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IB biology > topic 9.3/9.4 > Flashcards

topic 9.3/9.4 Flashcards

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1
Q

describe the type of growth that plants undergo

A

indeterminate growth

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2
Q

what enables the indeterminate growth of plants?

A

undifferentiated cells in the meristems of plants

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3
Q

what phenomenon sets plant cells apart from most animals?

A

many plant cells, including some fully differentiated types, have the capacity to generate whole plants (ie the cells are totipotent)

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4
Q

describe plant meristems

A

primary meristems are found at the tips of stems and roots (apical meristems)

many dicotyledonous plants also develop lateral meristems

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5
Q

what is the role of mitosis in plant growth?

A

mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves

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6
Q

describe the method by which the shoot apical meristem aids growth

A

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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7
Q

each apical meristem can give rise to additional meristems including

A

protoderm (gives rise to epidermis), procambium (gives rise to vascular tissue), ground meristem (gives rise to pith)

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8
Q

what is the function of plant hormones?

A

they control growth in the shoot apex

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9
Q

what are auxins?

A

plant hormones that initiate growth of roots, influence development of fruits and regulate leaf development

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10
Q

what is the most abundant auxin? and what is its role?

A

indole-3-acetic acid (IAA); control of growth in the shoot apex.

When produced by the shoot apical meristem, it promotes growth in the shoot apex via cell elongation and division
prevents/inhibits growth in lateral (axillary) buds - apical dominance

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11
Q

describe the sites of production and use of IAA

A

synthesised in the apical meristem of the shoot and transported down the stem to stimulate growth

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12
Q

give 2 additional examples of plant growth promoters

A

Gibberellins and Cytokinins

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13
Q

describe apical dominance

A
  • as the shoot apical meristem grows and forms leaves, regions of meristem are left behind at the node
  • growth here is inhibited by auxin produced by the shoot apical meristem
  • the further distant a node is from the apical meristem, the lower the concentration of auxin and the less likely that growth in the auxiliary bud will be inhibited by auxin
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14
Q

what is the role of cytokinins?

A

produced in the root and promote auxiliary bud growth. the relative ratio of cytokinins:auxins determine whether the auxiliary bud will develop

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15
Q

how do plants respond to their environment?

A

by tropisms (directional growth responses to directional external stimuli_

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16
Q

define phototropism

A

growth towards light

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17
Q

define gravitropism

A

growth in response to gravitational force

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18
Q

how does light influence patterns of gene expression?

A
  • when light falls on a plant, light energy is absorbed by phototropins (photoreceptor proteins), causing a change in their 3D shape
  • the altered shape of the phototropins allows them to bind to receptors inside the cell, affecting the expression of certain genes
  • the affected genes could code for glycoproteins called PIN3 proteins, thought to be involved with the transport of auxin from cell to cell
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19
Q

describe phototropism

A
  1. phototropins in the tip detect a greater intensity of light on one side of the stem than the other
  2. IAA is transported laterally from the light to the shaded side due to changed expression of PIN3 proteins
  3. higher concentrations of IAA on the shaded side cause greater growth on this side, so the stem grows in a curve towards the source of the brighter light
20
Q

in the root, auxin —— shoot elongation

A

inhibits

21
Q

describe gravitropism

A
  • when a root is placed on its side, auxin will accumulate on the lower side of the plant in response to the force of gravity
  • higher concentrations of auxin inhibit root cell elongation so the top cells elongate at a higher rate than the bottom cells, causing the root to bend downward
22
Q

auxin efflux pumps can

A

set up concentration gradients of auxin in plant tissue

23
Q

how does gravity cause accumulation of auxins at the bottom?

