Photosynthesis - The process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water

1. KS3 Biology
9C Plants and
Photosynthesis
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2. Contents
9C Plants and Photosynthesis
What is photosynthesis?
Leaves and glucose
Roots and water
Summary activities
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3. How do plants grow?
Many years ago people
thought that plants ate soil
and that made them grow.
Think about it, if that really
happened then there
wouldn’t be any soil left!
Plants actually grow by
making their own food,
not by eating soil!
So where does the stuff
that plants are made of
come from?
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4. How do plants make their own food?
One of the raw materials that plants need to make food
does come from the soil, the other comes from the air.
What are these two raw materials called?
carbon dioxide
(from the air)
water
(from the soil)
Plants use carbon dioxide and water to make their own food
in a chemical reaction. What is the name of this reaction?
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5. How do plants make their own food?
Plants make their food from carbon dioxide and water in a
chemical reaction called...
photosynthesis.
carbon dioxide
(from the air) glucose
oxygen
water
(from the soil)
The food made by photosynthesis is the sugar glucose.
Oxygen gas is also made as a by-product of photosynthesis.
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6. How do plants grow?
Plants need energy for photosynthesis to take place.
Where does this energy come from?
light energy
carbon dioxide
(from the air) glucose
oxygen
water
(from the soil)
The energy for photosynthesis comes from the Sun.
Where in a plant does photosynthesis take place?
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7. How do plants grow?
Plant cells in the upper surface of leaves have chloroplasts
which contain the green pigment called chlorophyll.
light energy
carbon dioxide chlorophyll
(from the air) glucose
oxygen
water
(from the soil)
It is chlorophyll that absorbs light energy from the Sun
to make photosynthesis happen.
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8. Photosynthesis summary
Plants make their own food by the process of photosynthesis.
In this chemical reaction, chlorophyll in plant cells absorbs light
energy to change carbon dioxide and water into glucose and
the by-product oxygen.
What is the word equation for photosynthesis?
light energy
carbon
dioxide water glucose oxygen
chlorophyll
This equation can be read as:
“carbon dioxide and water, in the presence of light
energy
and chlorophyll, produces glucose and oxygen”.
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9. What is needed for photosynthesis?
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10. Photosynthesis: word equation activity
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11. Contents
9C Plants and Photosynthesis
What is photosynthesis?
Leaves and glucose
Roots and water
Summary activities
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12. How are leaves adapted?
Leaves are small ‘factories’
that produce food for plants
by photosynthesis.
Leaves are adapted so that
photosynthesis can take place.
Plants need carbon dioxide,
water, sunlight and chlorophyll
to carry out this important
process.
What features of leaves
make them suitable for
photosynthesis?
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13. How are leaves adapted?
The features of leaf that make it
suitable for photosynthesis are:
 A leaf is broad and flat to
capture lots of sunlight.
 Veins carry water to the leaf
and take food from the leaf
to the rest of the plant. Veins
also help to support the leaf.
 Certain plant cells contain
chloroplasts with chlorophyll.
 Small holes called stomata in
the underside of a leaf allow
gases in and out.
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14. Inside a leaf
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15. What do plants use glucose for?
What do plants with the glucose made by photosynthesis?
Some glucose is used straight away in
respiration. Plants also carry out respiration to
release the energy they need for life processes.
Some glucose is converted into starch and other
glucose substances for storage. These stores of energy
can be used later when the plant needs them.
Some glucose is used to make new chemicals
such as proteins, sugars and fats that the plant
also needs to function properly.
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16. Testing leaves for starch
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17. Contents
9C Plants and Photosynthesis
What is photosynthesis?
Leaves and glucose
Roots and water
Summary activities
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18. 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?
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19. 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 water
them absorb lots of water.
How are roots adapted to their job?
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20. 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?
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21. Contents
9C Plants and Photosynthesis
What is photosynthesis?
Leaves and glucose
Roots and water
Summary activities
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2005

22. Glossary
chlorophyll – The green pigment inside chloroplasts
that plants need for photosynthesis to take place.
chloroplast – The part of a plant cell where
photosynthesis occurs.
glucose – The sugar plants make during photosynthesis.
palisade cell – A type leaf cell with lots of chloroplasts.
photosynthesis – The process by which plants use
carbon dioxide and water to produce glucose and oxygen
in the presence of light and chlorophyll.
starch – Extra glucose from photosynthesis is stored as
this substance which can be tested for with iodine.
stomata – Small holes in the lower surface of a leaf
that allow gases in and out.
xylem – Tubes in veins that carry water around a plant.
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23. Anagrams
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24. Multiple-choice quiz
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