9.3 growth in plants

Question 1

what are meristems (short defin.)

Answer 1

tissues in a plant consisting of undifferentiated cells of plants that allow for indeterminate growth

Question 2

meristems are found

Answer 2

• tips of shoots + roots
• axillary buds

Question 3

how do plants elongate? (short)

Answer 3

by mitosis in the shoot apex

Question 4

how do plant stems thicken? (short)

Answer 4

by mitosis of the lateral meristem in the vascular cambium

Question 5

what is tropism? (short defin.)

Answer 5

the ability of plants to respond to environmental stimuli by growing towards or away from them

Question 6

where is auxin mainly produced?

Answer 6

in the apical meristems at the tips of shoots and roots

Question 7

apical meristems gives rise to ______

Answer 7

lengthening

Question 8

lateral meristems give rise to _______

Answer 8

thickening

Question 9

the production of auxins prevents growth in ________

Answer 9

lateral (axillary) buds

Question 10

what is apical dominance?

Answer 10

• ability of the shoot apex (apical meristem) to inhibit the growth of lateral (axillary) buds through the release of auxin

Question 11

how does apical dominance help the plant to compete for sunlight with other plants? (3)

Answer 11

• apical dominance ensures the plant uses its energy to grow upwards toward the light
• the production of auxins prevents growth in lateral (axillary) buds
• only when e distance btw terminal bud and axillary bud incr will the inhibition of axillary bud by auxin diminish

Question 12

what hormone regulates plant growth?

Answer 12

auxin

Question 13

what do auxin efflux pumps do?

Answer 13

they set up concentration gradients of auxin within plant tissues

Question 14

how do auxin efflux pumps control plant growth? (4) (ref to direction of growth)

Answer 14

• auxin efflux pumps set up concentration gradients within tissues
  
  • the pumps can change position within the membrane
  • the pumps are activated by various factors
• control the distribution of auxin within plant -> control the direction of plant growth

Question 15

auxin regulates cell growth by changing the pattern of _________ __________

Answer 15

gene expression

Question 16

how does auxin affect the cell wall in a way that leads to elongation in shoots? (short)

Answer 16

it incr the flexibility of the cell wall, promoting plant growth

Question 17

what gene expression does auxin upregulate?

Answer 17

expression of expansin genes

Question 18

how is expansion possible under the effect of auxin? (5)

Answer 18

• auxin upregulates expression of expansin
• this stimulates the H+ pumps on plasma membrane
• more H+ ions are secreted into cell wall -> breaks bonds btw cellulose fibres
• thus cell walls more flexible -> more extensible
• loosening of cell wall also allows water to move into the cell -> cell expands

Question 19

name two types of tropisms plants experience

Answer 19

• phototropism
• geotropism

Question 20

how does auxin control geotropism in roots?

Answer 20

• auxin accumulates on the lower side of the roots in response to the force of gravity
• causes the roots to grow downwards

Question 21

in phototropism, _____ trigger the redistribution of auxin to the dark side of the plant

Answer 21

phototropins

Question 22

what triggers the redistribution of auxin?

Answer 22

phototropins

Question 23

what redistributes auxin?

Answer 23

auxin efflux pumps

Question 24

how do auxins lead to positive phototropism in the presence of light? (4)

Answer 24

• in e presence of light, phototropins trigger the redistribution of auxins to the darker side of the plant
• redistribution by auxin efflux pumps
• auxin binds to auxin receptors in cells at darker side -> cascades triggered, resulting in the transcription of specific genes for cell growth
• growth of cells on darker side -> bending of the plants -> grow toward light

Question 25

what is micropropagation? (short defin.)

Answer 25

technique used to produce large no.s of clones from a stock plant

Question 26

what characteristic of plants make micropropagation possible?

Answer 26

they can asexually reproduce

Question 27

what are a few advantages of micropropagation? (2/3)

Answer 27

• rapidly incr the no of new plants
• produces virus-free progeny
• produces plants from seeds that are difficult to germinate

Question 28

the plant tissue selected from the stock plant is called the….

Answer 28

explant

Question 29

what are the steps of micropropagation? (3)

Answer 29

1. explant is taken from root/shoot apex containing meristem cells
2. explant is surface sterilised, then placed in nutrient agar
3. a callus is formed and split into smaller calluses
4. each is induced to differentiate into plantlets using growth hormones
5. the plantlets are transplanted into soil for acclimatisation