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Why do plants need light?

Plants are beneficial to humans and other animals in a myriad ways. The most commonly thought of benefit, that plants provide, is that they give off oxygen while taking in carbon dioxide. They, namely trees, also provide shade and cooler temperatures. 

Plants are also used in manufacturing products such as paper, lighting, adhesives, medicine, clothing, cosmetics, fuel, charcoal as well as many other products. Additionally, plants provide food for people everywhere. But without light, plants- and life as we know it- would cease to exist. All plants and animals are fully dependent on photosynthesis for their energy. While some carnivores do not eat plants, directly, the vast majority consume animals that subsist on plants. But why exactly do plants need light? How does this miracle process work?

Photosynthesis process

“Plants need light for photosynthesis. Photosynthesis is the process of the plant making its own food,” said Matt Kostelnick, senior horticulturist, at Ambius. Photosynthesis occurs within the chlorophyll inside the chloroplasts. Chloroplasts are the sites of photosynthesis. This is a two-step process: the light reactions and then the Calvin cycle. 

The photosystems involved in the light reactions are: the water-splitting photosystem in which electrons are extracted from water and oxygen is released into the atmosphere. The second photosystem that takes place is what is referred to as the NADPH Photosystem, in which electrons are moved from the chlorophyll to NADP-producing NADPH. Together the two photosystems release energy to the chloroplast, which then uses it to drive cellular processes crucial for plant survival. 

Inside the thick double-membraned layer of the chloroplast is a thick fluid called stroma and inside is an apparatus of stacked green sacs known as grana. This is where the chloroplast molecules capture light energy. The energy from the light is utilized to produce ATP (adenosine triphosphate) as well as NADPH. 

ATP is the cellular molecule that supplies cells with the energy to do work. NADPH is an electron carrier used in the Calvin cycle where it transforms carbon dioxide into high energy sugar which, in turn, is used by cells to make glucose and other needed organic molecules. Alas, memories of high school biology class come flooding in while attempting to accurately recall all that was taught.

How plant leaves help

Kostelnick went on to explain that, “Plant leaves function a lot like solar-panels, instead of creating energy, they are creating food for the plant by harnessing light energy from the sun (or another light source).” 

Kostelnick’s easy to understand interpretation clearly defines the importance of the process utilized by plants and other organisms to convert light energy mainly from the sun, into chemical energy that will be used to fuel the organisms’ life-defining activities.