10 Fascinating Photosynthesis Facts

Glucose isn't just food.

While the sugar glucose is used for energy, it has other purposes, too. For example, plants use glucose as a building block to build starch for long-term energy storage and cellulose to build structures.

Leaves are green because of chlorophyll.

The most common molecule used for photosynthesis is chlorophyll. Plants are green because their cells contain an abundance of chlorophyll. Chlorophyll absorbs the solar energy that drives the reaction between carbon dioxide and water. The pigment appears green because it absorbs blue and red wavelengths of light, reflecting green.

Chlorophyll isn't the only photosynthetic pigment.

Chlorophyll is not a single pigment molecule, but rather is a family of related molecules that share a similar structure. There are other pigment molecules that absorb/reflect different wavelengths of light.

Plants appear green because their most abundant pigment is chlorophyll, but you can sometimes see the other molecules. In the autumn, leaves produce less chlorophyll in preparation for winter. As chlorophyll production slows, leaves change color. You can see the red, purple, and gold colors of other photosynthetic pigments. Algae commonly display the others colors, too.

Plants perform photosynthesis in organelles called chloroplasts.

Eukaryotic cells, like those in plants, contain specialized membrane-enclosed structures called organelles. Chloroplasts and mitochondria are two examples of organelles. Both organelles are involved in energy production.

Mitochondria perform aerobic cellular respiration, which uses oxygen to make adenosine triphosphate (ATP). Breaking one or more phosphate groups off of the molecule releases energy in a form plant and animal cells can use.

Chloroplasts contain chlorophyll, which is used in photosynthesis to make glucose. A chloroplast contains structures called grana and stroma. Grana resemble a stack of pancakes. Collectively, grana form a structure called a thylakoid. The grana and thylakoid are where light-dependent chemical reactions occur (those involving chlorophyll). The fluid around the grana is called the stroma. This is where light-independent reactions occur. Light independent reactions sometimes are called "dark reactions," but this just means light isn't required. The reactions can occur in the presence of light.

The magic number is six.

Glucose is a simple sugar, yet it is a large molecule compared to carbon dioxide or water. It takes six molecules of carbon dioxide and six molecules of water to make one molecule of glucose and six molecules of oxygen. The balanced chemical equation for the overall reaction is:

6CO₂(g) + 6H₂O(l) → C₆H₁₂O₆ + 6O₂(g)

Photosynthesis is the reverse of cellular respiration.

Both photosynthesis and cellular respiration yield molecules used for energy. However, photosynthesis produces the sugar glucose, which is an energy storage molecule. Cellular respiration takes the sugar and turns it into a form both plants and animals can use.

Photosynthesis requires carbon dioxide and water to make sugar and oxygen. Cellular respiration uses oxygen and sugar to release energy, carbon dioxide, and water.

Plants and other photosynthetic organisms perform both sets of reactions. In the daytime, most plants take carbon dioxide and release oxygen. During the day and at night, plants use oxygen to release the energy from sugar, and release carbon dioxide. In plants, these reactions aren't equal. Green plants release much more oxygen than they use. In fact, they are responsible for the Earth's breathable atmosphere.

Plants aren't the only organisms that perform photosynthesis.

Organisms that use light for the energy needed to make their own food are called producers. In contrast, consumers are creatures that eat producers to get energy. While plants are the best-known producers, algae, cyanobacteria, and some protists also make sugar via photosynthesis.

Most people know algae and some single-celled organisms are photosynthetic, but did you know some multicellular animals are, too? Some consumers perform photosynthesis as a secondary energy source. For example, a species of sea slug (Elysia chlorotica) steals photosynthetic organelles chloroplasts from algae and places them into its own cells. The spotted salamander (Ambystoma maculatum) has a symbiotic relationship with algae, using the extra oxygen to supply mitochondria. The oriental hornet (Vespa orientalis) uses the pigment xanthoperin to convert light into electricity, which it uses as a sort of solar cell to power nighttime activity.

There is more than one form of photosynthesis.

The overall reaction describes the input and output of photosynthesis, but plants use different sets of reactions to achieve this outcome. All plants use two general pathways: lights reactions and dark reactions (Calvin cycle).

"Normal" or C₃ photosynthesis occurs when plants have lots of available water. This set of reactions uses the enzyme RuBP carboxylase to react with carbon dioxide. The process is highly efficient because both the light and dark reactions can occur simultaneously in a plant cell.

In C₄ photosynthesis, the enzyme PEP carboxylase is used instead of RuBP carboxylase. This enzyme is useful when water may be scarce, but all of the photosynthetic reactions can't take place in the same cells.

In Cassulacean-acid metabolism or CAM photosynthesis, carbon dioxide is only taken into plants at night, where it is stored in vacuoles to be processed during the day. CAM photosynthesis helps plants conserve water because leaf stomata are only open at night, when it's cooler and more humid. The disadvantage is the plant can only produce glucose from the stored carbon dioxide. Because less glucose is produced, desert plants using CAM photosynthesis tend to grow very slowly.

Plants are built for photosynthesis.

Plants are wizards as far as photosynthesis is concerned. Their entire structure is built to support the process. The plant's roots are designed to absorb water, which is then transported by a special vascular tissue called xylem, so it can be available in the photosynthetic stem and leaves. Leaves contain special pores called stomata that control gas exchange and limit water loss. Leaves may have a waxy coating to minimize water loss. Some plants have spines to promote water condensation.

Photosynthesis makes the planet liveable.

Most people are aware that photosynthesis releases the oxygen animals need to live, but the other important component of the reaction is carbon fixation. Photosynthetic organisms remove carbon dioxide from the air. Carbon dioxide is transformed into other organic compounds, supporting life. While animals exhale carbon dioxide, trees and algae act as a carbon sink, keeping most of the element out of the air.

Photosynthesis Key Takeaways

• Photosynthesis refers to a set of chemicals reactions in which energy from the sun changes carbon dioxide and water into glucose and oxygen.
• Sunlight is most often harnessed by chlorophyll, which is green because it reflects green light. However, there are other pigments that also work.
• Plants, algae, cyanobacteria, and some protists perform photosynthesis. A few animals are photosynthetic, too.
• Photosynthesis may be the most important chemical reaction on the planet because it releases oxygen and traps carbon.