5.5 Plant Responses

Question 1

what are examples of abiotic factors?

Answer 1

• light
• soil moisture/minerals
• temperature
• pH
• gravity
• toxins

Question 2

what are examples of biotic factors?

Answer 2

• herbivory
• touch
• chemical signals

Question 3

what are the types of plant responses?

Answer 3

• responses to abiotic/biotic factors
• responses to herbivory
• tropisms
• nastic

Question 4

what are examples of tropisms?

Answer 4

• phototropism
• geotropism
• hydrotropism
• thigmotropism
• chemotropism

Question 5

what is a phototropism in response to?

Answer 5

light

Question 6

what is a geotropism in response to?

Answer 6

gravity

Question 7

what is a hydrotropism in response to?

Answer 7

water

Question 8

what is a thigmotropism in response to?

Answer 8

touch

Question 9

what is a chemotropism in response to?

Answer 9

chemicals

Question 10

what is a tropism?

Answer 10

a directional growth in response to a stimulus

Question 11

what are plant responses to herbivory?

Answer 11

producing:
- alkaloids
- pheromones
- tannins

Question 12

how do alkaloids defend plants against herbivores?

Answer 12

they are bitter tasting or toxic which deters or kills herbivores

Question 13

how do pheromones defend plants against herbivores?

Answer 13

they affect the behaviour of other organisms

Question 14

what are examples of plant responses to abiotic stress?

Answer 14

• closing stomata
• dropping leaves
• antifreeze chemicals
• forming a thick waxy cuticle
• rolling leaves

Question 15

What are nastic responses?

Answer 15

Non directional growth or movements in response to an external stimulus.

Question 16

What is an example of a nastic response?

Answer 16

thigmonasty
- a response to touch e.g. mimosa or venus flytrap

Question 17

What do plants use to respond?

Answer 17

Hormones.

Question 18

How are plant hormones different to animal hormones?

Answer 18

Plants don’t have endocrine glands. and one hormones can have different effects in different parts of the plant.

Question 19

What effects could plant hormones have?

Answer 19

• cell division
• cell differentiation
• cell elongation.

Question 20

What are five examples of major plant hormones?

Answer 20

• auxin
• cytokinins
• gibberellins
• ethylene
• abscisic acid

Question 21

Where is auxin produced or found?

Answer 21

Apical shoot. and meristem

Question 22

What is the function of auxin?

Answer 22

• suppresses growth of lateral buds
• stem elongation

Question 23

What is the function of cytokinins?

Answer 23

• stimulate cell division and differentiation alongside auxin

Question 24

Where are cytokinins found or produced?

Answer 24

They are produced in the roots and transported from there.

Question 25

What is the function of Gibberellins?

Answer 25

- Trigger seed germination - stem an internode elongation.

Question 26

Where are gibberellins produced or found?

Answer 26

The apical portions of roots and shoots.

Question 27

Where is ethylene produced or found?

Answer 27

- leaves - stems - young fruits

Question 28

What is the function of ethylene?

Answer 28

- hastens fruit ripening - controls the removal of leaves/flowers/fruit

Question 29

What is abscisic acid found or produced?

Answer 29

- root caps - mature leaves - fruits

Question 30

What is the function of abscisic acid?

Answer 30

- suppresses bud growth - involves in stomatal opening - promotes leaf senescence

Question 31

Where are the lateral buds of a plant?

Answer 31

On the sides of the stem.

Question 32

What is apical dominance?

Answer 32

the apical bud grows so it can become closer to the sun.

Question 33

What would happen when the apical bud is cut?

Answer 33

The lateral buds would grow because the auxin is no longer being produced so their growth is not being inhibited.

Question 34

How do gibberellins trigger seed germination?

Answer 34

1. water enters cell triggering the embryo to release gibberellins 2. gibberellins cause aleurone layer to produce amylase 3. amylase catalyses the breakdown of starch into maltose 4. maltose is converted to glucose 5. glucose is used for growth of the embryo so seed germinates

Question 35

what is the role of control variables?

Answer 35

- repeatability

Question 36

what was the experiment to prove apical dominance in plants?

Answer 36

When the apical bud was decapitated, auxin no longer diffused down the shoot, allowing the lateral buds to grow.

Question 37

what is a positive phototropism and where does it occur?

Answer 37

- when the shoot grows towards the light

Question 38

why do plants grow towards light?

Answer 38

to increase their surface area exposed to sunlight for photosynthesis

Question 39

what is the effect of a high concentration of auxin in the shoots?

Answer 39

the cells elongate and grow on the shaded side with more auxin

Question 40

what is the effect of a high concentration of auxin in the roots?

Answer 40

the growth on the shaded side is inhibited, so growth occurs downwards on the light side

Question 41

what is a negative phototropism?

Answer 41

- when roots grow away from light

Question 42

Outline what the investigations by Darwin, Boysen and Jensen proved about phototropism and auxin.

Answer 42

Auxin is produced at the tip of the shoot and must move down the stem to have an effect on growth. When light is evenly distributed at the tip auxin will also be evenly distributed so the plant has no directional growth. If light is unevenly distributed, auxin will accumulate on the shaded side causing the cells to elongate and the plant to grow towards the light.

Question 43

what is a positive geotropism?

Answer 43

when roots grow downwards due to gravity

Question 44

what is a negative geotropism?

Answer 44

when shoots grow upwards away from gravity

Question 45

what is the investigation for the effect of geotropism?

Answer 45

A plant is slowly rotated in a clinostat which keeps it at a constant angle. This would cause the plant to grow outwards instead of upwards because the effect of gravity is removed as it is equal on all sides.

Question 46

what does reproducibility mean?

Answer 46

someone can reproduce similar results from the same experiment

Question 47

what are meristems?

Answer 47

Regions of the plant where growth occurs by mitosis, differentiation and elongation.

Question 48

Outline the mechanism of auxin

Answer 48

1. Auxin binds to the hydrogen pump 2. H+ ions pumped into the cell wall 3. The cell wall weakens due to an increase in H+ ions as they disrupt hydrogen bonds and decrease pH 4. water can move in, causing the cell to elongate

Question 49

Outline the mechanism of action for abscisic acid in guard cells.

Answer 49

1. abscisic acid bind to ABA receptors on guard cell surface membrane 2. Ca2+ leave 3. water potential increases so water leaves the guard cell 4. guard cells are flaccid, stoma close

Question 50

What are the commercial uses of gibberelins?

Answer 50

- increase fruit size - brewing - sugar production - prevent lodging

Question 51

What are the commercial uses of auxin?

Answer 51

- herbicide - seedless fruit - plant cuttings

Question 52

What is the commercial use of ethene/ethylene?

Answer 52

induced fruit ripening

Question 53

What are the commercial uses of cytokinins?

Answer 53

- delay leaf senescence - encourage cell division for mass-produced plants

Question 54

What is leaf senescence?

Answer 54

where the leaf is growing old