3.6 Organisms Respond To Changes In Internal And External Environments

Question 1

What is a stimulus and why is it important to respond to them?

Answer 1

•A detectable change in the environment. These changes can be detected by cells that are called receptor.
•Increases chance of survival

Question 2

What is kinesis?

Answer 2

•organism moves to an area with harmful stimuli= increase the rate it changes direction to return to the favourable conditions quickly
•if it is in an area with beneficial stimuli it decreases speed
•non-directional response to unfavourable conditions

Question 3

What is taxis?

Answer 3

A directional response, where they move towards or away from a stimulus

E.g -ve chemotaxis = moving away from beneficial chemical
/ +ve phototaxis = moving towards light

Question 4

Why do organisms respond to temperature and humidity via kinesis?

Answer 4

Less directional stimuli where there is often no clear gradient from one extreme to the other

Question 5

What is the effect of IAA in the shoot tip?

Answer 5

•in unilateral light, IAA will diffuse towards the shaded side
•it causes the cells to elongate more and this will bend the top to the light source
=positive phototropism

Question 6

What is the effect of IAA in the root tip?

Answer 6

•IAA will move to the lower side of the root
•this will inhibit cell elongation so that roots anchor into the soil
= positive gravitropism and negative phototropism