Science 10 – Unit C BIOLOGY Chapter 1 – The Microscope

A section of human lung tissue affected by lung cancer. 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-in-hand 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 non-living 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 cross-section 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 single-celled 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 magnification low-power field diameter 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