow towards gravity

Question 13

negative phototropism

Answer 13

plant shoots grow away from gravity

roots grow away from light

Question 14

phototropism

Answer 14

leaves are in favourable position to capture light

roots are in position where they are better abled to absorb water and mineral ions