The purpose of this investigation was to determine how various factors affect the light reaction. A student set up the following experiment using a number of leaf disks (cut from a leaf with a hole punch). The student used a syringe to initially remove any gases that were in the leaf tissue. Once the gases were sufficiently removed, the disks sank to the bottom of the beaker.
Questions
1. Which gas would the leaf disks produce if they were carrying out the light-dependent reaction? What would this cause them to do?
2. Predict how light intensity would affect the light reaction by drawing a curve on the following graph:
Number of Leaf Disks that Rise to Top of a Container
exposed to Various Levels of Light Intensity
3. Predict how each of the following conditions would affect the light-dependent reaction:
• Temperature:
• Wavelength:
• Bicarbonate levels:
Answers
1. At any given point in this experiment, the number of floating leaf disks is an indirect measurement of the net rate of photosynthesis. In photosynthesis, plants use energy from the sun, water, and carbon dioxide (CO2) from the air to store carbon and energy in the form of glucose molecules.
2. (a) Light is a limiting factor in region A. The rate of a process will be limited by the factor which is in shortest supply which is called the limiting factor. Any change in the level of a limiting factor will affect the rate of
(a) Light is a limiting factor in region A. The rate of a process will be limited by the factor which is in shortest supply which is called the limiting factor. Any change in the level of a limiting factor will affect the rate ofreaction.
(a) Light is a limiting factor in region A. The rate of a process will be limited by the factor which is in shortest supply which is called the limiting factor. Any change in the level of a limiting factor will affect the rate ofreaction.(b) Light, carbon dioxide concentration and temperature may be limiting factors in region A.
(a) Light is a limiting factor in region A. The rate of a process will be limited by the factor which is in shortest supply which is called the limiting factor. Any change in the level of a limiting factor will affect the rate ofreaction.(b) Light, carbon dioxide concentration and temperature may be limiting factors in region A.(c) C represents the saturation of light. Here, light is no longer the limiting factor. The limiting factor here could be carbon dioxide concentration or temperature. D represents the point at which the maximum saturation of carbon dioxide has been reached which the plant requires for photosynthesis.
3.TEMPERATURE - Although the light dependent reactions of photosynthesis are not affected by changes in temperature, the light independent reactions of photosynthesis are dependent on temperature. They are reactions catalysed by enzymes. As the enzymes approach their optimum temperatures the overall rate increases.