topic 9.3/9.4

Question 1

describe the type of growth that plants undergo

Answer 1

indeterminate growth

Question 2

what enables the indeterminate growth of plants?

Answer 2

undifferentiated cells in the meristems of plants

Question 3

what phenomenon sets plant cells apart from most animals?

Answer 3

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

Question 4

describe plant meristems

Answer 4

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

many dicotyledonous plants also develop lateral meristems

Question 5

what is the role of mitosis in plant growth?

Answer 5

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

Question 6

describe the method by which the shoot apical meristem aids growth

Answer 6

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

Question 7

each apical meristem can give rise to additional meristems including

Answer 7

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

Question 8

what is the function of plant hormones?

Answer 8

they control growth in the shoot apex

Question 9

what are auxins?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

describe the sites of production and use of IAA

Answer 11

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

Question 12

give 2 additional examples of plant growth promoters

Answer 12

Gibberellins and Cytokinins

Question 13

describe apical dominance

Answer 13

• 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

Question 14

what is the role of cytokinins?

Answer 14

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

Question 15

how do plants respond to their environment?

Answer 15

by tropisms (directional growth responses to directional external stimuli_

Question 16

define phototropism

Answer 16

growth towards light

Question 17

define gravitropism

Answer 17

growth in response to gravitational force

Question 18

how does light influence patterns of gene expression?

Answer 18

• 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

Question 19

describe phototropism

Answer 19

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

Question 20

in the root, auxin —— shoot elongation

Answer 20

inhibits

Question 21

describe gravitropism

Answer 21

• 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

Question 22

auxin efflux pumps can

Answer 22

set up concentration gradients of auxin in plant tissue

Question 23

how does gravity cause accumulation of auxins at the bottom?

Answer 23

• 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

Question 24

describe how micropropagation is carried out

Answer 24

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.

Question 25

define micropropagation

Answer 25

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

Question 26

state and explain 3 uses of micropropagation

Answer 26

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

Question 27

multiplication phase of micropropagation

Answer 27

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

Question 28

why is the apical meristem free of viruses

Answer 28

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

Question 29

describe the relationship between flowering and gene expression

Answer 29

flowering involves a change in gene expression in the shoot apex

Question 30

what is the change involved in flowering?

Answer 30

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

Question 31

the switch to flowering in many plants is a response to

Answer 31

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

Question 32

long day plants

Answer 32

flower in summer when the nights have become short enough

Question 33

short day plants

Answer 33

flower in the autumn when the nights have become long enough

Question 34

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

Answer 34

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

Question 35

which is the active form of phytochrome and why?

Answer 35

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

Question 36

in long day plants

Answer 36

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

Question 37

in short day plants

Answer 37

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

Question 38

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

Answer 38

providing additional light in the middle of the night

Question 39

draw and label a diagram of an animal pollinated flower

Question 40

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

Answer 40

- 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.

Question 41

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

Answer 41

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.

Question 42

describe fertilisation in plants

Answer 42

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

Question 43

give 2 advantages of seed dispersal

Answer 43

- reduces competition between offspring and parent - helps to spread the species

Question 44

draw and label the internal and external structures of seeds

Question 45

explain the conditions needed for germination

Answer 45

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