Respiration

What is Respiration?

Respiration is the process by which all living cells continuously release energy from glucose.

Animals get their glucose from digested food, plants make their own glucose in photosynthesis. 

Respiration is an exothermic reaction because it releases energy. 

Energy is required for many living processes:

• To build large molecules from smaller ones, e.g. proteins from amino acids, starch and cellulose from glucose.
• To provide movement by contracting their muscles.
• To maintain a warm body temperature that is suitable for enzymes to work efficiently. 

The type of respiration a cell does is dependent on the amount of oxygen it receives. 

Aerobic Respiration

When cells receive sufficient oxygen, they will respire aerobically. 

Glucose and oxygen are converted into carbon dioxide and water, which releases energy.

Word equation:

Glucose   +   Oxygen  ————>  Carbon dioxide   +   Water   (+ energy)

Chemical equation:

C₆H₁₂O₆   +   6O₂    ————>  6CO₂   +   6H₂O   (+ energy)

 

Aerobic respiration is the most efficient way of releasing energy and takes place in the mitochondria.

Anaerobic Respiration

When cells do not receive enough oxygen, they respire anaerobically (without oxygen). 

The glucose is not fully oxidised so it is much less efficient than aerobic respiration and makes different products. 

 

Animals 

In animals, glucose is broken down into lactic acid if there is no oxygen.

Glucose   ————>  Lactic acid   (+ energy)

This often occurs in muscle cells during vigorous exercise as the body cannot supply them with enough oxygen.

 

Plants and Yeast

In plants and yeast cells, glucose is broken down into ethanol and carbon dioxide. 

Glucose   ————>  Ethanol   +   Carbon dioxide  (+ energy)

Anaerobic respiration in yeast cells is called fermentation and is a very important process in the production of food and drinks:

• Ethanol produced from fermentation is a type of alcohol which is used to make beers, wines and other alcoholic drinks.
• Carbon dioxide produced from fermentation is used to make bread rise.