Explain why the amount of energy used in photosynthesis is so much less that the amount of solar energy...?

Question

that reaches Earth.

This is a question from a summer assignment for a Biology class. In the textbook it says that only 1% of the solar energy that reaches the Earth is used in photosynthesis. However, it doesn't say why the other 99% cannot be or is not used.

Help?

Answer 1

Consider these contributing factors:

1. A large amount of the solar energy that reaches the earth is intercepted before it reaches the surface of the planet.

2. Of that which reaches the surface, a large portion is reflected back into space, especially in areas with high albedo, such as polar regions.

3. Photosynthesis takes place on only a small portion of the earth's surface.

4. Organisms that photosynthesize are usually green, and reflect the peak (versus highest energy) wavelength of our sun's radiation.

These factors alone should explain your quandry.

Answer 2

Every time energy is transferred from one molecule to another there is always lost energy in the form of heat.  This is in addition to the factors that are listed in the first respondent's answer.  There is never 100% transfer of energy from one molecule to another.

Some of the energy in the green wavelengths is absorbed poorly by most photosynthetic organisms.  Violet and blue wavelengths have the highest energy and are strongly absorbed.  Only a part of the red light is used in photosynthesis.  Of the energy absorbed by the plant, not all of it is converted into organic molecules.