Every organism on our planet, from bacteria to the largest animals, is built from cells. Each cell carries out essential functions to maintain life. Cell structure is the study of how organisms grow, function, and survive.
There are two types of cells, both crucial in the natural world: eukaryotic and prokaryotic. Eukaryotic cells are specialised organelles found in animals, plants, and fungi. Prokaryotic cells are much simpler and are found in bacteria. Microscopes help scientists to research how life works at a cellular level, from the mitochondria that provide energy to the chloroplasts in plant cells that enable photosynthesis.
This article will explain the structure of animal and plant cells, exploring their differences and the importance of microscopes to the exploration of life at its smallest scale. It is aimed at students preparing for their GCSE Biology examinations. It is suitable for GCSE Combined Science and covers all major exam boards, including AQA, Edexcel and OCR. If you need personalised help, TeachTutti has experienced GCSE Science tutors who can support your revision, such as by preparing revision notes.
Eukaryotic and Prokaryotic cells
There are two main types of cells: eukaryotic and prokaryotic. The main difference is the presence of a nucleus.
Eukaryotic cells
These cells are found in animals, plants, fungi and protists. They have a nucleus, which contains their DNA. They also have specialised organelles, such as mitochondria and ribosomes. Plant cells also contain chloroplasts. Eukaryotic cells can carry out complicated functions using these structures. This includes respiration and photosynthesis. Organisms with these cells can be multicellular (e.g. humans) or unicellular (e.g. protists).
Prokaryotic cells
Bacteria contain prokaryotic cells. These cells do not have a nucleus. Their genetic material instead floats freely in the cytoplasm. They are much smaller than eukaryotic cells and have a simpler structure. Prokaryotic cells contain ribosomes and plasmids, which are small loops of DNA. Some bacteria also have a flagellum, which is a tail-like structure that helps them move.
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What is a characteristic of prokaryotic cells?
Animal cell and plant cell structure
Animal and plant cells are eukaryotic: they have a nucleus and membrane-bound organelles. There are differences between them, which is partly due to the unique functions of plant cells, including photosynthesis.
Animal cells
There are several structures inside animal cells, known as organelles. Each structure has a function and they work together to keep the cell alive:
- Nucleus - Contains DNA and controls the cell’s activities.
- Cytoplasm - This is a jelly-like substance. Chemical reactions occur in the cytoplasm.
- Cell membrane - A semi-permeable barrier. It controls what enters and exits the cell.
- Mitochondria - Respiration occurs here to release energy.
- Ribosomes - Tiny structures responsible for making proteins.
Plant cells
Plant cells contain all the structures found in animal cells. They also have extra components to keep the cell rigid, grow towards sunlight and store nutrients:
- Cell wall - A rigid layer made of cellulose. It provides structure and support.
- Chloroplasts - These contain chlorophyll. It allows plants to carry out photosynthesis, converting sunlight into energy.
- Permanent bacuole – A large, fluid-filled sac. It stores nutrients and maintains cell pressure.
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What structure is unique to plant cells?
Microscopes and cell measurement
We can't see cells with the naked eye. This makes microscopes essential to study their structure. Microscope technology has developed to allow scientists to view cells in greater detail, leading to major discoveries in the field.
There are two main types of microscopes used to study cells:
- Light microscopes - These use light and lenses to magnify specimens. They are common in schools and show basic cell structure, including the nucleus and cytoplasm.
- Electron microscopes - A beam of electrons is used to magnify specimens. Scientists can examine sub-cellular structures, including ribosomes and mitochondria.
Measure cell size
Scientists use micrometres (micrometres) and nanometres (nm) to measure cells because they are so small.
- 1 millimetre (mm) = 1,000 micrometres (micrometres)
- 1 micrometre (micrometres) = 1,000 nanometres (nm)
Animal cells are normally around 10–30 micrometres in size. Plant cells can be 10–100 micrometres. Bacteria are even smaller in size and typically range from 0.2–2.0 micrometres.
Calculating magnification
We use the following formula to calculate the magnification of an image:
Magnification = Size of image / Real size of object.
For example, let's say the image of a cell is 100mm long, but the real cell is 50 micrometres. The magnification is: 100 × 1000 / 50 = 2000×. This means the image has been magnified 2000 times.
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How can we view sub-cellular structures in detail?
Comparing cell size
Cells come in different sizes. The human egg cell is relatively large compared to bacteria, which can only be observed under powerful microscopes. Understanding the difference in cell size furthers the study of how cells function and interact with their environment.
Most cells are measured in micrometres. Structures that are smaller than this use nanometres (nm). Even the smallest cells have components that are essential for survival:
- Human red blood cell | approximately 7 micrometres
- Typical animal cell | 10-30 micrometres
- Typical plant cell | 10-100 micrometres
- Bacterium | 0.2-2.0 micrometres
- Virus | approximately 100 nm (0.1 micrometres)
A virus is not always considered a living cell because it can't survive or reproduce without infecting a host.
Comparing cell types
Orders of magnitude are used to compare cells. They describe size differences as factors of ten. You can learn about orders of magnitude from this BBC Bitesize article. For example:
- A bacterium (1 micrometre) is ten times smaller than a red blood cell (10 micrometres).
- A human hair (100 micrometres) is 100 times thicker than a bacterium.
- HIV (100 nm) is a virus ten times smaller than a bacterium.
Scientists use these comparisons to describe in simple terms how cells relate to each other in size using ratios.
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Which cell is the smallest in size?
Examining cell structures and their functions
Scientists prepare carefully when studying cells. There are special techniques to ensure cells are visible, regardless of whether the cell is animal, plant or bacterial.
Most cells are colourless. This makes it hard to see them organically under a microscope. Stains and mounting techniques help scientists to see different structures and observe cell details effectively. It's particularly important in medical research, where the examination of cells helps to diagnose diseases.
Follow the steps below to view cells under a light microscope:
- Collect a sample - Use a small piece of plant tissue (e.g. an onion skin) or animal cells (e.g. cheek cells).
- Put the sample on a glass slide - Spread a thin layer to ensure a wider surface area for viewing.
- Add a stain - You only need a drop on the sample to see the cell structures. Iodine solution is used to stain plant cells, highlighting the nucleus and cell wall. Methylene blue stains animal cells to show the nucleus and cytoplasm. Crystal violet is used for bacteria.
- Add a coverslip - Put a thin piece of glass gently over the sample. It protects the microscope lens and stops the sample from drying out.
- Remove air bubbles - Press the coverslip gently with a needle. This avoids trapped air bubbles in the sample.
- View the sample - Place the prepared slide under the microscope and adjust the focus. You will be able to see a detailed image of the cell.
Use an electron microscope for a detailed view of organelles. You can study structures like mitochondria and ribosomes using this microscope. You can even view viruses. Bear in mind that an electron microscope requires more complicated sample preparation. This includes freezing and coating the sample with metal.
Watch out for the following mistakes when you prepare your slides:
- Using too much sample - Greater is not always better. A thick sample may stop light from passing through. This will make it hard to see details in the cell structure.
- Applying too much stain - The image will become too dark to analyse effectively.
- Trapping air bubbles - Bubbles in the sample will distort the view and may hide structures.
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Why is a stain used to prepare a cell slide?
Conclusion - Cell structure | GCSE Biology
Put simply, cells are the building blocks of life that living organisms are formed from. We have explored the difference between eukaryotic and prokaryotic cells, the unique features of plant and animal cells, and the importance of microscopes to the study of cell structure. We have also explained how to effectively prepare and measure cells using a microscope. The study of cells allows scientists to develop new medicines, diagnose diseases and improve their understanding of the natural world.
For further reading, Technology Networks has an in-depth article on the key differences between prokaryotes and eukaryotes. You can test your understanding of this topic using Study Mind's past papers on cell structure.
If you need more support studying this topic, TeachTutti has qualified GCSE Science tutors. Every tutor is DBS checked and can teach online or in person. They will cater lessons to your needs, such as preparing exam questions.
This post was updated on 30 Nov, -0001.
