Plants

And things that plants get up to..

KS3 Plants

• KS3 Sc1 Science• Green plants as organisms • 3) Pupils should be taught: • that plants need carbon dioxide, water and light for

photosynthesis, and produce biomass and oxygen • to summarise photosynthesis in a word equation• that nitrogen and other elements, in addition to carbon,

oxygen and hydrogen, are required for plant growth• the role of root hairs in absorbing water and minerals

from the soil• that plants carry out aerobic respiration.

KS4 Double award (Sc2)• Students should be taught • about similarities and differences in structure between

plant and animal cells• the reactants in, and products of, photosynthesis• that the rate of photosynthesis may be limited by light

intensity, carbon dioxide concentration or temperature• how the products of photosynthesis are utilised by the

plant• the importance to healthy plant growth of the uptake and

utilisation of mineral salt• the hormonal control of plant growth and development,

including commercial application• how plants take up water and transpire • the importance of water in the support of plant tissues • that substances required for growth and reproduction are

transported within plants.

Plants make their own food by photosynthesis.This process is a chemical reaction that uses light energy.

What is photosynthesis?

light energy

The word photosynthesis comes from the Greek language:

“photo” means “light”“synthesis” means “putting together”

Photosynthesis just means “putting together with light”.What do green plants “put together” to make their food?

The raw materials for photosynthesis come from the air and the soil.

What are these raw materials called?

What else do plants need to turn carbon dioxide and water into food?

Photosynthesis: raw materials

carbondioxide

water

Photosynthesis is a chemical reaction between carbon dioxide and water.

Energy is needed for this reaction to take place.

Where do plants get this energy from?

Photosynthesis: energy for the reaction

carbondioxide

water

light energy

Photosynthesis takes place in plant cells with chloroplasts.

Chloroplasts contain the green chemical called chlorophyll.

Chlorophyll absorbs the energy from sunlight that allows carbon dioxide and water to react.

What are the products of this reaction?

carbondioxide

water

light energy

chlorophyll

Glucose is the useful product for plants.

Some glucose is used straightaway by plant cells, some is converted to starch for storage and later used for food.

Oxygen is the ‘waste’ product. This gas is transported out of the leaf into the air.

Why is this important for humans and other living things?

carbondioxide

water

oxygen

light energy

chlorophyll

glucose

oxygen

glucose

Photosynthesis: summary

Summarize the process of photosynthesis in one sentence.

Photosynthesis is a chemical reaction which means it can also be summarized in a word equation.

What is the word equation for this vital chemical reaction?

Photosynthesis is a chemical reaction that takes place in the chloroplasts

in green plant cells, where light energy is used to convert carbon dioxide and water

into glucose and oxygen.

Photosynthesis: word equation

carbondioxide

water

oxygen

light energy

chlorophyll

glucose

glucose

light energy

chlorophyll

carbondioxide water oxygen

Photosynthesis: word equation activity

Photosynthesis: chemical formulae?

Photosynthesis is a chemical reaction involving molecules.

glucose

light energy

chlorophyll

carbondioxide water oxygen

CO2 H2O O2C6H12O6

The chemical formula of a glucose molecule is C6H12O6.

What are the chemical formulae of the simple molecules that make up carbon dioxide, water and oxygen?

6 6 6

Photosynthesis and respiration

Only green plants photosynthesize,

glucose

light energy

chlorophyll

carbondioxide water oxygen

Compare the reactants, products and energy results of these two chemical reactions. How are they connected?

carbondioxideglucose oxygen water

Photosynthesis

Respiration

but respiration occurs in the cells of all living things to release energy.

(energy needed)

(energy released)

12 a.m. 12 p.m. 12 a.m.

Photosynthesis and respirationHow will the amounts of oxygen and carbon dioxide in the air vary over 24 hours?

What overall effect do photosynthesis and respiration have on the levels of oxygen and carbon dioxide in the air?

amount of gas

in the air

amount of oxygen

amount of carbon dioxide

How does water enter a plant?

