Taxes, Kineses & Tropisms

Question 1

What is a stimulus?

Answer 1

A detectable change in the internal or external environment of an organism.

Question 2

What is a response?

Answer 2

A coordinated reaction to the stimulus that usually increases the chances of survival in an organism

Question 3

What happens between a stimulus and a response?

Answer 3

Stimulus -> Receptor -> Coordinator -> Effector -> Response

Question 4

What types of communication is there?

Answer 4

• Neuronal

- Hormonal

Question 5

What types of responses are there?

Answer 5

• Taxes

- Kineses

Question 6

What is a taxis?

Answer 6

A directional response

Question 7

What is negative taxis?

Answer 7

Movement away from an unfavourable stimulus

Question 8

What is positive taxis?

Answer 8

Movement towards a favourable stimulus.

Question 9

What is positive phototaxis?

Answer 9

Movement towards light

Question 10

What is negative chemotaxis?

Answer 10

Movement away from a chemical like glucose.

Question 11

What is a kinesis?

Answer 11

Non-directional response that changes the speed of movement and the rate of turning.

Question 12

Why are kineses used?

Answer 12

For less directional stimuli such as temperature or humidity.

Question 13

What is an example of an organism using kineses?

Answer 13

Woodlice that prefer damp conditions will increase the rate of movement/ turning if they approach a dry area.

Question 14

What are tropisms?

Answer 14

Directional growth in plants.

Question 15

What is positive phototropism?

Answer 15

The movement of shoots towards light

Question 16

What is negative gravitropism?

Answer 16

The movement of shoots against gravity.

Question 17

What type of growth do roots exhibit?

Answer 17

• Negative phototropism

- Positive gravitropism

Question 18

What system do plants use for growth?

Answer 18

Hormonal system

Question 19

Why are plant hormones better referred to as plant growth factors?

Answer 19

• affect growth
• may not necessarily be made by specific organs
• may affect tissues that make them rather than distant targets

Question 20

What is IAA (indoleacetic acid)?

Answer 20

An auxin

Question 21

What does IAA do?

Answer 21

Controls the elongation of plant cells

Question 22

How does IAA work in shoot cells?

Answer 22

1) IAA is synthesised by cells in the shoot tips
2) Then transported down the shoot
3) Light causes IAA to move to the shaded side.
4) IAA causes cells to elongate.

Question 23

What is the effect of IAA in root cells?

Answer 23

This causes the inhibition of cell elongation

Question 24

How does IAA work in root cells?

Answer 24

1) Cells in root tip produce IAA
2) These are transported up the root
3) Gravity causes IAA to be transported to the lower side of the root
4) IAA inhibits elongation of cell

Question 25

How does IAA affect cells?

Answer 25

• only affects young cells

- increases the plasticity of cell walls in the shoot

Question 26

What it the acid growth hypothesis?

Answer 26

The active transport of H+ from the cell cytoplasm into the spaces of the cell wall. This causes the cell wall to increase in plasticity. When water is taken up, the cell swells and elongates.