The Breath Of Life


Respiration in plants

All living things get the energy they need to live from a chemical reaction called respiration. This process needs glucose as a starting point. First we'll see how respiration works, and then look at how plants use respiration in combination with photosynthesis.


Living cells respire. Aerobic respiration is the chemical reaction used to release energy from glucose. It is called aerobic because oxygen from the air is also needed.

Here is the word equation for aerobic respiration. Energy is put in brackets because it not a substance:

glucose + oxygen → carbon dioxide + water (+ energy)

Interesting point is the word equation for respiration is the reverse of the word equation for photosynthesis.


Plant cells respire, just as animal cells do. If they stop respiring, they will die. Respiration is not the same as breathing. Thus, we need to remember - plants do not breathe.

As we can see from the word equations, respiration and photosynthesis are opposites. Respiration uses oxygen and produces carbon dioxide. Photosynthesis uses carbon dioxide and produces oxygen.

So what happens to a plant overall? This depends on whether it is in the dark or the light, and how bright the light is.

Plants respire all the time, whether it is dark or light. They photosynthesize only when they are in the light.

Photosynthesis usually results in a gain in glucose, after respiration, the plant has consumed the required amount of glucose for its process. This means that there is an increase in the biomass of the plant.

Plants that lose their leaves in winter store food produced during the summer by photosynthesis. They store enough food to last them over winter, and to provide energy reserves for new growth in the spring.

Respiration in animals

Respiration: The biological process in which food is utilized to produce energy is called respiration. Respiration is necessary for survival of the living beings. A living being cannot survive even for a few seconds, without respiration. During respiration, it is mainly the carbohydrates which is oxidized to produce energy. This can be shown by the following equation:

Carbohydrate + Oxygen → Carbon dioxide + Water + Energy

C6H12O6 + 6O2 → 6CO2 + 6H2 + Energy

Site of respiration: Respiration happens inside the cells. As respiration happens inside the cell, it is also called cellular respiration. A cell organelle; called mitochondria; is the site of cellular respiration.

Types of respiration:

Aerobic respiration: Aerobic respiration takes place in the presence of oxygen. Carbon dioxide and water are the end products of aerobic respiration. Aerobic respiration happens in most of the organisms.

Glucose (Presence of oxygen) → Carbon dioxide + Water + Energy

Anaerobic respiration: Anaerobic respiration takes place in the absence of oxygen. Anaerobic respiration usually happens in most of the microbes. Alcohol and carbon dioxide are formed at the end of anaerobic respiration. In some cases, lactic acid is formed at the end of anaerobic respiration.

Glucose (absence of oxygen) → Alcohol + Carbon dioxide + Energy

Glucose (absence of oxygen) → Lactic acid + Energy

Anaerobic respiration also happens in our muscle cells. When someone runs or walks too fast, one may feel a throbbing pain in calf muscles. This happens because of the deposition of lactic acid; produced by anaerobic respiration. Once the person takes rest for some time, the pain goes away.

Breathing: The process of taking in and giving out air; for respiration; is called breathing. Breathing involves two main steps, viz. inhalation and exhalation. During inhalation, we breathe in air which is rich in oxygen. During exhalation, we breathe out air which is rich in carbon dioxide.

Rate of breathing: When we are doing normal activities, the rate of breathing is normal. The rate of breathing increases when we do strenuous physical works; such as running, swimming, jogging, etc. The rate of breathing decreases when we take rest or when we are sleeping.