2. Consider changing this investigation to test if:
a. Sunlight is needed for respiration.
b. Oxygen is needed for respiration.
c. Water is produced as a waste product of respiration.
(Hint: there are many different ‘oxygen scavengers’ in the products we buy. These are made up of iron powder and sodium chloride that will be useful for testing b, and anhydrous copper sulfate may be useful for testing c.)
Germinating seeds produce heat and release carbon dioxide during respiration
Respiration and combustion analogy
An analogy means using similarities between different things to help us understand new ideas. For example, we can use the similarities between respiring food and burning wood or coal in a fire to help develop our understanding of respiration.
Combustion O2 Fuel CO2 + H2O + heat O2
Food (incl. glucose)
Enzymes » reactants
» products » energy transformations.
Respiration Mitochondria Fig. 3.3.5
Using an analogy to consider
combustion and respiration
CO2 + H2O + energy (incl. heat)
1. Using the image above, see if you can come up with statements to describe the analogy between these processes. Consider the following: » fuel
Start each statement: ‘In respiration the [fuel/reactant/product/energy transformation] is ________; in combustion the [fuel/reactant/product/energy transformation] is ________.’
2. Are there any weaknesses in this analogy? (Hint: consider the rate of energy release and the control of energy release.)
Learn more about combustion reactions in Chemical World 14.1 57 Limewater Seeds Air 3.3
