To most people, plants are the most obvious organisms using photosynthesis. The photosynthesis process is the ultimate source for the energy that fuels us, the oxygen we breathe and the organic molecules that form our bodies. It is the cornerstone for familiar ecosystems such as tropical forests, grasslands and coral reefs. In fact, each of these terms places an emphasis on the photosynthetic organisms forming the foundation of their respective ecosystem--trees, grasses and corals.
Photosynthesis provides the carbon and energy needed for many ecosystems to survive. This energy and carbon is spread transmitted throughout the ecosystem as the photosynthetic organisms are consumed or decomposed by other organisms.
Photosynthesis only provides food. Photosynthetic organisms such as plants convert the food into energy through cell respiration, just as animals do. Many plants stop photosynthesis during the winter and survive off food reserves produced during the spring and summer.
The sugar molecules produced by photosynthesis are also the building blocks for other organic molecules in living organisms, including proteins, lipids and amino acids.
Photosynthesis occurs only in plants and certain single-celled bacteria and protists. These organisms, along with chemosynthetic bacteria, are considered primary producers and provide the food directly or indirectly for all other organisms.
Location of Photosynthesis
Protists and plants conduct photosynthesis in specialized cell organelles called chloroplasts. Photosynthetic bacteria lack these specialized structures and carry out photosynthesis on the cell membrane.
Photosynthesis produces sugar molecules and releases oxygen from water, carbon dioxide and light energy. The overall equation for photosynthesis is six carbon dioxide molecules plus six water moluecules in the presence of light produces one glucose molecule plus six oxygen molecules (6 CO2 + 6 H2O + light -----> C6H12O6 + 6 O2).
Chlorophyll is the primary pigment of photosynthesis. Chlorophyll is a pigment that energizes electrons using specific wavelengths of light. Other pigments within the plant assist chlorophyll and include xanthophylls and carotenoids.
Chlorophyll breaks water molecules apart to replenish the electron it loses at the beginning of photosynthesis. The oxygen atoms from the water molecule form oxygen gas molecules.
Light and Dark Reactions
Photosynthesis occurs in two separate series of reactions often referred to as the light reactions (light-dependent reactions) and dark reactions (light-independent reactions). The light reactions use light energy to produce energy carrying molecules that provide the chemical energy needed in the dark reactions.
The principal limitations on the rate of photosynthesis are the available water, wavelength and intensity of light; available carbon dioxide; and temperature. Additional limitations to photosynthesis can arise from pH and nutrient levels.