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What are plants used for?
How many different uses of plants can you spot?
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Using plants
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How do plants get the food they need?
All living organisms need food to grow and survive.
This is because food provides raw materials for growth
and energy for chemical reactions.
Plants are known as producers
because they provide food for
many other organisms.
Without plants, other
organisms would have no raw
materials for growth or energy.
Unlike animals, plants cannot
move very much, so how do they
get the food that they need?
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Do plants eat soil?
It used to be thought that plants got
their food from the soil.
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.
Later experiments showed that plants
actually make their own food!
Plants are the only living organisms that can do this.
This means that all other organisms rely on plants.
What is the name of the process by which plants make food?
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What is photosynthesis?
Plants make their own food by photosynthesis.
This process is a chemical reaction that uses light energy.
light energy
The word photosynthesis comes from the Greek language:
 ‘photo’ means ‘light’
 ‘synthesis’ means ‘putting together’
Photosynthesis just means ‘putting together with light’.
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Photosynthesis
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Photosynthesis: summary
How can the process of photosynthesis be summarized in
one sentence?
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.
What is the word equation for this chemical reaction?
carbon
dioxide
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light energy
+
water
 glucose
+
oxygen
chlorophyll
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Photosynthesis: word equation activity
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What is the symbol equation for photosynthesis?
The reaction of photosynthesis can be represented by
the following equation:
carbon
dioxide
light energy
+
water
 glucose
+
oxygen
chlorophyll
What is the symbol equation for this reaction?
light energy
6 CO2
+
6 H2O

C6H12O2
+
6 O2
chlorophyll
Is this a balanced symbol equation?
How would you balance the equation?
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Word equation to symbol equation
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Photosynthesis equation quiz
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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.
Photosynthesis by plants
caused major alterations to the
atmosphere of Earth, turning it
from a hot and hostile planet
into one suitable for life.
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.
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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.
This is causing the Earth to
overheat, melting the ice caps
and endangering species.
Photosynthesis converts carbon dioxide into storable
sugars and oxygen. Planting more trees could help
reduce the amount of carbon dioxide in the atmosphere.
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How is glucose used?
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How can you test for photosynthesis?
The presence of starch in a leaf can be used to show that
photosynthesis has taken place.
Iodine is used to test for starch.
It reacts with starch and changes
colour from brown to blue-black.
The starch test can be used to
prove that photosynthesis
needs light, carbon dioxide and
chlorophyll to take place.
How would you set up an experiment to test the conditions
needed for photosynthesis?
How would you make the experiment fair and reliable?
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Testing leaves for starch
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Is chlorophyll needed for photosynthesis?
Chlorophyll cannot be removed from a plant without killing
the plant. Instead, variegated leaves can be used to show
chlorophyll is essential for photosynthesis.
Variegated leaves have pale parts,
which do not contain chlorophyll.
The green parts of the leaf contain
chlorophyll and are the control.
Which areas will react with iodine?
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
blue-black.
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Testing leaves for starch – activity
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What is the rate of photosynthesis?
Photosynthesis is a chemical reaction and so has a rate.
Like many reactions, photosynthesis requires enzymes.
Is the rate of photosynthesis always the same?
Which factors do you think affect the rate of photosynthesis?
light
carbon dioxide
temperature
How do these factors affect the rate of photosynthesis?
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How does light affect photosynthesis?
Light energy has to be absorbed by
chlorophyll for photosynthesis to take place.
carbon
dioxide
light energy
+
water
 glucose
+
oxygen
chlorophyll
The brighter the light, the more light energy there is,
so will photosynthesis be faster or slower?
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?
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Investigating photosynthesis – apparatus
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Investigation photosynthesis - experiment
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Investigation photosynthesis – results
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Carbon dioxide and the rate of photosynthesis
Carbon dioxide is one of the raw materials
used by plants to make their food.
carbon
dioxide
light energy
+
water
 glucose
+
oxygen
chlorophyll
The concentration of carbon dioxide in the air is actually
quite low (0.03%) .
Why is the concentration of carbon dioxide in commercial
greenhouses often raised to about 0.1%?
More carbon dioxide means more photosynthesis, so
plants make more food and grow more quickly.
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Does temperature affect photosynthesis?
Photosynthesis is controlled
by enzymes, which usually
work best at warmer
temperatures.
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.
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What is a limiting factor?
What is the ideal combination of factors for the maximum
rate of photosynthesis?
 enough light
 enough carbon dioxide
 ideal temperature (not too hot or cold).
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.
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Light intensity and photosynthesis
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Carbon dioxide and photosynthesis
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Temperature and photosynthesis
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Limiting factors – activity
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Limiting factors in a greenhouse
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How do leaves maximise photosynthesis?
Leaves are the most efficient
solar panels on Earth!
What does this mean?
Like solar panels, leaves
convert energy from the
Sun into usable chemical
energy.
Although leaves come in a
variety of shapes and sizes,
they share certain features
that enable the plant to
maximize photosynthesis.
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How are leaves adapted for photosynthesis?
To increase photosynthesis, leaves have certain key features:
 thin – this allows gases to
reach cells easily
 wide and flat – this create a
large surface area to absorb
as much light as possible
 veins – these carry water to the
cells and carry glucose away
and also support leaves
 stomata – these are pores on
the underside of leaves through
which gases move in and out.
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Structure of a leaf activity
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Take a look inside a leaf
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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.
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Leaf adaptations
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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).
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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.
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Anagrams
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Multiple choice quiz
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