One of the most defining characteristics of plants is that they are completely dependent on light for photons, which are used in order to perform a process called photosynthesis that produces a variety of sugars that are needed for the plant to grow. While all plants need light in order to grow and produce food, different plant species need different amounts of light.
Light is the transfer of energy through space. Light is usually thought of by physicists to be the fastest traveling force in existence. Atoms and molecules have the ability to absorb this energy and take in photons. The electrons, neutrons and protons that make up the photons have the potential to form new atoms that make up a variety of elements.
Leaves are plant structures usually found attached to the stem or branches. These leaves are usually flat and thin. There is debate over why leaves are flat: Some researchers think flat leaves evolved to absorb more light; others think this evolution occurred so leaves could absorb more carbon dioxide, which is necessary for leaves to perform photosynthesis. Leaves are made up of the epidermis, which covers the top and bottom parts of the leaf, the mesophyll, which contains the chloroplasts needed for photosynthesis, and the veins, which deliver water and nutrients to and from the leaves. Leaves are usually green because of the color of the chlorophyll within them. The greenness is because chlorophyll is good at absorbing blue and red but does not absorb as much green, and green light is reflected back to the eyes.
Photosynthesis occurs in the chlorophyll of the leaf when one photon is absorbed and one electron is lost. This causes a chain reaction of photons and electrons moving from pheophytin to quinone, leading to nicotinamide adenine dinucleotide phosphate (NADP) found in the plant. This initiates the Calvin Cycle, a long series of chemical reactions that eventually leads to the creation of starch, glucose, fructose and sucrose.
Starch is a train of glucose units bound together and is used as a form of storable energy in all green plants. This starch is considered the most important carbohydrate in the human diet. Glucose is the simple sugar that is the primary source of energy for all organisms. Fructose is the sweetest carbohydrate. Combined with glucose, fructose becomes sucrose, which is what is known as table sugar.
Plant growth occurs in a structure found in the plant cells called the vacuole. This is the largest part of the plant cell and contains most of the sugars, amino acids and amino compounds. The growth of the plant is dependent on the accumulation of these sugars, allowing for the expansion of plant cells. Plants that photosynthesize need enough light to maintain their leaves and root systems in order to survive and continue to grow. The amount of light a particular species of plant needs depends on where that plant originated from and how much sunlight the environment provided.