Science 10 – Unit C - BIOLOGY
Chapter 1 – The Microscope
C1.1 - A window on a new world
The microscope:

Early microscopes & lenses
o a better understanding of cells and the structure of living things came hand-in-hand with
o before the 1500s, scientists could only observe
o in the 1500s, the
 these theories allowed scientists to invent tools that

The Janssen brothers
o
invented the first
microscope in 1595
o the brothers were Dutch eye-glass makers
o considered to be a compound microscope because

Robert Hooke
o in 1660, improved on the Janssens’ design by adding:


o used his microscope to observe
o made detailed drawings of his observations and published
them in a book called Micrographia (Latin for “a record
very small objects”)
o Hooke observed a cross-section of cork, which



observing that it was full of empty air chambers, he
called these tiny chambers “cells”
these chambers turned out to be
Antoni van Leeuwenhoek
o working around the same time as Hooke
o the first person to observe
o Leeuwenhoek’s microscope only had a single lens – called a
o the lenses were of much higher quality, and allowed him to
magnify objects
Skills in microscopy


Magnification:
o 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
o practice problems
 What is the magnification of a microscope with a 10X ocular (eyepiece) lens, and
a 10X objective lens?
 How much more powerful is the magnification on high power compared to low
power?
Field of view:
o field of view can be described in terms of
o when the lens power increases, field of view
o the field diameter on low power can be measured by placing a ruler under the
microscope
o 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
o practice problems
 The image to the right is the view through low power. What is
the field diameter of this microscope?
 What is the field diameter on high power?
 How many times smaller is the field diameter on high power as on low power?
Scale:
o to calculate it, compare the diameter of the circle in the drawing with the diameter of the
field of view you calculated previously
o 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
o once you know the field diameter, you can estimate an object’s size by noting how much
of the field of view it occupies
o 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
o 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
o practice problems
 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?
 what is its size in micrometers? (hint: 1 mm = 1000 µm)
Homework: Skills practice p. 244 a & b Check and Reflect p. 246 #1, 3, 4, 8