Date ______
Factors Affecting Photosynthesis
Limiting factors
In 1905, when investigating the factors affecting the rate of
photosynthesis, Blackmann formulated the Law of limiting
factors. This states that the rate of a physiological process
will be limited by the factor which is in shortest supply. Any
change in the level of a limiting factor will affect the rate of
reaction.
Name ___________________
For example, the amount of light will affect the rate of
photosynthesis. If there is no light, there will be no
photosynthesis. As light intensity increases, the rate of
photosynthesis will increase as long as other factors are in
adequate supply. As the rate increases, eventually another
factor will come into short supply.
1. What is a “limiting factor?”
2. Looking at graph, explain why the rate of photosynthesis levels off as the light intensity from 800 cd to 1,000 cd.
3. List two potential limiting factors that could prevent an increase in the rate of photosynthesis even if the light
intensity is increased.
Carbon Dioxide and C3 and C4 Plants
Almost all plant life on Earth can be broken into two categories based on the way they assimilate carbon dioxide into the
Calvin cycle. C3 plants include more than 95 percent of the plant species on earth. (Trees, for example, are C3 plants.)
C4 plants include such crop plants as sugar cane and corn. They are the second most prevalent photosynthetic type.
It turns out that the important difference between C3
and C4 species for rising CO2 levels is that C3 species
continue to increase photosynthesis with rising CO2,
while C4 species do not. So, C3 plants that can respond
readily to higher CO2 levels, and C4 plants can make only
limited responses. Thus increased CO2 likely will mean
that some plant species will be stronger, more prolific,
and may overwhelm those less able to benefit.
Global is warming is caused by an increase of the CO2 in
the atmosphere due to the burning of fossil fuels. Most
scientists agree that global warming will be an ecological
catastrophe. However, some scientists believe that
global warming could be a good thing because an
increase in CO2 will cause the plants to photosynthesize
at a faster rate.
Date ______
Factors Affecting Photosynthesis
Name ___________________
4. Explain the difference between C3 plants and C4 plants?
5. Which type of plant, C3 or C4, would benefit the most from global warming caused by an increase of CO2
concentration? Use evidence to support your answer.
6. If the CO2 concentration in the atmosphere is increase from 600 ppm to 700 ppm, how will the rate of
photosynthesis be affected in a C3 plant. Explain our answer.
Temperature and Photosynthesis
Photosynthesis is a complex series of chemical
reaction thar would not occur without the help
of enzymes. Like all enzymes, the enzyme that
control photosynthesis work best at a certain
temperature. When the enzymes are not at an
optimal temperature the rate of photosynthesis
will be slowed down.
Many trees enter a period of dormancy during
the winter because the cold weather causes the
rate of photosynthesis to decrease. If the plant
is unable to photosynthesize fast enough than it
will be unable to grow and produce new leaves.
The old leaves eventually die and fall of the tree
as it enters the dormancy period for the winter.
Once the temperature increases, the tree will
use the energy stored in carbohydrates to
produce new leaves and resume photosynthesis.
7. Explain why cold temperatures cause the rate of photosynthesis to decrease?
8. According to the graph, what is the optimal temperature for photosynthesis?
9. Explain why the rate of photosynthesis decreases once the temperature gets above 100 oF.