Cell structure, microscopy, the cell cycle, mitosis and transport — the complete foundation of GCSE Biology.
Cell biology is the very foundation of GCSE Biology. Almost every other topic — genetics, immunity, photosynthesis, respiration — builds on what happens inside cells. Students who understand cell biology deeply find the rest of the course significantly easier. This guide covers everything from basic cell structure through to mitosis and the three types of transport across membranes.
Both animal and plant cells are eukaryotic — their genetic material is enclosed within a nucleus. They share several structures but plant cells have some additional ones.
Structures found in both animal and plant cells:
Additional structures in plant cells only:
Bacteria are prokaryotic — their genetic material is not enclosed within a nucleus. It floats freely in the cytoplasm as a single circular chromosome. Prokaryotic cells are significantly smaller than eukaryotic cells — typically 1–10 micrometres compared to 10–100 micrometres for eukaryotic cells.
Key structures in a bacterial cell:
The key difference between prokaryotic and eukaryotic cells: prokaryotes have no membrane-bound nucleus — their DNA is free in the cytoplasm. Eukaryotes have a true nucleus enclosed by a nuclear membrane. This single distinction drives most exam questions comparing the two cell types.
Microscopy questions appear frequently and involve calculation. The key formula:
Units matter enormously. Cells are measured in micrometres (μm) or nanometres (nm). Conversion: 1 mm = 1000 μm = 1,000,000 nm.
Electron microscopes have much higher magnification and resolution than light microscopes. A light microscope can magnify up to about ×2000 and resolve structures no closer than 200 nm apart. Electron microscopes can magnify up to ×2,000,000 and resolve structures 0.1 nm apart — allowing organelles like ribosomes and mitochondrial membranes to be seen clearly.
❌ Common error: confusing magnification and resolution. Magnification is how much larger the image is than the real object. Resolution is the ability to distinguish two separate points as distinct — a high-magnification image that is blurry has poor resolution. These are different properties of a microscope.
All cells in an organism contain the same DNA, yet they look and function differently. This is because different genes are active in different cell types — a process called differentiation. During development, cells become specialised for specific functions.
Examples of specialised cells and their adaptations:
Mitosis is cell division that produces two genetically identical daughter cells. It is used for growth, repair, and asexual reproduction. The process has distinct stages, but for GCSE you mainly need to understand what happens overall and why.
Before mitosis begins, the cell's DNA is replicated — each chromosome is copied exactly, so the cell has double the normal amount of DNA. During mitosis, the chromosomes line up in the middle of the cell, copies are pulled to opposite ends, and the cell divides to form two daughter cells. Each daughter cell has the same number of chromosomes as the original — 46 in human body cells (23 pairs).
The cell cycle includes: cell growth (the G1 phase), DNA replication (the S phase), further growth and preparation for division (G2), and mitosis itself (M phase). Cancer occurs when the cell cycle loses its normal controls and cells divide uncontrollably — producing a tumour.
Stem cells are undifferentiated cells capable of dividing and differentiating into specialised cell types. There are two main types at GCSE:
The AQA cell biology specification is at the AQA GCSE Biology specification page.
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