plant hormones - year 11 biology classroom -...

Plant Hormones

Can you explain what is happening. Click to reveal the answer.

Plant sensitivity

Plant sensitivity

The auxins diffuse down the shoot and cause cells behind the tip to elongate. There is greater growth on the shady side of the young shoot. The shoot grows towards the light - this is known as PHOTOTROPISM.

Auxins are produced in the shady side of the tip.

The animation shows the growth of a young shoot towards the light.

Can you explain what is happening.

Auxins are a class of plant growth substance

(often called phytohormone or plant hormone). Auxins play an essential role in coordination of

many growth and behavioral processes in the plant life cycle.

As auxins contribute to organ shaping, they are also fundamentally required for proper development of the plant itself. Without hormonal regulation and organization, plants would be merely proliferating heaps of similar cells.

An important principle of plant organization based upon auxin distribution is apical dominance, which means that the auxin produced by the apical bud (or growing tip) diffuses downwards and inhibits the development of ulterior lateral bud growth, which would otherwise compete with the apical tip for light and nutrients. Removing the apical tip and its suppressive hormone allows the lower dormant lateral buds to develop, and the buds between the leaf stalk and stem produce new shoots which compete to become the lead growth. This behavior is used in pruning by horticulturists.

Experiment Predict what will happen in each of these experiments. Click on each shoot to show its growth response.

Normal young shoot

Tip removed from shoot

Tip covered with a foil

cap

Tip removed and replaced with an

agar block containing auxin

Tip removed and replaced on one side

with a small agar block containing auxin

Phototropism experiments with coleoptiles

Can you explain the use of hormones in each diagram. Click to reveal the answer.

Applications of plant hormones


Fresh fruits are shipped around the world.

Plant hormones are used to slow the ripening of

the fruit, so they are just ripe as they reach the

supermarket.


When a gardener takes cuttings from a plant, the base of each

cutting is first dipped into a rooting compound to stimulate

the growth of roots. Many rooting compounds

contain auxin.



Auxins can be sprayed onto flowers so that the fruits

develop without pollination or fertilisation.

These fruits are seedless.




Weeds have broader leaves

than the grass on a lawn. The weeds will take up more auxin

than the grass when the lawn is sprayed.


Auxins can be used as herbicides.

The weeds will grow too quickly and die.

True or false?

Gardeners prune to create bushier plants. This is because pruning causes plants to create... 1. more auxin and this enables side shoots to grow 2. less auxin and this enables side shoots to grow 3. more auxin and this inhibits side shoots from growing 4. less auxin and this inhibits side shoots from growing

Which of the following statements is true? Click to reveal the answer.

True or false?

Gardeners prune to create bushier plants. This is because pruning causes plants to create... 1. more auxin and this enables side shoots to grow 2. less auxin and this enables side shoots to grow ü 3. more auxin and this inhibits side shoots from growing 4. less auxin and this inhibits side shoots from growing


True or false?

Young roots always grow downwards. This is because roots are... 1. positively phototropic 2. negatively hydrotropic 3. positively geotropic


True or false?

Young roots always grow downwards. This is because roots are... 1. positively phototropic 2. negatively hydrotropic 3. positively geotropic ü


Plant Hormones The End

plant hormones - year 11 biology classroom -...

Documents