A simple visual showing the process of photosynthesis.
Photosynthesis refers to the process through which organisms like plants, algae, and some bacteria take in sunlight, carbon dioxide, and water to produce food/energy, oxygen, and other chemical byproducts. This process is extremely important for life on Earth because it’s one of the major sources of oxygen in the atmosphere and the basis for the food chain.
Introduction
Simply put, photosynthesis is the process of capturing light energy to drive chemical reactions. Basically, the process is made up of two stages: the light-dependent reactions and the light-independent reactions, also known as the Calvin cycle.
Light-dependent reactions are the light-capturing process that occurs within the thylakoids in chloroplasts. Light falls on the pigments (like chlorophyll), which capture the energy from the light. In turn, the captured light energy causes the water to split into oxygen and hydrogen. Oxygen gets released into the atmosphere while the hydrogen contributes to making energy-rich molecules.
The energy from these molecules is then used by the light-independent reactions to help turn carbon dioxide from the atmosphere into glucose, a type of sugar. This stage takes place in the stroma of the chloroplasts. Glucose provides energy for the plant and is also a building block for other, more complex carbohydrates.
How Chlorophyll Works
Chlorophyll, which is what gives plants their green color, is responsible for photosynthesis in plants. It is best at absorbing light in both the blue and red parts of the light spectrum, and it reflects green light (thus making leaves look green). When it absorbs light, chlorophyll gets excited, transferring energy to produce a flow of electrons that, through the process of chemiosmosis, drives the production of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), the two critical agents needed in the Calvin cycle.
Water and Carbon Dioxide
Water acts as not only a medium but also as a reactant in photosynthesis. When the water molecules are split, they provide electrons for the light-dependent reactions and release oxygen. Carbon dioxide, taken from the air through the stomata in the leaves, provides the carbon atoms for glucose. The absorption of water and carbon dioxide has to be balanced for efficient photosynthesis.
Energy Transfer
The light energy, captured from the sun, does not remain in the chloroplasts but is converted into chemical energy in the form of ATP and NADPH, which in turn act as a source for the synthesis of organic compounds. This energy transfer process, in a way, is core to all life on Earth, since plants form the basis of the food chain, and herbivores eat the plants and carnivores eat the herbivores. This, technically, passes the captured solar energy along the food chain.
The Environment
Photosynthesis is a very influential process as far as our environment is concerned. Through the absorption of carbon dioxide, plants are considered carbon sinks that help alleviate the effects of climate change. The oxygen they produce also supports all the aerobic life on Earth. Through this process, plants help regulate water cycles by taking up water from the soil and releasing it into the atmosphere through transpiration.
Not all environments are identical in the way photosynthesis is carried out, however. In dense forests, understory plants have adapted to low light conditions, whereas in open fields or in savannahs, plants still need more sunlight. Meanwhile, aquatic plants have adaptations that allow them to deal with the diffusion of gases in water.
Adaptations for Photosynthesis
That being said, various plants have devised a number of ways to ensure that photosynthesis occurs most efficiently. Desert plants, like cacti, have adaptations to conserve water while still permitting photosynthesis. Other plants have leaves that track the sun's movement (heliotropism) to maximize light absorption. When light becomes scarce, plants may produce larger leaves or more chlorophyll to increase the chance of capturing light.
Photosynthesis isn't perfectly efficient. Only about 3-6% of the solar energy hitting a plant is converted into chemical energy. Factors like light intensity, carbon dioxide concentration, temperature, and water availability can limit the process. Too much light can also damage the photosynthetic "machinery", while too little light reduces the amount of energy captured.
Conclusion
Photosynthesis is a very cool biological process that keeps life on Earth going. It is actually a pretty complex interplay of light, water, and carbon dioxide, producing oxygen and carbohydrates in the process. While it supports plant life, it also forms the bedrock of ecosystems, influencing everything from climate to the availability of food.