Topic 16.3D · Core · Direct Paper 6 relevance
Seed Germination
Germination has exactly three required conditions in the current syllabus, and light is not one of them. That last point trips up more students than it should — a seed germinating in complete darkness is not an anomaly, it's the expected biology.
What germination is
Germination is the beginning of growth of the embryo in a seed. It follows on directly from fertilisation in a flowering plant, but it doesn’t happen automatically the moment a seed forms — a seed needs specific environmental conditions in place before growth actually resumes.
The three required conditions
Cambridge limits the required conditions to exactly three: water, oxygen, and a suitable temperature. All three are needed together — leaving out any one of them prevents germination, regardless of how favourable the other two are.
Water rehydrates the tissues of the seed and allows the enzyme-controlled metabolic reactions needed for growth to actually begin. Oxygen is needed for aerobic respiration, which releases the energy the growing embryo needs. A suitable temperature matters because germination depends on enzyme-controlled reactions: too cold, and those reactions proceed too slowly to support growth; too hot, and the enzymes and cells themselves can be damaged. A suitable temperature is the one that lets those reactions proceed effectively, not simply the warmest available temperature.
Light is not one of the three conditions Cambridge specifies here. Plenty of seeds germinate perfectly well underground, in complete darkness — germination and photosynthesis are different processes with different requirements, and it’s worth keeping that distinction explicit in an answer rather than assuming light must be involved because it matters so much to plants generally.
Investigating the conditions
Cambridge expects you to be able to investigate these requirements, not just recite them, which means knowing how to design a fair test around them. The logic is the same for each condition: change only the one factor being tested, and keep every other relevant condition comparable between the groups being compared.
To test whether water is required, compare seeds supplied with water against seeds kept dry, while holding oxygen availability and temperature the same for both groups. To test oxygen, compare seeds with normal access to oxygen against seeds where oxygen has been removed or significantly restricted, keeping water and temperature suitable for both. To test temperature, give comparable groups of seeds similar amounts of water and oxygen but keep each group at a different temperature. In every case, useful control variables include the species and number of seeds used and the duration of the investigation.
Results are usually recorded as the number or proportion of seeds that germinate, or the time taken for germination to begin. A sound conclusion follows directly from the comparison actually observed between groups — a seed batch with water germinating while a dry batch does not is what supports the conclusion that water is required, not the germination theory on its own.
Where this fits
This closes the plant-reproduction pathway that starts with flower structure and continues through pollination and fertilisation. The same sexual-reproduction principles — gamete fusion, genetic variation — reappear in a very different organism on the human side of the chapter, starting with sexual reproduction in humans.