What are cells?

  • All living things are made up of cells.

  • Most cells are so small that you can only see them with a microscope.

  • Cells have different components and each performs its own function within the cell.

Discover how a forensic scientist analyses cells to help solve crimes.

What’s in a cell?

Cells are the basic building blocks of all animals and plants.

Inside cells are various structures that are specialised to carry out a particular function. Both animal and plant cells have these components:

  • Cell membrane – this surrounds the cell and allows nutrients to enter and waste to leave it.

  • Nucleus – this controls what happens in the cell. It contains DNA, the genetic information that cells need to grow and reproduce.

  • Cytoplasm – this is a jelly-like substance in which chemical reactions happen.

  • Mitochondria – these are the powerhouse of the cell. They are structures where respiration takes place.

How are plant and animal cells different?

Plant cells have all the parts in the list above, plus a few extra structures:

  • Cell wall - this is an outer structure that surrounds the cell and gives it support.

  • Vacuole - this is a space within the cytoplasm of plant cells that contains sap.

  • Chloroplasts - these contain chlorophyll and are the site of photosynthesis.

A labelled cross-section of both a plant and animal cell

How big are cells?

Cells can vary greatly in size. You need a microscope to see most human cells.

Red blood cells are some of the smallest cells in the human body. These have a diameter of 0.008 mm, meaning a line of 125 red blood cells is only 1 mm long.

The ovum (or egg cell) is one of the largest cells in the human body. It has a diameter of roughly 0.1 mm, so you can see them without a microscope. A line of 10 egg cells is 1 mm long.

How do forensic scientists use cells?

Forensic scientists collect skin, blood and hair cells from a crime scene. They analyse DNA from these cells and compare it to DNA samples already collected from thousands of people. This helps them to identify suspects.

Activity - cells

Cells quiz

Find out how much you know in this quick science quiz!

Where next?

Discover more about this topic from around Bitesize.

What is DNA?
How to make a model plant cell
How to make a model animal cell