Plant responses 5.5.1

Question 1

What is abiotic stimuli?

Answer 1

Concerned with the non living part of the environment

Question 2

What is biotic stimuli?

Answer 2

Concerned with the living organisms in the environment

Question 3

Give 4 examples of plant responses

Answer 3

• tropisms
• response to abiotic stress
• responses to herbivory e.g. chemical defences and response to touch

Question 4

What are examples of abiotic stresses?

Answer 4

• Freezing
• Drought
• Increased soil water salinity
• Presence of heavy metals e.g. lead, copper, zinc

Question 5

How do plants respond to drought?

Answer 5

In ways that reduce water loss by transpiration:
- shutting stomata
- dropping leaves

Question 6

How can some plants respond to freezing temperatures?

Answer 6

By producing an antifreeze chemical in their cells that decreases the formation of ice crystals

Question 7

What stress factor is herbivory?

Answer 7

Biotic

Question 8

What are examples of chemicals that provide a defence against herbivory?

Answer 8

• alkaloids
• pheromones

Question 9

What are alkaloids mode of action

Answer 9

Bitter teasing or toxic, either deterring or killing herbivores

Question 10

What are pheromones mode of action

Answer 10

A signal to nearby plants of the same species that they are under attack from herbivores, triggering other defences
A single to attract a herbivorous insect’s natural predators

Question 11

Give an example of a plant that is sensitive to touch

Answer 11

Mimosa pudica

Question 12

What happens in Mimosa pudica (touch sensitive plant)

Answer 12

• Leaflets of touch-sensitive leaves fold rapidly when touched
• It is thought that this movement may be an adaptation to protect the leaflets from herbivorous insects, though it could also reduce transpiration when the leaves are no longer photosynthesising
• This response occurs very rapidly and is most likely caused by local bioelectrical signals

Question 13

What is a tropism?

Answer 13

A growth response of a part of a plant in response to a directional stimulus

Question 14

How can tropisms occur? (direction)

Answer 14

Towards a stimulus (positive tropisms) or away from a stimulus (negative tropisms)

Question 15

Give 5 examples of tropisms

Answer 15

• Phototropism
• Geotropism
• Hydrotropism
• Thigmotropism
• Chemotropism

Question 16

What is phototropism?

Answer 16

Response to light

Question 17

What type of stimulus is light?

Answer 17

Abiotic

Question 18

What is geotropism?

Answer 18

Response to gravity

Question 19

What type of stimulus is gravity?

Answer 19

Abiotic

Question 20

What is hydrotropism?

Answer 20

Response to moisture

Question 21

What type of stimulus is moisture?

Answer 21

Abiotic

Question 22

What is thigmotropism?

Answer 22

Response to touch

Question 23

What type of stimulus is touch?

Answer 23

Abiotic or biotic

Question 24

What is chemotropism?

Answer 24

Response to chemicals

Question 25

What type of stimulus are chemicals?

Answer 25

Abiotic or biotic

Question 26

Explain phototropism

Answer 26

Ensures plant gets access to as much light as possible, maximising photosynthesis

Question 27

Explain geotropism

Answer 27

Shoots allow negative geotropism (i.e. grow away from the pull of gravity) and roots show positive geotropism (i.e. grow towards the pull of gravity).
This ensures that shoots/roots grow in the right directions

Question 28

Explain hydrotropism

Answer 28

Root tips normally grow towards damper areas of soil, increasing their access to water

Question 29

Explain thigmotropism

Answer 29

Important in climbing plants.
Allows these plants to detect a living or non-living support and curl round it

Question 30

Explain chemotropism

Answer 30

Some plants show a tropic response to certain chemicals (i.e. pollen types grow down the flowers stigma towards the ovules due to chemotropism)