Plant Responses

Question 1

How do plants react to abiotic stress?

Answer 1

• Plants can respond to drought by shutting their stomata (reducing water loss)
• Some plants can respond to freezing by producing antifreeze chemical in their cells which decrease the formation of ice crystals that can kill plant cells
  Examples of abiotic stress:
  -Presence of heavy metals
  -Increased soil salinity

Question 2

What is herbivory?

Answer 2

The Consumption Of Plants by Herbivores

Question 3

What are the plant responses to herbivory?

Answer 3

Many plants produce herbivore-repellent chemicals in response to damage or stress caused by herbivory.

Question 4

What are the types of chemical plant defence responses?

Answer 4

Tannins, Alkaloids and Pheromones

Question 5

Alkaloids

Answer 5

Large group of compounds from amino acids
Chemicals with bitter tastes, smells that deter or kill herbivores e.g. tobacco plants produce alkaloid nicotine in response to tissue damage
Act as drugs which affect metabolism of animal that ingests it.
Located in growing tips of flowers

Question 6

Pheromones

Answer 6

Chemicals signal transmitter Released by one individual which affects behaviour and physiology which affect another member of the same species
e.g. Maple trees release a pheromone when being attacked, other branches absorb these pheromones and so they can protect themselves from being attacked.
examples sex,trail pheromones

Question 7

What is a plant tropism?

Answer 7

A directional growth response in which direction of response is determined by direction of external stimulus
May be positive - Growth response towards stimuli
Negative- Growth response away from stimuli

Question 8

What is phototropism?

Answer 8

Response to light, when shoot grows towards light enables photo synthesis = positive
Root will gain no light so it is negative phototropism

Question 9

What is geotropism?

Answer 9

When roots grow towards the pull of gravity.
Helps take up water for photosynthesis.

Question 10

What is thigmotropism?

Answer 10

Relates to touch, shoots can wind around other plants to gain support

Question 11

What is chemotropism?

Answer 11

Relates to chemicals
Growth of pollen tubes towards ovary

Question 12

Role of Hormones in Leaf Loss in Deciduous plants?

Answer 12

• Losing leaves helps plants to conserve water but in winter it will be difficult to absorb water = less light for photosynthesis
• Auxins inhibit leaf loss as leaf gets older less auxin is produced
  -Ethene stimulates leaf loss. abcission layer is produces at bottom of leaf stalk. Ethene produced causing abcission layer to expand causing cell wall to break and leaf loss.

Question 13

Role of Giberelllin in Seed Germination?

Answer 13

Water is absorbed
Gibberellins synthesised by embryo
Gibberellin stimulates aleurone lacells to synthesise amylase
Amylase hydrolyses starch to form maltose
Maltose converts to glucose
Glucose transported to embryo, providing energy for growth

Question 14

Role of Hormones in Stomatal Closure

Answer 14

ABA triggers stomatal closure.
ABA binds to specific receptors on guard cell membranes
ABA causes Ca ions to move into cytoplasm
Increases conc of Ca ions cause other ion channels to open
potassium Ions leave guard cell increase water potential inside guard cells.
Water leaves guard cell by osmosis
Guard cell becomes flaccid, stoma closes

Question 15

The Role of Auxins?

Answer 15

Group of hormones that regulate cell elongation and moved by diffusion and active transport in shoots and roots

Question 16

What is the auxin action in roots?

Answer 16

In roots, auxin inhibits cell elongation and the dark side of root becomes shorter and roots turn downwards.

Question 17

What is the auxin action in shoots?

Answer 17

In shoots, auxin stimulates cell elongation, the concentration of auxin increases on shaded side, shoot bends towards light

Question 18

Mechanism of auxin action in plant shoots to promote cell growth?

Answer 18

• Auxin activates proton pump in plasma membrane
  -Creates a secretion of H+ ions decreasing the pH
• This is the optimum pH of enzyme expanase
• Expanase break bonds in cellulose fibres
• Cell wall is flexible so cell takes in more water, elongating it

Question 19

Explain Nastic response with Mimosa pedica

Answer 19

A non-directional response to stimuli
Responds to touch by folding up its leaves due to rapid water uptake at base and rapid water loss from adjacent cells

Question 20

What is the role of plant hormones in controlling responses

Answer 20

Plant hormones are chemical messengers which coordinate responses in plants
E.g. cell elongation, differentiation and division

Question 21

What is the plant growth at meristems?

Answer 21

• Lateral bud meristem give rise to side shoots
• Apical meristems are at tips of roots and shoots, growth due to cell division and elongation
• Lateral meristems are responsible for width at roots and shoots

Question 22

Effects of the giberellin concentration on stem elongation?

Answer 22

• Gibberellin stimulates stem elongation and cell division
• Gibberellin is used in dwarf plants to stimulate growth.

Question 23

What is apical dominance?

Answer 23

The inhibition of lateral bud growth due to hormones produced by the apical bud.

Question 24

Importance of apical dominance?

Answer 24

• Ensures plant will use its energy for growth and outcompete the other plants

Question 25

Effects of Apical Dominance?

Answer 25

• Terminal buds releases auxin so this inhibits lateral growth
• Cutting terminal bud allows dormant lateral buds to grow which makes bushier plants

Question 26

How can ethene be used to control ripening?

Answer 26

Stimulates enzymes to break down chlorophyll, cell walls and convert starch to sugars in order for the fruit to be ripe, soft and ready to eat.

Question 27

How are auxins used as a rooting hormone?

Answer 27

Auxins make a cutting grow roots, the cutting can be planted and grown in a new plant.
Many cuttings can be made from an original plant and treated with rooting hormones = lots of the same plants can grow rapidly and cheaply from one plant

Question 28

How are auxins used in hormonal weed killers?

Answer 28

• Make weeds have longer stems instead of lots of leaves.
  -Makes weeds grow too fast, can’t get enough nutrients or minerals so they die.