The Cell Theory And how it developed

Problem: Cells are small Most cells are too small to be seen without magnification. Look at your hand? Do you see cells?

Sizes of cellular components

Solution: Magnification Simple magnifiers: drop of water or glass bead.

Compound magnification First microscope invented by Zacharias and Hans Janssen in the 1590's Uses a series of lenses to make larger images

Microscopes Various styles of microscope were developed by mid 1600’s, mostly to examine cloth

Robert Hooke - 1665 First recorded examination of biological material with microscope Looked at slices of cork Described structure as “cells”

Hooke’s observation

Hooke’s observations Cork was long-dead material – saw remains of cell walls only. Later examined fresh plant tissue – saw fluids inside.

Cells are the basic structural unit of living things. Impact: Cells are the basic structural unit of living things.

Good amateur microscope maker. Anton Von Leeuwenhoek Good amateur microscope maker. 1668 - Examined pond water with microscope: saw freely moving “beasties” or “animalcules”.

Von Leeuwenhoek Also examined blood. First to observe single-celled organisms in tooth debris.

Von Leeuwenhoek Considered the father of microbiology

A single cell can perform all life Impact: A single cell can perform all life functions.

Proposed that all living things were made of cells. Henri Dutrochet - 1824 Proposed that all living things were made of cells. based on observations of many organisms.

Technology – 1820’s on: Development of staining techniques improves visibility of cellular structure. unstained tissue mostly clear. Special chemical reactions can show structures, enzymes, whole cell shape, etc.

Staining makes bacterial cells stand out.

Robert Brown - 1831 Realizes that all cells have a dense region in the center. Calls it a nucleus. Function unknown.

Matthias Schleiden - 1838 Observed many plant samples Concluded that all plants are made of cells

Theodor Schwann - 1839 Observed many animal samples Concluded that all animals are made of cells.

Johannes Purkinje - 1839 Reported that all cells he observed were filled with jelly-like substance. Named this substance protoplasm. assumed to have special life-giving chracteristics.

Impact: All living things are made of cells

Rudolph Virchow - 1855 Observed cells dividing. True in plants and animals

All cells come from pre-existing cells Impact: All cells come from pre-existing cells

Cell Theory – late 1800’s All living things are made of cells and cell products. All cells carry on life activities. Life activities of multicelled organisms are combined product of all cells. New cells arise only from other cells by the process of cell division.

1939 – Electron microscope allows much greater magnification. Technology improves 1939 – Electron microscope allows much greater magnification. Uses electrons, rather than light. Allows much greater resolution, too. Specimens must be exposed to vacuum, so not good for living things.

Getting information from an image: Magnification tells how many times bigger the object appears. Bigger is easier to see. Resolution tells how much detail is available in the image. A bigger image with poor resolution is useless!

Electron Microscope

Scanning Electron Microscope Bounces electrons off surfaces without penetrating. Produces very detailed 3-D view of surface. No internal structure!

SEM Images

Transmission Electron Microscope Maximum magnification – can see large molecules! Electrons pass through very thin (0.2mm) slices of an object and are detected on a screen. Allows examination of structures within cells.

TEM Image

Compound Light Microscope Light passes up from the base and is focused through a diaphragm. It passes through the specimen, and a series of lenses in the objective magnify the specimen. Lenses in eyepiece provide a magnified view of the first image.

The specimen The object to be observed is placed on a glass slide. Must be thin and clear enough for light to pass through. It must be covered with water or another clear liquid. A thin cover glass is placed over the object and liquid.

Illumination Different types of illumination can emphasize different features of the specimen. Can be combined with special stains – UV light with fluroescent stains or labels for particular types of materials.

Types of Light Microscopy

Stereomicroscope A stereo or dissection microscope is a low power light microscope. Good for magnifying objects and getting a three dimensional view of surfaces. Light can bounce off the surface of the specimen, be transmitted through it, or both. You cannot typically see individual cells because of the low magnification, and because the objects are too thick for good resolution.

A stereo microscope Note the 2 light sources: From above, or epi-illumination From below, or transillumination

Stereomicroscope Also called a dissecting microscope, it is most useful for magnifying objects while they are being manipulated.

What to use? What type of microscope you use depends on what information you need. May use a stereomicroscope to obtain a tissue sample, a light microscope to look at the tissue, and transmission electron microscope to learn about the details within the cells.