In a typical ecosystem, plants are the producers. Plants take energy from the sun and through a process called photosynthesis, produce food. The food is sugar or glucose. In order to produce glucose, a plant needs the raw materials in order for photosynthesis to occur: light energy from the sun, water from the environment and carbon dioxide from the atmosphere.
Sunlight is the catalyst for photosynthesis. The process occurs primarily in the leaves. The light energy bring about a chemical reaction between water and carbon dioxide that occurs in the chloroplasts within the leaves. Chloroplasts are mini-organs or organelles within the plant cells. The energy splits the water molecules into its two components, oxygen and hydrogen. Oxygen leaves the plant through respiration. This is the source of oxygen in our atmosphere.
Photosynthesis consists of two processes, a light reaction and a dark reaction. As the names would imply, sunlight is required for the light reaction to happen. Without light, the plant is unable to produce energy in the form of adenosine triphosphate (ATP). This is the same energy chemical that we use to fuel any cell process in our bodies.
The dark reaction also occurs within the chloroplasts. This is when sugar is produced. Light isn't necessary as it is for the light reaction, but the product of it is required. ATP, another chemical called NADPH (nicotinamide adenine dinucleotide phosphate-oxidase) and carbon dioxide through a chemical process called the Calvin cycle produce glucose.
Chlorophyll is responsible for channeling the energy necessary for photosynthesis. It is also responsible for the green color of plants. The green color reflects the light waves from the sun which are not absorbed by the plants. In the case of plants, chlorophyll absorbs a mixture of blue and red waves. What we see is the result of what is not absorbed by chlorophyll.
Other agents can affect photosynthesis. Water is often the limited factor. Sunlight and carbon dioxide are readily available to plants. During times of drought or dry conditions, plants must adapt to low water resources. Plants have adapted to this possible stress. The stomata or pores of the leaves are the site of respiration or the exchange of water and gases from within the plant and the atmosphere. Carbon dioxide is taken in, and oxygen is released. During stressful times, plants can close their stomata to limit water loss. They can also open them at night as is the case with desert plants.
Using the three basic ingredients of water, sunlight, and carbon dioxide, plants are able to carry out photosynthesis. The result is glucose so that the plant can grow and perhaps provide food for wildlife and humans. Oxygen is also released into the atmosphere, making life possible. Indeed, without plants, life would cease to exist.