plant hormones

what is phototropism

the growth of a plant towards ligth

which hormones is related to phototropism

auxin also called (indoleacetic acid IAA)

what tissue is positively phototropic

leaf

what tissue is negatively phototropic

roots

what does auxin do

elongates the cell

when light fall evenly on a plant evenly what happens

the tip produces auxin and it diffuse down the plant evenly growth on all sides of the shoot

if light only hits one side of the plant what happens

auxin diffuses to the non illuminated side. This means there is an uneven distribution (key phrase) it causes the cells on the shady side to elongate and causes it to bend to the light.

what is geotropism caused by

what is it causes by auxin

what is geotropism

growth is the direction of gravity

what tissue is positively geotropism

roots

what tissue is negatively geotropism

leaf

describe the distribution of auxin in a seed

The force of gravity auxin to accumulate on the lower side of the root tips and shoots. Therefore there is an uneven distribution.

how does auxin affect the growth of roots and shoots

Auxin has opposite effects in roots and shoots. It stimulates and elongates the cells in the shoots and inhibits growth/ elongation in the roots. This causes the lower side of the root tip to have slower and the root to curve down. where as it increases the growth in the shoot causing it to curve upward.

explain what happens once the root and shoot are growing in the desired direction

The auxin becomes evenly distributed again. Growth an all sides of the root + shoot will now be equal

what is the role of gibberellins

It enables the seed to germinate and grow by altering gene transcription

where is gibberellins produced

the embryo in the seed

describe how fertilisation happens

1. the seed absorbs water and swells

2. This stimulates the embryo to secretes gibberellins that diffuses into the aleurone layer where they trigger the digestion of proteins to amino acids.

3. gibberellin is a transcription factor which stimulates the gene expression of amylase.

4. This then diffuses into the endosperm where it digests starch into glucose and maltose

5. the sugar is then absorbed by the embryo for respiration and as raw materials for bio synthesis of proteins carbs and lipids.

a

Gibberellins is a transcription factor. It prevents Della from psychically blocking the transcription of the gene responsible for amylase being transcribed. As a result, amylase can be produced though gene expression.