Organisms respond to changes in their internal and external environments

Question 1

what is sensitivity

Answer 1

ability of a living organism to detect changes in the environment (stimuli), and respond appropriately to them. many of these are automatic, fast and innate. these are reflexes

Question 2

the order of the reflex arc

Answer 2

stimulus - receptor - sensory neurone - cell body - synapse - relay neurone - motor neurone - effector (muscle/gland)

Question 3

what is a tropism

Answer 3

a growth response in a plant. they are controlled by specific growth in factors e.g. auxins

Question 4

phototropism

Answer 4

plant shoots are +ve trophic (grow towards light). the growth is controlled by the auxin-indoleacetic acid which is made in the shoot tip and moved down into the growing region of the shoot

Question 5

how does phototropism work

Answer 5

Auxin moves to the dark side of the shoot. the auxin promotes growth by interfering with the hydrogen bonds in the cell wall. his makes the cellulose more flexible, allowing elongation and division of the cell

Question 6

gravitropsim/ geotropism

Answer 6

roots are +ve gravitropic - they grow towards gravity. this is due to the presence of dense organelles called amyloplasts

Question 7

how deos gravitropiam work

Answer 7

as amyloplasts move to the bottom of the roots, they take the IAA with them. In the roots, the IAA inhibits growth and division

Question 8

define taxis

Answer 8

a directional movement response. a positive taxis, movement towards stimulus

Question 9

define kinesis

Answer 9

a non-directional movement. the rate of movement and frequency of turns increases as the stimulus is less favourable