Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-Level Biology > 16 Plant responses > Flashcards

16 Plant responses Flashcards

1
Q

What does auxin do?

A
  • control cell elongation
  • prevent leaf fall (abscission)
  • involved in tropisms
  • maintain apical dominance
  • prevent lateral bud growth
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does gibberellin (growth hormones) do?

A
  • Gibberellins stimulate stem elongation and seed germination
  • Taller plants have more Le gene which codes for enzymes that forms gibberellins
  • stimulate pollen tube growth in fertilisation
  • Seed absorbs water, water reaches endodermis layer and stimulates release of gibberellins. Gibberellins stimulate seed germination by triggering the breakdown of starch into glucose. Glucose used as substrate for respiration by the plant embryo and can release energy needed for growth.
  • They also stimulate side shoot formation
  • gibberellins switch on genes which code for amylases and proteases- the digestive enzymes required for germination.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does ethene do?

A

Causes fruit ripening, promotes abscission

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What does ABA (Abscisic acid) do?

A

Maintains dormancy of seeds and buds, stimulates stomatal closing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are examples of auxins?

A

Indoleacetic acid (IAA)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are tannins?

A

phenols, toxic to insects: they bind to the digestive enzymes produced in saliva and inactivate them.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are alkaloids?

A
  • Alkaloids are a large group of very bitter tasting, nitrogenous compounds found in many plants.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What hormones play a role in seed germination?

A

Gibberellins and ABA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How does seed germination occur?

A

1) When seeds absorb water, the embryo is activated and begins to produce gibberellins.
2) They in turn stimulate the production of enzymes that break down the food stores found in the seed.
3) The embryo plant uses these food stores to produce ATP for building materials so it can grow and break through the seed coat.
4) Evidence suggests that gibberellins switch on genes which code for amylases and proteases- the digestive enzymes required for germination.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Where is indoleacetic acid produced?

A

Indoleacetic acid is produced in the shoots and roots in flowering plants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the role of auxins such as indoleacetic acid?

A
  • They stimulate the growth of the main, apical shoot.
  • Evidence suggests that auxins affect the plasticity of the cell wall; the presence of auxins means the cell wall stretches more easily.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is apical dominance?

A
  • When high concentrations of auxins suppress the growth of lateral shoots.
  • The apical bud (the shoot at the top) is dominant over the lateral buds.
  • Prevents side shoots from growing
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does synergism mean?

A

When different hormones work together and complement each other, giving a greater response than on their own.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Give an example of when hormones are synergistic?

A

Auxins and gibberellins work together to help plants grow very tall.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does antagonism mean?

A

When hormones have opposite effects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Give an example of when hormones are antagonistic.

A

Gibberellins stimulate growth of side shoots but auxins inhibit the growth of side shoots.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What do low concentrations of auxins promote?

A

Root growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is abiotic stress? Give examples.

A

Abiotic stress is anything that’s potentially harmful to a plant e.g changes in day length, cold and heat, lack of water, excess water, high winds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is photoperiodism?

A

When plants are sensitive to a lack of light in their environment

20
Q

How do leaves respond to the falling auxin concentration?

A

They produce the gaseous plant hormone ethene

21
Q

What is the abscission zone?

A
  • base of the leaf stalk is a region called the abscission zone
  • made up of two layers of cells sensitive to ethene.
22
Q

What does ethene do?

A

Ethene seems to initiate gene switching in cells resulting in the production of new enzymes.
- These digest and weaken the cell walls in the outer layer of the abscission zone (separation zone)

23
Q

How do leaves fall off?

A
  • phytochromes detect low light levels, higher levels of ethene and low levels of auxins, ethene triggers production of digestive enzymes like cellulase in the abscission zone. Cellulase digests the cell wall in the separation zone
  • The vascular bundles which carry materials into and out of the leaf are sealed off. At the same time fatty material is deposited in the cells on the stem side to form a protective scar when the leaf falls, preventing entry of pathogens.
  • Further abiotic factors such as low temperatures, strong winds puts further strain and leaf separates from the plant.
  • A neat waterproof scar is left behind
24
Q

How do leaves prevent freezing?

