C HAPTER 2 Section 2

E ARLY M ICROSCOPES 1500s – 1 st microscope was made Mid 1600s – Antonie van Leeuwenhoek Made a simple microscope with a tiny glass bead for a lens Could magnify objects 270 times The object was 270 times larger than its actual size

M ODERN M ICROSCOPES Depending on how many lenses a microscope contains it is called simple or compound Simple: like a magnifying lens – it has only one lens The image is enlarged and directs light toward your eye The change in size of the object is the magnification Not all microscopes have the same magnification

M ODERN M ICROSCOPES The microscope most commonly used in life science is the compound microscope Compound microscope: 2 sets of lenses Eyepiece lens Objective lens Eyepiece lenses – can be one or two of these Two eyepieces: the object is 3-D One eyepiece: The object is not 3-D Objective lens Typically 2-4 moveable objective lenses with different magnifications

M AGNIFICATION Two pieces of information needed to determine magnification 1 st determine the magnification of the eyepiece – typically 10x magnification Objective lenses – the magnification will be on the lens Example 10x Total magnification: (10) x (10) 100x magnification

E LECTRON M ICROSCOPE If the object is too small to be seen with a light or compound microscope then an electron microscope must be used Instead of using lenses, a magnetic field in a vacuum is used to direct a beam of electrons Types of electron microscopes 1. Scanning electron microscope Produce a 3-D image 2. Transmission electron microscope Produce a 2-D image of a thinly sliced specimen

C ELL T HEORY Cells were not discovered until the microscope was improved 1665 – Robert Hooke cut a thin slice of a cork and called the small boxes he observed under the microscope cells 1830s – Matthias Schleiden used a microscope to study plants and concluded that they are made of cells

C ELL T HEORY Theodor Schwann concluded that all animals are made of cells He combined his idea with Schleiden’s and they concluded that all living things are made of cells Rudolf Virchow hypothesized that all cells divide to form new cells Every cell comes from a cell that already existed

C ELL T HEORY 1. All organisms are made up of one or more cells All organisms can be one cell or many cells like most plants and animals 2. The cell is the basic unit of organization in organisms Even in complex organisms, the cell is the basic unit of structure and function 3. All cells come from cells Most cells can divide to form two new, identical cells