Unit 2 | Life Cycles (Angiosperms) | Biodiversity

Angiosperm

A flowering plant which forms seeds inside a protective chamber called an ovary.

Angiosperm Life Cycle | Step 1

Sporophyte (2n, diploid plant)

The visible flowering plant is the sporophyte.

It makes flowers that contain reproductive organs.

Angiosperm Life Cycle | Step 2

Male Gametophyte (pollen grain, n)

Inside the anthers: microsporocytes (2n) do meiosis → microspores (n). (Makes 4 Microspores)

Each microspore becomes a pollen grain (male gametophyte).

Pollen = 2 cells: tube cell + generative cell (makes sperm).

Angiosperm Life Cycle | Step 3

Female Gametophyte (embryo sac, n)

Inside the ovary: megasporocyte (2n) → meiosis → 4 megaspores (n), but only 1 survives.

This grows into the embryo sac (female gametophyte).

Embryo sac has 7 cells, 8 nuclei (includes the egg + 2 polar nuclei).

Angiosperm Life Cycle | Step 4

Pollination

Pollen lands on stigma.

Pollen tube goes down style → reaches ovule.

2 sperm travel down tube.

Angiosperm Life Cycle | Step 5

Double Fertilization

(unique to angiosperms!)

1 sperm + egg → zygote (2n).

1 sperm + 2 polar nuclei → endosperm (3n) (food for embryo).

Angiosperm Life Cycle | Step 6

Seed & Fruit Formation

Fertilized ovule → seed (embryo + endosperm + seed coat).

Ovary → fruit (helps with seed dispersal).

Angiosperm Life Cycle | Step 7

Seed Germination → New Sporophyte

Seed grows into a new flowering plant (sporophyte).

Cycle restarts.