Photosynthetic organisms capture energy from sunlight to power biochemical reactions. These biochemical reactions provide food for the primary producers.
A photon is a packet of energy that can cause molecules to “excite.” The excited chlorophyll molecule passes this energy on to the reaction center of the photosystem.
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Chlorophyll is a green pigment that gives plants their color and enables them to absorb energy from sunlight. This energy is used to synthesise carbohydrates from water and carbon dioxide in a process called photosynthesis. The photosynthetic reactions take place within the thylakoid membranes of the chloroplast.
During the light-dependent reactions, a chlorophyll molecule loses one of its electrons to another pigment molecule in a process called charge separation. This causes the pigment to become excited and pass on this excitement to another molecule in a process known as photoexcitation.
The different side groups on the chlorophyll molecules allow them to absorb specific wavelengths of light. Chlorophyll a, for example, absorbs blue and red-light waves and reflects green-light waves. It also has a long hydrocarbon tail that allows it to bind to a protein that carries out the rest of the photosynthesis process. Other types of chlorophyll include chlorophyll b, chlorophyll c, and chlorophyll d, which have slightly different absorption spectra.
A carbohydrate is any organic compound containing carbon, hydrogen and oxygen atoms in proportions that approximate the empirical formula Cm(H2O)n (the m is the number of carbon and oxygen atoms). The term is used broadly to include sugars, starches, cellulose, gums and other polysaccharides.
Carbohydrates are the direct products of photosynthesis and are the primary energy storage compounds in plants. They provide energy for plant growth, cell wall formation and oxidative respiration. They are also major constituents of many fruits, vegetables and legumes.
The carbon dioxide that’s incorporated into carbohydrates in photosynthesis is known as “fixed carbon.” Living and dead organisms release carbohydrates into water, contributing to the pool of dissolved organic material in lakes and streams. This material serves as a food source for microorganisms that can incorporate it into other types of organic molecules needed by cells. Carbohydrates can also penetrate the hydrophobic cuticle of a leaf and reach epidermal or guard cells to trigger a number of signaling events and defense reactions.
Oxygen is a colorless, odorless gas that is present in the atmosphere in small quantities. It is formed when two oxygen atoms strongly bind to each other with a covalent double bond to form the molecular species dioxygen or O2. Oxygen also exists as the triatomic molecule ozone or O3. It has a strong affinity for binding to other atoms and molecules and readily forms compounds such as oxides, hydroxides, carbonates and sulfides. It is a weak oxidizing agent and does not burn. Oxygen has two spectrophotometric absorption bands that peak at wavelengths near 687 and 760 nm, which makes it possible for satellites to detect the presence of oxygen in vegetation canopies.
During photosynthesis, plants use oxygen to split water into hydrogen and oxygen, and then convert the hydrogen to sugar in a process called the Calvin cycle. The resulting glucose is a type of sugar that provides energy to living things, including humans and animals. The oxygen produced by photosynthesis is essential for life. It is thought that photosynthetic organisms, such as cyanobacteria, were responsible for the early accumulation of oxygen in Earth’s atmosphere around 2.5 billion years ago.
Water is a key element of photosynthesis, as it helps to build and break down larger molecules in cells. In addition, it transports energy from the Sun to help power photosynthesis.
During photosynthesis, six molecules of carbon dioxide combine with 12 molecules of water (H2O) to form one glucose molecule. A reducing agent, like hydrogen sulfide or carbonate, is also present in this reaction, allowing the plant to extract electrons from the water and produce oxygen.
The released electron travels through a series of protein complexes that create ATP and NADPH, which are then used in the next step of photosynthesis to capture carbon dioxide. During this step, the electron passes through an “electron hole” in the chlorophyll pigment, which is filled by splitting water molecules.