7-1 Life is Cellular The cell is the common structure that makes up every living thing
The discovery of the cell • Without the instruments to make them visible, cells remained unknown for most of human history.
Early MIcroscopes • In 1665, Englishman Robert Hooke used an early compound microscope to look at a thin slice of cork, a plant material. • Under the microscope, cork seemed to be made of thousands of tiny, empty chambers. • He called these chambers “cells” bacause they reminded him of a monastary’s tiny rooms, which were called cells.
Early Microscopes • In Holland around the same time, Anton van Leeuwehoek used a single-lens microscope to observe pond water and other things
The Cell Theory • Numerous observations soon made it clear that cells are the basic units of life • 1838-Matthias Schlieden concluded that all plants were made of cells • 1839-Theodor Schwann states that all animals were made of cells
The Cell Theory • The cell theory states: • All living things are composed of cells • Cells are the basic units of structure and function in living things • New cells are produced from existing cells
Exploring the Cell • Light itself limits the detail, or resolution, of images that can be made with the light microscope. • Light waves are diffracted, or scattered, as they pass through matter making it impossible to visualize tiny structures such as proteins and viruses with a light microscope
Electron Microscopes • Electron microscopes are capable of revealing details as much as 1000 times smaller than those visible in light microscopes. • Transmission electron microscopes (TEMs) make it possible to explore tiny structures, but specimens must be cut into ultrathin slices • Scanning electron microscopes (SEMs) scan a beam of electrons over the surface of the specimen, specimens do mot have to be sliced
Scanning Probe Microscopes • These have made it possible to observe single atoms • DNA and proteins have also been made visible by these
Prokaryotes and Eukaryotes • All cells have 2 things in common: they are surrounded by a thick barrier called a cell membrane, and they contain DNA • The nucleus is a large membrane enclosed structure that contains the cell’s DNA • Eukaryotes are cells that contain nuclei • Prokaryotes are cells that do not contain nuclei
prokaryotes • Prokaryotic cells are generally smaller and simpler than eukaryotic cells. • Prokaryotic cells have genetic material not contained in a nucleus
eukaryotes • Eukaryotes are generally larger and more complex than prokaryotic cells. The nucleus separates their genetic material from the rest of the cell