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Biology > 9.3 Growth in plants > Flashcards

9.3 Growth in plants Flashcards

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1
Q

What are the 2 types of growth?

A
  • Determinate growth - there is a defined juvenile or embryonic period or growth stops when a certain size is reached or a structure is fully formed
  • Interdeterminate growth - cells continue to divide indefintely
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2
Q

What does it mean when plants have indeterminate growth?

A

The cells continue to divide indefinitely

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3
Q

How do many plants have the capcity to generate whole plants?

A

the cells are totipotent
this is what sets plant cells apart from most animals

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4
Q

Where is growth in plants confined to?

A

to regions known as meristems

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5
Q

What are meristems composed of?

A

undifferentiated cells that are undergoing active cell division

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6
Q

What are the 2 types of meristems?

A
  • Apical meristems - found in the tips of stems and roots
  • Lateral meristems - present in many dicotyledenous plants
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7
Q

What are primary and secondary growth caused by?

A

Primary growth - by apical meristems
Secondary growth - by lateral mechanisms

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8
Q

what is the root apical meristem responsbile for?

A

The growth of the root

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9
Q

Where can the shoot apical meristem be found?

A

at the tip of the stem

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10
Q

What mechanism do many dicotyledenous plants also develop?

A

lateral meristems

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11
Q

Which is more complex: root or shoot apical meristems?

A

Shoot apical meristems

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12
Q

How is the shoot apical meristem more complex?

A
  • it throws off the cells that are needed for the growth of th stem
  • aso produces the groups of cells that grow and develop into leaves and flowers
  • with each division, one cell remains in the meristem while the other increases in size and differentiates as it is pushed away from the meristem region
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13
Q

What happens to cells from the shoot apical meristem as they increase in size and differentiates?

A

they are pushed away from the meristem region

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14
Q

What size are cells in the meristem?

A

small

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15
Q

What do the cells in meristem do?

A

they go through the cell cycle repeatedly to produce more cells, by mitosis and cytokinesis

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16
Q

How do new cells produced in the meristem increase in volume and mass?

A

they absorbed nutrients and water

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17
Q

Which meristem does this show?

A

Shoot apical meristem

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18
Q

Each apical meristem can give rise to additional meristems. what are the 4?

A
  • Leaf primordia - give rise (produce) to young leaves
  • Procambium - give rise to vascular tissues e.g. xylem and phloem
  • Protoderm - give rise to epidermal tissue
  • Ground meristem - give rise to parenchyma tissue (found between xylem vessels)
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19
Q

What plays a large role in determining which type of specialized tissue arises from unspecialized plant cells?

A

chemical influences

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20
Q

Where are young leaves produced?

A

at the sides of the shoot apical meristem
they appear as small bumps known as leaf primordia

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21
Q

What is a hormone?

A

a chemical message that is produced and released in one part of an organism that have an effect in another part of the organism

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22
Q

What are Auxins?

A

hormones that have a broad range of functions

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23
Q

What are 3 function of auxins?

A
  • initiating the growth of roots
  • influencing the development of fruits
  • regulating leaf development
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24
Q

What is the most abundant auxin?

A

indole-3-acetic acid (IAA)

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25
Q

What is the role of IAA?

A

promotes the elongation of cells in stems

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26
Q

Where is IAA synthesized?

A

In the apical meristem of the shoot and is transported down the stem to stimulate growth

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27
Q

What is the effect of IAA at very high concentrations?

A

it can inhibit growth

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28
Q

How does IAA stimulate growth?

A

via cell elongation and division

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29
Q

What is another example of a plant hormone thats not IAA?

A

Gibberellins

30
Q

What do Gibberellins contribute to?

A

Stem elongation

31
Q

What are axillary buds?

A

are shoots that form at the junction, or node, of the stem and the base of a leaf

32
Q

As the shoot apical ersitem grows and forms leaves, what are left behind at the node?

A

regions of meristem

33
Q

What is growth at the nodes inhibited by?

A

auxin produced by the shoot apical meristem

34
Q

What is apical dominance?

A

The production of auxin additionally prevents growth in lateral buds
* ensures that a plant will use it energy to grow up towards the light in order to outcompete other plants
* As the distance between the terminal bud and axillary bud increases, the inhibition of the axillary bud by auxin diminishes

35
Q

What can be expected of the concentration of auxin the further distant a node is from the shoot apical meristem?

A

the lower the concentration of auxin

36
Q

How does lower concentration of auxin affect growth in the axillary bud?

A

It is less likely that growth in the axillary bud will be inhibited by auxin

37
Q

What are is the hormone cytokinins produced in?

A

in the root

38
Q

What does cytokinins promote?

A

promote axillary bud growth

39
Q

What determines whether the axillary bud will develop?

A

the relative ration of cytokinins and auxins

40
Q

What do plants use hormones for?

A

to control the rate and direction of growth

41
Q

What two external stimuli influence the direction in which stems grow?

A

light and gravity

42
Q

What is tropism?

A

Directional growth responses to directional external stimuli

43
Q

What is phototropism?

A

Growth towards the light

44
Q

What is gravitropism?

A

growth in response to gravitational forces
Grow upwards, opposite direction to gravity

45
Q

How do auxin infleunce cell growth rates?

