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EDEXCEL INTERNATIONAL GCSE (9-11) BIOLOGY
UNIT-3 PLANT PHYSIOLOGY
CHAPTER 10 – PLANTS AND FOOD
Plant physiology is the branch of biology that deals with the internal activities of
plants, like nutrition, movement, and reproduction in plants
...
Starch is the main storage carbohydrate in plants because it is insoluble,
compact, and can be easily broken down
...

PHOTOSYNTHESIS
Plants use carbon dioxide and water in the presence of chlorophyll and light to
make glucose and oxygen
...

Carbon dioxide +
6CO2

+

water ______________
6 H2O ______________

glucose

+ oxygen

C6H12O6 + 6O2

PHOTOSYNTHESIS CONVERTS LIGHT ENERGY INTO CHEMICAL
ENERGY
...
CHLOROPHYLL
We can show with an experiment that chlorophyll is essential for photosynthesis
...
g
...
Variegated plants have green (chlorophyll is present) and
white (chlorophyll is absent) areas in their leaves
...
Remove one leaf
and carry out the starch test
...

Conclusion: Starch is only made in the areas of the leaf where chlorophyll is
present, showing chlorophyll is necessary for photosynthesis
...
CARBON DIOXIDE
We can do an experiment to show that carbon dioxide is necessary for
photosynthesis
...

Before the experiment, the plants should be kept in a dark place e
...
, a cupboard
for 24 to 48 hours, so that any starch present in the leaves is used up
...


Method: The 2 plants are left side by side in sunlight
...

Results: If the procedure is carried out on 2 leaves from jar A and jar B, results
will be as follows:
Leaf from jar A stains brown with the starch test, showing that there is no starch
present
...

Conclusion: Conditions in the 2 jars were the same, except jar B contained carbon
dioxide
...


3
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We can conduct an
experiment to show that it is essential for it
...
g
...

Method: The cork is pinned on one leaf of the plant
...
The cork is removed from the leaf and the starch test is done
on the leaf
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The rest of the
leaf stains blue-black
...
This experiment shows light is essential for photosynthesis
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Iodine turns starch from yellow-brown to blueblack
...

• A leaf is removed from a plant and placed in the water for 30 seconds
...

• The Bunsen burner is switched off
...

• The tube is placed in the beaker of hot water
...

• This removes the chlorophyll from the leaf
...

• The leaf is removed and washed in cold water to soften it
...

• The iodine will stain the leaf blue if starch is present in the leaf
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Take care not to splash boiling water
...

Iodine solution will badly stain everything, including the skin
...
Sodium hydrogen carbonate powder (to supply carbon dioxide to the
plant), test tube, water plant e
...
, Elodea or Hydrilla
...
Leave it for 2 days
in a place where it will receive sunlight
...

Conclusion: only oxygen has the power to relight a glowing splint, so oxygen has
been released during photosynthesis
...
No gas collects in the test tube
...
Leaf apex: this is the tip of the leaf
...
Petiole: it attaches the leaf to the plant stalk
...
Lamella: it is the blade of the leaf
...
It is the main
site for photosynthesis
...
The leaf stalk allows the lamella to be angled at the right
angle to allow for maximum sun exposure
...
Midrib veins: this is the middle vein of the leaf
...

5
...

6
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Their function is to protect the emerging
leaf or bud
...
Upper and lower epidermis: this is the outermost layer of cells covering the
leaf
...
The cuticle reduces water loss by evaporation
...

2
...
They are
present mainly in the lower epidermis
...

They allow carbon dioxide to diffuse into the leaf to reach the
photosynthetic tissues and oxygen and water vapor to diffuse out
...
These
cells can change their shape to open or close the stomata
...
Mesophyll layer: This layer is present between the upper and lower
epidermis
...

• Palisade mesophyll layer: This layer is present just below the upper
epidermis
...
It is
the main site for photosynthesis
...
It contains
loosely packed round cells with air spaces between them
...
They form the main gas exchange surface of the
leaf
...

4
...
The transport
of water and minerals through the roots, stems, and leaves of a plant is

called a transpiration stream
...

5
...


FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS
• Light intensity
• Carbon dioxide concentration
• Temperature
A limiting factor is a component of the reaction that is in short supply so that it
prevents the rate of reaction from increasing
...

At high light intensity, the plant carries out photosynthesis at a much higher rate
than it respires
...
A plant
only produces more carbon dioxide than it uses up, in dim light
...
At night
there is no photosynthesis, levels of carbon dioxide rise in the air
...


Increasing light intensity increases the rate of photosynthesis
...
Beyond this point even
if the light increases the photosynthesis rate will not increase unless more carbon
dioxide or temperature is produced
...

If there is both light intensity and a high level of CO2, the temperature may limit
the rate of photosynthesis, by limiting the rate of chemical reactions in the cell
...
Very low temperatures slow the
reaction rate whereas very high temperatures reduce the rate of photosynthesis by
denaturing enzymes
...
The table below shows the color that the indicator turns at different levels
of carbon dioxide concentration
...
10cm of indicator solution is placed in the bottom of 4 boiling tubes
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3 large leaves are taken from a plant and placed in the tops of the tubes
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3
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4
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5
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RESULTS
• Tube 4 was the control
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• Tubes 1,2 and 3 show the effect of increasing the light intensity
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• The tissue paper stopped some of the light from reaching the leaf in tube 2
and the leaf in tube 3 received the most light
...

• The rate of photosynthesis was greatest in the leaf in tube 3 and it had the
greatest net absorption of CO2
...
the effect of light intensity can then be investigated
...
The rate of photosynthesis can be shown by using an aquatic
plant e
...
, Elodea
...

Method: A beaker of water is taken
...
A cut piece of weed attached to a paperclip is
placed in a test tube
...
A lamp is used to
alter the light intensity by altering the distance between the lamp and the
pondweed
...

Safety note: Wash hands after collecting and preparing pondweed
...

PLANTS USES FOR GLUCOSE
Compounds that plant cells make from glucose:
•
•
•
•
•
•

Sucrose for transport
Starch for storage
Cellulose for cell walls
Proteins and DNA (mineral ions from soil e
...
, nitrates, phosphates)
Lipids (oil in seeds)
Chlorophyll (magnesium ions from the soil)

MINERAL NUTRITION
A plant only takes water and mineral ions from the soil for growth
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KNOP’S SOLUTION
0
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2g magnesium sulfate
0
...
2g potassium dihydrogen phosphate
Trace iron (III) phosphate

MINERAL IONS NEEDED BY PLANTS
MINERAL ION
Nitrate

USES
making amino acids, proteins
chlorophyll, DNA, and many

DEFICIENCY SYMPTOMS
limited growth of the plant
older leaves turn yellow

other compounds
...

Potassium
dead

needed for enzymes of
respiration and photosynthesis

leaves turn yellow with
spots
...

Magnesium

part of chlorophyll molecule

leaves turn yellow



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