Aerobic respirationIB MYP Biology: Revision notes

Respiration is the chemical reaction that releases energy from food. It happens in every living cell, all day and night, in plants, animals and microorganisms. It is not the same as breathing: breathing moves gases in and out of the lungs, but respiration happens inside cells.

Aerobic respiration uses oxygen. Glucose is broken down and the energy stored in it is released. It takes place in the mitochondria, so cells that need a lot of energy, such as muscle cells, contain many mitochondria.

Word equation:

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

Balanced symbol equation:

$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$

Count the atoms to check it balances: 6 C, 12 H and 18 O on each side. The reaction releases energy, so it is an exothermic reaction, and some of that energy is transferred to the surroundings as heat.

Glucose comes from digested food (in animals) or from photosynthesis (in plants). It is carried to the cells in the blood. Oxygen is taken in through the lungs (or the leaves and roots in plants) and is carried by red blood cells.

Carbon dioxide leaves the cells, travels in the blood to the lungs, and is breathed out. Water is either used by the cell or lost, for example in breath and sweat.

When you exercise, your muscles respire faster, so your heart rate and breathing rate increase to deliver more oxygen and glucose and to remove more carbon dioxide.

The energy released in respiration is used for:

• movement: muscle contraction in animals
• warmth: keeping a constant body temperature in mammals and birds
• active transport: moving substances across cell membranes against a concentration gradient
• building molecules: for example joining amino acids to make proteins

Plants also respire. They use the energy for growth, active transport of minerals into the roots and building molecules, but they do not move around like animals.