A
  • The cytoplasm of the plant cells and the sap in the vacuoles contain solutes which lower the freezing point.
  • Some plants produce sugars, amino acids and even proteins which act as antifreeze to prevent cytoplasm from freezing
  • Most species produce chemicals which make them hardy and frost resistant during winter months
25
Q

How does the hormone abscission acid (ABA)trigger stomatal closure?

A

1) ABA binds to the receptors on the guard cell membranes. This causes specific ion channels to open, which allows calcium ions to enter the cytosol from the vacuole.
2) The increased concentration of calcium ions in the cytosol causes other ion channels to open. These ion channels allow ions (potassium ions) to leave the guard cells, raising the water potential of the cells.
3) Water then leaves the guard cells by osmosis.
4) The guard cells become flaccid and the stomata close.

26
Q

How are auxins antagonistic to ethene?

A

Auxins inhibit leaf loss (as the leaf gets older, less auxin is produced leading to leaf loss) whereas ethene stimulates leaf loss (as leaves get older, more ethene is produced)

27
Q

What is a pheromone?

A

A pheromone is a chemical made by an organism which affects the social behaviour of other members of the same species.

28
Q

Give an example of pheromones.

A

If a maple tree is attacked by insects, it releases a pheromone which is absorbed by leaves on other branches. These leaves then make chemicals such as callose to help protect them if they are attacked.

29
Q

What are volatile organic compounds?

A

Chemicals. that act like pheromones between themselves and other organisms e.g insects

30
Q

Give an example of when volatile organic compounds are used.

A

When corn plants are being eaten by caterpillars, they can produce pheromones which attract parasitic wasps. These wasps then lay their eggs in the caterpillars, which eventually kill them.

31
Q

Give an example of a plant that folds up in response to being touched.

A

Mimosa pudica, it contains a toxic alkaloid and has sharp prickles
- It frightens off larger herbivores and dislodges small insects

32
Q

What is tropism?

A

A tropism is a response of a plant to a directional stimulus

33
Q

What is phototropism?

A

The growth of plants in response to light

34
Q

What is geotropism?

A

The response to gravity

35
Q

What is chemotropism?

A

The growth of plants in response to chemicals

36
Q

What is thigmotropism?

A

The plant growth in response to touch

37
Q

Shoots are ______ phototropic

A

Shoots are positively phototropic

38
Q

Roots are __________ phototropic

A

negatively

39
Q

Shoots are _______ geotropic

A

negatively

40
Q

Roots are _________ geotropic

A

positively

41
Q

Why is ethene commercially used in climacteric fruits?

A
  • Ethene stimulates enzymes that break down cell walls, break down chlorophyll and convert starch into sugars.
  • This makes the fruit soft, ripe and ready to eat
42
Q

How is ethene used to ripen bananas?

A

Bananas are harvested and transported before they’re ripe so they’re less likely to be damaged this way. They’re then exposed to ethene on arrival so they all ripen at the same time on the shelves and in peoples homes.

43
Q

How is auxin used in selective weed killers?

A

They make weeds produce long stems instead of lots of leaves. This makes the weeds grow too fast, so they can’t get enough water or nutrients, so they die.

44
Q

How are auxins used as rooting hormones? (e.g in rooting powder)

A

They make a cutting grow roots.

  • The cutting can then be planted and grown into a new plant.
  • Many cuttings can be taken from just one original plant and treated with rooting hormones, so lots of the same plant can be grown quickly and cheaply from just one plant.
45
Q

what do cytokinins do ?

A

overrides apical dominance and promotes lateral bud growth

46
Q

why do plants need to be able to respond to their environment ?

A
  • maximise photosynthesis
  • avoid herbivory
  • avoid abiotcic stress
  • cope with changing conditions
  • ensure germination in suitable conditions

A-Level Biology (41 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions