Download Biology - Photosynthesis Rate

Photosynthesis and Rate
 Aims:
 Must be able to outline the factors that affect the rate of
photosynthesis in plants.
 Should be able to explain why these factors affect photosynthetic
rate.
 Could be able to outline the energy transfers involved in
environments.
Factors Affecting
Photosynthetic Rate
 The rate at which plants can make food (the
photosynthetic rate) is dependent on
environmental factors.
 These include:
 the amount of light available.
 the level of carbon dioxide (CO2).
 the temperature.
Factors Affecting
Photosynthetic Rate

The effect of light intensity
on photosynthetic rate is
shown.

Experiment was carried out at
a constant temperature and
constant carbon dioxide level.

The rate of photosynthesis
increases exponentially with
light intensity until a
maximum rate is achieved.

At this point increasing the
light intensity has no effect on
photosynthetic rate and the
rate of photosynthesis
reaches a plateau.
Rate of photosynthesis (mm3CO2 cm-2h-1)
Light intensity vs
photosynthetic rate
90
80
70
60
50
40
1
2
3
4
5
6
Units of light intensity (arbitrary scale)
7



Photosynthetic rate increases
as the CO2 concentration
increases.
At high concentrations, the
rate of photosynthesis begins
to slow as limiting factors other
than CO2 become important.
An increase in temperature
increases photosynthetic rate
because of its effect on
enzyme activity.
Temperatures exceeding the
optimum will decrease due to
denaturation of enzyme
Light intensity, CO2, and temperature
vs photosynthetic rate
Rate of photosynthesis (mm3CO2 cm-2h-1)

Factors Affecting
Photosynthetic Rate
High CO2 at 30°C
240
200
High CO2 at 20°C
160
120
Low CO2 at 30°C
80
40
Low CO2 at 20°C
1
2
3
4
5
6
Units of light intensity (arbitrary scale)
Increasing the temperature when CO2 is
limiting has little effect on photosynthetic rate.
7
Action Spectrum
An action spectrum profiles the effectiveness of different wavelength light
in fueling photosynthesis. It is obtained by plotting wavelength against some
measure of photosynthetic rate (e.g. CO2 production).
Rate of photosynthesis (as percent of rate at 670 nm)

100
Action spectrum for photosynthesis
(Effectiveness of different wavelengths in fueling photosynthesis)
80
60
40
20
The action spectrum closely
matches the absorption spectrum
for the photosynthetic pigments.
0
400
500
Wavelength (nm)
600
700
Limiting Factors
 Light Intensity, Carbon dioxide concentration, Temperature or
chlorophyll concentration (affected by the amount of Nitrogen
present) are the main LIMITING FACTORS of photosynthesis.
 The above factor that is furthest from it’s optimum level for
photosynthesis will control the amount of photosynthesis that
takes place.
 E.g. if the temperature of the plant is furthest from it’s optimal
level then the increasing the amount of carbon dioxide and
light will not affect the rate of photosynthesis.
Questions
 Biozone Book:
Answer questions from p49
Complete p44 - 48
Summary of Energy
Transformations
 Sunlight is primary source of energy in Autotrophs and Heterotrophs:
 Sunlight energy – chemical energy in Glucose (PHOTOSYNTHESIS).
 Chemical energy released to produce ATP (RESPIRATION) [more
easily transported form].
 Can be stored as GLYCOGEN in animals or as FAT in adipose cells
when liver is full, STARCH in plants (mostly roots).
 ATP releases energy as required for growth, repair, communication,
movement, Active Transport, reproduction and biosynthesis.