Module 5.1.5 - Plant responses

Question 1

What do plants respond to?

Answer 1

• changes in environment
• abiotic stress
• herbivory

Question 2

What are changes in the environment?

Answer 2

Phototropism - grows towards light
Gravitropism - roots grow down, shoots grow up
Phygomotropism - sense of touch

Question 3

What is abiotic stress?

Answer 3

• non living factor, causes harm
• plants either survive or dies
  e.g. drought, too much water, high/;low temps, change in light intensity, day/season length

Question 3

What are chemical responses to herbivory?

Answer 3

Tannins - toxic to microorganisms and larger herbivores, bad tasting
Alkaloids - found in growing tips and flowers, taste bitter
Terpenoids - antibacterial and antifungal properties

Question 4

What are pheremones?

Answer 4

Chemical released that affect behaviour of
others of same species

Question 5

What is leaf loss in deciduous trees?

Answer 5

• changes in day length causes changes in light and temp
• during autumn, glucose needed to release energy needed to protect plant from freezing is greater than glucose produced by photosynthesis
• trees lose leaves and remain dormant until spring
• due to antagonistic response of auxin and ethene

Question 5

How does auxin cause leaf loss in deciduous trees?

Answer 5

• inhibits leaf loss
• produced by young leaves
• less produced as leaf gets older

Question 6

What is tropism?

Answer 6

Directional growth towards an external stimuli

Question 7

What is a nastic response?

Answer 7

Non directional response to external stimuli

Question 7

How does ethene cause leaf loss in deciduous trees?

Answer 7

• stimulates leaf loss
• older leaves produce more ethene
• causes formation of abscission layer by causing cells to expand and break cell walls
• stimulates production of enzymes called cellulase (breaks down cellulose and cell walls)

Question 8

How do plants control their response?

Answer 8

• coordinate responses to environment
• not produced in endocrine glands but by cells in variety of tissues
• when hormones reach target cells, they bind to receptors on plasma membrane which can influence cell division, cell elongation or cell differentiation

Question 8

What is auxin?

Answer 8

Plant hormone, made in tip of growing shoots/roots, unequally distributed in response to light/gravity, elongates roots, shortens shoots

Question 9

Why does the shaded part of a plant bend towards the light?

Answer 9

Has more auxin

Question 10

Where is auxin produced and what does it do?

Answer 10

• at bottom of roots due to gravity
• prevents growth of root cells so opposite side continues to grow and elongate causing curve

Question 11

What is the growth of apical bud dominant over?

Answer 11

Lateral bud

Question 12

How does apical dominance happen?

Answer 12

• if plant shoot tip is cut, plant grows from lateral bud
• auxins from apical bud prevent lateral buds from growing when shoot is cut
• auxin levels drop and buds grow

Question 12

What are plant hormones involved in?

Answer 12

Germination of seeds, growth of stems, ripening of fruit and falling of leaves

Question 13

What gas is used to ripen climatic fruits?

Answer 13

Ethene

Question 14

What are climatic fruits?

Answer 14

Continue to ripen after harvesting due to peak of ethene production triggering series of chemical reactions

Question 15

What are some examples of climatic fruits?

Answer 15

Bananas, tomatoes, mangoes, avocadoes

Question 16

What are non-climatic fruits?

Answer 16

Don’t produce large amounts of ethene, don’t ripen as much after picking

Question 17

What are some examples of non-climatic fruits?

Answer 17

Oranges, strawberries, watermelon

Question 18

Why are fruits harvested when fully formed but not long before ripe?

Answer 18

• Less easily damaged during transport as they are harder
• prevents wastage during transport and increase time available to be sold - exposed to ethene gas to ripen to be sold

Question 19

What is hormone rooting powders and micropropagation?

Answer 19

• auxin affects shoots and roots growth
• auxin on cut shoots stimulates production of roots
• dipping cut stems into hormone rooting powder increases chances of roots forming and successful propagation taking place
• plant hormones essential as control production of mass new cells and then differentiation of clones into tiny new cells

Question 20

What are hormonal weedkillers?

Answer 20

• weeds interfere with crop plants, competing for light, space, water and minerals
• balance of hormones enables plants to grow
• synthetic auxin acts as very effective weedkillers
• broad leaved plants absorb auxin and their metabolism is affected, growth rate increases and becomes unsustainable/dies
• narrow leaved plants aren’t affected, continue to grow normally, freed from competition

Question 21

What is synthetic auxin?

Answer 21

Simple, cheap to produce, decreases toxicity to mammals

Question 22

What can produce seedless fruits?

Answer 22

Auxin

Question 23

What can promote fruit dropping in plants?

Answer 23

Ethene

Question 24

What does cytokinin do?

Answer 24

Used to prevent ageing of ripened fruits and products, micropropagation to control tissue development

Question 24

What does gibberellin do?

Answer 24

Delay ripening and ageing in fruits, improve size/shape in fruits, speed up malting process in beer brewing
- initiate seed germination, end seed dormancy, promote flowering, increase length of stem