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1 of 48 © Boardworks Ltd 2007

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What are plants used for?

How many different uses of plants can you spot?


Using plants


All living organisms need food to grow and survive.

How do plants get the food they need?

Plants are known as producers

because they provide food for

many other organisms.

Unlike animals, plants cannot

move very much, so how do they

get the food that they need?

This is because food provides raw materials for growth

and energy for chemical reactions.

Without plants, other

organisms would have no raw

materials for growth or energy.


This means that all other organisms rely on plants.

Later experiments showed that plants

actually make their own food!

This was proved to be untrue by

measuring the mass of the soil in a

plant pot before and after growth.

The soil did not decrease in mass,

even though plant mass increased.

Do plants eat soil?

It used to be thought that plants got

their food from the soil.

What is the name of the process by which plants make food?

Plants are the only living organisms that can do this.



Plants make their own food by photosynthesis.

What is photosynthesis?

light energy

The word photosynthesis comes from the Greek language:

This process is a chemical reaction that uses light energy.

‘photo’ means ‘light’ ‘synthesis’ means ‘putting together’

Photosynthesis just means ‘putting together with light’.


Photosynthesis


Photosynthesis: summary

How can the process of photosynthesis be summarized in

one sentence?

What is the word equation for this chemical reaction?

Photosynthesis is a chemical reaction that takes

place in the chloroplasts of green plant cells, where

light energy is used to convert carbon dioxide and

water into glucose and oxygen.

light energy

chlorophyll

carbon dioxide + water oxygen+glucose


Photosynthesis: word equation activity


What is the symbol equation for photosynthesis?

The reaction of photosynthesis can be represented by

the following equation:

CO2 H2O C6H12O2 O2+ +

Is this a balanced symbol equation?

How would you balance the equation?

6 6 6

light energy

chlorophyll


light energy

chlorophyll

What is the symbol equation for this reaction?


Word equation to symbol equation


Photosynthesis equation quiz


Does photosynthesis change the air?

The evolution of photosynthesis,

hundreds of millions of years

ago, was one of the biggest

changes to shape the Earth.

It lowered the levels of carbon dioxide in the atmosphere

and raised the levels of oxygen, which is used by most

organisms for respiration. Oxygen also lead to the formation

of the ozone layer, which filters out harmful UV rays.

Photosynthesis by plants

caused major alterations to the

atmosphere of Earth, turning it

from a hot and hostile planet

into one suitable for life.


Why are plants important to climate change?

Carbon dioxide is a greenhouse gas. This means it traps

heat from the Earth and stops it escaping into space, like a

pane of glass in a greenhouse.

Burning fossil fuels, increased travel

and deforestation have caused

atmospheric carbon dioxide levels

to rise dangerously high.

Photosynthesis converts carbon dioxide into storable

sugars and oxygen. Planting more trees could help

reduce the amount of carbon dioxide in the atmosphere.

This is causing the Earth to

overheat, melting the ice caps

and endangering species.



How is glucose used?


How can you test for photosynthesis?

The presence of starch in a leaf can be used to show that

photosynthesis has taken place.

The starch test can be used to

prove that photosynthesis

needs light, carbon dioxide and

chlorophyll to take place.

Iodine is used to test for starch.

It reacts with starch and changes

colour from brown to blue-black.

How would you set up an experiment to test the conditions

needed for photosynthesis?

How would you make the experiment fair and reliable?


Testing leaves for starch


Only the green areas of the leaf

react with the iodine and turn

blue-black. Without chlorophyll,

the pale areas have been unable

to produce starch and do not turn

Is chlorophyll needed for photosynthesis?

Variegated leaves have pale parts,

which do not contain chlorophyll.

The green parts of the leaf contain

chlorophyll and are the control.

Chlorophyll cannot be removed from a plant without killing

the plant. Instead, variegated leaves can be used to show

chlorophyll is essential for photosynthesis.

Which areas will react with iodine?

blue-black.


Testing leaves for starch – activity



Like many reactions, photosynthesis requires enzymes.

Photosynthesis is a chemical reaction and so has a rate.

What is the rate of photosynthesis?

light

Which factors do you think affect the rate of photosynthesis?

