Photosynthesis in Plants

Chlorophyll, the green pigment common to all photosynthetic cells, absorbs all wavelengths of visible light, except green, which it reflects, to be detected by our eyes.

The hydrogen ions also called protons, are made available by splitting up of water. Non-cyclic photophosphorylation needs a constant supply of water molecules. The net result of non-cyclic phosphorylation is the formation of oxygen, NADPH and ATP molecules. Oxygen is produced, as a waste product of photosynthesis.

Carbon dioxide, either in the atmosphere or in solution in surface waters, is the major source of carbon for living organisms. It is converted to organic form, by the autotrophs, which use it as sole carbon source. The most important in this conversion, are the photosynthetic autotrophs (seed plants on land and algae in water) that carry out oxygen producing type of photosynthesis.

Photosynthetic phosphorylation or photophosphorylation is the process of phosphate group transfer into ADP to synthesize energy rich ATP molecule making use of light, as external energy source. Down flow of protons from high to low concentration along H⁺ conc. gradient through ATPase complex, provides the energy that allows an ATP synthase enzyme, to produce ATP from ADP + Pi

The material within the chloroplast, is called the stroma. It contains one or more molecules of small circular DNA. It also contains ribosomes, however most of its proteins, are encoded by genes contained in the host cell nucleus, with the protein products, transported to the chloroplast. The enzymes necessary for carbon fixation, occur in the stroma of the chloroplast.

Photosynthetic phosphorylation or photophosphorylation is the process of phosphate group transfer into ADP to synthesize energy rich ATP molecule making use of light, as external energy source. Down flow of protons from high to low concentration along H⁺ conc. gradient through ATPase complex provides the energy, that allows an ATP synthase enzyme, to produce ATP from ADP + Pi

The energy released in chemical reactions is known as chemical energy. Energy can also be stored in matter as chemical energy which depends on how the particles of matter are arranged. Therefore, chemical energy depends on the positions of objects and is a form of potential energy.

Oxygen and carbon dioxide enter and leave the cell via simple diffusion. Water enters and leaves via osmosis. During the day the leaf takes in carbon dioxide and releases oxygen and water vapour. Since it is also using energy, it will also give off small amounts of carbon dioxide. At night, it is not carrying on photosynthesis, so the oxygen and water vapour, are not being given off. The carbon dioxide that is being produced by respiration, is used in the dark reactions making sugar. Living cells need ATP to carry on active transport. Using energy, ions and small molecules may be pumped into or out of a cell, even against a concentration gradient.

O₂ gas is the by product being produced during photosynthesis . It can only pass out of the leaf through the opened stomata.

Chloroplasts are specialized organelles, found in all higher plant cells. These organelles contain the plant cell's chlorophyll, hence provide the green color. They have a double outer membrane. Within the stroma are other membrane structures - the thylakoids and grana (singular = granum) where photosynthesis takes place.

Light strikes photosystem-2 by exciting the electrons. The electron comes from a water molecule that has been split into hydrogen and oxygen. The excited electrons then travel down a short electron transport chain, and while doing so, they pump H⁺ into the inner thylakoid space across the thylakoid membrane from the stroma. The electrons are then passed, at the end of the transport chain, to photosystem 1, where they are re-excited by light.

The light reaction happens in the thylakoid membrane and converts light energy to chemical energy. This chemical reaction must take place in the light.

The dark reaction takes place in the stroma, within the chloroplast, and converts CO₂ to sugar. This reaction does not directly need light in order, to occur, but it does need the products, of the light reaction (ATP and another chemical called NADPH). The dark reaction involves a cycle, called the Calvin cycle, in which CO₂ and energy from ATP are used, to form sugar.

The plants look green in color, due to the presence of peculiar organelle, referred as chloroplast and presence of light absorbing pigment, such as chlorophyll. The chlorophyll pigment in chloroplast, is capable to trap the sunlight, as primary source of energy, are able to fix the carbon dioxide present in the air and in turn produce the food molecule, in form of glucose or carbohydrates.

Light reactions occur mostly in the thylakoid stacks of the grana. Here, sunlight is converted to chemical energy in the form of ATP (free energy containing molecule) and NADPH (high energy electron carrying molecule).