Cells: The Building Blocks of Life
- Biology
- Ages 11–14 · Grades 6–8
What you’ll find out
- All living things are made of cells; the cell is the basic unit of life, and new cells come from existing cells.
- Cells are specialised for their jobs, and organisms may be single-celled or many-celled.
- Organelles such as the nucleus, membrane, mitochondria and chloroplasts each have a function.
No sign-up and no real names. In the lesson you check your understanding as you read, and practise until it sticks.
Everything alive is made of cells
Every living thing is made of cells, the smallest units that can be called alive. Most cells are so small that you need a microscope to see them. Some organisms, such as bacteria, consist of a single cell, while others, including humans, contain trillions. Cells come in many shapes that suit their jobs: nerve cells are long and thin to carry signals, and red blood cells are flat discs that squeeze through tiny blood vessels. New cells only ever form when existing cells divide.
Inside a cell
Inside every cell are smaller parts, each with a particular job. The cell membrane surrounds the cell and controls what enters and leaves. The jelly-like cytoplasm fills the cell, and it is where many chemical reactions happen. The nucleus acts as the control centre, holding the instructions the cell needs. Tiny mitochondria release energy from food. Plant cells also have a rigid cell wall for support, a large vacuole filled with sap, and green chloroplasts that make food using sunlight.
Curriculum links: NGSS MS-LS1-1 · NGSS MS-LS1-2 · England KS3: Structure and function of living organisms · Cambridge Lower Secondary Stages 7–9: Biology · NCERT Science, Classes 6–8