Plant responses

Why is it important for plants to respond to the environment

To avoid abiotic stress

To avoid herbivory

To maximise photosynthesis

Help ensure germination/fertilisation

Responses to abiotic stress

Freezing

Drought

Increase soil water salinity

What is phototropism

What is positive phototropism (give example)

What is negative phototropism (give example)

It is the plants growth response to light

Positive = growth towards light eg: stem tip

Negative = growth away from light eg: root tip

What is geotropism

What is positive geotropism

What is negative geotropism

Plants growth response to the earths gravitational field

Positive = roots growing towards gravitational attraction

Negative = stem growing away from gravitational attraction

What is hydrotropism

The plants growth response to earths water (positive hydrotropism is shown by growing towards the water)

What is Thigmotropism

And give example

A plants growth response to touch (eg: Mimosa puddica and Venus flytrap respond to touch)

What is chemotropism

Plants growth response to chemicals

Plants chemical defences to herbivory (animals trying to eat them)

Give examples

Produces Alkaloids which are very bitter tasting nitrogenous compounds found in plants

Eg: caffeine is toxic to fungi and insects

Eg: nicotine is a toxin produced in roots of tobacco plants (highly poisonous to insects)

Produces tannins - which have a bitter taste and are toxic to insects

Terpenoids - Large group of compounds produced by plants which form oils but act as toxins to insects and fungi

Pheromones- a signal to nearby plants that the same species are under attack from herbivores

What does the plant hormone cytokinnins do

Promote cell division in roots and shoots . They do this by promoting more mitosis meaning there are more cells meaning there is more plant growth

What do the hormone gibillerins do

The seed is watered, it absorbs the water and causes gibillerins to be synthesised (made) in the embryo

It acts as a transcription factor for DNA to be turned into RNA and translated into amylase and protease

They also stimulate cell division and elongation in stem

What does the plant hormone ABA (Abscisic Acid) do

it is involved in stomata opening and closure

Stomata close to not use too much water

Roots cells synthesise and release ABA

ABA is transported to leaves

ABA molecules bind to receptors on the plasma membrane of guard cells

Ionic concentration of guard cells decrease

The water potential in guard cells decrease

Water moves out of cell by osmosis

reduced tugor causes the stomata to close

What does the plant hormone auxin do

Causes shoots to bend towards light

Causes roots to grow towards gravitational pull

Involved in apical dominance (plant grows as high and fast as it can)

Can inhibit ethene

How does auxin enable phototropism

Auxins are made in the shoot tip and diffuse down the shoot tip

Sunlight breaks down auxins

shaded area has the highest auxin concentration

Causing more cell division on the shaded side of the shoot.

This leads to the shoot bending towards the light.

How does auxin enable geotropism

Auxin gathers on side of root with the most gravitational pull

This inhibits cell devision

So side of root with less gravitational pull will undergo mitosis more

This cause root to grow down towards gravitational pull

What does the plant hormone ethene do

Promotes fruit ripening

Promotes leaf fall (abcission)

Leaves are lost as more energy/glucose is neede to keep them in winter. More darkness means less auxin . This means more ethene is produced and stimulates enzymes to digest end of the leaf petiole so leaf falls off and it puts fatty deposits to prevent pathogens entering

How do fruits ripen with ethene

Once picked they are stored in a cool place and just when they are about to be sold they are exposed to ethene

How is auxin used commercially

They are used in rooting powders to stimulate root growth

They are also good to produce seedless plants

synthetic auxins can be used in weeds to promote growth so they die to leave other d crops to grow without competition. This method is cheap and less harmful to environment

How are gibberellins used commercially

They produce malt which is involved in beer making process

Can be used to delay ripening

How are cytokinins used commercially

Prevent ageing in ripened fruit

Auxin, cytokinnins and gibbilerins aid In what

Fruit dropping

ethene preserves what

Cut flowers/green flowers

Auxin role in apical dominance experiment

3 roots

On first shoot the tips are removed so there is no auxin and stems do not grow

On the second shoot the tips are covered up and auxin moves to all parts of the stem causing growth

on the third shoot the tips are lit from one side causing the auxin to be broken down meaning the shaded side grows more

Experiment on gibberellins

Row of gibberellins each time increasing concentration of it. This means more stem growth of plants