5.1.5 - PLANT + ANIMAL RESPONSES

Question 1

What is herbivory?

Answer 1

Plants being eaten by animals (herbivory)

Question 2

Explain how plants respond to herbivory

Answer 2

Have chemical defences

• Pheromones - chemicals released by a species to affect another organism in the same species (e.g. ETHENE causing ripening of fruit in nearby plants)
  ^— ETHENE also toxic to insects
• Alkaloids - chemicals with bitter tastes, noxious smells or poisonous characteristics that deter/kill herbivores (e.g. tobacco plants produce alkaloid NICOTINE in response to tissue damage)
• Tannins - bitter tasting | can bind to proteins in the gut in some herbivores (e.g. cattle), making the plant hard to digest

Question 3

What is abiotic stress?

Answer 3

Anything harmful that is natural but non-living

E.g. drought

Question 4

Explain how plants respond to abiotic stress

Answer 4

Carrots produce antifreeze proteins at low temps
^— proteins bind to ice crystals + lower temperature that water freezes at, stopping more ice crystals from growing

Question 5

Explains how plants respond to being touched

Answer 5

• If a single leaflet (mini leaf-shaped structure that makes up part of a leaf) of this plant Mimosa pudica is touched, a signal spread through the whole leaf, causing it to quickly fold up
• COULD help protect Mimosa pudica against herbivory in many ways: knocking off small insect feeding on the plant, scaring of animals trying to eat it

Question 6

What is a tropism?

Answer 6

The response of a plant to a directional stimulus (coming from a particular direction)

Question 7

What is a positive tropism?

Answer 7

Growth towards the stimulus

Question 8

What is a negative tropism?

Answer 8

Growth away from the stimulus

Question 9

List the FIVE types of tropism

Answer 9

• Phototropism
• Geotropism
• Hydrotropism
• Thermotropism
• Thigmotropism

Question 10

What is phototropism?

Answer 10

Growth of a plant towards the light

• SHOOTS ARE POSITIVELY PHOTOTROPIC (grow towards light)
• ROOTS ARE NEGATIVELY PHOTOTROPIC (grow away from light)

Question 11

What is geotropism?

Answer 11

Growth of a plant in response to gravity

• SHOOTS ARE NEGATIVELY GEOTROPIC (grow upwards)
• ROOTS ARE POSITIVELY GEOTROPIC (grow downwards)

Question 12

What is hydrotropism?

Answer 12

Plant growth in response to water

ROOTS ARE POSITIVELY HYDROTROPIC (grow towards water)

Question 13

What is thermotropism?

Answer 13

Plant growth in response to temperature

Question 14

What is thigmotropism?

Answer 14

Plant growth in response to contact with an object

Question 15

What are deciduous plants?

Answer 15

Deciduous plants - plants that lose their leaves in winter
^— losing their leaves helped plants conserve water (lost from leaves) during the cold part of the year when its difficult to absorb water from soil (soil water may be frozen) + there’s less light for photosynthesis

Question 16

Explain the role of plant hormones in leaf loss in deciduous plants

Answer 16

Leaf loss is triggered by shortening day length in the autumn + controlled by hormones

• Auxins inhibit leaf loss (as leaf gets older, less auxin is produced, leading to leaf loss
• Ethene stimulates leaf loss - produced by ageing leaves (as leaves get older, more ethene is produced)
  ^— a layer of cells (called abscission layer) develops at the bottom of the leaf stalk (where leaf joins the stem) | layer separated leaf from res of plant + ethene stimulates the cells in the abscission layer to expand, breaking the cell walls + causing the leaf to fall off

Question 17

Explain the role of plant hormones in seed germination

Question 18

Explain the role of plant hormones in stomata closure

Answer 18

• Plants need to be able to close their stomata in order to reduce water loss through transpiration
  ^— done using guard cells (found on either side of a stomata pore)
• When guard cells are full of water, they are plump and turgid + the pore is open - when the guard cells lose water they become flaccid, making the pore close
• The plant hormone abscisic acid (ABA) is able to trigger stomata closure
  ^— binds to receptors on the guard cell membranes - causes specific ion channels to open, allowing calcium ions to enter the cytosine from the vacuole
  ^— increased conc. of calcium ions in cytosol causes other ion channels to open - these ions channels allow ions (e.g. K ions) to leave the guard cells, raising the water potential of the cells
• Water then leaves guard cells by osmosis - guard cells become flaccid + stomata close

Question 19

What are auxins?

Answer 19

• Produced in the tips of shoots in flowering plants
• Works by stimulating cell elongation

Question 20

Give an example of an auxin

Answer 20

INDOLEACETIC ACID (IAA)

Question 21

Outline the role of IAA

Answer 21

• IAA moved around the plant to control tropisms - moves via diffusion + active transport over short distances + via the phloem over long distances
  ^— Results in different parts of the plants having different amounts of IAA | uneven distribution of IAA means there is uneven growth of the plants

Question 22

Outline the effect IAA has on phototropism

Answer 22

• IAA moves to the more shaded parts of the shoots + roots so there’s uneven growth
• Cells elongate where IAA is (shaded parts) causing shoot to bend towards the light
• When IAA moves to the shaded side of the roots, growth is inhibited so the roots bends away from the light

Question 23

Outline the effect IAA has on geotropism

Answer 23

• IAA moves to the underside of shoots + roots so there’s uneven growth
• IAA moves to the shaded side of the shoots, cells elongate so the shoots grows upwards
• IAA moves to the shaded side of the root - growth is inhibited so the root grows downwards

Question 24

What is apical dominance?

Answer 24

• The shoot tip at the top of a flowering plant is called the apical bud
• Auxins stimulate the growth of the apical bud + inhibit the growth of side shoots from lateral buds
• Prevents side shoots from growing, saving energy + preventing side shoots from the same plant competing with the shoot tip for light

Question 25

Explain the role of auxins in the control of apical dominance

Answer 25

Because energy isn’t being used to grow side shoots, apical dominance allows a plant in an area where there are loads of other plants to grow tall very vast - past smaller plants to reach sunlight
- If you remove the apical bud then the plant wont produce auxins, so the side shoots will start growing by cell division + cell elongation
- BUT if you replace the tip w/ a source of auxin, side shoots development is inhibited - demonstrates apical dominance is controlled by auxins
- Auxins become less concentrated as they move away from the apical bud to the res of the plant | Is a plant grows very tall, the bottom of the plant will have a low auxin concentration so side shoots will start to grown near the bottom