Water is one of the raw materials needed for plants to carry out photosynthesis.

How does water enter a plant?

Water from the soil enters a plant through the roots.

You can’t normally see them but roots are a very important part of a plant.

Why are roots branched and spread out through the soil?

How are roots adapted?

Roots are branched and spread out for two reasons:

to absorb water (and mineral salts) from a large amount of soil.

to anchor the plant in the soil.

Taking a closer look, roots are covered in root hair cells.

Root hair cells have thin walls and a large surface area to help them absorb lots of water.

How are roots adapted to their job?

water

Why do plants need water?

Water is needed by plants for photosynthesis but this important liquid is also used in many other ways:

to provide dissolved minerals that keep the plants healthy;

to transport substances around the plant;

to keep the plant rigid and upright;

to keep the plant cool;

to allow other chemical reactions to occur in plant cells.

What happens to a plant if it does not get enough water?

Tropisms

Plant responses to light, water and gravity are givenspecial names.

Can you work out what the name of each tropism means?

water

gravity

light

hydrotropism

geotropism

phototropism

Which parts of a plant respond to these different stimuli?

What do different tropisms mean?

Phototropism and auxins – light from one side

Why does the shoot bend towards the light when it gets light from one side?

There are more auxins on the shaded side of the shoot, so the shaded side grows faster making the bright side bend towards the light.

light light

Geotropism and auxins

If a plant is laid on its side, why does the root grow down and the stem grow up?

Auxins slow down growth on the lower side of the root, so the root curves down.

Auxins speed up growth on the lower side of the stem, so the stem curves up.

Plant Responses

Response to light

Response to water

Response to gravity

Using plant hormones

Summary quiz

What do plants respond to?

Contents

What are plant hormones used for?

Plant hormones can be used in gardening and agriculture to control how plants grow and develop.

Plant hormones are naturally-occurring chemicals but can also be produced synthetically for the following commercial uses:

growing cuttings

killing weeds

ripening fruit

Using plant hormones – growing cuttings

A cutting is a part of plant that is removed from the main shoot.What does a cutting no longer have, when it is removed from a plant?

A cutting does not have roots and so has no supply of water or minerals.

Rooting powder contains plant growth hormones. Dip a cutting into rooting powder and the plant hormones stimulate the cutting to grow new roots.

Why does the gardening business use cuttings and rooting powder to grow new plants?

Grow your own plant cutting

Using plant hormones – killing weeds

A surprising use of plant hormones is for killing weeds.

Why are weeds a problem in farming and gardening?

Weeds are unwelcome plants that compete with the plants being grown by gardeners and farmers.

Many chemicals that are potential weedkillers are toxic to animals and humans as well as plants.

Why might a weedkiller with plant hormones that only affects plants be a more favourable option?

Using plant hormones – killing weeds

Cereal crops like wheat are grasses with narrow leaves.

Most weeds that grow in fields and gardens have broad leaves.

Selective weedkillers contain plant hormones at concentrations that will only affect plants with broad leaves.

What effect will this type of weedkiller have on a field of wheat overgrown with weeds?

These selective weedkillers upset the normal growth of broad-leaved plants and so kill off any weeds.

The growth of cereal crops and grasses is not affected.

Using plant hormones – ripening fruit

Fruit is usually ripe and ready to eat when it is bought from a greengrocers or supermarket.

Fruit farmers are able to control when fruit ripens using plant hormones.

Why is this important for their business?

Fruit has often travelled many miles before being bought from the shops.

Is it better for fruit to be ripe or unripe during a long journey?

Using plant hormones – ripening fruit

Fruit that is picked before it is ripe is usually hard.

There is less chance of unripe fruit being damaged when transported, which is important to the farmer and the buyer.

Plant hormones can be sprayed onto unripe fruit during transportation. These hormones ripen fruit in time for its arrival in the shops.

Why is it a good idea to wash fruit before you eat it?