Chapter7

Microscopes and cells

Where does cork come from?

• The bark of an oak tree that grows in Spain and Portugal

• The bark is dead• All that is left are the

cell walls enclosing air

Microscopes reveal cell structure

• Robert Hooke , an English scientist, invented the microscope in the 1600’s to view cork

• He named the “little boxes” he saw, “cells”

Anton van Leeuwenhoek

• 10 years after Hooke’s findings

• Used a microscope to view pond water

• He named the single-celled organisms he discovered “animalcules”

Measuring the size of cell structures

• Measurements are in metric units

• International System of Measurements (SI)

• Based on powers of 10• Micrometers are one-

millionth of a meter ( the size of a bacterial cell)

Characteristics of microscopes Magnification vs. Resolution- makes an image -makes an image

appear larger than appear more or less

its actual size clear

BOTH are needed to view the details of extremely small objects clearly

Different types of microscopes

Light microscopes Electron Microscopes

Light passes through uses a beam of electrons

one or more lenses to form an image

to produce an enlarged

image

Compound Light Microscope

• Used in high school labs• Total magnification=ocular lens x objective lens• Most powerful magnifies 2,000x • Can view live specimens• Much less powerful than electron microscope

Staining Cells

– Problem with light microscopy is that most living cells are nearly transparent, making it difficult to see the structures within them.

– Using chemical stains or dyes can usually solve this problem.

– Some of these stains are so specific that they reveal only compounds or structures within the cell.

Electron Microscopes

• Can magnify up to 200,000x

• Specimen must be viewed in a vacuum

• No live specimens can be viewed

Electron Microscope

• Uses a beam of electrons

• Higher resolution

• Two major types– Transmission– Scanning

• Must be viewed in a vacuum

• All specimens that are viewed must be dead

Transmission Electron Microscope

-Reveal internal structures of the cell

TEM of sperm

TEM

• Can see– Cell structures – Large Proteins

• Samples must be cut in ultra thin slices

• Produces flat 2-d images

Scanning Electron Microscope

-Shows 3-D images of cell surfaces

SEM of sperm cells

SEM

• Pencil-like beam of electrons scanned over the surface of the specimen

• Produces a 3-d image

Rules when using the Microscope

• Carry the microscope by the arm and base.

• Place the microscope 4 – 6 inches from the edge of the lab table.

• Do not use the coarse adjustment when on high power.

Field of View

• 3 things to include in a

Microscope drawing:

1.Title

2.At least 1 label

3.Total magnification