A
  • cellular organelles called statoliths accumulate on the lower side of cells
  • this leads to distribution of PIN3 transporter proteins to the bottom of the cell
24
Q

describe how micropropagation is carried out

A
  1. Tissues from the stock plant are sterilized and cut into pieces called explants (for most applications, the least differentiated tissue serves as the source tissue such as a meristem).
  2. The explant is placed into sterilized growth media that includes plant hormones.
  3. Inclusion of equal proportions of auxin and cytokinin into the media leads to the formation of an undifferentiated mass called a callus. If the growth media contains a ratio of auxin that is greater than ten times the amount of cytokinin, then this is called rooting media and roots develop. If the ratio of auxin to cytokinin is less than 10:1, then this is called shoot media and shoots develop.
  4. Once roots and shoots are developed, the cloned plant can be transferred to soil.
25
Q

define micropropagation

A

When plant tissues are cultured in the laboratory (in vitro) in order to reproduce asexually

26
Q

state and explain 3 uses of micropropagation

A
  • rapid bulking up of new varieties
  • production of virus-free strains of existing varieties
  • propagation of orchids and other rare species with desired characteristics
27
Q

multiplication phase of micropropagation

A

The growing shoots can be continuously divided and separated to form new samples

28
Q

why is the apical meristem free of viruses

A

viruses are transported within a plant from cell to cell through vascular tissue and via plasmodesmata

29
Q

describe the relationship between flowering and gene expression

A

flowering involves a change in gene expression in the shoot apex

30
Q

what is the change involved in flowering?

A

a trigger causes the shift from vegetative phase (young plant) -> reproductive phase, when meristems in the shoot start to produce parts of flowers instead of leaves

31
Q

the switch to flowering in many plants is a response to

A

the length of light and dark periods in many plants (where length of darkness is what matters)

32
Q

long day plants

A

flower in summer when the nights have become short enough

33
Q

short day plants

A

flower in the autumn when the nights have become long enough

34
Q

what is used to measure the length of dark periods in plants? and how?

A

phytochrome (pigment) that can switch between two forms, Pr and Pfr

  • when Pr absorbs red light of wavelength 660nm it is converted into Pfr
  • when Pfr absorbs far-red light of wavelength 730nm it is converted into Pr (this is not of great importance as sunlight contains more light of wavelength 660nm so in normal sunlight phytochrome is rapidly converted to Pfr)
  • Pr is more stable so in darkness Pfr very gradually changes into Pr
35
Q

which is the active form of phytochrome and why?

A

Pfr; receptor proteins are present in the cytoplasm to which Pfr but not Pr binds

36
Q

in long day plants

A

large amounts of Pfr remain at the end of short nights and bind to the receptor, which then promotes transcription of genes needed for flowering

37
Q

in short day plants

A

Pfr inhibits transcription of the flowering time gene (FT gene), preventing flowering; so flowering requires low levels of Pfr (resulting from long nights)

38
Q

methods used to induce short-day plants to flower out of season

A

providing additional light in the middle of the night

39
Q

draw and label a diagram of an animal pollinated flower

A
40
Q

give the functions of
- nectar-secreting glands
- petals
- sepals
- anthers
- filaments
- carpel (stigma, style, ovary)

A
  • nectar-secreting glands attract insects, especially bees
  • petals are large and colourful, helping insects to find the flower.
  • sepals protect the flower bud during its development and at night when buds close.
  • anthers produce pollen, containing the male gametes.
  • filaments hold the anthers in a position where they are likely to brush pollen onto visiting insects
  • female part of the flower is called a carpel. It consists of a stigma, style and ovary. The stigma is sticky and will capture pollen from the visiting insect. The stigma is held up by the style. The ovary is located inside a small rounded structure called an ovule.
41
Q

why do most flowering plants use mutualistic relationships with pollinators in sexual reproduction? what does this involve?

A

sexual reproduction in flowering plants depends on the transfer of pollen from the stamen to a stigma of another plant

pollinators gain food in the form of nectar; plant gains a means to transfer pollen to another plant.

42
Q

describe fertilisation in plants

A
  1. from each pollen grain on the stigma a tube grows down the style to the ovary
  2. the pollen tube carries male gametes to fertilise the ovary, which is located inside a small rounded structure called an ovule
  3. the fertilised ovule develops into a seed and the ovary develops into a fruit
43
Q

give 2 advantages of seed dispersal

A
  • reduces competition between offspring and parent
  • helps to spread the species
44
Q

draw and label the internal and external structures of seeds

A
45
Q

explain the conditions needed for germination

A

Oxygen – for aerobic respiration (the seed requires large amounts of ATP in order to develop)
Water – to metabolically activate the seed (triggers the synthesis of gibberellin, which stimulates mitosis and cell division)
Temperature and pH – for optimal function of enzymes

IB biology (60 decks)

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