Plant and Animal Cells

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.

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Eukaryotic Cells

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.

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Animal Cell Structure

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.

Key Points About Animal Cells

• Animal cells do not have a cell wall, chloroplasts, or a permanent vacuole.
• The shape of an animal cell is generally irregular or rounded.
• Mitochondria have their own DNA and a double membrane — the inner membrane is folded into cristae to increase surface area for respiration.
• Ribosomes are extremely small (about 20 nm) and are not visible under a light microscope.

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."

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Plant Cell Structure

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.

Summary Table: Animal vs Plant Cells

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.

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Visualising Cell Structure

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

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Drawing and Labelling Cells

In the exam, you may be asked to draw and label a plant or animal cell. Follow these guidelines:

1. Use a sharp pencil and draw clear, continuous lines.
2. Make your drawing large — at least half the space provided.
3. Use straight label lines with a ruler, and do not cross them.
4. Label all organelles clearly with their names and functions.
5. For plant cells, always include the cell wall, permanent vacuole, and chloroplasts.
6. Do not shade or colour your drawings.

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Functions of Organelles in Detail

The Nucleus

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

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

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

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)

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Common Exam Mistakes

• Saying mitochondria "make" energy — energy is transferred, not created.
• Stating that all plant cells have chloroplasts — only cells in green parts do.
• Confusing the cell membrane (thin, flexible, controls entry/exit) with the cell wall (rigid, made of cellulose, provides support).
• Forgetting that plant cells also contain mitochondria — they respire as well as photosynthesise.

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Summary

• Eukaryotic cells have a nucleus and membrane-bound organelles.
• Animal cells contain a nucleus, cell membrane, cytoplasm, mitochondria, and ribosomes.
• Plant cells have all the above plus a cell wall, permanent vacuole, and chloroplasts.
• The nucleus controls cell activities and contains DNA.
• Mitochondria are the site of aerobic respiration.
• Ribosomes are the site of protein synthesis.
• Chloroplasts are the site of photosynthesis and contain chlorophyll.
• The cell wall is made of cellulose and provides structural support.
• The permanent vacuole contains cell sap and maintains turgor pressure.

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.