The Economy of Nature

The only practical source of nonbiological carbon, CO2, has an extremely low concentration in the atmosphere (about 0.03%). Carbon dioxide enters plant cells because there is a higher concentration of CO2 in the atmosphere than there is in the cells, where CO2 is continually used up by photosynthesis. However, the atmosphere-to-plant difference in the concentration of CO2 is much, much less than the plant-to-atmosphere difference in the concentration of water vapor, which drives water out of plant cells into the surrounding air. This makes water conservation a problem for terrestrial plants, especially in arid environments. Plants evaporate 500g of water from their leaves, more or less, for every gram of carbon they assimilate. (p. 30)

Vision and the photochemical conversion of light energy to chemical energy by photosynthetic organisms occur primarily within that portion of the solar spectrum at the earth’s surface that contains the greatest amount of energy. (p. 35)

To function in a complex and changing environment, organisms must be able to sense environmental change, detect and locate objects, and navigate the landscape. A predator must find its fodd before it can eat it. Salmon must recognize the proper river at the end of their spawning migration. Plants must sense the changing season to flower at the right time. The senses an organism uses generally match the types of physical stimuli available in the environment and the ways in which the organism relates to it (plants, for example, don’t need the acute vision that some predators have). (p. 42)

That so many organisms rely on vision to sense the environment is not surprising, considering the high energy levels available in the visible portion of the spectrum and the fact that light travels in straight line, allowing accurate location and resolution of objects. (p. 42)