How do Organisms Reproduce? — Part 2: Sexual reproduction in flowering plants: visual lesson, CBSE Class 10 Science

Lesson

Sexual reproduction in flowering plants

Part 2 — why two parents create more variety, and how a flower turns into a fruit full of seeds.

In this lesson you will

Explain why germ cells carry half the DNA of body cells
Label the parts of a flower and state their roles
Describe pollination, fertilisation and the formation of seeds and fruits
Identify the parts of a germinating seed

Concept

Why two parents? Germ cells with half the DNA

Sexual reproduction combines DNA from two parents, so offspring get new combinations and more variation. To keep the amount of DNA constant, germ cells (gametes) carry only half the chromosomes of a body cell. When a male and a female germ cell fuse, the zygote has the full set again.

Worked example

Worked example 1: counting chromosomes

Body cells of a potato plant have 48 chromosomes. How many are there in (a) its egg cell, (b) a pollen grain’s male germ cell, (c) the zygote?

Step 1 — Germ cells carry half the body-cell number: $\dfrac{48}{2} = 24$ .
Step 2 — (a) Egg cell: 24. (b) Male germ cell: 24.
Step 3 — (c) Zygote $=$ male $+$ female germ cell $= 24 + 24 = 48$ .
Check — the zygote has the same number as the parent’s body cells, so the number stays constant across generations.

Worked table: body cell 48, egg 24, male germ cell 24, zygote 48 chromosomes
Cell	Chromosomes
Body cell of the plant	48
Egg cell (female germ cell)	24
Male germ cell	24
Zygote	48

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