Plant responses

Question 1

Alkaloids

Answer 1

Chemicals with bitter tastes, noxious smells or poisonous characteristics that deter or kill herbivores e.g. tobacco plants creating nicotine in response to tissue damage highly poisonous to insects.

Question 2

Tannins

Answer 2

Taste bitter, and in some herbivores can bind to proteins in the gut making it hard to digest the plant.

Question 3

Tropism

Answer 3

The response of a plant to a directional stimulus

• Plants respond to stimuli by regulating growth
• Positive tropism = growth towards the stimulus
• Negative tropism = growth away from the stimulus

Question 4

Phototropism

Answer 4

Growth of a plant in response to light

• Shoots are positively phototrophic and grow towards light
• Roots are negatively phototrophic and grow away from light.

Question 5

Geotropism

Answer 5

Growth of a plant in response to gravity

• Shoots are negatively geotropic and grow upwards
• Roots are positively geotropic and grow downwards.

Question 6

Growth hormones

Answer 6

Some plants respond to stimuli through growth hormones- chemicals speed up or slow down growth- produced in shoot tips & leaves. Gibberellin stimulates seed germination and stem elongation and flowering- Auxins stimulate growth of shoots by cell elongation.

Question 7

Indoleacetic acid (IAA)

Answer 7

• Stimulates cell elongation
• Is a auxin
• Controls tropisms moves by diffusion and active transport for short distances and via phloem for longer ones
• Results in different parts of the plant having different amounts of IAA means uneven distribution = uneven growth.

Question 8

Apical dominace

Answer 8

Inhibits growth of side shoots from lateral buds

Allows a plant to grow tall very fast in a area where there are lots of other plants to reach sunlight

Question 9

What happens when the apical bud gets removed?

Answer 9

The plant will not produce auxins so side shoots will start growing by cell division and cell elongation. But if you replace the tip with a source of auxin shoot development is inhibited shows apical dominance controlled by auxin.

Question 10

Gibberellins

Answer 10

• Produced in young leaves and in the seeds- stimulate seed germination, stem elongation, side shoot formation and flowering they do not inhibit plant growth and causes starch to be broken down into glucose then can use glucose to grown (seed germination)

Question 11

Synergistic Auxins and gibberellins.

Answer 11

When auxins and gibberlllins work together to help the plant to grow

Question 12

Antagonistic auxins and gibberellins

Answer 12

When they oppose each other eg auxins inhibit side shoots growth and gibberellins stimulate them

Question 13

What hormones are leaf loss controlled by?

Answer 13

Auxins inhibit leaf loss- produced by young leaves and as the leaf grows older, less auxin produced leading to leaf loss
Ethene stimulates leaf loss- Produced by ageing leaves as it gets older, more is produced a layer of cells called the abscission layer develops at the leaf stalk and separates the leaf from from the plant ethene stimulates the cells to expand and the leaf breaks off.

Question 14

Stomatal closure and ABA

Answer 14

Hormone ABA (abscisic acid) is able to trigger stomatal closure. ABA binds to receptors on guard cell membranes- causes specific ion channels to open which allows calcium to enter the cytosol from the vacuole. Increase of of calc ions causes other ion channels to open allows other ions to leave raising water potential water than leaves guard cells by osmosis stomata closes.

Question 15

Commercial use of ethene

Answer 15

Stimulates ions that breakdown cell walls and chlorophyll and convert starch to sugars makes fruit ripe and soft to eat.

Question 16

Commercial use of auxins

Answer 16

Used in selective weed killers- auxins make weeds produce long stems instead of long leaves making the weed grow to fast so they cant get enough nutrients to grow so they die. also used as rooting hormones auxins make cutting of the plant grow roots. The cutting then can be replanted.