9.3 Growth In Plants

Question 1

What are meristems?

Answer 1

Is a plant tissue consisting of of undifferentiated cells capable of intermediate growth

Question 2

What can meristems allow plants to do?

Answer 2

Regrow structures and form new plants (like totipotent stem cells for animals)

Question 3

How do meristems regrow structures and form new plants?

Answer 3

By cell enlargement and repeated cell divides on (mitosis and cytokinesis)

Question 4

What are the two different types of meristems?

Answer 4

Apical and lateral meristems

Question 5

What do apical meristems do and where does this occur?

Answer 5

Occurs at shoots and root tips and responsible for primary growth (gives rise to new leaves and flowers)

Question 6

What do lateral meristems do and where do they do this?

Answer 6

They occur at the cambium and are responsible for secondary growth (plant widening and thickening) (production of bark)

Question 7

Where in the stems does growth of meristems occur?

Answer 7

Nodes, with remaining (lateral) buds having the potential to form new branching shoots

Question 8

What controls the growth of the stem and the formation of new nodes?

Answer 8

By plant hormones (including auxins)

Question 9

What happens when auxins are produced by the shoot apical meristem?

Answer 9

It promotes growth in the shoot apex via cell elongation and division

Question 10

What happens when auxins are produced by the terminal buds?

Answer 10

Prevents growth in lateral buds -> apical dominance

Question 11

What does apical dominance (in lateral buds) ensure? (Also what happens when the distance between te terminal bud and auxiliary bud)

Answer 11

That a plant will use its energy to grow up towards the light to outcompete other plants
(As the distance between the terminal bud and the auxiliary bud increases, the inhibition of the auxiliary bud by auxin diminishes)

Question 12

What does terminal bud releasing auxins do?

Answer 12

Inhibits growth of lateral buds

Question 13

What does removing the terminal bud via selective pruning do?

Answer 13

Allows dormant lateral buds to develop, producing bushier plants

Question 14

What do auxin efflux pumps do?

Answer 14

Set up a concentration gradient in tissues, changing the distribution of auxins in the plant

Question 15

What can auxin efflux pumps do?

Answer 15

Change position within the membrane (due to fluidity) and be activated by various factors

Question 16

What do auxin efflux pumps do in shoots? (The 4 step process)

Answer 16

1. Auxin activates the proton pump in the plasma membrane which causes the secretion of H+ in cell wall
2. Decrease in pH causes cellulose fibres in cell wall to loosen (breaking bonds)
3. Auxin upregulates expansion expression which increases elasticity
4. The cell wall becomes more flexible causing an influx of water to be stored in vacuole (causing cell size to increase)

Question 17

What do auxins do in the roots?

Answer 17

Auxins inhibit cell elongation and the high concentration high conc of auxin limit growth (cells become relatively smaller)

Question 18

What is tropism? (description)

Answer 18

Growth/turning movement of plant/response to a directional external stimulus

Question 19

What is phototropism?

Answer 19

Growth move to in response to a unidirectional light source

Question 20

What is geotropism?

Answer 20

Growth movement in response to gravitational forces

Question 21

What does high auxin concentration do in shoots when light shines on the plant?

Answer 21

Promotes cell elongation
On dark side -> shoot elongated and shoot grows towards the light (positive phototropism)

Question 22

What does high auxin concentration do in roots when light shines on the plant?

Answer 22

High concentration inhibits cell elongation
Dark side-> roots become shorter and grows away from the light (negative phototropism)

Question 23

What does high auxin concentration do in shoots on lower side of the plant? (Gravity)

Answer 23

Lower side-> shoot elongates and shoot grows away from ground

Question 24

What does high auxin concentration do in roots on lower side of the plant? (Gravity)

Answer 24

Lower side-> root is shorter and root turn downward into the ground

Question 25

What is micropropagation?

Answer 25

Technique to produce large number of identical plants (clones) from a selected plant

Question 26

Why does micropropagation work?

Answer 26

Plants can produce asexually from meristems because they are undifferentiated cells capable of intermediate growth

Question 27

What is the 9 step process for propagation?

Answer 27

1. Small pieces of parental tissue are taken called explants
2. Sterilise the explants
3. Transferred to plates/test tubes with sterilise agar jelly
4. Plant hormone is added
5. Cells grow rapidly in small masses of tissue called callus
6. Growth regulators added to encourage callus to grow shoot and roots
7. Tiny plant lets are transferred to potting tract (soil) which develop in plant clones
8. Good conditions (light, temp, minerals and CO2)
9. New plants are genetically identical