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This lesson covers the structure and function of eukaryotic cells, focusing on plant and animal cells as required by the AQA GCSE Biology specification (4.1.1). Understanding cell structure is the foundation of all biology — cells are the basic building blocks of all living organisms. You need to be able to identify the sub-cellular structures (organelles) found in both animal and plant cells and explain the function of each one.
Eukaryotic cells are cells that contain a nucleus and other membrane-bound organelles. Both animal and plant cells are eukaryotic. The term "eukaryotic" comes from the Greek words for "true" and "kernel" (referring to the nucleus). Eukaryotic organisms include animals, plants, fungi, and protists.
All eukaryotic cells share certain features, but plant cells have additional structures that animal cells do not possess. You must be able to recognise, draw, and label both types of cell.
Exam Tip: When asked to "describe" a cell, always refer to the sub-cellular structures (organelles) and their functions. Simply listing organelles without functions will lose you marks.
An animal cell contains the following sub-cellular structures:
| Organelle | Function |
|---|---|
| Nucleus | Contains the genetic material (DNA) organised into chromosomes. Controls the activities of the cell, including cell division and protein synthesis. |
| Cell membrane | A selectively permeable barrier that controls which substances enter and leave the cell. Made of a phospholipid bilayer with embedded proteins. |
| Cytoplasm | A jelly-like substance where most of the cell's chemical reactions take place. Contains enzymes that speed up these reactions. |
| Mitochondria | The site of aerobic respiration, where glucose and oxygen react to release energy for the cell. Often described as the "powerhouses" of the cell. |
| Ribosomes | Tiny structures found in the cytoplasm (and on the rough endoplasmic reticulum) where protein synthesis occurs. Proteins are assembled from amino acids following instructions from the DNA. |
Exam Tip: Remember that mitochondria are the site of aerobic respiration, NOT "energy production". Energy is transferred during respiration, not created. The correct term is "the site where energy is released by aerobic respiration."
A plant cell contains all of the organelles found in an animal cell, plus three additional structures:
| Organelle | Function |
|---|---|
| Cell wall | A rigid outer layer made of cellulose that provides structural support and prevents the cell from bursting when it absorbs water by osmosis. |
| Permanent vacuole | A large, fluid-filled space in the centre of the cell containing cell sap (a solution of sugars, salts, and sometimes pigments). Maintains turgor pressure to keep the cell firm. |
| Chloroplasts | Contain the green pigment chlorophyll, which absorbs light energy for photosynthesis. This is where carbon dioxide and water are converted into glucose and oxygen. |
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Nucleus | Yes | Yes |
| Cell membrane | Yes | Yes |
| Cytoplasm | Yes | Yes |
| Mitochondria | Yes | Yes |
| Ribosomes | Yes | Yes |
| Cell wall | No | Yes (cellulose) |
| Permanent vacuole | No (may have small temporary vacuoles) | Yes (large, central) |
| Chloroplasts | No | Yes (in green parts only) |
| Shape | Irregular / rounded | Regular / rectangular |
Exam Tip: Not all plant cells contain chloroplasts. Root cells, for example, are underground and do not photosynthesise, so they lack chloroplasts. Only cells in the green parts of the plant (leaves, stems) contain them.
The following diagram shows the relationship between the organelles found in animal and plant cells:
graph TD
A["Eukaryotic Cells"] --> B["Animal Cells"]
A --> C["Plant Cells"]
B --> D["Nucleus"]
B --> E["Cell Membrane"]
B --> F["Cytoplasm"]
B --> G["Mitochondria"]
B --> H["Ribosomes"]
C --> D
C --> E
C --> F
C --> G
C --> H
C --> I["Cell Wall (cellulose)"]
C --> J["Permanent Vacuole"]
C --> K["Chloroplasts"]
style A fill:#4a90d9,color:#fff
style B fill:#e67e22,color:#fff
style C fill:#27ae60,color:#fff
In the exam, you may be asked to draw and label a plant or animal cell. Follow these guidelines:
The nucleus is the control centre of the cell. It contains DNA (deoxyribonucleic acid) in the form of chromosomes. Human cells contain 46 chromosomes (23 pairs). The DNA carries the genetic code that determines which proteins the cell makes. Proteins include enzymes, structural proteins, hormones, and antibodies.
Mitochondria are the sites of aerobic respiration. The reaction can be summarised as:
glucose + oxygen → carbon dioxide + water (+ energy transferred)
Cells that require a lot of energy — such as muscle cells, sperm cells, and nerve cells — contain large numbers of mitochondria. Mitochondria are typically 1–10 micrometres in length.
