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BIO206H5 Chapter Notes -Transmission Electron Microscopy, Scanning Electron Microscope, Hydrogen Atom


Department
Biology
Course Code
BIO206H5
Professor
George S Espie

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Introduction to Cells
(pgs 1-36) 30/05/2010 20:30:00
All living this are made of “cells”: small, membrane-enclosed, units filled
with a concentrated aqueous solution of chemicals and endowed with the
extraordinary ability to create copies of themselves by growing and
dividing in two
[Cells are the fundamental units of life]
UNITY & DIVERSITY OF CELLS
Cells vary enormously in appearance and function (Figure 1-1 pg 3)
Some cells are clad only in a flimsy membrane & some cover this delicate
layer by cloaking themselves in an outer layer of slime, building
themselves rigid cell walls, or surrounding themselves with hard,
mineralized material, such as that found in bone
There is a division of labour in cells (allowing some cells to become
specialized to an extreme degree for particular tasks and leaving them
dependent on their fellow cells for many basic requirements)*
All cells are composed of the same sorts of molecules that participate in
the same types of chemical rxns
All present-day cells have apparently ‘evolved’ from the same ancestor
“Genome”-the complete set of genetic material in a cell (specifically its
DNA)
CELLS UNDER THE MICROSCOPE
“Light Microscope”- use visible light to illuminate specimens
“Electron Microscope”- use beams of electrons instead of beams of
light as the source of illumination (making it possible to see the fine
details of cells and even making some of the larger molecules visible
individually)
“Transmission Electron Microscope”- type of electron microscope
used to look at thin sections of tissue (similar to a light microscope, but
transmits a beam of electrons instead)
“Scanning Electron Microscope”- type of electron microscope which
scatter electrons off the surface of the sample and so is used to look at
the surface detail of cells and other structures

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“Cell Theory”- all living things are made up of cells and cells arise from
pre-existing cells [proved by Louis Pasteur & his broth]
A tissue usu has to be fixed by embedding in a solid wax or resin, cut or
sectioned into thin slices, and stained before it is viewed (regardless of
the type of microscope)
THE PROCARYOTIC CELL
‘Pro’= before, ‘Karyon’= kernel, nut, or nucleus
Bacteria have the simplest structure and come closest to showing us life
stripped down to its essentials:
oNo organelles
oNo membrane-bound nucleus to hold its DNA
Typically spherical, rod-like, or corkshrew-shaped, and small (0.1-10 μm
diameter, 1000X less volume than Eukaryotes)
Have a protective coat, called a ‘cell wall’, surrounding the plasma
membrane (i.e. cell membrane)
Cell reproduce quickly by dividing into two
With sufficient food, some can duplicate itself in as little as 20 min.
Fortunately for their;
oLarge numbers
oRapid growth rates,
oAnd ability to exchange bits of genetic material by a process
akin to sex,
Pops of prokaryotic cells can evolve fast, rapidly acquiring the
ability to use new food source or to resist being killed by a new
antibiotic
Most live as single-celled orgs (although some join together to form
chains, clusters, or other organized multicellular structures)
In terms of chemistry, they are the most diverse and inventive class of
cells
Live in a variety of conditions
oSome are aerobic and some are anaerobic
oSome can live entirely on inorganic substances; CO2 in the
atmosphere, N from N2 in the atmosphere, O, H, S, & P in the
air, water, and inorganic minerals

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oSome perform ‘photosynthesis’ (getting energy from sunlight)
oOther derive their energy from the chemical reactivity of
inorganic substances in the env. (E.g. Beggiatoa)
It is almost certain that chloroplasts have evolved from photosynthetic
bacteria that found a home inside the plant cell’s cytoplasm
Two Domains:
“Bacteria” – include most of the prokaryotes familiar from everyday life
“Archaea”- usu live in hostile conditions
THE EUCARYOTIC CELL
‘Eu’ = true, ‘Karyon’ = kernel, nut or nucleus
Bigger and more elaborate (as compared with Prokaryotes)
Some live as single-celled orgs (E.g. Amoeba, Yeasts)
Other live in multicellular assemblies
Main Organelles:
“Nucleus”
i. usu the most prominent organelle
ii. enclosed within two concentric membranes that form that ‘nuclear
envelope’
iii. contains molecules of DNA
“Mitochondria”
i. present in all Eukaryotic cells
ii. contain their own DNA
iii. reproduce by dividing into two
iv. generators of chemical energy for the cell (i.e. power-house of the cell)
v. harness energy from the oxidation of food molecules, such as sugar, to
produce ATP (i.e. ‘Cellular Respiration’)
It is evident that there is a symbiotic rltnshp in which the host eukaryote
and the engulfed bacterium helped one another to survive and reproduce
“Chloroplast”
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