Biodiversity and
Interdependence
Photosynthesis (d)
Learning Intention
• To be able to give the word equation for
photosynthesis.
• To be able to describe the role of
chlorophyll in photosynthesis.
Photosynthesis
• Photosynthesis is the process by
which green plants make food using
light energy.
Carbon Dioxide
+
Water
Glucose
+
Oxygen
Chlorophyll
• Photosynthesis happens in the chloroplasts
of a plant cell.
• Chloroplasts contain chlorophyll which
absorbs the light energy needed to power
photosynthesis and changes it to chemical
energy.
Chlorophyll
Testing For Starch
• If a leaf has been carrying out
photosynthesis, it will have starch present.
• This is because the plant stores food as
starch.
• Iodine solution is used to test for starch.
Learning Intention
• To be able to describe the photolysis
stage of photosynthesis.
Photolysis
• Photosynthesis happens as a series of
enzyme controlled reactions.
• The first stage of photosynthesis is called
photolysis.
Photolysis
• The light energy is
used to split water
into hydrogen and
oxygen.
• The oxygen is
released as a byproduct.
Photolysis
• The hydrogen that is produced in
photolysis is needed for the next
stage of photosynthesis.
• It joins with a hydrogen carrier
which ‘carries’ it on to the next
stage.
H H H H H
Learning Intention
• To be able to describe the carbon
fixation stage of photosynthesis.
Carbon Fixation
• The second stage of photosynthesis
is called Carbon Fixation.
• The raw material needed for this
stage is carbon dioxide.
Carbon Fixation
• Carbon Fixation is
an enzyme
controlled cycle.
• The hydrogen from
photolysis
combines with the
CO2 to form
glucose.
Used in
photolysis
Released
during
photolysis
Chlorophyll and
light
Carbon dioxide + Water
Used in
carbon
fixation
Used in
photolysis
Glucose + Oxygen
Produced
during carbon
fixation
Learning Intention
• To be able to state the different
fates of carbon dioxide in
photosynthesis.
Fates of CO2
• The CO2 that is taken in during
photosynthesis is used to make glucose,
which the plant can use as a source of
energy.
• The glucose can then be turned into:
– Starch for storage
– Cellulose to build the cell wall
Learning Intention
• To be able to name the limiting
factors for photosynthesis
Photosynthetic Rate
• What factors might affect the rate of
photosynthesis?
1. Light Intensity
2.CO2 concentration
3.Temperature
Limiting Factors
• If any of these are in short supple
then the rate of photosynthesis will
be slowed down or limited.
• Therefore if one factor is in short
supply we call this a limiting factor.
Examples of Limiting Factors
1. If there is a lack of carbon dioxide in the
air, the rate of photosynthesis is reduced.
2. If there is a lack of light the rate of
photosynthesis will also be reduced.
3. Finally low temperature also affects the rate
of photosynthesis.
Investigating the Effect of
Varying Light Intensity
Results
Results
Results
Light is a limiting
factor at low
light intensities.
There comes a point that extra
light will not increase the rate of
the reaction. At this point light is
no longer a limiting factor.
There is a point at which further
addition of CO2 will not increase the
rate of photosynthesis. Carbon
dioxide is not the limiting factor.
When the concentration of
carbon dioxide is low the rate
of photosynthesis is also low.
When you’re asked what the limiting factor is
at a point where the graph is rising, you look
DOWN and whatever the factor on the x axis
is ,this is your limiting factor
LIGHT
50
Rate of
Photosynthesis
40
30
20
A
10
0
10
20
Light Intensity
30
40
50
When you are asked what the limiting factor is at a
point where the graph is level, you look up and see
what the difference is between the two lines this is
your limiting factor.
Temperature
50
Rate of
Photosynthesis
20oC
40
B
30
15oC
20
10
0
10
20
Light Intensity
30
40
50
TEMPERATURE
30oC
50
Rate of
Photosynthesis
C
40
20oC
15oC
30
20
10
0
10
20
Light Intensity
30
40
50