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.

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Head

Arm

Coarse knob

Fine knob

On/off switch

Base

Ocular lens

Nose piece

Objectives

Stage

Mechanical stage

Condenser

Light source

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Ocular

Objectives

diaphragm

Stage control

knobs

Condenser

Light source 4

1. MagnificationOcular (10x) x objective (40x) = 400x

2. Parfocal and parcentral imagingParfocal: 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 focusIs the vertical distance between the lens and

the object. Thickness of the specimen decreases as magnification increases.

400x

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

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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.

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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

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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

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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.

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cytoplasm cell wall

plasma membrane

nucleolus

nucleus

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Human cheek cells wet mount Identify: plasma membrane, cytoplasm, nucleus.

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plasma membrane

nucleus

cytoplasm

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