plant hormones

What stimuli can plants detect? (3)

• light (phototropism)

• gravity (geotropism)

• some can sense touch

Describe auxins (3)

• stimulate growth of shoots and inhibit growth of roots

• produced in the tips

• diffuse backwards along root/shoot

Explain phototropism in shoots (2)

• positively phototropic, grow towards light

• auxins accumulate on shaded side rather than sunny side, these cells grow faster causing it to bend towards the light

Explain geotropism in shoots (2)

• negatively geotropic, grow away from the ground

• auxins accumulate on the lower side rather than upper side, these cells grow faster causing it to bend away from the ground

Explain tropisms in roots + what would happen if roots detected light? (4)

• negatively phototropic (grow away from light)

• positively geotropic (grow down towards ground)

• if they detect light, auxins accumulate on lower shaded side

• as roots inhibit growth, the upper side will grow faster causing the root to bend downwards

Adding auxins to plants (3)

• will stimulate plant growth

• add a medium containing auxin (and other nutrients plants need) to plant cells in a tissue culture to create lots of plant clones

• place cuttings in soil and add rooting powder (which contains auxins), the cutting will grow roots and grow into a plant

Using auxins as weed killers (3)

• adding lots of auxins can disrupt a plant’s growth pattern and cause it to die

• most weeds are broad-leaved, most commerical plants are narrow leaved

• we can create a selective weed killer that can be sprayed everywhere and kill weeds but not kill commerical plants

Gibberelin being used to control dormancy (4) For the first point, tell me what dormancy is

• dormancy is the period before a seed germinates

• use gibberelin to induce germination e.g during a season where it wouldn’t usually happen

• allows farmers to produce multiple crops a year

• means plants start growing at the same time

Gibberelin being used to induce flowering (2)

• flowering normally only takes place when conditions are right

• gibberelin encourages plants to make more flowers or bigger flowers

3 uses of gibberelin (3)

• control dormancy

• induce flowering

• produce bigger fruits

Describe ethene/how is it used? (3)

• stimulates ripening of fruit/controls ripening process

• fruits picked before they are ripe to allow time for transport

• once they get to destination, fruit is exposed to ethene so that they are ready for sale