 The unaided eye can distinguish objects more than 0.1 mm in diameter.
Since most cells are between 0.1-0.01 mm in diameter, scientists use
microscopes to view very small objects such as cells.
 Light microscopes bend visible light using optical devices such as
lenses and prisms to magnify the apparent image size.
 We will discuss the compound light microscope , you should learn all
the parts and their functions, and know the proper care and use of one.
2
Ocular lens
Head
Arm
Nose piece
Objectives
Stage
Coarse knob
Fine knob
On/off switch
Mechanical stage
Condenser
Light source
Base
3
Ocular
Objectives
diaphragm
Stage control
knobs
Condenser
Light source
4
 1. Magnification
 Ocular (10x) x objective (40x) = 400x
 2. Parfocal and parcentral imaging
 Parfocal: image remains in focus when switching lenses.
 Parcentral: image remains in the center of field of view
when lenses are changed.
Field of view
40x
5
 3. Depth of focus
 Is the vertical distance between the lens and the object.
Thickness of the specimen decreases as magnification
increases.
A 3-colored thread slide was
focused. Note that one thread is in
focus and the others are not. The
clearly focused thread lies on top
of the mount.
Top
Middle
Bottom
400x
6
 4. Image orientation
 The image seen will be real,
inverted, and magnified by
the objective.
 Notice the letter “e” is
upside down in the
slide.
 When viewed through the
microscope, it is right side
up.
7
 5. Resolving power: the degree at which two adjacent
points on a specimen are seen as separate detailed
images.
 Difference between blurry and sharp images.
 6. Contrast: how well the details of a specimen stand
out against a background. Stains and lighting are used
to increase contrast to see detail.
Protista Volvox seen
through the microscope
8
 In Greek the term for “cell” is “cyto” ; therefore, cytology is the study of
cells and how they function.
Types of cells
 There are two fundamental kinds of cells: prokaryotic and eukaryotic.
 Prokaryotes: means “before the nucleus”. Lacks nuclear membrane.
 Example: bacteria
This is a Bacillus type bacteria
 Eukaryotes: “eu” means “real” or “true nucleus”. Eukaryotes can be
uni- or multicellular organisms.
 Example: plans, animals, protists, fungi.
This picture is a dinoflagelate, of the group Protista.
9
 Elodea wet mount
 Identify: cell wall, chloroplast, plasma membrane, cytoplasm
10
cell wall
plasma membrane
chloroplast
cytoplasm
11
 This is the membrane between
the thick layers of the onion.
 Identify: plasma membrane,
cell wall, nucleus, nucleolus,
cytoplasm.
12
cytoplasm
cell wall
plasma membrane
nucleolus
nucleus
13
 Human cheek cells wet mount
 Identify: plasma membrane, cytoplasm, nucleus.
14
plasma membrane
nucleus
cytoplasm
End
15