Respiration: Question 8
Syllabus 12.2
A student places germinating pea seeds inside a sealed, transparent chamber that is kept well supplied with oxygen throughout the investigation. The seeds are respiring aerobically.
(a) State the word equation for the aerobic respiration taking place in the germinating seeds. [2]
(b) Write the balanced chemical symbol equation for this reaction. [1]
(c) Show that the balanced equation you gave in (b) has the same number of carbon atoms, the same number of hydrogen atoms and the same number of oxygen atoms on each side. [3]
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Worked solution
Part (a): The word equation for aerobic respiration
The germinating pea seeds are kept well supplied with oxygen, so they are respiring aerobically, breaking glucose down completely using oxygen:
glucose + oxygen → carbon dioxide + water
Part (b): The balanced chemical symbol equation
Writing this reaction using chemical formulae, and balancing the number of atoms of each element on both sides, gives:
C6H12O6 + 6O2 → 6CO2 + 6H2O
Part (c): Checking that the equation is balanced
Left-hand side, C6H12O6 + 6O2:
- carbon atoms: 6 (from C6H12O6)
- hydrogen atoms: 12 (from C6H12O6)
- oxygen atoms: 6 (from C6H12O6) + 6 × 2 = 12 (from 6O2) = 18
Right-hand side, 6CO2 + 6H2O:
- carbon atoms: 6 × 1 = 6 (from 6CO2)
- hydrogen atoms: 6 × 2 = 12 (from 6H2O)
- oxygen atoms: 6 × 2 = 12 (from 6CO2) + 6 × 1 = 6 (from 6H2O) = 18
Both sides have 6 carbon atoms, 12 hydrogen atoms and 18 oxygen atoms, so the equation is correctly balanced.
Final answers
- (a) glucose + oxygen → carbon dioxide + water
- (b) C6H12O6 + 6O2 → 6CO2 + 6H2O
- (c) Both sides of C6H12O6 + 6O2 → 6CO2 + 6H2O have 6 carbon atoms, 12 hydrogen atoms and 18 oxygen atoms, so the equation is balanced.