When seeds disperse it is important that there roots grow down into the soil, this anchors the seed and keeps it stable whilst also taking up water and minerals needed for healthy growth

Shoots also need to grow upwards towards light

Roots are sensitive to gravity, growing down in the direction of the force of gravity.
Shoots are sensitive towards gravity and light, growing towards light and against the force of gravity, whichever way the seed lands, the plant will always grow the right way up

Easy to see ij young seedlings but can also happen in adult plants, an example being that the stems of a house plant left on a windowsill will soon bend towards light

The responses of plant roots and shoots to gravity and light are known as tropisms, or tropic responses

The response of a plant to light is known as phototropism.
The response of a plant to gravity is known as gravitropism

Controlled by a hormone called auxin, the response happens because of an uneven distribution of the hormone in the shoot or root

Phototropism:
A shoot will bend so it is growing towards the light, auxin moves from the side of the shoot, where the light is falling to the unlit side of the shoot. The cells on the unlit side will respond by growing more thus, the shoot grow towards the light, once light falls evenly on both sides of the shoot, the levels of auxin will be equal on all sides and the shoot grows straight again

Gravitropism:
Auxin has different effects on the root and shoot cells, high levels inhibit growth of root cells whilst increasing growth pf shoot cells, this is why roots and shoots respond differently to gravity

Plant hormones can increase success rates of home grown plant and crops

Planting and growing cuttings from plants allows one to know exactly what the result of this growth will be, taking a small piece of stem and putting it in specially prepared compost and having luck on your side will allow, in time for new roots to grow.

Contained in rooting powders, dipping the cut end of a cutting in the powder, the chances of successfully growth are greatly increased, because the hormone stimulates growth of new roots.

Scientists have found that they can be used to make effective weedkillers by spraying it on the leaves of plants the additional auxin can lead the plant to death. The amount of hormone weed killer absorbed by the leaf depends on it's surface area, so broad leaved weeds absorb far more than plants with narrow leaves, as a result, crop plants remain somewhat unaffected whilst the weeds wither and die. Hormone weed killers are one of the reasons why the yield of crops has increased all over Europe

Are also used in modern processes as part of the plant cloning process

Used in the brewing industry to end seed dormancy.

Used to assist flowering throughout the year, especially in pot plants

Controls ripening of fruit, harvesters harvest the fruit whilst unripe the firm green fruits are transported chilled, the fruit is then stored. A warm temperature and ethene added to the atmosphere will rapidly ripen the fruits getting them to the perfect stage for being sold