Ch. 1: Cell Structure & Function – Seeing It All - Microscopes – Cell Theory -
Sect. 1: Discovering Cells - Microscopes – - Cell Theory -
With the invention of microscopes, scientists were now able to examine organisms too small to be viewed with the naked eye.
The human eye is only capable of seeing objects 0.5 mm and above, hence the need for microscopes.
The discovery of cells were limited by the size restrictions inherent in cells.
Cells size is dictated by geometry. Cells require a specific surface-area to volume ratio in order to be able to acquire nutrients and expel waste products. The average size of a plant or animal cell is between 10 and 100 µm (micrometers) (0.01mm – 0.1mm) This is why larger organisms don’t have larger cells just more cells.
Microscopy
is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye).
There are three well-known branches of microscopy 1.
Optical microscopy
the "light microscope", is a type of microscope which uses visible light and a system of lenses to magnify images of small samples. uses light to magnify an image by bending the light that passes through them. Optical microscopes are the oldest design of microscope and were invented in 1590.
Zacharias & Hans Janssen; Dutch eyeglass makers
2.
Optical microscopes were easy to develop and are popular because they use visible light so the sample can be directly observed by eye.
2 categories of optical or light microscopes 1. Simple: contains only one lens. 2. Compound: contains 2 or more lenses. Electron microscopy
Type of microscope that produces an electronicallymagnified image of a specimen for detailed observation. The electron microscope (EM) uses a particle beam of electrons to illuminate the specimen and create a magnified image. The microscope has a greater resolution than a lightpowered or optical microscope Example: Transmission Electron Microscope
3.
Scanning probe microscopy
is a branch of microscopy that forms images of surfaces using a physical probe that scans the specimen. SPM was founded with the invention of the scanning tunneling microscope in 1981. SPM’s are capable of showing atomic level resolution. Examples
Scanning Electron Microscope Scanning Tunneling Microscope
Properties of Microscopes
Magnification is the ability to enlarge an image.
To determine magnification of compound optical microscopes Multiply
the magnification of the lenses of the microscope.
Example) Lens 1: 10 x Lens 2: 20 =
Total magnification = 200 (times)
Example) Lens 1: 15 x Lens 2: 15 x Lens 3: 10
Total magnification = 2250 (times)
Resolution is the clarity or sharpness of an image.
Also called the resolving power. Defined
as the minimum distance 2 points can be separated and still be distinguished as 2 separate points.
The resolution of electron microscopes are superior to that of light microscope. Because it uses electrons that have wavelengths about 100,000 times shorter than visible light it can achieve magnifications of up to 2,000,000 times. Light microscopes are limited to 2000 times magnification
Robert Hooke In 1663, used a compound microscope to look at slices of cork. Named the rectangular, empty spaces “cells.” “Cells” means small rooms.
Anton van Leeuwenhoek 1st to use a simple microscope to observe single-celled microorganisms. He called this organisms “animalcules” meaning “little animals.”
Matthias Schleiden
1838 concluded all plants are made of cells. In 1832 Barthelemy Dumortier (1797–1878) of France had already described cell division or “binary fission” in plants.
Theodor Schwann
1839 concluded that all animals are also made of cells, therefore all living things are made of cells. Jan Purkyňe (1787–1869), or Purkinje, in 1837 proposed not only that animals were composed principally of cells and also that the "basic cellular tissue is again clearly analogous to that of plants."
Rudolf Virchow
1855 proposed that new cells are formed only from cells that already exist. Credited with the phrase “Omnis cellua e cellua”
“All cells from cells”
Robert Remak (1852–1865), published his observations on cell division in 1852 stating that binary fission was the means of reproduction of new animal cells.
Binary fission is a form of cell division used by all prokaryotes, some protozoa, and some organelles within eukaryotic organisms. This process results in the reproduction of a living prokaryotic cell by division into two parts which each have the potential to grow to the size of the original cell.
ď Ź
The Cell Theory is a widely accepted explanation of the relationship between cells and living things. 1. 2.
3.
ď Ź
All living things are composed of cells. Cells are the basic units of structure and function in living things. All cells are produced from cells.
The cell theory is applied to all living things, no matter how big or how small.
“Modern” cell Theory
The generally accepted parts of modern cell theory include: The cell is the fundamental unit of structure and function in living organisms. All cells arise from pre-existing cells by division. Energy flow (metabolism and biochemistry) occurs within cells. Cells contain hereditary information (DNA) which is passed from cell to cell during cell division. All cells are basically the same in chemical composition in organisms of similar species. All known living things are made up of one or more cells. Some organisms are made up of only one cell and are known as unicellular organisms others are multi-cellular and composed of a number of cells. The activity of an organism depends on the total activity of independent cells.
Cell Theory exceptions Viruses are considered alive by some, yet they are not made up of cells. Viruses have many features of life, but by definition of the cell theory, they are not alive. The first cell did not originate from a preexisting cell. There was no exact first cell since the definition of cell is imprecise. Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell.