15 interesting biology facts: from the cell to the blue whale

Biology is the science of life — from tiny bacteria to the giant whale, from grass to the banyan tree. Life on Earth is so varied that every new fact surprises us. Here are 15 interesting biology facts, also linked to the syllabus of Classes 6 to 10.

The cell: the unit of life

1. The word "cell" arrived in 1665: the English scientist Robert Hooke looked at a thin slice of cork under a microscope and named the tiny boxes he saw "cells".
2. Trillions of cells in our body: an adult human body is estimated to have more than 30 trillion cells.
3. The powerhouse of the cell: mitochondria release energy from food, which is why they are called the "powerhouse of the cell".
4. Why leaves are green: leaves contain a pigment called chlorophyll, which absorbs red and blue light and reflects green light.

The world of plants

1. Meat-eating plants: plants such as the Venus flytrap catch and digest insects, because they grow in soil that is poor in nitrogen.
2. The banyan — the national tree: the roots hanging from a banyan's branches (prop roots) reach the ground and become new trunks. The "Great Banyan Tree" in Kolkata's Acharya Jagadish Chandra Bose Botanic Garden is one tree, yet it looks like a small forest.
3. Plants respond too: the leaves of the touch-me-not (chhui-mui) fold up as soon as they are touched. The Indian scientist Jagadish Chandra Bose built the "crescograph" to measure how plants respond.

Did you know? The earthworm is called "the farmer's friend". It digs tunnels in the soil that let in air and water, and eats rotting leaves to make rich manure.

Wonders of the animal world

1. The starfish has no brain: a starfish has no brain, yet its network of nerves runs its body. Many starfish can regrow a broken arm.
2. The fastest heartbeat: in flight, a hummingbird's heart can beat more than 1,000 times a minute.
3. The biggest heart: the blue whale's heart weighs hundreds of kilos — the biggest heart of any living thing on Earth.
4. The longest pregnancy: a baby elephant stays about 22 months in its mother's womb, the longest of any mammal.
5. Almost indestructible: tiny animals called tardigrades (water bears) can survive extreme cold, heat, drought and even the vacuum of space for a while.
6. Spider silk: weight for weight, a spider's thread is stronger than steel.
7. The sleepy koala: Australia's koala sleeps 18 to 22 hours a day, because its food — eucalyptus leaves — gives very little energy.
8. India's biodiversity: India is one of the world's few "megadiverse" countries; the Western Ghats and the Eastern Himalayas are counted as biodiversity hotspots.

A study tip

The best way to remember biology is to observe — look closely at the trees, birds and insects around you and ask questions about them. Keep a small "nature diary" and write about one living thing every day.

Read more: Science questions · Class 4 quiz: animals and birds.