Life Sciences 11 · Biology · Lesson 2.1
Cell theory & cell types
- Level
- Grade 11
- Reading time
- 14 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
The cell theory; prokaryotic vs eukaryotic and plant vs animal cells.
What is the cell theory?
Short answer
The cell theory is a foundational principle of biology with three parts: all living things are made of one or more cells, the cell is the basic unit of structure and function in life, and all cells arise from pre-existing cells. It unified biology by establishing the cell as the common basis of every organism, from bacteria to humans.
Concept preview
What you will be able to do
- 01State the three principles of the cell theory and who established them.
- 02Compare prokaryotic and eukaryotic cells in structure and size.
- 03Compare plant and animal cells and explain the reasons for their differences.
- 04Explain why cells are small using the surface-area-to-volume ratio.
In 1665 Robert Hooke shaved a sliver of cork, put it under an early microscope, and saw a honeycomb of tiny empty boxes he called 'cells' — the word survives from that first look. A few years later Antonie van Leeuwenhoek, grinding better lenses, became the first person ever to see living single-celled organisms swimming in pond water, which he called 'animalcules'. For the first time humans could see that life is built from units far too small for the naked eye. Every idea in this course rests on the tools and observations that began in those two moments.
School Plan
Cell theory & cell types
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Related topics
Frequently asked questions
- What are the three parts of the cell theory?
- All organisms are made of cells; the cell is the basic unit of life; and all cells come from existing cells.
- What is the difference between prokaryotic and eukaryotic cells?
- Eukaryotic cells have a membrane-bound nucleus and organelles; prokaryotic cells (bacteria and archaea) do not.