Ribosomes are responsible for protein synthesis. They read the instructions carried by messenger RNA (mRNA), which is copied from the DNA in the nucleus. Ribosomes link amino acids together in the correct order to form specific proteins. Ribosomes are found free in the cytoplasm or attached to the endoplasmic reticulum.
Chloroplasts are the site of photosynthesis. They contain the pigment chlorophyll, which absorbs light energy (mainly red and blue wavelengths) and reflects green light, giving plants their green colour. The reaction of photosynthesis can be summarised as:
carbon dioxide + water → glucose + oxygen (using light energy)
Exam Tip: A common 6-mark question asks you to compare plant and animal cells. Structure your answer with a clear comparison — state what is the same, then what is different, and always include the function of each organelle you mention.
A student examines a palisade mesophyll cell from a leaf and counts the following organelles: 1 nucleus, 1 cell membrane, 1 cytoplasm, 1 cell wall, 1 permanent vacuole, 80 chloroplasts, 200 mitochondria, and many ribosomes.
Question: Suggest why this cell contains so many chloroplasts and so many mitochondria.
This worked example shows how cell structure is always linked to function — a recurring theme throughout GCSE Biology.
Common mistake: Students often write that a palisade cell has "a chloroplast" (singular). Palisade mesophyll cells typically contain dozens of chloroplasts that can reposition within the cytoplasm to optimise light absorption. Always use the plural and, if possible, quote a realistic order of magnitude (tens to hundreds).
| Organelle | Function | Found In |
|---|---|---|
| Nucleus | Stores DNA; controls the cell | Animal and plant |
| Mitochondria | Site of aerobic respiration | Animal and plant |
| Ribosomes | Site of protein synthesis | Animal and plant |
| Chloroplasts | Site of photosynthesis (contain chlorophyll) | Plant (green parts only) |
| Cell wall (cellulose) | Rigid support; prevents bursting | Plant |
| Permanent vacuole | Contains cell sap; maintains turgor pressure | Plant |
| Cell membrane | Selectively permeable; controls exchange | Animal and plant |
| Cytoplasm | Site of many chemical reactions | Animal and plant |
Exam-style question (4 marks): Compare the structure of a typical animal cell with that of a typical plant cell.
Grade 4–5 answer: Both cells have a nucleus, cytoplasm and cell membrane. Plant cells have a cell wall and chloroplasts but animal cells do not. Plant cells have a big vacuole.
Grade 8–9 answer: Both animal and plant cells are eukaryotic and contain a nucleus (with DNA), cytoplasm, a selectively permeable cell membrane, mitochondria (for aerobic respiration) and ribosomes (for protein synthesis). Plant cells have three additional structures: a cellulose cell wall that provides rigid support and prevents the cell from bursting when water enters by osmosis; chloroplasts (in cells from the green parts of the plant) that contain chlorophyll and are the site of photosynthesis; and a large permanent vacuole containing cell sap, which maintains turgor pressure to keep the cell firm. A common misconception is that every plant cell has chloroplasts — cells from the roots do not, because they are underground and do not photosynthesise.
Common mistake: Writing that "animal cells have no cell wall or vacuole." Animal cells do often contain small, temporary vacuoles (for example, in white blood cells). The correct distinction is that plant cells always have a large permanent vacuole, whereas animal cells, if they have vacuoles at all, have small temporary ones.
A useful way to revise sub-cellular structures is to think about cause and effect: each organelle exists because the cell needs to carry out a particular function. For example, a liver cell has an exceptionally large number of mitochondria because the liver is metabolically active — it detoxifies alcohol, regulates blood glucose, and produces bile. By contrast, a red blood cell has no nucleus and no mitochondria, because its role is simply to transport oxygen; losing these organelles creates more space for haemoglobin. A plant palisade cell has many chloroplasts to capture light, whereas a root hair cell has none because it is underground. When you identify a cell in an exam, first ask: "what does this cell do?" then predict which organelles it will have in abundance.
This thinking also helps with unfamiliar cells: a cell described as having "many mitochondria, no nucleus, and a flagellum" should immediately suggest a sperm cell, because those three features match the function of swimming to, and fertilising, an egg.
Exam Tip: Whenever a question gives you an unfamiliar cell and asks you to suggest its function, list its prominent organelles first, then reason from organelle function to likely cell role. This structured approach works in both 2-mark and 6-mark "suggest" questions.
AQA alignment: This content is aligned with AQA GCSE Biology (8461) specification section 4.1 Cell biology — specifically 4.1.1.1 Eukaryotes and prokaryotes and 4.1.1.2 Animal and plant cells. Assessed on Paper 1.