Master Review: Seeds — Structure and Germination (Sections 6.1 to 6.6)

(Narrator’s voice, reflective and steady, like a teacher drawing the last diagram of the lesson on the board)

1. What is a Seed? (6.1)

  • Fruit = ripened ovary, fruit wall enclosing the seed (mango, pea pod).
  • Seed = ripened ovule, contains embryo + seed coat (bean, pea).
  • Grain = fruit wall fused with seed coat (maize, wheat).
  • Dormancy: embryo inactive but alive, waiting for the right conditions.

Terms to fix in mind: fruit, ovary, ovule, seed coat, embryo, dormancy, grain.

2. Classification and Structure of Seeds (6.2)

  • Monocotyledonous: one cotyledon (maize, grasses).
  • Dicotyledonous: two cotyledons (pea, bean, gram).
  • Seeds vary in size: dust-like orchids → giant double coconut.
  • Based on endosperm:
    • Albuminous: endosperm persists, cotyledons thin (poppy, cereals).
    • Exalbuminous: endosperm used up, cotyledons thick (pea, mango).

Technical parts in dicot (bean): testa, tegmen, hilum (scar), micropyle (pore), cotyledons (food), embryo (radicle = root, plumule = shoot).
Technical parts in monocot (maize): scutellum (cotyledon), coleorhiza (root sheath), coleoptile (shoot sheath), endosperm, aleurone layer.

Terms to fix: cotyledon, albuminous, exalbuminous, testa, tegmen, hilum, micropyle, radicle, plumule, scutellum, coleoptile, coleorhiza, aleurone.

3. Germination (6.3)

  • Definition: process of seedling formation from the embryo.
  • Dormant embryo awakens when water, oxygen, and warmth are present.
  • Fresh seeds may not sprout immediately → need dormancy period for physiological maturation.
  • Conditions required:
    1. Water → swelling, rupturing coat, enzyme activity.
    2. Temperature → optimum 25–35°C (too low = inhibits, too high = kills).
    3. Oxygen → needed for respiration and energy.
  • Seeds sown too deep often fail: no oxygen, no pushing force.

Terms to fix: germination, dormancy, optimum temperature, respiration, enzyme action.

4. Experiments on Germination (6.4)

  • Water required: seeds on wet vs dry cotton (only wet germinates).
  • Temperature required: seeds at room vs refrigerator (only room germinates).
  • Oxygen required: flask with oxygen removed vs flask with air (only with air germinates).
  • Three-bean experiment:
    • Top seed → only oxygen, no water (no germination).
    • Middle seed → water + oxygen (germinates).
    • Bottom seed → water but little oxygen (fails after tiny sprout).

Exam anchor: three conditions (water, temp, oxygen) proven experimentally.

5. Types of Germination (6.5)

  • Epicotyl = region above cotyledons. Hypocotyl = region below cotyledons.
  • Hypogeal germination: epicotyl elongates, cotyledons stay underground (pea, maize, gram).
  • Epigeal germination: hypocotyl elongates, cotyledons lifted above ground (bean, castor).
  • Trade-off logic:
    • Hypogeal = protection, suited for deeper/heavier soils.
    • Epigeal = faster growth, cotyledons may photosynthesise, but exposed to danger.

Terms to fix: epicotyl, hypocotyl, hypogeal, epigeal.

6. Germination in Some Common Seeds (6.6)

  • Pea (Hypogeal): testa bursts, radicle root system, plumule arched upward, cotyledons underground.
  • Maize (Hypogeal): radicle emerges through coleorhiza (dies off, replaced by new roots), plumule emerges through coleoptile, scutellum absorbs food from endosperm, cotyledon stays underground.
  • Bean (Epigeal): hypocotyl arch lifts cotyledons above ground, they may turn green and photosynthesise briefly.
  • Vivipary (special in mangroves): seed germinates inside fruit while still attached to parent; seedling drops into soil and anchors (e.g., Rhizophora).
  • The Seedling: final stage; roots absorb minerals, leaves photosynthesise, seedling becomes independent.

Terms to fix: vivipary, coleorhiza, coleoptile, scutellum, seedling.

The Big Picture (Exam-Ready Mental Map)

  1. Seed basics (fruit vs seed vs grain; structure).
  2. Classification (monocot vs dicot; albuminous vs exalbuminous).
  3. Parts of seed (bean vs maize; dicot vs monocot).
  4. Dormancy & Germination (conditions: water, oxygen, temperature).
  5. Experiments proving conditions.
  6. Types of germination (hypogeal vs epigeal → logic & trade-offs).
  7. Examples (pea, maize, bean, mangrove vivipary).
  8. Seedling (independence, photosynthesis, growth).

(Narrator’s closing reflection)
“Think of a seed not as a dry fact, but as a living story: food store, protective coats, a sleeping embryo, and strategies for waking into the world. From bean to maize, pea to mangrove, each plant answers life’s challenge differently — but the lesson is one: patience, adaptation, and survival.”