Aerobic respirationIB MYP Sciences: Revision notes
Section 1
What is respiration?
Respiration is the process that releases energy from glucose in all living cells. It is not the same as breathing. Breathing brings oxygen into the body, but respiration is the chemical reaction that takes place inside cells.
Every living cell respires all the time: muscle cells, root cells, even yeast and bacteria. The energy cannot be made, only released from the chemical energy stored in glucose.
Respiration is not breathing. Breathing (ventilation) moves air in and out of the lungs; respiration happens in the cells.
Section 2
The equations for aerobic respiration
Aerobic respiration uses oxygen. Glucose and oxygen react to make carbon dioxide and water, and energy is released.
Word equation: glucose + oxygen → carbon dioxide + water
Symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
The equation is balanced: 6 carbon atoms, 12 hydrogen atoms and 18 oxygen atoms on each side. Glucose and oxygen reach the cells in the blood, and the carbon dioxide is carried away to the lungs and breathed out.
Learn the word equation first. If you are asked for the symbol equation, check that you have 6 O₂ on the left and 6 CO₂ and 6 H₂O on the right.
Section 3
Where respiration happens
In animal and plant cells, most aerobic respiration takes place in the mitochondria (one is called a mitochondrion). These are tiny structures in the cytoplasm.
Cells that need a lot of energy, such as muscle cells and nerve cells, contain many more mitochondria than cells that need little energy. This is why a hummingbird's flight muscles or a runner's leg muscles are packed with them.
Section 4
What the energy is used for
The energy released by respiration is used for:
- Movement, such as muscle contraction
- Keeping warm: birds and mammals keep a constant body temperature
- Active transport, moving substances into cells
- Building large molecules, such as proteins from amino acids
- Growth and repair of cells
Plants do not move, but they still respire to build molecules and take up minerals through their roots.
Section 5
Respiration and exercise
When you exercise, your muscle cells respire faster to release more energy. This means they need more glucose and oxygen and make more carbon dioxide. Your breathing rate and heart rate both go up to deliver oxygen and glucose more quickly and to remove the carbon dioxide.
Worked example: A student's heart rate is 70 beats per minute at rest and 140 during a run. The heart pumps blood twice as fast, so the muscles receive oxygen about twice as quickly.
Must Know
- Respiration releases energy from glucose in all living cells
- Word equation: glucose + oxygen → carbon dioxide + water
- Symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
- Most aerobic respiration happens in the mitochondria
- Energy is used for movement, warmth, active transport and building molecules
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Aerobic respiration
- A long-distance runner in Nairobi trains every morning. Her muscle cells release energy from glucose using oxygen that she breathes in and her blood carries to them. The reaction goes on all the time, but it speeds up a great deal during a run.Write the word equation for aerobic respiration.2 marks
- A hummingbird hovers in front of a flower and drinks sugary nectar. Its flight muscles beat about 50 times each second and are packed with a very large number of tiny structures in their cells. The bird breathes quickly and its heart beats very fast while it hovers.Explain why the hummingbird's breathing rate and heart rate both increase while it hovers.2 marks
- A student in Dubai wants to show that living cells release energy. She fills two identical vacuum flasks, each with 100 g of dried peas that have been soaked in water. In flask A the peas are germinating. In flask B the peas have been boiled to kill them. Each flask is sealed with a cotton wool plug and a thermometer, and both start at 21.0 °C. After 24 hours the temperature in flask A is 26.5 °C and in flask B it is 21.3 °C.Identify the independent variable, the dependent variable and one control variable in this investigation.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).