When you get hungry, grab a snack from your fridge or pantry. But what can plants do when they get hungry? You probably know that plants need sunlight, water, and a home (like soil) to grow, but where do they get their food from? You do it yourself!
Plants are called autotrophs because they can use light energy to synthesize or manufacture their own food source. Many people think that they are “feeding” a plant by planting it in soil, watering it, or putting it outside in the sun, but none of this counts as food. Rather, plants use sunlight, water, and the gases in the air to make glucose, a form of sugar that plants need to survive. This process is called photosynthesis and is carried out by all plants, algae and even some microorganisms.
Let’s understand in detail what is photosynthesis and how plant make their own food.
What Is Photosynthesis?
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar.
Most life on Earth depends on photosynthesis. Photosynthesis is the process used by plants, algae and certain bacteria, which capture energy from sunlight to produce oxygen (O2) and chemical energy stored in glucose (a sugar). Herbivores then obtain this energy by eating plants, and carnivores obtain it by eating herbivores.
What Is the Process of Photosynthesis?
During photosynthesis, plants take in carbon dioxide (CO2) and water (H2O) from the air and soil. Within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose. The plant then releases the oxygen back into the air, and stores energy within the glucose molecules.
All green plant tissues can photosynthesize, but in most plants, but the majority of photosynthesis usually takes place in the leaves. The cells in a middle layer of leaf tissue called the mesophyll are the primary site of photosynthesis.
Small pores called stomata—singular, stoma—are found on the surface of leaves in most plants, and they let carbon dioxide diffuse into the mesophyll layer and oxygen diffuse out.
Each mesophyll cell contains organelles called chloroplasts, which are specialized to carry out the reactions of photosynthesis. Within each chloroplast, disc-like structures called thylakoids are arranged in piles like stacks of pancakes that are known as grana—singular, granum.
The membrane of each thylakoid contains green-colored pigments called chlorophylls that absorb light. The fluid-filled space around the grana is called the stroma, and the space inside the thylakoid discs is known as the thylakoid space. Different chemical reactions occur in the different parts of the chloroplast.
Light-dependent reactions vs. light-independent reactions
While there are many steps behind the process of photosynthesis, it can be broken down into two major stages: light-dependent reactions and light-independent reactions.
The light-dependent reaction takes place within the thylakoid membrane and requires a steady stream of sunlight, hence the name light-dependent reaction. Chlorophylls absorb this light energy, which is converted into chemical energy through the formation of two compounds, ATP—an energy storage molecule—and NADPH—a reduced (electron-bearing) electron carrier. In this process, water molecules are also converted to oxygen gas—the oxygen we breathe!
The light-independent stage, also known as the Calvin Cycle, takes place in the stroma, the space between the thylakoid membranes and the chloroplast membranes, and does not require light, hence the name light-independent reaction. During this stage, energy from the ATP and NADPH molecules is used to fix carbon dioxide and produce three-carbon sugars—glyceraldehyde-3-phosphate, or G3P, molecules—which join up to form glucose.
Overall, the light-dependent reactions capture light energy and store it temporarily in the chemical forms of ATP and NADPH end text. There, ATP is broken down to release energy, and NADPH donates its electrons to convert carbon dioxide molecules into sugars. In the end, the energy that started out as light winds up trapped in the bonds of the sugars.
C3 and C4 photosynthesis
Not all forms of photosynthesis are created equal, however. There are different types of photosynthesis, including C3 photosynthesis and C4 photosynthesis.
C3 photosynthesis is used by the majority of plants. It involves producing a three-carbon compound called 3-phosphoglyceric acid during the Calvin Cycle, which goes on to become glucose.
C4 photosynthesis, on the other hand, produces a four-carbon intermediate compound, which splits into carbon dioxide and a three-carbon compound during the Calvin Cycle. A benefit of C4 photosynthesis is that by producing higher levels of carbon, it allows plants to thrive in environments without much light or water.
Why Is Photosynthesis Important?
Photosynthesis is arguably the most important biological process on earth. By liberating oxygen and consuming carbon dioxide, it has transformed the world into the hospitable environment we know today.
Photosynthesis is critical for the existence of the vast majority of life on Earth. It is the way in which virtually all energy in the biosphere becomes available to living things. As primary producers, photosynthetic organisms form the base of Earth’s food webs and are consumed directly or indirectly by all higher life-forms.
Additionally, almost all the oxygen in the atmosphere is due to the process of photosynthesis. If photosynthesis ceased, there would soon be little food or other organic matter on Earth, most organisms would disappear, and Earth’s atmosphere would eventually become nearly devoid of gaseous oxygen.
Why Is Photosynthesis Important to Humans?
Directly or indirectly, photosynthesis fills all of our food requirements and many of our needs for fiber and building materials. The energy stored in petroleum, natural gas and coal all came from the sun via photosynthesis, as does the energy in firewood, which is a major fuel in many parts of the world.
This being the case, scientific research into photosynthesis is vitally important. If we can understand and control the intricacies of the photosynthetic process, we can learn how to increase crop yields of food, fiber, wood, and fuel, and how to better use our lands. The energy-harvesting secrets of plants can be adapted to man-made systems which provide new, efficient ways to collect and use solar energy.
These same natural “technologies” can help point the way to the design of new, faster, and more compact computers, and even to new medical breakthroughs.