Photosynthesis:
8.
More complex graphical analysis
involving more than one
limiting factor controlling the rate of photosynthesis
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More complex graphical analysis involving more than one
limiting factor controlling the rate of photosynthesis
Reminder: The limiting factor is one that controls the maximum possible rate of
the photosynthesis reactions for given set of conditions.
-
In experiments using eg Canadian
pondweed, you can immerse the green weed in sodium hydrogencarbonate
solution to supply the carbon dioxide (one variable) needed for
photosynthesis.
-
The other two photosynthesis rate
variables are temperature and light intensity.
-
Remember, one of the three variables
must be kept constant for a given set of experiments involving the
changing of the other two variables.
-
Graph 4.
-
Graph 4.
Combined limiting factors of light intensity and temperature
-
Graph 4. Rate of photosynthesis
versus light intensity at different temperatures (2 factors)
-
Initially the graph lines are linear
as the rate of photosynthesis is proportional to the light intensity
(see also Graph 1), so light intensity is the limiting factor.
-
However, just prior to point X on the
graph, the increase in rate slows down, and finally at point X on the
graph becomes horizontal, and the rate of photosynthesis reaches a maximum irrespective of the
light intensity - the graph becomes horizontal.
-
This is shown by the graph line
becoming horizontal, and the maximum rate is now dependent on the
temperature ie the higher the temperature the greater the maximum rate
of photosynthesis possible - the temperature has become the limiting
factor.
-
For these experiments a suitable concentration of CO2/NaHCO3 must be chosen and
kept constant!
-
-
-
Graph 5.
-
Graph 5.
Carbon dioxide concentration and light intensity as combined limiting
factors
-
Graph 5. Rate of photosynthesis versus light
intensity with different carbon dioxide (CO2 from NaHCO3
solution)
concentrations (2 factors)
-
Initially the graph lines are linear
as the rate of photosynthesis is proportional to the light intensity
(see also Graph 1) - so the light intensity is the limiting factor.
-
However, just prior to point X on the
graph, the increase in rate slows down, and finally at point X the
graph has becomes horizontal, and the rate of photosynthesis reaches a maximum irrespective of the
light intensity.
-
This is shown by the graph line
becoming horizontal, and the maximum rate is now dependent on the
concentration of the carbon dioxide (from the 1%-3% NaHCO3
solution) i.e. the higher concentration of carbonate/carbon dioxide, the greater the maximum rate of photosynthesis
possible.
-
For these experiments a suitable temperature must be chosen and kept
constant! (eg lab. temp.
of ~20-25oC)
-
-
-
Graph 6.
-
Graph 6.
Carbon dioxide concentration and temperature combined as limiting
factors
-
Graph 6. Rate of photosynthesis
versus CO2/NaHCO3 at different temperatures (2
factors)
-
Initially the graph lines are linear
as the rate of photosynthesis is proportional to the carbon dioxide (or
sodium hydrogencarbonate) concentration (see also Graph 3).
-
However, just prior to point X on the
graph, the increase in rate slows down, and finally at point X the
graph becomes, and the rate of photosynthesis reaches a maximum irrespective of the
carbon dioxide concentration.
-
This is shown by the graph line
becoming horizontal, and the maximum rate is now dependent on the
temperature i.e. the higher the temperature the greater the maximum rate
possible.
-
For these experiments a suitable
light intensity must be chosen and kept constant!
-
-
-
Graph 7.
-
Graph 7. Light intensity
and carbon dioxide concentration combined as limiting factors
-
Graph 7. Rate of photosynthesis
versus CO2/NaHCO3 concentrations at light
intensities (2 factors)
-
Initially the graph lines are linear
as the rate of photosynthesis is proportional to the carbon dioxide (or
sodium hydrogencarbonate) concentration (see also Graph 3).
-
However, just prior to point X on the
graph, the increase in rate slows down, and finally at point X the
graph becomes horizontal, and the rate of photosynthesis reaches a maximum irrespective of the
carbon dioxide concentration.
-
This is shown by the graph line
becoming horizontal, and the maximum rate is now dependent on the light
intensity ie the higher the light intensity the greater the maximum
rate possible.
-
For these experiments a suitable temperature (eg 20-25oC) must be chosen and kept
constant!
-
-
Keywords, phrases and learning objectives for this part on
photosynthesis
In the context of photosynthesis, be able to
analyse, understand and explain more complex graphical analysis
involving more than one limiting factor controlling the rate of
photosynthesis.
This may involve combined factors of light
intensity, temperature, carbon dioxide level and chlorophyll
concentration in the chloroplasts.
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