Plant responses

Question 1

What are tannins?

Answer 1

Found on the upper epidermis.
Toxic to microorganisms and larger herbivores

Question 2

What are alkaloids?

Answer 2

Derived from amino acids and they are a feeding deterrent to animals, tasting bitter

Question 3

What are pheromones?

Answer 3

Chemicals released by one individual can affect the behaviour or physiology of another

Question 4

What does tropism mean?

Answer 4

Directional growth responses of plants

Question 5

What are the four types of responses?

Answer 5

• Phototropism
• Geotropism
• Chemotropism
• Thigmotropism

Question 6

What is phototropism?

Answer 6

Shoots grow towards light which enables them to photosynthesise

Question 7

What is geotropism?

Answer 7

Roots grow towards the pull of gravity. Anchors them in the soil and helps them to take up water which is needed for support as a raw material for photosynthesis and to help cool the plant

Question 8

What is chemotropism?

Answer 8

On a flower, pollen tubes grow down the style, attracted by chemicals towards the ovary where fertilisation can take place

Question 9

What is thigmotropism?

Answer 9

Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support

Question 10

What is:

• Positive tropic response
• Negative tropic response

Answer 10

• If a plant responds towards a stimulus
• If a plant responds away from a stimulus

Question 11

What is thigmonasty?

Answer 11

Non directional response to touch

Question 12

What are the role of plant hormones?

Answer 12

Coordinate plant responses to environmental stimuli
They are not produced in endocrine glands but by cells in a variety of tissues in the plant

Question 13

How to plant hormones work?

Answer 13

Hormones bind to receptors on the plasma membrane once they reach their target cells
Specific binding makes sure that the hormones open the correct tissues
Some hormones can amplify or cancel each other’s effects

Question 14

What are the five plant hormones?

Answer 14

• Cytokines
• Abscisic acid
• Auxins
• Gibberlins
• Ethene

Question 15

What is the role of cytokines?

Answer 15

• Promote cell division
• Delay leaf senescence
• Overcome apical dominance
• Promote cell expansion

Question 16

What is the role of abscisic acid?

Answer 16

• Inhibits seed germination and growth
• Causes stomatal closure when the plant is stressed by low water availability

Question 17

What is the role of auxins?

Answer 17

• Promote cell elongation
• Inhibit growth of side shoots
• Inhibit leaf abscission

Question 18

What is the role of gibberelins?

Answer 18

• Promote seed germination and growth of stems

Question 19

What is the role of ethene?

Answer 19

• Promotes fruit ripening

Question 20

What is apical dominance?

Answer 20

Inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the tip of the plant shoot

Question 21

What was the researchers hypothesis about apical dominance?

Answer 21

Researchers suggested that auxins from the apical bud prevents lateral buds from growing
When the tip is removed, auxin levels in the shoot drop and the buds grow

Question 22

How was the researchers hypothesis around apical dominance tested?

Answer 22

First step: Scientists applied a paste containing auxins to the cut end of the shoot and the lateral buds did not grow

• Manipulation of plants could have had an unexpected effect upon exposure to O2

Second step: Applied a ring of auxin transport inhibitor below the apex of the shoot. The lateral buds grew

• Concluded normal auxin level in lateral buds inhibit growth

Question 23

What is abscisic acid’s role in apical dominance?

Answer 23

Inhibits bud growth
High auxins in the shoot may keep abscisic acids levels high in the bud
When the tip is removed, abscisic acids levels drop and buds grow

Question 23

What is a problem with the conclusion the researchers reached about apical dominance?

Answer 23

Auxin levels and growth inhibition may have no effect on each other but may be affected by a third variable

Question 25

What is cytokinin’s role in apical dominance?

Answer 25

Promote bud growth
Directly applying cytokinins to buds can override apical dominance effect
High levels of auxin - shoot apex a sink for cytokinins produced in the roots - most of the cytokinins goes to the shoot apex

• When the apex is removed, cytokinins spreads evenly around the plant

Question 26

What is stem elongation and what hormone is it done by?

Answer 26

Gibberelin
Fungus causes a disease which makes rice grow very tall
The fungal compounds involved are gibberlins and includes gibberllic acid (GA3)

Question 27

What are uses of auxins?

Answer 27

• Taking cuttings - dipping the end of a cutting in rooting powder before planting it encourages root growth
• Seedless fruit - applying auxin promotes ovule growth, which triggers automatic production of auxins by tissues in the developing fruit, helping complete the developmental process
• Herbicides - promote growth of weeds so much that the stem cannot support itself

Question 28

What is a commercial use of cytokinins?

Answer 28

• Prevent yellowing of lettuce leaves after being picked as it can delay leaf senescence
• Used in tissue culture to help mass produce plants

Question 29

What are commercial uses of gibberellins?

Answer 29

• Produce malt which happens as gibberellins causes germination of seeds used in beer brewing
• Used to delay ripening and ageing in fruit
• Improves fruit shape and size

Question 30

What are commercial uses of ethene?

Answer 30

Control of fruit ripening

• Climatic fruit such as bananas, tomatoes and mangoes ripen with the gas ethene

Preserves cut flowers/ green vegetables

Question 31

What do a lack of auxin, cytkinins and gibberellins do?

Answer 31

Aid in fruit dropping