# Cell Structure

> CIE A-Level Biology · CIE 9700 A-Level
> Source: https://www.owlsprep.com/study/cie-9700-u1-overview/
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This unit introduces the fundamental building blocks of life, the tools to study them, and the structure of all major cell and virus types. It forms the foundational knowledge for every other topic in A-Level Biology.

**Prerequisites:** Basic secondary school level knowledge of cells and biological concepts

## Learning objectives

- Explain the principles of microscopy and calculate cell size, actual size and magnification correctly
- Name and describe the function of key structures in eukaryotic, prokaryotic, and viral particles
- Compare and contrast structural features of eukaryotic and prokaryotic cells
- Relate cell structure to cellular function, building a foundation for all subsequent biology topics

## Unit at a glance

This unit follows a logical sequence: we start with how biologists see and measure cells, before diving into the detailed structure of each major type of biological entity. You will first learn about eukaryotic cells (the complex cells that make up plants and animals), then simpler prokaryotic cells, then acellular viruses, before finishing with a direct comparison of the two main cell types.

Mastery of this unit is critical: all later topics from cell division to immunology to physiology rely on understanding cell structure and function.

This unit covers the following core sub-topics:
- [Microscopy and cell measurement](https://www.owlsprep.com/study/cie-9700-u1-microscopy-and-cell-measurement/) — Learn how light and electron microscopes work, and master calculations for magnification, image size and actual size.
- [Eukaryotic cell ultrastructure](https://www.owlsprep.com/study/cie-9700-u1-eukaryotic-cell-ultrastructure/) — Explore the structure and function of all major membrane-bound and non-membrane-bound organelles in plant and animal cells.
- [Prokaryotic cell structure](https://www.owlsprep.com/study/cie-9700-u1-prokaryotic-cell-structure/) — Understand the key structural features of bacterial prokaryotic cells.
- [Virus structure](https://www.owlsprep.com/study/cie-9700-u1-virus-structure/) — Learn the acellular structure of viruses, including their core common components.
- [Comparison of eukaryotic and prokaryotic cells](https://www.owlsprep.com/study/cie-9700-u1-comparison-of-eukaryotic-and-prokaryotic/) — Summarize key structural similarities and differences between eukaryotic and prokaryotic cells.

## Common pitfalls

- **Wrong:** Confusing magnification and resolution
  - Why it fails: Students often mix these two distinct properties of microscopes, which is a common exam question trap
  - Correct: Remember: magnification makes an image larger, resolution is the ability to distinguish two separate points as distinct
- **Wrong:** Classifying viruses as prokaryotic cells
  - Why it fails: Viruses are non-cellular, so they do not fit into the prokaryote/eukaryote classification
  - Correct: Always categorize viruses as acellular infectious particles, not prokaryotic cells
- **Wrong:** Forgetting that prokaryotes have ribosomes
  - Why it fails: Students often assume prokaryotes have no organelles at all, but ribosomes are present
  - Correct: Remember prokaryotes have small 70S ribosomes, which are not membrane-bound

## Cheatsheet

| Concept / Formula | Key Detail |
| --- | --- |
| Magnification formula | $Magnification = \frac{Image\ size}{Actual\ size}$ |
| Resolution | Ability to distinguish two separate adjacent points as distinct |

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From [OwlsPrep](https://www.owlsprep.com) — free study guides for A-Level, IB, AP and IGCSE, written against the official syllabus. Canonical page: https://www.owlsprep.com/study/cie-9700-u1-overview/