Post-Fertilisation Structures and Events 🌸

Once fusion is complete, a plant flower shifts focus to building food for the embryo, shaping the young plant, and wrapping everything in a protective fruit. These steps are called post-fertilisation events.

1. Endosperm – the Food Factory 🍚

  • The primary endosperm cell (formed right after triple fusion) divides fast to create a triploid tissue (\(3n\)) packed with food.
  • First, many nuclei share one big cytoplasm—this free-nuclear endosperm later gains walls and becomes cellular. Coconut water is a classic free-nuclear stage, while the white kernel is the cellular stage.
  • If the embryo “eats” the endosperm before the seed matures (e.g., pea, groundnut, beans), the mature seed is non-albuminous. When some endosperm stays for germination (e.g., castor, coconut), the seed is albuminous.

2. Embryo – the Baby Plant 🌱

The zygote divides only after enough endosperm forms—ensuring a steady food supply. Early shapes are globular ➜ heart-shaped ➜ mature.

2.1 Typical Dicot Embryo 🌿

  • Two cotyledons hug an embryonal axis.
  • Above cotyledons: epicotyl ending in the plumule (future shoot).
  • Below cotyledons: hypocotyl ending in the radicle (future root) capped by a root cap.

2.2 Typical Monocot Embryo 🌾

  • Single cotyledon called the scutellum sits on one side.
  • Lower axis: radicle + root cap inside a sheath (coleorrhiza).
  • Upper axis: epicotyl with shoot apex and young leaves inside a hollow sheath (coleoptile).

3. Seed – the Survival Capsule 🪺

  • A seed = tough coat + cotyledon(s) + embryo axis.
  • Seed coat forms from hardened integuments; the micropyle stays open for water & air.
  • As the seed dries to ~10–15 % water, metabolism slows and dormancy may begin—perfect for storage.
  • Left-over nucellus can persist as perisperm (e.g., black pepper, beet).
  • Seed longevity varies: Lupinus arcticus (≈10 000 years!) and date palm (≈2000 years) hold record viabilities.

4. Fruit – the Seed Delivery Vehicle 🍉

  • While ovules turn into seeds, the ovary wall becomes the pericarp. Fruits may be fleshy (mango, guava) or dry (groundnut, mustard).
  • If other flower parts (thalamus) join in, we get false fruits (apple, strawberry, cashew). True fruits arise from ovary alone.
  • Fruits without fertilisation are parthenocarpic (e.g., banana). Plant hormones can trigger this, giving seedless treats.

Why Seeds Rock 🎉

  1. Water-free pollination & fertilisation make reproduction reliable.
  2. Hard coat + food reserves = safe, nourished seedling launch.
  3. Built-in dormancy lets seeds wait for perfect growth conditions.
  4. Wide dispersal and genetic mixing boost survival of the species.

High-Yield NEET Nuggets 🔥

  • Order matters: Endosperm (\(3n\)) develops before the embryo—vital for nutrition.
  • Recognise seed types: albuminous (wheat, maize, castor) vs non-albuminous (pea, groundnut).
  • Embryo contrast: Two cotyledons with plumule & radicle (dicot) versus scutellum, coleoptile & coleorrhiza (monocot).
  • Parthenocarpy produces seedless fruits like banana—often induced by growth hormones.
  • Micropyle opening stays in the seed coat—it is the entry gate for oxygen & water during germination.