A seed is a living plant embryo packaged with stored food and a protective covering. This structure allows plants to survive unfavorable seasons, travel to new places, and begin growth when conditions improve. Understanding seed structure helps explain how a tiny dry seed can become a seedling with roots, leaves, and a growing stem.
Germination is important in agriculture, ecology, and food production because it controls when and where new plants establish.
Key Facts
- A typical seed contains an embryo, stored food, and a protective seed coat.
- The embryo includes the radicle, which becomes the root, and the plumule, which becomes the shoot.
- Cotyledons store or absorb food for the young seedling; dicots usually have two cotyledons and monocots usually have one.
- Germination requires water, oxygen, and a suitable temperature; many seeds also need correct light or darkness conditions.
- Imbibition is water uptake by a dry seed, causing it to swell and activate enzymes.
- Percent germination = number of seeds germinated / total number of seeds x 100%
Vocabulary
- Embryo
- The young plant inside a seed that can grow into a seedling when conditions are suitable.
- Cotyledon
- A seed leaf that stores food or absorbs food from endosperm to nourish the developing embryo.
- Seed coat
- The tough outer covering of a seed that protects the embryo from drying, injury, and pathogens.
- Dormancy
- A resting state in which a viable seed does not germinate until specific internal or environmental conditions are met.
- Radicle
- The embryonic root that usually emerges first during germination and anchors the seedling.
Common Mistakes to Avoid
- Calling the whole seed the embryo is wrong because the seed also includes stored food tissue and the seed coat.
- Assuming all seeds germinate as soon as they get wet is wrong because dormant seeds may also need temperature changes, light cues, scarification, or time.
- Forgetting oxygen during germination is wrong because the embryo needs cellular respiration to release energy from stored food.
- Confusing cotyledons with true leaves is wrong because cotyledons are seed leaves that mainly support early growth, while true leaves develop later and carry out most photosynthesis.
Practice Questions
- 1 A student plants 40 bean seeds and 34 germinate. Calculate the percent germination.
- 2 A packet contains 120 seeds with an expected germination rate of 85%. How many seedlings should grow if conditions are suitable?
- 3 A seed is kept in warm, moist soil but does not germinate because the soil is waterlogged. Explain why too much water can prevent germination even when temperature and moisture seem favorable.