5.1.5 Plant Responses COMPLETE

Question 1

Directional plant growth

Answer 1

Known as tropisms and are controlled by plant hormones

Question 2

Non Directional plant growth

Answer 2

Known as Nastic Responses and are not controlled by hormones. They are fast and controlled by temporary changes in the cells such as turgidity.
Examples: Venus Fly Trap

Question 3

Responses to Herbivory

Answer 3

• Physical Defences
• Chemical Defences
• Pheromones
• Thigmonasty

Question 4

Chemical Defences

Answer 4

ALKALOIDS- Bitter toxic chemicals
TANNINS- Binds to digestive enzymes
TERPENOIDS- Smell may deter insects

Question 5

Pheromones

Answer 5

Chemicals produced by an individual to affect the behaviour of another, damaged plants create them so that other plants build their defences.

Question 6

Thigmonasty

Answer 6

Move quickly in response to touch, sudden folding of leaves may dislodge small insects and scare others.

Question 7

Responses to Abiotic Stress

Answer 7

• Leaves fall in autumn
• Antifreeze production, genes are switched on to produce antifreeze proteins which stop crystallisation
• Stomatal Closure

Question 8

Tropisms

Answer 8

Geotropism
Phototropism
Chemotropism
Thigmotropism

Question 9

Geotropism

Answer 9

Roots show positive and shoots grow away from gravity so is negative

Question 10

Phototropism

Answer 10

Shoots grow towards the light, positive

Question 11

Chemotropism

Answer 11

Pollen tubes grow towards chemicals directing them to the ovary.

Question 12

Thigmotropism

Answer 12

Winding around a structure as seen in climbing plants.

Question 13

Features of plant hormones

Answer 13

• Produced in a variety of tissues
• Move by active transport, diffusion, mass flow
• Bind to complimentary receptors
• Slow
• Permanent changes
• Present in small quantities
• Work antagonistically and synergistically

Question 14

Auxins

Answer 14

Promote cell elongation
Inhibits the growth of side shoots
Inhibits leaf abscission

Question 15

Cytokinins

Answer 15

Promote cell division

Question 16

Gibberellins

Answer 16

Causes stem elongation

Promotes seed germination

Question 17

Abscisic Acid

Answer 17

Maintains seed and bud dormancy
Stimulates stomatal closure
Stimulates antifreeze

Question 18

Ethene

Answer 18

Promotes fruit ripening

Promotes leaf abscission

Question 19

Role of the plant tip

Answer 19

Required for growth
Where light is sensed for phototropism
When tip is removed or shaded it doesn’t grow towards light

Question 20

Effect of the addition of a mica sheet

Answer 20

Found that auxin does down shaded side of the plant

When the sheet blocks the shaded side the curvature stops but continues if the illuminated side is blocked.

Question 21

Effect of gelatine when inserted in a cut tip

Answer 21

Jelly allows normal growth and a repose to light as the auxin can diffuse through it still.

Question 22

Effect of soaking agar in auxin

Answer 22

The coleoptile bends even in the dark

The angle increases alongside the concentration of auxin however then begins to decrease again

Question 23

Auxins

Answer 23

Made in the meristem near tips

Causes plant elongation

Question 24

How auxins work

Answer 24

Bind to receptors on the cell surface membrane and promotes the active transport of H+ ions into the cell walls
Causes a drop in pH making it more acidic
This weakens cellulose bonds and activates enzymes that breaks them down more
As water is taken in by osmosis the cell permanently elongates as cell wall is weakened
As cell matures auxins are destroyed and cell wall becomes rigid again.

Question 25

Auxins and Phototropism

Answer 25

Cells in the shoot and tip contain PHOTOTROPINS When hit by blue light they become phosphorylated causing auxin produced in the shoot to be moved into the shade So the cell therefore bends/ elongates

Question 26

Different effects of auxins

Answer 26

In the stem auxins gather at the bottom and stimulates growth so it bends up In the root auxin gathers at the bottom and inhibits growth so it bends down

Question 27

Apical Dominance

Answer 27

A region near the top of the terminal bud contains the apical meristem This shows dominance over the lateral buds The plant therefore grows straight up and can compete for light If the tip is cut off then the lateral buds start growing and it bushes out

Question 28

Control of apical dominance

Answer 28

Auxin is made in the apical bud where it causes cell elongation It diffuses down to the lateral buds where it inhibits them Its thought the auxins keeps levels of abscisic acid high in the lateral buds which inhibits growth, when cytokinins applied it'll override the inhibition

Question 29

Gibberellins Details

Answer 29

Produced in young leaves and stems and cause growth of the stem in the internodes Works by affecting gene expression Causes cell division and cell elongation SYNERGISTIC- Plant grows tall ANTAGONISTIC- Auxin inhibits side shoots

Question 30

Gibberellins and Germination

Answer 30

When water is absorbed the embryo releases gibberellin Travels to the aleurone layer in the endosperm of the seed This switches on genes which codes for amylases and proteases Stored starch is hydrolysed into glucose providing a substrate for respiration so the embryo can grow

Question 31

Leaf abscission in Deciduous Plants

Answer 31

In winter theres less light and lower temp so less photosynthesis Water is lost through leaves, exposure to fungal infection and frost damage means its best to lose leaves

Question 32

Abscission explained

Answer 32

Reduced light means less auxin and balance shifts to there being more ethene which causes ageing. This stimulates enzymes to weaken thin walls and the cellulose bonds are broken A layer of Suberin develops underneath for protection Vascular bundles are sealed off and the leaf is blown away by the wind

Question 33

Role of Abscisic acid

Answer 33

-Plants produce ABA under abiotic stress to close the stomata which helps reduce transpiration

Question 34

Effect of Abscisic acid

Answer 34

ABA binds to receptors on the cell surface membrane on the guard cells Ca2+ enters the cell causing K+ to leave Water potential in the cell increases Water leaves by osmosis Guard cells become flaccid and close the stomata

Question 35

Commercial use of Auxin

Answer 35

- Selective weed killer - Used in cuttings to grow roots - Seedless fruits

Question 36

Commercial use of Gibberellins

Answer 36

- Improve plant shape - Delay fruit ripening - Larger grapes - Longer sugar canes

Question 37

Commercial use of Cytokinins

Answer 37

- Stops lettuces going yellow once packaged | - Causes shoot growth in tissue culture

Question 38

Commercial use of Ethene

Answer 38

- Causes fruit to drop at a certain time - Speeds up the ripening process - Promotes female flowers