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How small can you see? Most people can only see objects that
are larger than 0.1mm. We can say that the resolving power of
the human eye is about 0.1mm
Resolution The ability of the eye (or
any other image-making instrument) to distinguish between separate objects that are close together.
E.g. See the spots in figure D, compared to E.
The Cell Most cells are smaller than 0.1mm. A few like the paramecium, are barely
visible to the human eye. Approximately five paramecium could
fit on the period at the end of a sentence in a textbook.
No small wonder they went unobserved for so many years!
Micro-organisms …Microscope…
In order to discover micro-organisms, scientists needed a tool to extend the abilities of human vision.
They needed a microscope. Invented at the end of the sixteenth
century. Early microscopes were used to
observe organisms that people knew already existed. Early microscopes only magnified 50x their actual size.
Common First Microscope Observations
Insect parts Plant seeds Sand grains
Robert Hooke
Hooke didn’t make microscopes
Looked at tree bark, cork
Coined the term ''cell''
Antony van Leeuwenhook
Self-taught scientist who introduced the world to the micro-universe.
Reported observations on the microscope in 1670
Used a single lense microscope (quartz) that was no larger than the palm of your hand.
Due to his ability to grind glass he could magnify items 500x greater.
Built 450 microscopes in his career, only 9 remain today.
The Modern Compound Light Microscope
19th century saw improvements in glass-making techniques allowing lens-makers to remove distortion effects and coloured halos that plagued earlier microscopes.
Ability to produce microscopes that magnified 2000x greater.
Many of the cells that we will observe in Biology 11 were discovered during this time period.
1. To carry a microscope, always use one hand to hold the arm and your other hand to support the base.
2. To keep the lens clean, never touch their surfaces with your fingers. Use only lens tissue (Kimwipes) to clean their surfaces.
3. Do not adjust any of the focussing knobs until you are ready to use the microscope.
continued…
4. Always focus using the coarse adjustment knob first, with the low-power objective lens in position.
5. Do not use the coarse adjustment knob when either the medium-power lens or high-power objective lens is in position.
6. Cover the microscope when it is not in use, or store in the appropriate cupboard after finishing.
In the Lab…