National 4/5 Biology
Unit 1: Cell Biology
Section a: Cell Structure and Function
We are learning to:
• Work out the size of cells using two
calculations:
– Total magnification
– Conversion of millimetres to micrometres
Total Magnification
• Total magnification =
magnification of x magnification of
objective lens
eye piece
• Example
if eyepiece has a magnification of x5
and objective lens has magnification
of x40. Total magnification is 200x
(5 x 40)
Total magnification calculations
• Calculate the total magnification for the
following:
1. Eyepiece is 5x and objective lens is 25x
2. Eyepiece is 5x and objective lens is 50x
3. Eyepiece is 5x and objective lens is 250x
Cell size
• 1 millimetre (mm) = 1000 micrometres (um)
• Therefore a field of view of 2mm diameter =
2000 micrometres
• So if 10 cells are going across the diameter
• each cell will be 200 micrometres (2000/10 =
200)
Calculations
• How wide are the cells in micrometres?
2mm = 2000um
2mm
3 cells across field of view
2000/3 = 666.67um
Calculations 2
• How long are the onions cells in micrometres?
5mm = 5000um
5mm
5 cells across the field of view
5000/5 = 1000um
Calculations 3
• The following slide has been magnified 100x.
How long is one cell?
5mm = 5000um
5 cells in field of view
5000/5 = 1000um
1000/100 = 10um
Your turn!
• In pairs come up with two examples for your
class mates to work out
• Remember you are the teacher you have to
know the answer
• If you want to make it more difficult show the
working with an error that they have to spot!
For fun
•
•
•
•
Using plasticine
Build models of a plant or animal cell
Label the structures and state their functions
Extra:
– State how the cell you have chosen is similar or
different to the three other types of cell you have
studied