A

by changing the pattern of gene expression

46
Q

How does auxin influence gene expression? (phototropism)

A
  • Light is absorbed by photoreceptors
  • When proteins called phototropins absorb light of an appropriate wavelength their conformation changes
  • They can bind to receptors within the cell, which control the transcription of genes that code for a group of glycoprotein (PIN3 proteins) located in the plasma membrane of cells in the stem that transport the plant hormone auxin from cell to cell
47
Q

What can auxin efflux pumps set up?

A

cconcentration gradients of auxin in plant tissue

48
Q

What can be varied so auxin can be transported to where growth is needed?

A

the position and type of PIN3 proteins can be varied

49
Q

What happens to auxin when phototropins in the tip detect a greater inensity of light on one side of the stem than the other?

A
  • auxin is transported laterally from the side with brighter light to the more shaded side
  • high concentrations of auxin on the shadier side of thes stem cause greater growth on this side
  • so the stem grows in a curve towards the source of the brighter light
  • the leaves attached to the stem will therefore recieve more light and be able to photosynthesize at a greater rate
50
Q

What does gravitropism also depend on like phototropism?

A

auxin

51
Q

What does the upward growth of shoots and downards growth of roots occur in response to?

A

gravity

52
Q

What happens if a root is placed on its side in terms of gravitropism?

A
  • gravity causes cellular organelles called statoliths to accumulate on the lower side of cells
  • this leads to the disribution of PIN3 transporter proteins that direct auxin transport to the bottom of the cells
  • high concentration of auxin inhibit root cell elongation so the top cells elongate at a higher rate than the bottom cells
  • causing the root to bend downwards
53
Q

How does auxin have a different effect to roots and shoots?

A

Auxin has an opposite effect
* inhibit cell elongation in roots
* promotes cell elongation in shoots

54
Q

What is the auxin mechanism in shoots?

A
  • auxin increases the flexibility of the cell wall to promote plant growth via cell elongation
  • Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
  • the resultant decrease in pH causes cellulose fibres within the cell wall to loosen (by breaking the bonds between them)
  • additionally, auxin upregulates expression of expansins, which similarly icnreases the elasticity of the cell wall
  • with the cell wall now more flexible, an influx of water (to be stored in the vacuole) causes the cell to icnrease in size
55
Q

What is micropropagation?

A

an in vitro procedure that produces large numbers of genetically identical plants

56
Q

What is micropropagation often used as?

A

a way to produce a clone from a parent plant that has a desireable feature

57
Q

What does micropropagation depend on?

A

the totipotency of plant tissue extracted from meristems
i.e. their ability to differentiate into any functional plant part

58
Q

What are the steps to micropropagation?

A
  1. fragments of desireable plants (explants) are removed from the selected parent plant
  2. the surface of each explant is sterilised with a disinfectant solution then rinsed with sterile water to reduce the chance of contamination from microorganisms
  3. transfer to a sterile tissue culture vessel, e.g. petri dish, containing a sterile growth medium e.g. agar jelly
  4. the growth medium contains auxin and cytokinins that encourage the growth and division of the plant tissue cells to form a mass of cells, called a callus
  5. the callus develops roots, stems and leaves and becomes a plantlet
  6. once the roots and shoots are developed, the cloned plant can be transferred to soil
59
Q

What does equal proportions of auxin and cytokinin in the growth medium for micropropagation lead to?

A

the formation of an undifferentiated callus

60
Q

If the growth medium of micropropagation contains a ratio of cytokinin to auxin that is greater thsan 10:1, what develops?

A

roots develop

61
Q

if the growth medium of micropropagation contains a ratio of cytokinin to auxin that is less than 10:1, what develops?

A

shoots develop

62
Q

What does a typical tissue culture growth medium contain?

A
  • Growth hormones - auxin and cytokinin
  • mineral ions - potassium, sodium, nitrates, magnesium, phosphorus
  • water
  • glucose - allow respiration which will produce ATP
63
Q

Why is micropropagation not easy to acheive without speicialised equipement and suitable precautions?

A

it requires sterile conditions to prevent contamination from unwanted microorganisms which would otherwise use up all the nutrients and could infect the desirable plants

64
Q

What conditions would need to be controlled when growing the plantlets into plants?

A
  • light intensity
  • temperatyure
  • CO2 conc
  • humidity
  • wind speed
65
Q

What risk does international exchange of plant material carry?

A

risk of transmission of pathogens

66
Q

What can micropropagation techniques be used to produce?

A

virus-free strains of plants

67
Q

Where are viruses transported within a plant?

A

from ell to cell through vascular tissue and via plasmodesmata

the apical meristem is therefore often free of viruses

68
Q

How is micropropagation better than traditional methods of production?

A

faster and takes up less space

69
Q

What does the bulb production of engangered varities allow for?

A

wild replanting and commercial production

70
Q

For seeds that are difficult to germinate, i.e. orchid, how would micropropagation help?

A

asexual reproduction is often more successful

71
Q

What is cryopreservation?

A

a technique where micropropagated plantlets can be stored in liquid nitrogen.

Is equivalent in function to a seed bank

72
Q

Some advantages and disadvantages of micropropagation?

A

Biology (57 decks)

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