BIOLOGY

Photosynthetic cells

Cells get their nutrients from the environment but where do those nutrients come from? It comes from organic material produced by the cells that convert energy from the Sun into energy-containing macromolecules. This process is called photosynthesis.

Photosynthesis is essential to the global carbon cycle and organisms that conduct photosynthesis represent the lowest level in most food chain.

Photosynthesis is important because it is the process used by plants, algae and certain bacteria to harness energy from sunlight and turn it into chemical energy.

Most living things depend on photosynthetic cells to manufacture the complex organic molecules they require as a source of energy. Photosynthetic cells are quite diverse and include cells found in green plants, phytoplankton, and cyanobacteria.

During the process of photosynthesis, cells use carbon dioxide and energy from the Sun to make sugar molecules and oxygen. These sugar molecules are the basis for more complex molecules made by the photosynthetic cell, such as glucose. Then, via respiration processes, cells use oxygen and glucose to synthesize energy-rich carrier molecules, such as ATP, and carbon dioxide is produced as a waste product. Therefore, the synthesis of glucose and its breakdown by cells are opposing processed.

The building and breaking of carbon-based material from carbon dioxide complex organic molecules (photosynthesis) then back to carbon dioxide (respiration) is part of what is commonly called the global carbon cycle. Indeed..

However, photosynthesis doesn't just drive the carbon cycle it also creates the oxygen necessary for respiring organisms. Interestingly, although green plants contribute much of the oxygen in the air we breathe, phytoplankton and cyanobacteria in the world's oceans are thought to produce between one-third and one half of atmospheric oxygen on Earth.

Photosynthesis takes place in two sequential stages:
1. The light-dependent reactions:
2. The light-independent reactions, or Calvin Cycle.

What is light dependent-reaction?
Light-dependent reactions require sunlight. In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll and converted into stored chemical energy, in the form of the electron carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate) and the energy currency molecule ATP (adenosine triphosphate). The light-dependent reactions take place in the thylakoid membranes in the granum (stack of thylakoids), within the chloroplast.

—In the light-independent reactions or Calvin cycle, the energized electrons Thom the light-dependent reactions provide the energy to form carbohydrates from carbon dioxide molecules.

—The light-independent reactions are sometimes called the Calvin cycle because of the cyclical nature of the process.

—Although the light-independent reactions do not use light as a reactant (and as a result can take place at day or night), they require the products of the light- dependent reactions to function.

—The light-independent molecules depend on the energy carrier molecules, ATP and NADPH, to drive the construction of new carbohydrate molecules.

—After the energy is transferred the energy camier molecules return to the light-dependent reactions to obtain more energized, plactrong in addition, several enzymes of the light independent reactions are acvated by light

THYLAKOIDS tiny compartments found inside of chloroplasts

Photosystems are functional units of photosynthesis, defined by a particular pigment organization and association patterns, whose work is the absorption and transfer of light energy, which implies transfer of electrons.