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…