The term photosynthesis comes from the Greek words φῶς or phōs, which means “light”, and σύνθεσις, or synthesis, which means “putting together.”
Photosynthesis takes place within plants; particularly within the delicate mesophyll tissue, that makes up part of the leaves of green plants (Leaves are made up of mesophyll tissue, epidermal tissue, which covers the whole plant, and xylem and phloem which transport water, minerals and sucrose around the plant).
During the photosynthesis chemical reaction, carbon dioxide and water are converted into glucose (the plant’s food) and oxygen. The reaction requires light energy, which is absorbed by a green substance within leaf cells, called chlorophyll. These tiny leaf cells contain chloroplasts, which in turn, hold the chlorophyll.
Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.
Three factors can limit the speed of photosynthesis – the sunlight’s strength, carbon dioxide concentration and temperature. Without enough light, even if there is plenty of water and carbon dioxide, a plant cannot photosynthesise fast enough. The higher the sunlight levels and intensity, the faster the speed of photosynthesis will be. Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. If it gets too cold, the rate of photosynthesis will decrease. Conversely, plants cannot photosynthesise if it gets too hot.
In summary- photosynthesis happens within leaves of all green plants, and occurs to varying degrees of intensity according to four factors-:
1. Sunlight (beating down on the leaves, it provides the energy required for photosynthesis)
2. Chlorophyll (which is contained in the leave’s chloroplasts)
3. Water (which reaches the cells through the xylem)
4. Carbon Dioxide (which diffuses into the leaf)
Photosynthesis is the process which maintains atmospheric oxygen levels, and it supplies all of the organic compounds and most of the energy necessary for all life on Earth. This makes it one of nature’s most important chemical reactions.
Dr Kathryn Bates is a graduate of archaeology and history. She has excavated across the world as an archaeologist, and tutored medieval history at Leicester University. She joined the administrative team at Oxford Open Learning twelve years ago. Alongside her distance learning work, Dr Bates is a bestselling novelist, and an itinerant creative writing tutor for primary school children.