BiologyBiology

The Study The Study of Lifeof Life

Cell Theory: Before Microscopes

• Before microscopes, most people believed in spontaneous generation (The belief that living things could arise from non-living matter).

1668: Francesco Rediattempts to disprove thespontaneous generation

in maggots.

1745: John Needham attemptsto prove spontaneous generation.Attributes results to a “life force”

Spontaneous generation was upheld until the mid-1800s.

• In 1859, Louis Pasteur finally disproved the theory of spontaneous generation.

• Used a swan-shaped flask to show that if no microbes could get into the broth, nothing would grow

• What made his experiment good?

Controlled Variables- Same broth, light, temp.

Manipulated Variable

- Whether or not microbes have access to broth

Responding Variable

- Whether or not microbes grewWhat impact do you think this had on medical practice.

The Development of the Microscope

• Explain the following statement:“You may owe your life to the invention of the microscope.”

• 1595: The Janssen Bros. invent the first microscope.

- It was compound (2 lenses)

• 1665: Robert Hooke improves on the design

- Observes first tiny units of life and calls them “cells”

•Antoni van Antoni van Leeuwenhoek was Leeuwenhoek was the first person to the first person to see living cells.see living cells.

Cell Theory: Gets It’s Start …

•1839: M.J. Schleiden, Theodor Schwaan put forth a three part cell theory:

1) All living things are made up of one or more cells.

2) Cells are the smallest functional units of organisms (i.e. the organism’s needs are the cells’ needs).

- Take in nutrients- Use energy to do work (life processes)- Get rid of wastes- Maintain certain temperatures and chemical conditions (e.g. acidity)

Multi-cellular organisms are just cells working together to accomplish these basic tasks

Cell Tissue Organ System Body

3) All cells come from pre-existing cells through the process of cell division. (not from spontaneous generation)

• The Compound Light Microscope

Microscopes as Windows to Cells

– Light passes through the specimen

– Lenses enlarge, or magnify, the image.

– micrometres (μ) are used to measure very tiny objects. (1mm = 1000μm)

(a) Light micrograph (LM) of a white blood cell (stained purple) surrounded by red blood cells

Magnification

•To calculate the magnification of the microscope – ocular x objective

•An increase in the specimen’s apparent size.

PowerOcular Lens

MagnificationObjective

MagnificationTotal

Magnification

Low 10X 4X 40X

Medium 10X 10X 100X

High 10X 40X 400X

Field of View (F.O.V.): The diameter of the circular region of the slide visible under the microscope

• the higher the magnification, the smaller the field of view.

F.O.V.

Power Magnification F.O.V.

Low 40x

Medium 100x

High 400x

Field of view can be used to estimate the actual size of objects

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Determining the F.O.V. of Higher Magnifications

• The field of view under higher magnification can be less than 1mm.

• We can estimate by using the low magnification and F.O.V. in a formula.

Determining the F.O.V. of Higher Magnifications

Example:

High F.O.V. (HP) = Low F.O.V. (LP) x LP magnification ÷ HP magnification

Example:

HP magnification = 40XLP magnification = 4XLP F.O.V. = 4500µm

HP F.O.V. = 4500µm x 4X ÷ 40X

HP F.O.V. = 4500µm x 0.1

HP F.O.V. = 450µm

Resolution

• The ability to distinguish individual objects.

• The greater the magnification, the smaller the objects that can be resolved.

Contrast

• dark vs. bright• phase contrast microscopes enhance contrast.

Staining Nucleus isstained

Fluorescent Stains

• used to increase contrast and to show specific parts of cells.

• The Electron Microscope (EM)

– It uses a beam of electrons

– It has a higher resolving power than the light microscope

• The electron microscope can magnify up to 100,000X

• Such power reveals the diverse parts within a cell

Human height

Length of somenerve andmuscle cells

Frogeggs

Chickenegg

Plant andanimalcells

Nucleus

Most bacteria

Mitochondrion

Smallest bacteriaViruses

Proteins

Smallmolecules

Atoms

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SEM• The scanning electron

microscope (SEM) is used to study the detailed architecture of the surface of a cell

(b) Scanning electron micrograph (SEM) of cilia (above)And a white blood cell

TEM• The transmission electron microscope (TEM)

is useful for exploring the internal structure of a cell

(c) Transmission electron micrograph (TEM) of a white blood cell & cilial

Homework

• Read page 510 of your textbook and complete the Instant Practice Problems

• Using page 508 of your textbook, completely label the microscope picture.