Cell Theory

Cell Theory
Understanding of cells required
1.Improvement of microscopes
2.Hundreds of years of research and observations
The Cell Theory states
1.All living things are made of cells
2.Cells are the basic units of structure and function in living things
3.Cells come from pre-existing cells

Exceptions to cells theory
1. Where did the first cell come from?
2. Viruses: non-living genetic material; need to

act as parasites to reproduce
3. Mitochondria and chloroplasts have their own DNA; partially reproduce on their own

Cell Theory Timeline
1590s: Zacharias Janssen worked with his father and invented the first compound microscope 1665: Robert Hooke observes cork under a microscope and names the tiny boxes he saw
“cells”
1673: Anton von Leeuwenhoek observed single-celled organisms and blood cells

Cell Theory Timeline
1801: Robert Brown discovers the nucleus of the cell
1838: Matthias Schleiden (ShLY-dun) says all plants are made of cells
Theodor Schwann says all animals are made of cells 1855: Rudolph Virchow (FUR-koh)says cells only come from other cells

Cell scale
cell scale

Levels of organization
Cells: Smallest structural and functional unit of

an organism
E.g. Skin cells, Nerve cells

Tissues: a group of similar cells that perform

particular functions
E.g. Nerve, muscle, connective, epithelial

Organs: groups of tissues working together
E.g. Heart, Kidney

Organ systems: a group of organs working

together
E.g. Digestive system, nervous system

Basic Cell Structure
The cell membrane: A thin, flexible barrier

around the cell.
Cell wall: