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CHAPTER 2 : Basic components of living systems
Microscopy
Seeing is believing
-A microscope allows you to magnify an object
-Light microscopes were developed in the 16th to 17th century
-The cell theory states:
Both plant and animal tissue is composed of cells
Cells are the basic units of all life
Cells only develop from existing cells
-Light microscopes are easily available, cheap, used to observe living, dead and
prepared specimens
Cell theory timeline
-1665: cell first observed
-1674 / 83: first living cells observed
-1832: evidence for the origin of new plant cells
-1833: nucleus first observed
-1837 / 38: birth of a universal cell theory
-1844 / 55: evidence for the origin of new animal cells
-1860: spontaneous generation disproved
How a light microscope works
-Compound light microscope has 2 lenses
Objective lense, placed near to specimen
Eyepiece lense, through which the specimen is viewed
-Objective lense magnifies the image, which is magnified again by the eyepiece
lense
-Objective/ eyepiece lense configuration allows for higher magnification and reduced
chromatic aberration than that in a simple light microscope
-Illumination is usually provided by a light underneath the sample
-Opaque specimens can be illuminated from above with some microscopes
Different staining
-Distinguish two types of organisms that would otherwise be hard to identify
-Differentiates between organelles of a single organism within a tissue sample
Gram stain technique
-Separates bacteria into two groups
Gram-positive bacteria
Gram-negative bacteria
-Crystal violet and iodine are added to bacterial specimen on a slide
-Slide is washed with alcohol

-Gram-positive retain crystal violet stain, appears blue or purple under a microscope
-Gram-negative has thinner cell walls and therefore loses the stain
It’s then stained with safranin dye, a counterstain
This bacteria will appear red
-Gram-positive bacteria are susceptible to the antibiotic penicillin, which inhibits
formation of cell walls
-Gram-negative bacteria have thinner cell walls that aren’t susceptible to penicillin
Acid-fast technique
-Differentiates species of mycobacterium from other bacteria
-Lipid solvent carries carbolfuchsin dye into cells being studied
-Then cells are washed with a dilute acid-alcohol solution
-Mycobacterium aren’t attracted by acid-alcohol and retain carbolfuchsin stain (bright
red)
-Other bacteria lose stain and are exposed to methylene blue stain (blue)
-Stages involved in the production of making these slides
Fixing - chemicals like formaldehyde are used to preserve specimens as nearnatural state as possible
Sectioning - specimens are dehydrated with alcohols, then placed in a mould
with wax or resin to form a hard block, then sliced with a microtome (knife)
Staining - specimens are treated with multiple stains to show different
structures
Mounting - specimens are secured to a microscope slide with a cover slip
Risk management
-Stains are toxic or irritants
-Carry out risk assessment
List of rules for producing good scientific drawings
-Title
-State magnification
-Use sharp pencils (labels and drawing)
-White, plain paper
-Use as much paper possible for drawing
-Smooth, continuous lines
-No shading
-Clearly defined structures
-Correct proportions
-Label lines should not cross or have arrowheads
-Label lines should be parallel to the top of the page, drawn with a ruler



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