Photosynthesis is the process by which plants, algae and photosynthetic bacteria use the energy from the sun and convert it into chemical energy that is used by plants and other living organisms that depend on them. The process of photosynthesis absorbs carbon dioxide (CO2) from the atmosphere and releases oxygen. The process of photosynthesis occurs in chloroplasts, which are organelles within certain cells, where pigment molecules known as chlorophyll absorb sunlight. For photosynthesis to occur, plants must use carbon dioxide, water and light to produce glucose and oxygen.
Light from the sun
The primary source of energy for most life on Earth is the sun. The energy from the sun is received on the biosphere by the process of photosynthesis. Plants, algae and some types of bacteria use photosynthesis to produce organic compounds. When light from the sun reaches a green plant, a number of reactions occur that cause the plant to store energy in the form of sugar molecules. Carbon dioxide and water combine with sunlight to produce oxygen and glucose. Oxygen is needed by all living things on the planet, and glucose is used to fulfill the metabolic needs of various organisms.
Photosynthesis (two-step process)
Photosynthesis occurs in the chloroplasts of plants and algae. Photosynthesis also occurs in single-celled organisms, such as sanctuary, which lack chloroplasts. Photosynthesis reactions are divided into two distinct stages: light-independent reactions, consisting of electron and proton transfer reactions, and light-dependent reactions, also known as the Calvin Cycle, which is the biosynthesis of organic compounds from CO2. Photosynthesis is initiated when a photon is absorbed by an antenna molecule and then transported between large protein complexes in a plant.
This type of reaction occurs when the sun's energy is captured by the plant. During this reaction, one photon is absorbed by a molecule of chlorophyll, losing one electron. This electron is transferred to a pheophytin, which is a modified form of chlorophyll, which then passes the electron to a quinone molecule, starting a flow of electrons along an electron transport chain. The whole process leads to a series of chemical reactions that convert this energy into ATP and NADPH. Water molecules are split in the process, releasing oxygen into the atmosphere as a by-product of the photosynthetic reaction.
Light-independent reaction (Calvin Cycle)
In the-light independent reactions, organic compounds such as carbohydrates are produced from carbon dioxide in a process known as carbon fixation. This reaction occurs when ATP and NADPH are used to manufacture glucose from the synthesis of CO2. This occurs in the stroma of chloroplasts, when CO2 is captured by an enzyme known as RuBisCO. The enzyme attaches one carbon molecule to a five-carbon compound, producing two molecules of three-carbon compounds. These molecules obtain energy from ATP and NADPH, eventually creating one molecule of glucose.
For most plants, when they stop receiving the energy from the sun on a sunny day, such as when the sun hides below the horizon, the light-dependent reaction ceases. The glucose produced during photosynthesis serves two main purposes, including energy reserves for plants during times of scarce sunlight and also as a major component of the structure of plants. According to the freedictionary.com, photosynthesis maintains normal levels of atmospheric oxygen, is the source of organic carbon needed by all organisms and is also the main source of energy for the majority of life on the planet.