Science 10 – Unit C
BIOLOGY
Chapter 1 – The Microscope
C1.1
A window on a new world
A section of human lung tissue affected by lung cancer.
Early microscopes & lenses
a better understanding of cells and the
structure of living things came hand-inhand with the development of microscope
technology
before the 1500s, scientists could only
observe what they could see with the
naked eye
The average human can see objects no smaller than 0.1mm (or 10-4m).
How small is that?
Post-1500s
in the 1500s, the theory of optics and
lenses was developed
these theories allowed scientists to invent
tools that made more detailed
observations possible
The Janssen brothers
Hans & Zacharias Janssen
invented the first
microscope in 1595
the brothers were Dutch
eye-glass makers
considered to be a
compound microscope
because it used more than
one lens
Robert Hooke
in 1660, improved on
the Janssens’ design by
adding:
– a third lens
– a light to illuminate the
objects
Robert Hooke
used his microscope to
observe living and nonliving objects
made detailed drawings of
his observations and
published them in a book
called Micrographia
– Latin for “a record very small
objects”
Robert Hooke
Hooke observed a crosssection of cork, which he
thought was non-living
observing that it was full of
empty air chambers, he called
these tiny chambers “cells”
these chambers turned out to
be the remnants of living cells
Antoni van Leeuwenhoek
working around the same time
as Hooke
the first person to observe the
movement of living singlecelled organisms
Leeuwenhoek’s microscope
only had a single lens – called a
simple microscope
the lenses were of much higher
quality, and allowed him to
magnify objects up to 250X
Skills in microscopy
Magnification:
– how many times larger the image is compared
to the original
– magnification = (power of the objective lens)
x (power of the eyepiece)
eyepiece lens – always 10X
objective lens
– low power: 4X
– medium power: 10X
– high power: 40X
Magnification – practice problems
What is the magnification of a microscope with a
10X ocular (eyepiece) lens, and a 10X objective
lens?
– magnification = (10X)(10X) = 100X
How much more powerful is the magnification
on high power compared to low power?
– magnification high = (10X)(40X) = 400X
– magnification low = (10X)(4X) = 40X
– the high powered magnification is 10 times more
powerful
Field of view
the area that can be seen through the
microscope with a particular objective lens
field of view can be described in terms of
field diametre or field area
when the lens power increases, field of
view decreases
Field of view
the field diameter on low power can be
measured by placing a ruler under the
microscope
the field diameter on high power can be
calculated using this formula:
high-power field diameter
low-power field diameter
=
low-power magnification
high-power magnification
Field of view – practice problems
The image to the right is
the view through low
power. What is the field
diameter of this
microscope?
– 29 mm
What is the field diameter
on high power?
– 2.9mm
How many times smaller is
the field diameter on high
power as on low power?
– one tenth
Scale
a comparison between the size of a
drawing and the actual size of the object
to calculate it, compare the diameter of the
circle in the drawing with the diameter of
the field of view you calculated previously
e.g. a drawing with a diameter of 90mm
done from low power would roughly have
a scale of 90mm:29mm or 3:1.
Actual size
once you know the field diameter, you can
estimate an object’s size by noting how much of
the field of view it occupies
this can be done by estimating how many times
across the object would fit
– e.g. if it would fit 10 times across, it takes up 1/10th of
the field of view
e.g. if the field of view is 29mm and a cell takes
up about 1/3 of the field of view, it’s actual size is
about 10mm
Actual size – practice problem
our field of view on
high power was found
to be 2.9mm. What is
the actual size of this
cell, as viewed under
high power?
– (2.9mm)(1/2)=1.45mm
what is its size in
micrometers? (hint: 1
mm = 1000 µm)
– 1.45mm = 1450 µm
Homework:
Skills practice p. 244 a & b
Check and Reflect p. 246 #1, 3, 4, 8