Plant hormones ( auxins)

what are auxins, where are they produced and how do they move?

they are a plant growth hormone produced in the tips of the roots and shoots and they move via diffusion

what are plant tropisms?

a plant growth response to stimulus

what are positive and negative tropisms?

a positive tropism is a growth towards a stimulus and a negative tropism is a growth away from a stimulus

Geotropism

a plant's growth response to gravity

phototropism

A growth response to light

Why is phototropism important?

it increases the surface area of the leaves exposed to light so that the plant can get more light for photosynthesis

what happens if light shines all around the tip of a plant?

auxins are distributed evenly throughout and the cells shoot grow at the same rate (happens with plants growing outside)

what happens if a plant is exposed to unidirectional light?

the auxins diffuse down the shaded side and gather there, the auxins cause elongation of the cells on the shaded side to curve the stem upwards towards the light stimulus (maximises light for photosynthesis) away from the pull of gravity so negatively geotropic

shoots are _______ phototropic and _______ geotropic

positively, negatively

why are there more auxins on the shaded side?

because light breaks down auxin so there'll be more on the shaded side

why are there more auxins on the lower side of the root?

gravity pulls auxins downwards so there'll be more auxin on the lower side

What do gibberellins do?

initiate seed germination and growth of stems, naturally produced in seeds

what does ethene do?

controls cell division and stimulates ripening of fruits

how do auxins work in gravitropism?

auxins produced in tips of roots and shoots diffuse downwards accumulating on the lower side of the roots due to the pull of gravity, so the upper side of the roots grows faster than the lower side causing the root to grow downards in the direction of gravity

auxins cause cell elongation in the shoots and inhibit it in the roots causing the gravitropic response

what are the uses of ethene?

- used to artificially ripen fruits after being transported to final destination as transporting ripened fruits is bad as they’re softer so more easily damaged

what are the uses of auxins?

- weed killers ( to reduce competition between crops and weeds for space and nutrients from the soil)

- rooting powders ( to encourage growth of newly taken cuttings as they encourage the rapid development of roots)

- promoting growth in tissue culture (for clones produced in a petri dish that are then taken and planted and allowed to grow in soil)

what is the effect of everyday use of plant hormones as weed killers on biodiversity?

can have a negative impact on biodiversity as many plants classified as weeds commercially are a food source to other organisms or a potential habitat

having negative effects on other organisms in the ecosystem

what are the uses of gibberelins?

- end seed dormancy

- increase fruit size

- promote flowering