The of a is the amount of biomass produced through photosynthesis per unit area and time by plants, the primary producers. Primary productivity is usually expressed in units of energy (e.g., joules m day ) or in units of dry organic matter (e.g., kg m year ). Globally, primary production amounts to 243 billion metric tons of dry plant biomass per year. The total energy by plants in a community through photosynthesis is referred to as (). Because all the energy fixed by the plant is converted into sugar, it is theoretically possible to determine a plant's energy uptake by measuring the amount of sugar produced. A proportion of the energy of gross primary productivity is used by plants in a process called . Respiration provides a plant with the energy needed for various plant physiological and morphological activities. The general equation for respiration is:
Biomass is a renewable energy source because the energy it contains comes from the sun. Through the process of photosynthesis, chlorophyll in plants captures the sun's energy by converting carbon dioxide from the air and water from the ground into carbohydrates, complex compounds composed of carbon, hydrogen, and oxygen. When these carbohydrates are burned, they turn back into carbon dioxide and water and release the sun's energy they contain. In this way, biomass functions as a sort of natural battery for storing solar energy. As long as biomass is produced sustainably—with only as much used as is grown—the battery will last indefinitely.
This process is extremely important for life on earth as it provides the oxygen that all other life depends on.
Just like humans and other living things, plants also need this food for many things. Let's see a few:
Glucose resulting from photosynthesis is used during respiration to release energy that the plant needs for other life processes.
The plant cells also convert some of the glucose into starch for storage. This can then be used when the plant needs them. This is why dead plants are used as biomass, because they have stored chemical energy in them)
Glucose is also needed to make other chemicals such as proteins, fats and plant sugars that are all needed for the plant to carry out essential growth and other life processes.
“Photosynthesis has evolved in plants, algae and some other bacteria and in each case the mechanism does the best possible job for the organism in question,” said BBSRC’s Director of Research Janet Allen. “However, there are trade-offs in nature, which mean that photosynthesis is not as efficient as it could be—at around only 5 percent, depending on how it is measured. There is scope to improve it for processes useful to us by, for example, increasing the amount of food crop or energy biomass a plant can produce from the same amount of sunlight. This is hugely ambitious research, but if the scientists we are supporting can achieve their aims, it will be a profound achievement.”
Photosynthesis can be measured in many ways as it involves the production of oxygen, the uptake of carbon dioxide and an increase in biomass. For example, aquatic plants release oxygen bubbles during photosynthesis and so these can be collected and measured. The uptake of carbon dioxide is more difficult to measure so it is usually done indirectly. When carbon dioxide is absorbed from water the pH of the water rises and so this can be measured with pH indicators or pH meters. Finally, photosynthesis can be measured through an increase in biomass. If batches of plants are harvested at a series of times and the biomass of these batches is calculated, the rate increase in biomass gives an indirect measure of the rate of photosynthesis in the plants.