Plant Hormones

What is Auxin?

A plant hormone that controls growth near the tips of shoots and roots

Plants produce hormones to…

Coordinate and control growth and responses to light (phototropism) and gravity (gravitropism or geotropism).

What is Phototropism

When plant shoots grow towards the light

Describe the experiments scientists did to find out how phototropism worked

1)Scientists shined light towards shoots from one side only and this led to shoots grow towards light

2)They wondered if this was controlled by hormones so they removed the very tips of the shoots and they found that the shoots did not grow towards the light

3)This suggested that shoot tips produce a plant hormone called auxin

4)The Scientists then covered the tips of the shoots with foil to block out the light and again the shoots did not grow towards the light which tells us that tips are sensitive to light

5)Scientists then used foil to cover lower parts of the shoots and the shoots grew towards the light as normal which tells us the lower parts of shoots aren’t sensitive to light

How do shoots use auxin to grow towards the light

1)So when a shoot tip is exposed to light, light causes auxin to concentrate on the darker side of the shoot tip, auxin will now spread down the shoot, so now cells on darker side grow faster than cells on the lighter side.

2)This causes the Thor to grow towards the light

What are the three uses for Auxin?

1)Klilling weeds-Selective weedkillers have been developed using auxins, which only affect the weeds( broad-leaved plants). They disrupt their growth pattern which soons kill them without disrupting grass and crops.

2)Growing from cuttings with rooting powder-Cutting is a part of a plant that has been cut off. Normally it does not grow if you stick it in soil. But if you add rooting powder which contains auxins they will produce roots rapidly and start growing as new plants. Enabling growers to produce lots of clone

3)Growing cells in tissue culture-Tissue culture can be used to grow clones of a plant from a few of its cells. To do this auxins needs to be added to growth medium to stimulate cells to divide.

What are the uses of Gibberellin

1)End Dormancy-Lots of seeds won’t germinate until they’ve been through certain conditions. Seeds can be treated with gibberillin to force the seed to germinate faster that it would normally

2)Encourage plants to flower-Some plants need conditions to flower. If these plants are treated with gibberellin they flower without any change in their environment.

3)Fruit grow larger-Seedless varieties of fruit like seedless grapes often don’t grow as large as seeded fruit. However, if gibberellin is added to these fruits they will grow larger to match the normal types

What can Ethene do

-It influences the growth of the plant by controlling cell division. It also stimulates enzymes that cause fruit to ripen.

-Commercially it can be sued to speed up ripening of fruits during transports to the shops.

-This means fruit can be picked while unripe and gas is then added to the suit on its way to supermarket so it’s perfect just as it reaches the shelves

How can ripening be delayed?

While the fruit is in storage you can add chemicals that block Ethene effect on the fruit or reduce amount of theme that a fruit can produce.

How can auxin effect the biodiversity?

-Weed killers can impact biodiversity as killing weed that serve as food or habitat for other organisms can leading to reduction in plants species diversity and could affect the entire ecosystem.