One cell becomes many

The idea

Complex organisms begin life as a single cell, the egg, which divides repeatedly to form a living being made of many cells, called a multicellular organism.

Where did all your cells come from?

Your body has many cells. But the life of every complex living being begins with a single cell: the egg.

How do you think one egg cell becomes a body with many cells?

• The egg cell divides again and again
• Many cells enter from outside
• The one cell just grows bigger and bigger

Divide the egg cell

Tap to divide the egg cell. Each tap divides every cell in two.

Divide, divide, divide

Complex organisms begin as a single cell, the egg. The egg divides repeatedly to form a living being made of many cells. Such a living being is called a multicellular organism.

Animals, including humans, and plants are all multicellular organisms.

Notes

Complex organisms begin life as a single cell, the egg. It divides repeatedly to form a body of many cells: a multicellular organism.

Check yourself

An egg cell divides once, and then every cell divides again, and again. After 3 rounds of division, how many cells are there?

Answer: 8

1, 2, 4, 8: after 3 rounds there are 8 cells.

What is the single cell called from which a complex living being begins?

The yolk of an ostrich egg is a single cell, about 130 mm to 170 mm across. What does this tell us?

• The egg — correct. Yes. Life begins with a single cell, the egg.
• The tissue. A tissue is a group of similar cells, so it comes later.
• The organ. An organ is made of different tissues, so it comes much later.
• A single cell can be big enough to see, and it is the largest known cell — correct. Yes. The yolk of an ostrich egg is a single cell, the largest known cell in the living world.
• All cells are as big as an egg yolk. No. Most cells are far too small to see.
• An ostrich egg is made of many tiny cells in the yolk. The yolk is one single cell. The shell and the white liquid are extra non-cellular material.