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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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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.
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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.
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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’.
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Photosynthesis
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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
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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:
CO2 H2O C6H12O2 O2+ +
Is this a balanced symbol equation?
How would you balance the equation?
6 6 6
light energy
chlorophyll
carbon dioxide + water oxygen+glucose
light energy
chlorophyll
What is the symbol equation for this reaction?
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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.
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.
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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.
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.
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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.
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?
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Testing leaves for starch
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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.
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Testing leaves for starch – activity
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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?
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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
carbon dioxide + water oxygen+glucose
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 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
carbon dioxide + water oxygen+glucose
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%?
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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.
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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).
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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 greenhouseLimiting factors in a greenhouse
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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.
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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:
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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