Chapter 14 - Responses To Stimuli

Question 1

What is involved in the pathway that allows organisms to detect and respond to danger to aid survival

Answer 1

1) stimulus - this is a detectable change in the internal or external environment of an organism
2) receptor- this detects specific types of stimulus
3) coordinator - this coordinates a suitable response to a stimulus
4) effector - this produces a response to a stimulus
5) response- this is the action produced by the effector

Question 2

Why are responses to stimuli crucial for survival

Answer 2

As it allows organisms to:
- navigate to food resources
- evade predators or harmful conditions
Which both increases the probability of survival and successful reproduction

Question 3

What is a Taxis (Taxes - plural)

Answer 3

a simple response whose direction is determined by the direction of the stimulus. They guide organisms either towards a beneficial stimulus or away from a harmful one.
(Directional response)

Question 4

What is a positive and negative taxis

Answer 4

• Positive taxes lead towards a favourable stimulus.
• Negative taxes prompt movement away from unfavourable stimuli.

Question 5

Positive phototaxis

Answer 5

when an organism moves towards light

Question 6

Negative phototaxis

Answer 6

when an organism moves away from light

Question 7

Positive chemotaxis

Answer 7

when an organism moves towards a region where a specific chemical is more concentrated

Question 8

Examples of taxis

Answer 8

Positive phototaxis
Negative phototaxis
Positive chemotaxis

Question 9

What is Kinesis/Kineses

Answer 9

When the movement speed and turning frequency of an organism is adjusted based on the favourability of the environment.
(Non directional)

Question 10

How is kinesis impacted in different conditions

Answer 10

• Increased turning in unfavourable conditions.
• Accelerated movement in favourable conditions.

Question 11

What is a tropism

Answer 11

the growth of a part of an organism in response to a directional stimulus.

Question 12

What is phototropism

Answer 12

directional growth of parts of the plant towards or away from light.

Question 13

What is gravitropism (or geotropism)

Answer 13

directional growth of parts of the plant towards or away from the gravitational pull.

Question 14

What type of tropism does the shoot demonstrate

Answer 14

positive phototropism and negative gravitropism, to optimise light absorption for photosynthesis.

Question 15

What type of tropism does the roots demonstrate

Answer 15

negative phototropism and positive gravitropism, to increase the probability that roots will grow into the soil, where they can absorb more water and mineral ions.

Question 16

Two types of responses organism does in response to the environment

Answer 16

Kinesis
Taxis

Question 17

Differences between plant and animal hormones

Answer 17

• Plant hormones usually act locally at the site of production, while animal hormones usually act on distant organs.
• Plant hormones are produced in a variety of tissues throughout the plant, while animal hormones are produced in specialised cells within glands.

Question 18

What is hydrotrophism

Answer 18

directional growth of parts of the plant towards or away from moisture.

Question 19

Where is IAA synthesised (made)

Answer 19

In the meristems of shoots and roots where the cells are dividing

Question 20

Role of IAA

Answer 20

• stimulates cell elongation in shoots
• inhibit cell elongation in roots

Question 21

How does positive phototropism/ negative geotropism occurs in the shoots

Answer 21

1) IAA is produced in cells in the tip of the plant shoot.
2) IAA is transported down the plant shoot.
3) Light stimulates IAA to move from the light side of the shoot to the shaded side.
4) IAA becomes concentrated and stimulates more cell elongation on the shaded side of the shoot.
5) The shoot bends towards the light.

Question 22

How does negative phototropism and positive gravitropism occur in plant roots

Answer 22

1) IAA is produced in cells in the tip of the plant root.
2) IAA is transported along the plant root.
3) Any light available stimulates IAA to move from the light side of the root to the shaded side.
4) Gravity also pulls IAA from the upper side of the root to the lower side of the root.
5) IAA becomes concentrated and inhibits cell elongation in the lower, shaded side of the root.
6) The root bends away from any available light and downwards towards the pull of gravity.

Question 23

How does auxin play a role in shoot growth via cell elongation

Answer 23

1) Auxin binds to the cell-surface membrane.
2) Hydrogen ions are actively transported from the cytoplasm into the cell wall.
3) The cell wall becomes more plastic.
4) Cells elongate and the plant grows.