Learning objectives
- Label a seed and state each part's function
- List the conditions necessary for germination and design a controlled experiment
- Distinguish epigeal from hypogeal germination and name the main hormones
1. Seed structure
The testa is the protective seed coat; the micropyle is the small pore through which water enters; the embryo consists of the plumule (future shoot), radicle (future root) and cotyledons, which store or absorb food. In maize the endosperm stores the food instead.
2. Conditions for germination
Water for imbibition and enzyme activation, oxygen for aerobic respiration to release energy, and a suitable temperature for enzyme activity. The classic experiment uses four boiling tubes: full conditions, no water, no oxygen (boiled water under oil), and low temperature in a refrigerator.
3. Types of germination
Epigeal germination brings the cotyledons above the soil (bean, groundnut) because the hypocotyl elongates. Hypogeal germination leaves the cotyledons below the soil (maize, rice) because the epicotyl elongates.
4. Growth and hormones
Growth occurs at meristems: apical meristems at root and shoot tips increase length, lateral meristems (cambium) increase girth.
Auxin promotes cell elongation and causes phototropism and geotropism; gibberellin breaks dormancy and promotes stem elongation; cytokinin promotes cell division; abscisic acid closes stomata and enforces dormancy; ethylene ripens fruit.
Key definitions
- Germination
- The resumption of active growth of the embryo of a seed under suitable conditions.
- Dormancy
- A period during which a viable seed will not germinate even under favourable conditions.
- Viability
- The ability of a seed to germinate and produce a normal seedling.
Exam tips
- Do not write 'sunlight' as a condition for germination — it is a very common error.
- In experiment questions, always name the control and the variable being tested.
Practice exam questions & model answers
Q1.State three conditions necessary for seed germination and explain why each is needed.
Water — to soften the testa and activate enzymes that mobilise stored food; oxygen — for aerobic respiration to release energy for growth; suitable temperature — because germination enzymes work best within an optimum temperature range.
Q2.Differentiate between epigeal and hypogeal germination with one example each.
In epigeal germination the hypocotyl elongates and the cotyledons are carried above the soil surface, e.g. bean. In hypogeal germination the epicotyl elongates and the cotyledons remain below the soil, e.g. maize.
Q3.Explain the role of auxin in phototropism.
Auxin accumulates on the shaded side of the shoot, causing greater cell elongation on that side, so the shoot bends towards the light.
Continue revising
Plant Cell Structure and Function
Plant BiologyPhotosynthesis: Process, Equation and Limiting Factors
BotanyLeaf Structure, Stomata and Transpiration
Agricultural SciencePlant Nutrition, NPK and Soil Fertility
Put the theory to work — diagnose a real leaf photo or browse the disease library.