9.1 4 Chemical Control Systems In Plants

Question 1

Plants are sensitive

Answer 1

To light

In terms of direction , light intensity and length of daily exposure to light

Question 2

Light affects how much

Answer 2

Plants grow , the direction of growth and when they reproduce

Question 3

Other factors plant are sensitive to

Answer 3

Gravity , water and temperature and in some cases to touch and chemicals

Question 4

Different parts of the plant

Answer 4

May react differently to the same stimulus

Shoots grow towards light where as roots grow away from it

Question 5

Plants respond to

Answer 5

Internal chemical signals

Question 6

Goals of the plant

Answer 6

Photosynthesis and reproduction

Question 7

Plant hormones

Answer 7

Many act as plant growth regulators

Produced in one area of the plant and transported around the body of the plant and have an effect on cells elsewhere

Question 8

Tropism

Answer 8

Plant growth responses to environmental cues

Question 9

Other way plant hormones can affect

Answer 9

Differentiation and development of plant cells and processes such as fruit ripening and leaf fall

Question 10

Main areas of cell division in plants

Answer 10

Are the meristems that occur behind the tip of the root and the shoot
Regions of cell division and cell elongation
Particularly sensitive to plant growth substances

Question 11

How do chemical messengers act

Answer 11

Make it easier for cellulose walls to be stretched making it easier for the cells to expand and grow

Question 12

Auxins

Answer 12

Powerful growth stimulants that are effective at low concentrations
Produced in young shoots and move down the plant
Through active transport and some calcium ions
Stem is the source of auxins

Question 13

Apical dominance

Answer 13

Suppress the growth of lateral shoots so that one main stem grows the fastest

Question 14

The more auxins transpired down the stem

Answer 14

The more root growth occurs

Question 15

Auxins seem

Answer 15

To effect the ability of the cell wall to stretch

Question 16

IAA

Answer 16

Made in the top of the shoot and diffuses back towards the zone of elongation
Bind to specific receptor sites on the cell surface membranes
Active pumping of hydrogen ions into the cell wall spaces
Provide optimum pH for enzymes to break bonds between adjacent cellulose microfibrils
Allows microfibrils to slide past each other easily
Keeping the walls plastic and flexible
Cells absorb water and stretch
IAA is eventually destroyed and pH restored

Question 17

Side not illuminated

Answer 17

Contains less auxin

Question 18

Light causes

Answer 18

Auxin to move laterally across the shoot
Shoot tip acts as a photoreceptor
More cell elongation on the dark side
Shoot bends towards the light

Question 19

Once the shoot is growing towards the light

Answer 19

Unilateral stimulus is removed

Asymmetrical transport of auxin ends and the shoot is growing towards the light

Question 20

Auxins

Answer 20

Diffuse away from the tip

Question 21

When auxin destroyed by enzymes

Answer 21

Cells become rigid no further cell elongation is possible

Question 22

Gibberellins

Answer 22

Growth regulators
Affect internodes of stems stimulating the elongation of growing cells
Promote fruit growth
Breaking dormancy in seeds and germination stimulate the formation of enzymes in seeds
Stimulate bolting a period of rapid growth and flowering

Question 23

Germination

Answer 23

Seed absorbs water and swells
The embryo is activated
Embryo secretes gibberellin that diffuse into the aleurone layer
Causes aleurone layer to produce amylase that diffuses to the endosperm and breaks down the food stores to provide the embryo with materials for respiration and growth
Enzymes produced in response to gibberellin digest the endosperm
Products released from the endosperm are used by the embryo to make new cells and germinate

Question 24

Cytokinins

Answer 24

Growth regulators
Promote cell division in apical meristems and the cambium through interactions with auxins
Promote lateral bud development which can overcome apical dominance of leading shoot is removed or damaged .
Cytokinins work synergistically with ethene in the abscission of leaves flowers and fruits

Question 25

Synergy

Answer 25

Work in interaction with other substances
If work together giving a greater response = Synergy
E.g. auxins and gibberellins work synergistically in growth of stems
If work opposite = antagonism
Auxins and cytokinins work antagonistically on the maintence of apical dominance

Question 26

What happens in apical dominance

Answer 26

One lead shoot grows bigger and faster than all the others and the growth of all the other lateral buds is inhibited
As a result high auxins levels produced by the first shoot to emerge

Question 27

As first shoot grows

Answer 27

away the inhibition of auxin is reduced and cytokinin becomes dominant so lateral buds lower down in the plant begin to grow

Question 28

If apical bud is removed

Answer 28

Auxin inhibition in lateral buds is removed and cytokinins can have its full effect and many lateral buds grow rapidly

Question 29

If auxin is added artificially to cut apical stem

Answer 29

Antagonistic effect returns and the lateral shoot grows again

Question 30

Abscission

Answer 30

Shedding leaves , flower plants or fruits from a plant