Respiration is an essential process by which all living organisms release energy. Organisms respire aerobically when oxygen is available and anaerobically when it is lacking.
What is Respiration?
Respiration is the process by which all living cells continuously release energy from glucose.
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.
When cells receive sufficient oxygen, they will respire aerobically.
Glucose and oxygen are converted into carbon dioxide and water, which releases energy.
Glucose + Oxygen ————> Carbon dioxide + Water (+ energy)
C6H12O6 + 6O2 ————> 6CO2 + 6H2O (+ energy)
Aerobic respiration is the most efficient way of releasing energy and takes place in the mitochondria.
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.
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.
Respiration Example Questions
Question 1: Define respiration.
The process by which all living cells release energy from glucose.
Question 2: What is the balanced chemical equation for aerobic respiration?
C6H12O6 + 6O2 ————> 6CO2 + 6H2O
1 mark for products.
1 mark for reactants.
1 mark for balanced equation.
Question 3: Describe the process of anaerobic respiration in yeast cells and give one use in the food and drinks industry.
When there is no oxygen, yeast cells break down glucose into ethanol and carbon dioxide.
Any 1 from:
- Ethanol is used to make alcoholic drinks.
- Carbon dioxide makes bread rise.
Gold Standard Education