You probably are aware that plants need sunlight, water, and usually soil to grow, but do you know where they get their food? They make it via photosynthesis and that is extremely important. Photosynthesis is a process that happens in plants that allows them to take energy from the Sun and convert it into chemical energy that can be used by the plants. In fact all the energy humans get from food is derived from the energy that comes directly from plants or indirectly from animals that consume plants. So without the sun and a plant's ability to carry out photosynthesis, there would be no energy to sustain life on earth.

Another reason why photosynthesis is important to humans is that photosynthesis is responsible for the oxygen that we need to breathe. Without the oxygen produced by photosynthesis, the atmosphere would not contain enough oxygen to support human life. If photosynthesis does not occur in plants, then plants cannot synthesize their food, the plants will not produce oxygen, and no animal life will be able to survive due to the absence of oxygen. Humans without oxygen and food, means life on this planet would be extinct.

Plants are considered "autotrophs" because they are able to form nutritional organic substances from simple inorganic molecules such as carbon dioxide by using energy from sunlight to make their own food source, glucose molecules, that go on to form starch and cellulose for example. Gardeners may think they are "feeding" a plant when it gets planted in soil, watered, fertilized and planted in the sunlight. But these things are not considered food by the plant. Rather, plants use sunlight, water, and carbon dioxide in the air to make glucose, a form of sugar that plants need to survive. Fertilizer added as "plant food" to plants simply provides minerals and micronutrients needed for adequate development.

This sunlit process called photosynthesis is performed by ALL plants, including algae, and some microorganisms. For photosynthesis to take place, plants need three things: carbon dioxide, water, and sunlight. By taking in water H2O through the roots, carbon dioxide CO2 from the air, and light energy from the Sun, plants use photosynthesis to make glucose (sugars) and oxygen.

Animals and humans breathe the oxygen formed via respiration. During respiration all of the gases in the atmosphere are inhaled, but only oxygen is retained. Plants on the other hand, take in carbon dioxide from the atmospheric gases. Carbon dioxide enters through tiny holes in a plant’s leaves called stomata. Plants also require water in addition to the carbon dioxide to make their food, sugar.

The last requirement for photosynthesis is an important one that comes from the Sun since it provides the energy to make sugars. This energy from sunlight enables a chemical reaction that combines molecules of carbon dioxide and water to make the sugar (glucose) and releases oxygen gas. The oxygen that is produced is released from the same tiny stomata holes through which the carbon dioxide entered. The oxygen released is used by humans and animals for their survival. As plants grow and are consumed by humans and animals or used as components in other things such as wood in structures, the impact of plant photosynthesis goes on and on.

Though some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 19th century. The equation for photosynthesis is:

The whole process of photosynthesis is a transfer of energy from the Sun to a plant. In each sugar molecule created, there is a little bit of the energy from the Sun, which the plant can either use or store for later. Plants can harvest sunlight because they have cells called chloroplasts that are full of the green pigment chlorophyll, it is green in color because the chloroplasts absorb red and blue light leaving green. When the Sun’s rays hit plants, they absorb the light’s red and blue colors but not the green, which gets reflected, giving most plants their distinctive green color as observed by human eyes. Chloroplasts are unique to plants, and they are where photosynthesis takes place.

Plants use the sugars they make to fuel their growth and combine them into more complex molecules like cellulose to make other materials. This process of taking carbon dioxide from the air and using it to make large molecules makes plants extremely useful. Ironically, photosynthesis also was behind many of the world’s fossil fuels that were formed from decayed prehistoric plants and animals.

Through photosynthesis in their leaves, trees take in carbon dioxide and water and use the energy of the sun to form sugars that feed the tree. The tree releases oxygen produced as a by-product. It is suggested that one large tree can provide a day’s supply of oxygen for up to four people. In releasing oxygen, the tree provides an essential gift of life for all living things, the ability to remove a potentially harmful gas like carbon dioxide from the air. Trees also store carbon dioxide in their internal fibers. According to the Arbor Day Foundation, in one year a mature tree will absorb more than 48 pounds of carbon dioxide from the atmosphere while releasing oxygen by photosynthesis.

Photosynthesis by plants, algae, and some bacteria, play a key ecological role in that their photosynthesis affects the makeup of Earth’s atmosphere. The considered arrival of photosynthesis in bacteria is estimated at over 3-4 billion years ago when life forever changed on Earth. Those bacteria gradually released oxygen into Earth’s oxygen-poor atmosphere, and that increase in oxygen concentration is thought to have influenced the evolution of life forms that used oxygen for cellular respiration.

Photosynthetic plants also remove large quantities of carbon dioxide from the atmosphere and use the carbon atoms to build larger organic molecules. Without Earth’s abundance of plants and algae that continually take up carbon dioxide, that gas would build up in the atmosphere. Many scientists believe that preserving forests and other expanses of vegetation are increasingly important to combat the rise in carbon dioxide levels that may be affecting earth’s atmosphere.

Through photosynthesis plants build their "food" that humans consume to thrive. Humans, other animals, fungi, and some microorganisms cannot make food in their own bodies like plants so they totally rely on plant photosynthesis. For example, when eating something such as chicken, humans are indirectly transferring energy from the sun into their bodies because, at some point, plants were consumed by the chicken. So the next time you grab a snack to replenish your energy, think about how plants created the snack, and thank the Sun for it.

In actuality, details of the enormously complex photochemistry of plants fill many volumes in scientific literature. Hopefully this introduction to plant photosynthesis and the role it plays in life peaked your interest.