How do these factors affect the rate of photosynthesis?

carbon dioxide temperature

Is the rate of photosynthesis always the same?


How does light affect photosynthesis?

Light energy has to be absorbed by

chlorophyll for photosynthesis to take place.

The brighter the light, the more light energy there is,

so will photosynthesis be faster or slower?

light energy

chlorophyll


More light energy means that photosynthesis will be faster.

If light intensity is too high plant cells can be damaged.

How is photosynthesis affected if this happens?


Investigating photosynthesis – apparatus


Investigation photosynthesis - experiment


Investigation photosynthesis – results


Carbon dioxide is one of the raw materials

used by plants to make their food.

Carbon dioxide and the rate of photosynthesis

The concentration of carbon dioxide in the air is actually

quite low (0.03%) .

light energy

chlorophyll


More carbon dioxide means more photosynthesis, so

plants make more food and grow more quickly.

Why is the concentration of carbon dioxide in commercial

greenhouses often raised to about 0.1%?


Photosynthesis is controlled

by enzymes, which usually

work best at warmer

temperatures.

Does temperature affect photosynthesis?

Does increasing the

temperature always increase

the rate of photosynthesis?

If it gets too hot (above 40°C),

the enzymes needed for

photosynthesis begin to break

down and are destroyed or

denatured. The rate of

photosynthesis decreases or

even stops completely.


What is the ideal combination of factors for the maximum

rate of photosynthesis?

What is a limiting factor?

enough light

How does restricting one of these facts affect the rate?

If one of the factors is restricted, the rate of photosynthesis

will be below the maximum possible rate.

The restricted factor controls how quickly photosynthesis

occurs and so limits the rate. It is called the limiting factor.

enough carbon dioxide

ideal temperature (not too hot or cold).


Light intensity and photosynthesis


Carbon dioxide and photosynthesis


Temperature and photosynthesis


Limiting factors – activity


Limiting factors in a greenhouseLimiting factors in a greenhouse



Leaves are the most efficient

solar panels on Earth!

How do leaves maximise photosynthesis?

Although leaves come in a

variety of shapes and sizes,

they share certain features

that enable the plant to

maximize photosynthesis.

What does this mean?

Like solar panels, leaves

convert energy from the

Sun into usable chemical

energy.


wide and flat – this create a

large surface area to absorb

as much light as possible

thin – this allows gases to

reach cells easily

stomata – these are pores on

the underside of leaves through

which gases move in and out.

veins – these carry water to the

cells and carry glucose away

and also support leaves

How are leaves adapted for photosynthesis?

To increase photosynthesis, leaves have certain key features:


Structure of a leaf activity


Take a look inside a leaf


How do gases enter and leave plants?

On the underside of leaves are small holes, or pores, called

stomata. A single hole is called a stoma. Each stoma is

surrounded by two guard cells.

When guard cells gain water,

they curve outwards. This

opens the stoma, allowing

gases in and out.

Losing water causes the guard

cells to come closer together,

closing the stoma. This stops

the movement of gases, but

also prevents water loss.


Leaf adaptations







Glossary (1/2)

cellulose – An insoluble carbohydrate made from glucose. It is used to make cell walls.

chlorophyll – The green pigment inside chloroplasts that is needed for photosynthesis to take place.

chloroplast – The plant cell structure where photosynthesis occurs.

cuticle – A waxy layer on the surface of the leaf that prevents water loss.

epidermis – A protective outer layer of cells found on the top and underside of leaves. This layer is clear to allow photosynthesis.

guard cells – A pair of cells that control the opening and closing of a stoma (single hole).


Glossary (2/2)

palisade – A layer of cells in the leaves, which contain lots of chloroplasts. It is the main site of photosynthesis.

photosynthesis – The process by which plants use carbon dioxide and water to make glucose and oxygen in the presence of light and chlorophyll.

spongy layer – A layer of cells that contains large spaces between cells. This allows the diffusion of gases between the stomata and palisade layer.

stoma (singular) – A single hole on the lower surface of the leaf that allows gases in and out.

stomata (plural) – Small holes in the lower surface of leaves that allow gases in and out.

variegated – A leaf containing areas without chlorophyll.


Anagrams


Multiple choice quiz

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