First 245 words of the document:
Auxin is a plant growth hormone. Although it stimulates growth in the shoot, when present in the
roots, it inhibits growth.
Keywords to remember:
Positive phototropism is when a plant shoot grows towards light
Negative geotropism is when a plant shoot grows away from gravity
Positive geotropism is when a plant root grows towards gravity
Shoots grow towards light:
When a plant is exposed to light, auxin accumulates on the side that's in the shade. This causes the
cells in the shade to elongate, causing the plant shoot to bend towards the light.
Shoots grow away from gravity:
When a shoot is growing sideways, gravity produces an unequal distribution of auxin on the lower
side of the shoot. This causes the cells to elongate on the lower side, bending the shoot upwards,
away from gravity.
Roots grow towards gravity:
When a root is growing sideways, the same thing will happen; more auxin will accumulate on the
lower side. But, in roots, extra auxin inhibits growth. This means the lower side will not grow,
causing the upper side to bend downwards, towards gravity.
Roots grow towards moisture:
When there is moisture near a root, more auxin will accumulate on the side with more moisture.
This will inhibit grown on that side, causing the other side to grow quicker, towards the moisture.
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Plant Hormones in Agriculture
Weeds in crop fields are mostly broad leaved. However, crops have very narrow leaves. You can use
selective weed killers which are made of plant hormones which kill the broad leaved weeds, but
leave the crops untouched.
When planting plant cuttings, they won't always grow quickly or at all in the soil. Rooting powder
which also contains plant hormones can be used so that the plant cuttings quickly produce roots and