Plant Responses

Question 1

Alkaloids

Answer 1

These are chemicals with bitter tastes, noxious smells or poisonous characteristics that deter or kill herbivores.

E.g. tobacco plants produce nicotine in response to tissue damage. Nicotine is highly poisonous to many insects.

Question 2

Tannins

Answer 2

These taste bitter and in some herbivores they can bind to proteins in the gut making the plant hard to digest. This deters animals from eating the plant.

Question 3

Pheromones

Answer 3

Signalling chemicals which produce a response in other organisms.

Some plants release alarm pheromones into the air in response to herbivores grazing. This causes nearby plants to begin to produce chemical defences.

When corn plants are being eaten by caterpillars, they produce pheromones that attract parasitic wasps. These wasps then lay eggs in the caterpillars which kills them.

Question 4

Gibberellin

Answer 4

Stimulates seed germination, cell elongation, side shoot formation and flowering.

They stimulate seed germination by triggering the breakdown of starch into glucose in the seed. The embryo in the seed can then use the glucose to start respiring and release the energy it needs to grow.

Inhibited by abscisic acid

Question 5

Auxin

Answer 5

Stimulate growth of shoots by cell elongation.

They are produces in the tips of shoots of flowering plants and diffuse backwards to stimullate the cell just behind the tips to elongate- this is where the cell walls become loose and stretchy so the cell gets longer.

High conc inhibits growth in the roots.

Inhibits side shoots

Inhibits lead loss

Question 6

Indoleacetic acid IAA

Answer 6

Is an important auxin produced at the tips and shoots of flowering plants. Its moved by diffusion and active transport over short distances, and phloem for big distances.

Question 7

Ethene

Answer 7

Stimulates leaf loss

Stimulates enzymes the break down cell walls, break down chlorophyll and convert starch into sugars. This makes fruit ripe and ready to eat.

As leaves get older, more ethene is produced. A layer of cells called the abcission layer develops at the bottom of the leaf stalk. This seperates the leaf from the rest of the plant. Ethene stimulated the cells in the abcission layer to expand, breaking the cell waalls and causing the leaf to fall off.

Deciduous plants lose their leaves in winter. This helps them conserve water during cold seasons where it may be difficult to absorb water from the soil.and when there is less light for photosynthesis.

Question 8

Abscisic acid

Answer 8

Stomatal closure

1. ABA binds to proteins on the guard cell membranes. This causes specific ion channels to open, which allows calcium ions to enter the cytoplasm.
2. The increased Ca2+ conc causes other ion channels to open. These ion channels allow ions to leave the guard cells, raising the water potential.

Question 9

Commercial use of auxin

Answer 9

Selective weed killers that produce long stems instead of lots of leaves. This makes the weeds grow too fast so they die.

Used as rooting hormones.

Question 10

carrots

Answer 10

carrots produce antifreeze proteins at low temperatures to stop ice crystals growing

Question 11

mimosa pudica

Answer 11

respond to touch by closing leaves