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Factors effecting the rate of photosynthesis

This version was saved 14 years, 4 months ago View current version     Page history
Saved by Ben Vallee
on November 6, 2009 at 8:36:58 pm
 

These are the factors.

 

 

Light

 

At first as light intensity is increased, the rate of photosynthesis is increased but then it plateaus because of limiting factors.  Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis.

 

How Light Affects Photosynthesis:

 

  • Bright light is a basic element of photosynthesis, but variations in the color of light have an effect on plants. The entire spectrum of light hits the plant's leaves at the same time, but there are some colors that are known to cause higher amounts of photosynthesis than others. Chlorophyll is the cause of each plant's individual coloring and there are four kinds of pigments that create the chlorophyll. They are called Chlorophyll A, Chlorophyll B, Xanthophyll, and Carotene. Some leaves have more of a certain color pigment than they have of others, creating leaves that are bright green, blue-green, yellow-green or even orange or red. This pigmentation makes no difference with photosynthesis.

Different Color Light Affects Plants Differently

  • The color that has the highest influence on photosynthesis is blue, which is why many plant growers use blue lights to grow indoor plants. Red light is next best for photosynthesis and yellow light creates the lowest amount of light absorption. When tests are done on photosynthesis rates it is crucial to create an experiment where natural light cannot touch the leaf that is being exposed to differing colors of light. Any light that is not a part of the experiment itself should be carefully screened from the experimentation area. An absolutely dark room is essential and the use of white light as a control for the experiment is needed because white light is also a part of the spectrum of variants and serves for a control element in the experiment.

Adequate Lighting and Plant Growth

  • If a plant does not receive adequate light it will attempt to reach the light by growing taller. This results in a taller yet paler plant compared to other specimens of the same species that did receive adequate light from the time they sprouted until they began to leaf out. If you place a bucket upside-down over the top of a young plant and leave it that way, the result will be a very tall and usually bent over plant with very unnaturally pale coloring. When it is exposed to sunlight, however, the same plant will adapt to its new environment and begin to produce more chlorophyll through photosynthesis from sunlight.

 

 

CO2

 

rate of photosynthesis plotted against carbon dioxide concentration. the rate begins to slow as the carbon dioxide concentration continues to increase

 

Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. If CO2 is added the graph will keep going up until about .10% CO2. At this point the graph will plateau out. 

 

How plants adapt to varying CO2:

Alpine plants of Oxyria digyna have higher apparent photosynthesis rates at various carbon dioxide concentrations than arctic, sea-level plants of the same species. The ability to utilize carbon dioxide effectively at low concentrations may be involved in the survival of plants at high elevations.

Oxyria Digyna: (mountain sorrel, wood sorrel, Alpine sorrel or Alpine mountainsorrel) is common in the tundra of Arctic. Further south, it grows in high mountainous areas like the Alps, Sierra Nevada, and Cascade Range.

It grows in dense tufts, with stems 10-20 cm high. Both flowering stems and leaf stalks are somewhat reddish. Leaves are kidney-shaped, somewhat fleshy, on stalks from the basal part of the stem. Flowers are small, green and later reddish, and are grouped in an open upright cluster. The fruit is a small nut, encircled by a broad wing which finally turns red. Forming dense, red tufts, the plant is easily recognized. Grows in wet places protected by snow in winter. Oxyria (from Greek) means sour.

 

Temperature

 

rate of photosynthesis plotted against temperature. the rate begins to slow as the temperature continues to increase

If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.

Furthermore, the rate drops if the temperature is too high because photosynthesis requires an enzyme, in both light and light independent reactions. The light reactions use ATP synthase, while Rubisco is found in the "dark reactions". Since these are both enzymes, a temperature too high will cause them to denature, which brings down the rate. The optimal temperature that gives the highest rate of reactions is 25 degrees Celcius.

This picture shows the details in the photosynthesis process, and how temperature affects it more specifcally at certain points. For example, it points and helps us to visualize that at 25 degrees C, the rate is at its optimum. This explains why the area saturated with the most plant life surrounds the equator in rainforests, due to the optimal temperature that plants have adapted to taking advantage of. 

 

Water

Water effects the rate of photosynthesis because water is one of the reactants in the photosynthesis reaction. If not enough water is being pulled out of the ground via the roots and up the plant through the xylem, then the leaves and plant might become dehydrated. If this happens, then the stoma on the leaves of the plant will close shut in order to conserve the water in the plant, as water is constantly exiting the plant through the stoma. When the stoma of the plant are shut, this also prevents CO2 in the air from entering the plant, and as a result, the rate of photosynthesis plummets.

 

 

 

 

 

 

This is a picture of a closed and open stoma. The top picture is a closed stoma and the bottom picture  is an open stoma.

 

 

Humidity 

The effect of humidity on the rate of photosynthesis in a plant is very similar to that of water. If there is a lot of humidity in the air around the plant, less water from the plant evaporates. This allows the plant to open its stoma wider because there is no risk of losing excessive amounts of water. Because of this, the rate of photosynthesis increases as the humidity increases. Another factor of the humidity in the air is that the ground can be more moist, so the plant's roots can extract more water from the ground.

 

This diagram looks at the 3 (main) factors that effect the rate of photosynthesis as a whole.

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