B11 Plant Hormones

Lessons 7 & 8

define tropism

directional growth responses

plants respond to stimuli to:

avoid being eaten

improve chances of offspring

enhance survival

In shoots, what kind of phototropism

and in roots, which kind?

shoots = positive, towards light

roots = negative, away from light

In shoots, what kind of gravitropism

and in roots, which kind?

shoots = negative

roots = positive

tropisms are caused by the hormone …

auxin

auxin is a…

growth hormone

explain phototropism in terms of auxin

auxin = less growth

sunlight breaks down auxin

so there is more growth on side of plant not exposed to light

so plant bends into light as more growth on light side

In roots, auxin … growth

In shoots, auxin … growth

roots = speeds up

shoots = slows down

gravitropism: auxin gathers on the … side of both shoots and roots

lower

But in roots, it … growth, so roots grow …,

But in shoots it … growth, so shoots grow ….

But in roots, it slows down growth, so roots grow downwards,

But in shoots it speeds up growth, so shoots grow up.

artificially, Auxins are used in … and …

rooting powder

and selective weedkiller

Dipping a cutting in rooting powder encourages the cutting to..

grow new roots

Selective weedkiller works by…

containing plant hormones at concentrations which only affect plants with broad leaves

they upset growth in the weeds (broad leaved)

but leave the crop alone.

gibberellins are used for… (3)

initiating seed germination

promoting flowering

increasing fruit size

Ethene is used for…

controlling fruit ripening during storage and transport

controlling cell division