Molecular Biology

A Short Introduction to Photosynthesis



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Photosynthesis is a complex process whereby plants, algae and some bacteria receive energy from the sun. The energy from sunlight is used to synthesize carbon dioxide and water into glucose and oxygen.

Photosynthesis converts electromagnetic energy from sunlight into a chemical energy stored in glucose and oxygen. The chemical reaction for photosynthesis is six molecules of carbon dioxide plus six molecules of water plus light energy produces one molecule of sugar plus six molecules of oxygen or 6 CO2 + H2O + light energy produces C6H12O6 + 6O2.

Photosynthesis in plants takes place in the chloroplasts, usually within leaf cells. Leaves obtain CO2, or carbon dioxide, from the air. Chloroplasts absorb different wavelengths of light according to the type of molecules within the chloroplasts. Chlorophyll is the molecule within the leaf or plant cell that captures light, which usually shows up as green to the human eye, but however is reflected blue and red light.

The leaves

The leaves of plants can be thought of as solar collectors. Leaves receive water and carbon dioxide from the atmosphere and convert to glucose and oxygen. Leaves themselves are complex organisms that are made up of cuticles, an upper and lower epidermis, palisade mesophyll cells and spongy mesophyll cells, a bundle sheath cell, the guard cell, xylem, phloem, the stroma and veins. Most of the leaf's chloroplasts are located in the mesophyll cells and most photosynthesis takes place in the these mesophyll cells.  

The chloroplasts

The chloroplasts are made up of the stroma, thylakoids, granum (stack of thylakoids), an intermembrane space, and the inner and outer membranes. The thylakoids are the structural units of photosynthesis. The thylakoids are located within the stroma, usually piled on top of each other in stacks called the granum. Chlorophyll is located in the membranes of the thylakoids.

Two parts to photosynthesis

There are two parts to photosynthesis: The light reaction and the dark reaction. The light reaction takes place in the thylakoid, where light energy is converted to chemical energy. The pigments such as chlorophyll and beta-carotene are located in the thylakoid and involved in the light reaction. The dark reaction takes place in the stroma and converts carbon dioxide to sugar.

Carbon sinks

Plants act as carbon sinks that absorb carbon dioxide from the atmosphere and also produce some oxygen through respiration. Animals produce carbon dioxide and plants absorb carbon dioxide and release oxygen. Therefore plants are important to the environmental cycle of carbon dioxide and oxygen with the process of photosynthesis, which converts carbon dioxide and water to sugar and oxygen, which are important components for the lives of humans and animals. Deforestation has contributed to global warming and climate change due to fewer leaves which would absorb the dangerous carbon dioxide levels that are now in the atmosphere. With less CO2 absorption and the lack of photosynthesis there is also less oxygen in the air for humans and animals to breathe.

Photosynthesis is an important and highly complex process whereby plants, algae and some bacteria receive energy in the form of glucose and oxygen from the sun. The photosynthesis process is needed by plants and animals for the survival of the planet.  Therefore, plants and trees are extremely important so that photosynthesis can take place.

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  • InfoBoxCallToAction ActionArrowhttp://www.emc.maricopa.edu/faculty/farabee/biobk/biobookps.html
  • InfoBoxCallToAction ActionArrowhttp://biology.clc.uc.edu/courses/bio104/photosyn.htm