Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the Sun, into chemical energy that can be later released to fuel the organisms' activities.owever, not all organisms that use light as a source of energy carry out photosynthesis, since photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon. In plants, algae and cyanobacteria, photosynthesis releases oxygen.
Describe the mechanism of clonal selection. The binding of an antigen receptor to an epitope initiates events that activate the lymphocyte. Once activated, a B or T cell undergoes multiple cell divisions. For each activated cell, the result of this proliferation is a clone.ntibodies and B cell receptors. Antibodies have the same Y-shaped organization as B cell antigen receptors, but they are secreted rather than membrane bound. It is the antibodies, rather than the B cells themselves, that actually help defend against pathogens.
Extracellular molecules such as: hormones; neurotransmitters; cytokines; growth factors; cell recognition molecules; nutrients; or waste products; all react with the archetypical receptor to induce changes in the metabolism and activity of a cell.he seven-transmembrane Î±-helix structure of a G-protein-coupled receptor. Cell surface receptors (membrane receptors, transmembrane receptors) are specialized integral membrane proteins which communicate signals between the cell and the outside world.