By Kai Singh
Edited by Sarah Nauman
There are six types of energy users, the two most common being heterotrophs and autotrophs. Humans are heterotrophs that eat other organisms to get energy, while most plants are autotrophs and produce their own energy; this is one of the many differences between humans and plants and how they function. Humans and most animals need oxygen to keep our cells working and create energy. But where does the oxygen come from? It’s a well known fact that plants produce oxygen but the real question is how do these plants produce oxygen? We breathe out carbon dioxide as a waste product of the process our bodies do called cellular respiration. To answer that question in the simplest terms, plants basically do the same thing but instead of using sugar to make energy, plants use energy to make sugar; and that reversed cellular respiration is known as photosynthesis.
So now that we have established that photosynthesis is, in essence, reversed cellular respiration, we need to go more in depth of what that means. We as humans do cellular respiration constantly. In this process we take glucose from food we’ve ingested and we mix it with our oxygen to produce energy, or ATP, water, and carbon dioxide (those last two being waste products that are breathed out and sweated/urinated out.)
Rather, photosynthesis takes energy from the sun and carbon dioxide to produce glucose and water which in turn becomes oxygen. Oxygen is their waste product and is removed through the leaves and the glucose is stored in the plant to be broken down later.
Let's discuss the process of photosynthesis. Carbon dioxide and sunlight is collected by the leaves. After all the materials are collected, the plant enters the first stage of photosynthesis, which is called the light dependent reaction. This reaction takes place in the leaves, specifically in a part of small holes in the leaves called stomata. In those stomata we have thylakoids, which have chlorophyll in their membranes which collects energy from sunlight. This sunlight is converted into chemical energy by creating two molecules called ATP (adenosine triphosphate) which stores energy and NADPH (Nicotinamide adenine dinucleotide phosphate) which is a reduced electron carrier. The waste product of this process is water which is then broken down into oxygen, which is expelled through the stomata.
The next stage of photosynthesis is called the light independent reaction, but your teachers will most likely call it the Calvin cycle.This process occurs in the stromata and doesn’t require light, hence the name. What this process does is take the ATP and NADPH produced beforehand and breaks ATP to release energy and uses NADPH to create three-molecule sugars —glyceraldehyde-3-phosphate, or G3P, molecules— with carbon dioxide, which conjoin and create glucose.
In conclusion, photosynthesis has two main parts; the light dependent reaction and the Calvin cycle. In the light dependent reaction, the reactants -carbon dioxide and sunlight- to make energy (ATP and NADPH). In the Calvin cycle, the ATP is broken down to release energy and the NADPH helps convert the carbon dioxide to make glucose.