Overview of Photosynthesis


Light EnergyWord Origin

From the Greek: photo, “light”, and synthesis, “putting together”.

Definition of Photosynthesis

Photosynthesis is the process by which green plants, algae and some forms of bacteria make carbohydrates from carbon dioxide, water and inorganic salts, in the presence of chlorophyll, using light energy captured from the sun.

Need a definition that is easier to understand?

Photosynthesis is the process by which plants and some organisms produce their own food using carbon dioxide, water and energy from sunlight.

General Equation for Oxygenic Photosynthesis

General Photosynthesis Equation




Which means….

carbon dioxide + water + light energy ——> glucose + oxygen + water

Lets take a closer look at this equation…

Six molecules of carbon dioxide and twelve molecules of water, are consumed, while glucose, six molecules of oxygen and six molecules of water are produced.

The equation above shows that water is both a reactant and a product of photosynthesis. Because twelve molecules of water are consumed and six molecules of water are produced, the equation can be simplified as shown below.

Simplified Photosynthesis Equation




This is the equation that is most widely used.

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Oxygenic vs. Anoxygenic Photosynthesis

Organisms capable of synthesizing their own food from inorganic substances, using sunlight as a source of energy are called Photoautotrophs. Most photosynthetic organisms or photoautotrophs, absorb carbon dioxide and produce oxygen. This is known a oxygenic photosynthesis. There are some species of bacteria, however, that perform anoxygenic photosynthesis. This means that they consume carbon dioxide but do not release oxygen.

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Why is Photosynthesis important?

Photosynthesis is vital for maintaining life on earth and can be considered as the ultimate source of energy for nearly all living creatures.

Carbohydrates which are derived from photosynthesis are necessary for the growth and development of plants and animals.

Photosynthesis is responsible for maintaining oxygen levels in the atmosphere. Oxygen, which is crucial to human survival, is a by-product of photosynthesis.

Green plants help to balance global temperatures by absorbing excess carbon dioxide in the atmosphere all in an effort to perform photosynthesis.

Discovery of Photosynthesis

Although photosynthesis has existed since the beginning of time, it was not discovered until the 1800s.

Photosynthesis was partially discovered in the 1600’s by Jan Baptista van Helmont. His 5-year experiment proved that plants need water to grow.

John Priestly, a chemist, also conducted experiments that contributed to the discovery of photosynthesis. His experiments proved that air contains oxygen.

In the 1770s, Jan Ingenhousz performed a series of experiments that proved that plants produce oxygen.

In 1796, Jean Senebier, a Swiss botanist, demonstrated that plants absorb carbon dioxide and release oxygen with the help of sunlight.

Julius Robert Mayer, a German physician and physicist, proposed that plants convert light energy into chemical energy.

Between 1862-64 Julius Sachs investigated how starch is produced using light and in relation to chlorophyll. He eventually wrote the general equation for photosynthesis.

It is important to note that many other scientists and researchers contributed to the discovery of photosynthesis through experiments that were conducted over a period spanning more than 200 years.

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