Plant responses

Question 1

how can plants respond to changes in their environment

Answer 1

• produce chemicals and hormones

Question 2

how can plants respond to changes to herbivory

Answer 2

• alkaloids
• tannins
• alarm pheromones
• fold upw

Question 3

what are alkaloids

Answer 3

• chemicals with bitter tastes, noxious smells
• deter or kill herbivores

Question 4

what are tannins

Answer 4

• taste bitter
• bind to proteins in the gut making the plant hard to digest

Question 5

what are alarm pheromones

Answer 5

• cause nearby plants to detect chemicals and can make chemical defences

Question 6

how can some plants fold up

Answer 6

• mimosa pudicana
• knock off small insects
• scare off animals

Question 7

what is the abiotic response

Answer 7

• carrots can produce antifreeze proteins at low temperatures
• proteins bind to ice crystals and lower the temperature that water freezes at
• prevents more ice crystals forming

Question 8

what is a tropism

Answer 8

response of a plant to a directional stimulus

Question 9

what is phototropism

Answer 9

• growth of a plant in response to light
• shoots = positively phototrophic
• roots = negatively phototrophic

Question 10

what is geotropism

Answer 10

• growth of a plant in response to gravity
• shoots = negatively geotropic
• roots = positively geotropic

Question 11

what is hydrotropism

Answer 11

• plant growth in response to water

Question 12

what is thigmotropism

Answer 12

• plant growth in response to contact with an object

Question 13

what is thermotropism

Answer 13

• plant growth in response to temperature

Question 14

what are growth hormones

Answer 14

• produced in growing regions of the plant and move to where they are needed in the plant
• gibberellins = stimulate seed germination, stem elongation, side shoot formation
• auxins = shoot growth, cell elongation
• high concentrations of auxin inhibits root growth

Question 15

what is indoleacetic acid

Answer 15

• type of auxin
• stimulates cell elongation
• moved around the plant to control tropisms
• moves by active transport and diffusion over short distances and phloem for long distances
• uneven distribution of IAA means uneven growth

Question 16

how does indoleacetic acid control tropisms

Answer 16

Phototropism
- IAA moves to shaded parts of shoots and roots = uneven growth

Geotropism
- IAA moves to the underside of shoots and roots = uneven growth

Question 17

how are auxins involved in apical dominance

Answer 17

• auxins stimulate the growth of apical bud
• auxins inhibit growth from lateral buds
• apical dominance = apical bud is dominant over lateral buds
• prevents side shoots from growing
• can grow tall faster as it has more energy
• remove apical buds no auxin is produced and side shoots grow
• replace tip with a source of auxin and side shoot development is inhibited
• auxin becomes less concentrated the further away from the apical bud

Question 18

what are gibberellins

Answer 18

• produced in young leaves and seeds
• stimulate seed germination, stem elongation, side shoot formation, flowering

Question 19

how do gibberellins stimulate seed germination

Answer 19

• triggers breakdown of starch into glucose in the seed
• plant embryo in the seed can use the glucose to respire and release energy to grow
• inhibited by abscisic acid

Question 20

how do auxins inhibit leaf loss

Answer 20

• auxins are produced by young leaves
• as leaf gets older less auxin is produced
• more leaf loss

Question 21

how does ethene stimulate leaf loss

Answer 21

• ethene produced by ageing leaves
• older leaf = more ethene produced
• abscission layer develops at the bottom of the leaf stalk
• layer separates leaf from the plant
• ethene stimulates cells in layer to expand breaking the cell wall and leaves fall

Question 22

how are hormones involved in stomatal closure

Answer 22

• abscisic acid triggers stomatal closure
• ABA binds to receptors on guard cell membranes
• ion channels open
• calcium ions enter cytosol from vacuole
• other ion channels open
• potassium ions leave the guard cells
• water potential of cell is raised
• water leaves the guard cells
• guard cells become flaccid and close

Question 23

how does the fruit industry use plant hormones

Answer 23

• ethene stimulates enzymes that break down cell walls
• break down chlorophyll and convert starch into sugars
• fruit is soft and ripe

Question 24

how are auxins commercially used by farmers

Answer 24

• used in herbicides
• auxins make weeds produce long stems instead of leaves
• weeds grow fast