1.1 Observing cells
Summary: Look around you. Can you see any dust? Most dust in your home is made of dead cells. These come from anything living in your house. To see the cells, you need to look through a microscope. Tags: science oxford-science student-book-7 biology Created: 2026-05-19 Last Updated: 2026-05-19
After this topic, you will be able to:
- define a cell
- describe how to use a microscope to look at very small objects
- calculate the total magnification used to look at an object.
Think back
- What equipment can you use to look at small objects in detail?
- What are the main structures in a plant?
- Name some organs in the human body.
Key idea Cells are the building blocks of life.
Key words organism, cell, microscope, lens, observation
Look around you. Can you see any dust? Most dust in your home is made of dead cells. These come from anything living in your house. To see the cells, you need to look through a microscope.
What are living organisms made of?
All living things, often called organisms, are made of cells. Cells are the building blocks of life. They are the smallest units found in an organism. Organisms like bacteria are made up of only one cell. Larger organisms, like you, are made up of millions of cells that are joined together.
A How many cells do you think make up a cat? Hundreds, thousands, or millions?
Seeing cells
Cells were first seen around 350 years ago. Robert Hooke, a scientist, used a microscope to look at a thin slice of cork (a type of tree bark). He saw tiny room-like structures which he called ‘cells’. You can see these cells in Figure 1. They are plant cells.
Figure 1This is the drawing that Hooke made of cork cells.
B State what a microscope is used for.
Making an observation
To see a tiny object in detail, you need to use a microscope. A microscope magnifies images using lenses (singular: lens). Looking carefully and in detail at an object is called making an observation. To make an observation with a microscope, the object needs to be thin. This is so that Light can travel through it. Sometimes, you might need to add coloured dye. This is to make the object easier to see, like the different types of blood cell in Figure 2.
Figure 2There are different types of cell in your blood.
Parts of a microscope
You can see the different parts of a microscope in Figure 3. Follow the steps below to look at an object using a microscope:
- Move the stage to its lowest position.
- Place the object on the stage.
- Choose the objective lens with the lowest magnification.
- Look through the eyepiece. Turn the coarse-focus wheel slowly until you see the object.
- Turn the fine-focus wheel until the object comes into focus.
- Repeat Steps 1 to 5. This time, use an objective lens with a higher magnification to see the object in greater detail.
Figure 3Parts of a microscope. Full text alternative to the content
C Name the part of a microscope that holds slides.
Magnification
The eyepiece lens and objective lens in a microscope have different magnifications. Together, they magnify the object.
For example, if you have an eyepiece lens of ×10 and an objective lens of ×4, the object would be magnified 40 times. This means the object looks 40 times bigger than it actually is.
You can calculate magnification using this formula:
Maths skills You are going to look at an onion cell using a microscope.
- The eyepiece lens has a ×10 magnification.
- The objective lens has a ×40 magnification. Calculate the total magnification. Total magnification = eyepiece lens magnification × objective lens magnification
Stretch zone
- Copy and complete the sentences. All living organisms are made ofblank. To observe (look at) cells in detail, you need to use ablank. A microscope blankan object.
- Describe what these parts of the microscope do. lensstagefocusing wheel
Stretch zone
- A drop of dye is added to a white flower petal before it is looked at under a microscope. State why the dye was added.Choose which magnification (×40/×100/×400) should be used first to look at the petal. Give a reason for your answer.