2.1 Cell structure

Cells are the smallest units from which all organisms are made. They are the basic building blocks of life.

Multicellular organisms are made of millions of cells. Examples include humans, plants, and animals. These organisms have many cells working together to perform different functions.

Unicellular organisms are made of just a single cell. Examples include bacteria and yeast. Despite having only one cell, these organisms can carry out all the processes necessary for life.

To see cells clearly, we need to use microscopes because cells are very small.

A light microscope is the type commonly used in school laboratories. It works by:

• Shining light through the specimen
• Using glass lenses to magnify and focus the image
• Can magnify up to about $\times 1500$

With a light microscope, you can see most of the main structures in plant and animal cells, including:

• Cell membrane
• Cytoplasm
• Nucleus
• Large vacuoles in plant cells
• Chloroplasts in plant cells

An electron microscope provides much greater magnification and detail:

• Uses a beam of electrons instead of light
• Can magnify up to $\times 500000$
• Produces images called electron micrographs
• Reveals much smaller structures inside cells, such as ribosomes and mitochondria in detail