The first step is known as the light responses because it occurs exclusively in the presence of light. Water is consumed and oxygen is liberated during these first reactions. Sunlight energy is transformed into a little quantity of ATP and an energy carrier known as NADPH. The photosynthetic electron transport chain is composed of several protein complexes inside the cell membrane that use sunlight to oxidize water and reduce carbon dioxide to carbohydrate products, which cells can use for fuel or building materials.
The end product of photosynthesis is not sugar but rather organic compounds such as proteins, fats, and nucleic acids. These are the same molecules that make up all living things, so they are called "organic nutrients." Some organisms cannot synthesize these compounds but instead obtain them from their environment. Others recycle certain elements within themselves for reuse. For example, plants take in carbon dioxide and give off oxygen; animals consume both plants and other animals; and microbes decompose organic matter using energy from chemicals they absorb through their roots or walls. This process is called "biomass recycling". None of these activities would be possible without the help of sunlight because they require the full spectrum of light waves from ultraviolet to visible red to infrared. Only light can activate chemical reactions and drive energy transformations.
Eukaryotes (animals plus fungi) contain more than 95% of all living organisms on earth.
The first step of photosynthesis is the light responses. The energy from light is turned into chemical energy in these processes. The light reactions occur in the thylakoid membrane. Water (a reactant in photosynthesis) is divided, releasing electrons and hydrogen ions (H+). These electrons are used by electron carriers such as ferricyanide to reduce it to cyanide. Cyanide is a strong inhibitor of mitochondrial oxygen evolution, so more oxygen is released than consumed. This creates a large transmembrane potential that can be used by other enzymes to make molecules for storage or export.
The photoreactions continue in the chloroplast until all the red light has been absorbed. At this point, the remaining blue light is filtered out by the next set of membranes, the etioplasts. The green plants we see today contain both chloroplasts and etioplasts. Etio means dark inside; plastids are bodies that contain DNA but cannot divide without special treatment. When the seed germinates, the etiophores break down and the embryo develops within the protective casing of the seed coat.
After the blue light passes through the second set of membranes, it reaches the reaction center proteins in the grana stacks. Here, the photons trigger a cascade of changes in the state of the protein complexes, which eventually results in the formation of NADPH and FAD.
The light processes absorb energy from the sun and convert it into chemical energy, which is stored in NADPH and ATP molecules. As a byproduct of the light processes, oxygen gas is produced. Ozone depletion occurs when ultraviolet B (UVB) radiation from sunlight breaks down ozone molecules. The result is an increase in the amount of UV radiation with wavelengths less than 290 nm at high levels of exposure. This can lead to increased rates of skin cancer.
Solar radiation consists of electromagnetic waves that are part of the spectrum of light. These waves have lengths in time that are comparable to those of electrons moving around inside the atoms that make up matter. Thus, solar radiation is able to cause physical changes inside living organisms. For example, when high-energy photons collide with organic molecules, they can break them apart or rearrange their molecular structures. These changes can be beneficial or harmful depending on what part of the organism is exposed to them. Healthy plant cells will try to protect themselves by producing new molecules that are identical to the ones that were damaged by solar radiation. Sick plant cells won't be able to do this repair work properly and will therefore die.
Human beings are composed of many different types of cells. Some of these cells divide regularly all the time, while others don't divide for much longer periods. Human blood cells only last about 120 days before they must be replaced.
The "light reaction" is the photosynthetic process that turns solar energy into chemical energy in the form of NADPH and ATP. Photosynthesis is the only known natural source of oxygen that we know affects every organism on Earth positively or negatively depending on how much of it they produce. About 10% of the oxygen we breathe is produced this way by plants.
Oxygen is produced when water vapor in the atmosphere absorbs light energy from the sun. The oxygen then combines with other substances to form more stable compounds. This process is called photorespiration because both photons (light particles) and gases are involved. Photons trigger the reaction while gases play a role in its direction. During photorespiration, plants use up some of their precious liquid carbon dioxide supply in order to carry out this reaction.
Some organisms can perform photosynthesis even under low light conditions. These organisms are called autotrophs ("self-feeder"). They do not need any other kind of cell to survive. Autotrophs include most plant and algae species. Some bacteria and fungi are also autotrophic.
In contrast, heterotrophs ("other feeder") must get their energy from outside sources unless they find a way to produce their own using chemicals derived from other molecules.