BIOLOGY · Stage 7 · Chapter 2: Cells and Organisation
Biology 2.2 The cell story — Microscopes and Cell Theory — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 6 parts Lesson 2 of 10
Lesson summary
2.2 The cell story — Microscopes and Cell Theory — Alhussan International Academy — Biology (Stages 7–9) notes: Describe how improvements in microscopes led to the discovery of cells and the development of cell theory.Cell size — cells are far too small to see, so nobody knew bef…
- Invention of the microscope
- New technology
- Hooke's cells
- Van Leeuwenhoek
- Scientific theory
- Spontaneous generation
Section 1 of 6Why cells were discovered late
- Cell size
- cells are far too small to see, so nobody knew before the 1600s that living things are made of cells.
- Invention of the microscope
- the first cells were seen in Europe in the 17th century, about 350 years ago.
- Early microscopes used polished glass lenses, and they were tiny and did not look like modern ones.
- Better lens making allowed scientists to see more detail.
- New technology
- the story of the cell shows how new technology leads to new knowledge.
Section 2 of 6Early microscopists
| Date | Scientist | Discovery |
|---|---|---|
| 1665 | Robert Hooke | Looked at a thin slice of cork with a simple microscope, saw a honeycomb structure and called each unit a cell |
| 1670–1683 | Anton van Leeuwenhoek | Made fine polished lenses, looked at pond water and was the first person to see living cells |
| 1833 | Robert Brown | Saw the internal structure of plant cells and discovered the nucleus, which contains the genetic material |
- Hooke's cells
- he saw only the walls of dead cork cells, and he made careful drawings.
- Van Leeuwenhoek
- he was not a trained scientist, and he made detailed drawings of the tiny living organisms he saw.
Section 3 of 6Development of the cell theory
| Date | Scientist | Discovery |
|---|---|---|
| 1838 | Matthias Jakob Schleiden | Suggested that all plant tissues are made of cells, which are the building blocks of plants |
| 1839 | Theodor Schwann | Stated that the cell is the basic unit of structure of all organisms and that all organisms consist of one or more cells |
| 1845 | Carl-Heinrich Braun | Simplified the wording: cells are the basic unit of life |
| 1855 | Rudolf Virchow | Proposed that new cells come from existing cells |
- Credit
- Schwann is given the credit for the modern cell theory.
Section 4 of 6Statements of the cell theory
- All living organisms are made of one or more cells.
- The cell is the basic unit of structure and function in living things.
- All cells arise from pre-existing cells by cell division.
- Scientific theory
- a well-tested explanation supported by a lot of evidence, not just a guess.
- It can be changed if new evidence is found.
- Spontaneous generation
- the older idea that living things could appear from non-living material such as rotting meat, which the third statement replaced.
Section 5 of 6Why the cell theory was accepted in the 19th century
- Doubt earlier
- many people did not believe Hooke and van Leeuwenhoek because good microscopes were hard to make.
- Without a microscope nobody could see the cells and microorganisms that were described.
- Better microscopes
- more people had good microscopes in the 19th century.
- Communication
- easier communication between countries let scientists compare findings and agree on what they saw.
- Cumulative science
- scientific knowledge is built by many people over time, each using and testing the work of others.
Section 6 of 6From light to electron microscopes
- Light microscope
- magnifies up to about 1000 times and shows the nucleus, cytoplasm and chloroplasts.
- Electron microscope
- developed in the 1930s, it uses beams of electrons and magnifies up to 1 million times.
- It reveals ribosomes, the detail of mitochondria and the cell membrane.
- Cell membrane
- it is too thin to see with a light microscope.
- Its existence was shown first by experiments on how substances enter cells and later confirmed with the electron microscope.
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