Photosynthesis is the process
in which plants use sunlight, water and carbon dioxide to produce food
or glucose. As an incredible bonus, plants produce a by-product, oxygen
that we all need to survive. |
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Equation |
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Carbon Dioxide
+ Water |
Chloroplasts absorb
sunlight
--------> |
Glucose +
Oxygen |
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Structure of a Leaf |
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1. Thin waxy cuticle
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2. Palisade cells
Palisade cells are designed for
photosynthesis and are packed with chloroplasts. They have a tall shape
to increase the exposed surface area for CO2 and
light.
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3. Spongy Mesophyll
This is the ordinary area with normal,
unspecialised cells and are situated in the centre of the leaf.
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4. Stomata & guard cells
The guard cells are a special kidney shape
which opens and closes the stomata (open pore) as the cells go turgid
(closed) and flaccid (open). They have a thin outer wall and thick inner
walls to allow the opening and closing function to work properly. These
cells are also sensitive to light and close at night to conserve water.
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5. Phloem
They are made of living cells with perforated
end plates to allow food to flow through. They transport food across the
whole of the plant (they also transport sugars, fats, protein)
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6. Xylem
They are composed of dead cells joined end
to end with no end walls between them. The side walls are strong and
stiff and contain lignin. This gives the plant support. They carry water
and mineral form the roots up to the leaves in the transpiration stream.
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So, the sunlight is absorbed
by the green pigment chlorophyll in the chloroplasts, which again are in
the palisade cells on the upper layer of the leaf.
The carbon dioxide is brought in by the stomata on the underside of the
leaf.
The water is brought from the roots, which by the light energy absorbed
by the chlorophyll is split to produce oxygen and to reduce carbon
dioxide. As a result ATP is made to energise the synthesis process.
These all combine to create glucose (food), which is exchanged through
the plant by sap.
So this is how plants use photosynthesis to produce food.
Photosynthesis is affected by the amount of three things:
- the amount of light
- the amount of carbon dioxide
- the temperature
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