BIO 101 lesson

The cell and cell theory

Define the cell, retell how it was discovered, and state the three points of cell theory.

BIO CH.1-7.pdf, book pp. 20–21, 29–30

Understand the idea

The cell is the lowest living structure that can carry out life’s jobs. It is the structural and functional unit of life. Most cells are 1–100 micrometres wide. Unicellular examples are Amoeba, Paramecium, and Chlamydomonas. Multicellular examples are humans, cats, and Spirogyra. All must take in nutrients, remove wastes, respond, and reproduce.

Robert Hooke improved a compound microscope in 1665 and saw tiny pores in cork. He named them cells because they looked like monastery rooms, and he published Micrographia. Leeuwenhoek’s simple microscope magnified 200–300 times; he saw bacteria and protozoa (‘animalcules’) and described sperm in 1677.

Schleiden (plants, 1838) and Schwann (animals, 1839) argued that cells make up plants and animals. They were wrong about how new cells appear. Rudolf Virchow stated in 1855 that all cells come from existing cells. Cell theory now has three points: living things are made of cells; the cell is the smallest unit of a living thing; new cells come from pre-existing cells.

What to remember

Hooke named cells (1665); Leeuwenhoek saw microbes.
Schleiden and Schwann proposed cell theory; Virchow added origin from existing cells.
Unicellular = one cell; multicellular = many specialised cells.

Check your understanding: Cell theory says new cells come from which source?

Spontaneous dustPre-existing cellsSeeding by the nucleus onlyCrystalising body fluids

Practice check. This does not award XP or affect your assessment score.

Recap

A cell is life’s unit. Microscopes revealed it. Cell theory’s three lines are your exam core: composition, smallest unit, and origin from other cells.