For living organisms, there are two sources of energy: light and food. Light is used by plants so that they can create their own food, and therefore their own energy, through photosynthesis. Plants are autotrophic organisms.
As for food, it's the source used by other living organisms, such as animals, which cannot produce their own energy. They will thus use cellular respiration to extract the energy they need from food.
Photosynthesis is a synthesis reaction that takes place in plant cells. This reaction allows plants to produce glucose using solar energy.
This process is mainly achieved through chlorophyll, a pigment contained in the chloroplasts of plant cells, which give plants their green colour. This pigment is responsible for capturing light energy.
Plants are also called producers. They are the first link in the food chain since they have the capacity to transform simple molecules into complex molecules (synthesis reaction).
The equation for the photosynthesis reaction is as follows.
|
|6 \space CO_{2(g)}| |
|+| |
|6 \space H_{2}O_{(l)}| |
|+| |
|\text {Energy}| |
|\rightarrow| |
|C_{6}H_{12}O_{6(s)}| |
|+| |
|6 \space O_{2(g)}| |
|
Carbon dioxide |
|
Water |
|
Light |
|
Glucose |
|
Oxygen |
In this synthesis reaction, the inputs are water and carbon dioxide, as these are the molecules that react together to form new substances under specific conditions (such as the presence of light). As for oxygen and glucose, these are the outputs of the reaction. The oxygen will be released into the air and will contribute to the survival of living organisms while the glucose will be used by the producer as a source of energy.
Cellular respiration is a combustion reaction taking place in the mitochondria of cells that converts glucose into energy.
The cells will use the energy produced during cellular respiration to carry out the various activities required to ensure their survival.
Cellular respiration can be compared to that of the combustion of a piece of wood. In a fire, oxygen helps to activate combustion (by acting as an oxidizer) and this will result in the release of energy, especially in the form of heat, and in the discharge of water and carbon dioxide.
The equation for cellular respiration is as follows.
|
|C_{6}H_{12}O_{6(s)}| |
|+| |
|6 \space O_{2(g)}| |
|\rightarrow| |
|6 \space CO_{2(g)}| |
|+| |
|6 \space H_{2}O_{(l)}| |
|+| |
|\text {Energy}| |
|
Glucose |
|
Oxygen |
|
Carbon dioxide |
|
Water |
|
|
In this combustion reaction, the inputs are glucose and oxygen. Carbon dioxide, water, and energy are the outputs of the reaction. The chemical energy thus extracted is more readily available for use by the cell than it was in the form of glucose.
The photosynthesis chemical equation is the reverse of the cellular respiration chemical equation.