Plant Hormones

What are auxins?

A family of plant hormones made in meristems.

What do auxins do?

They increase plant growth by promoting cell division and elongating cells.

Why do plants grow in the optimal direction?

Due to hormones

What is phototropism?

A plants growth in response to light.

What is positive gravitropism?

Growing downwards due to gravity.

How do auxins work?

Auxins move to even out all areas, so if one side of a plant is more in the shade than the other it will move to the shaded side.

What happens to a plants auxin production if it has no new stems?

No auxins will be produced.

What happens to a root on the shaded side?

The shaded side has more auxins so grows less causing the root to bend away from the light.

What else do auxins do?

It promotes growth in tissue cultures, makes rooting powder for cuttings and can be used as a weedkiller.

What is ethene gas?

A plant hormone that promotes fruit to ripen.

What do gibberellins do?

Increases fruit yield, ends seed dormancy and promotes seed germination.

What is negative geotropism?

When a stem grows against the force of gravity (upwards)

What is positive geotropism?

When a root grows in the direction of gravity (downwards)

What happens to the auxins in a root placed horizontally?

The bottom side of the root has more auxins and grows less.

What happens to the auxins in a stem placed horizontally?

The bottom side has more auxins and grows more, causing it to grow upwards.

What is the method for the Effect of light / gravity on growth Required Practical

1. Put cotton wool into 3 petri dishes and add an equal volume of water into each

2. Add 10 seeds to each dish and place them in a warm place

3. Allow seeds to germinate and add more water if wool dries out.

4. Once seeds have germinated ensure each dish has equal number of seeds.

5. Put one petri dish in full light, one in partial light and one in a dark cupboard.

6. Every day for a week measure the heigh of each seedling and record results.

7. Calculate mean height and compare results.

What is the independent variable(s) of the required practical?

Different light conditions /colours /intensity /direction

What are selective weedkillers?

Kill certain plants and contains a growth hormone that causes the weed to grow to quickly and die.

What is rooting powder?

They control plant growth and are used to encourage rapid growth of roots.