1. Starter
You are observing a specimen of squamous tissue under high power.
Each individual cell has an average diameter of 60mm and the diameter of the field of view is 2mm.
Calculate the maximum number of cells that are visible in the field of view.
Field of view = 2000micrometers. So 2000/60 = Q asks for whole cells so 33.

2. Measuring objects, using a graticule (PAG 1 and M1.8, M2.2)
Calculating Cell Size
Measuring objects, using a graticule
(PAG 1 and M1.8, M2.2)

3. Objectives and Success Criteria
Use the magnification formula
Examine and draw specimens
Use and manipulate the magnification formula
Prepare a specimen for observation and measure organelles and cells.

4. Key Terms
Resolution: the ability to distinguish two separate points as distinct from each other
Magnification: the number of times greater an image is than the object

5. Practicing magnification maths
There are:
nanometres (nm) in a millimetre (mm)
1000 micrometres (mm) in a millimetre
1000 millimetres in a metre (m)
micrometres in a metre
nanometres in a metre.

6. Calculating Actual Size
Actual size = image size
magnification
Magnification = image size
actual size
Worksheet

7. Worked Example Image size is 15mm (15 000 mm) 15 000/2.6 = 5769 times
Actual size is 15mm. More practice on worksheet – cell size and mags in folder.
Image size is 15mm ( mm)
15 000/2.6 = 5769 times

8. Eye Piece Graticule Microscopes can be fitted with an EPG
Ruler etched on it
A specimen can be measured in eyepiece units (an arbitrary measurement, the image changes size depending on the magnification, but the graticule stays the same size for each magnification.
To measure the size of objects in the field of view, the graticule needs to be calibrated)

9. Calibration - Using Stage Micrometer
Place a stage graticule on the stage
The ruler is 1mm long and split into 100 divisions
Each division = 10µm (0.01mm)
1µm is equal to 1 millionth of a metre
The mitosis PAG1 sheet in the folder explains this well – they could use the relevant page and measure something on prepared slides, or make cheek cell/onion cell/leaf peel slides.

10. Calibration - Using Stage Micrometer
Align the eyepiece graticule with the stage micrometer
Find the value of one eyepiece division
(1mm or 1000mm)
In (a) where mag = x40,
The stage graticule is equal to 40 eyepiece divisions.
Each eyepiece division =
1000mm/40 = 25mm
In (b) where mag = x100
The stage graticule is equal to 100 epd
Each epd = 1000mm/100 = 10mm
Remember the stage graticule is 1mm or 1000mm)

11. Calculating size In the image (a), the nucleus is 3.2epd
With x100 mag. 1epd = 10mm
So: the nucleus is 3.2x10 = 32mm
Look at your graticule and stage
Micrometer.
Use them to calculate the size of
an onion cell and a cheek cell.

12. Calculate Cell Size Prepare an onion cell slide
Measure the size of a cell

13. Plenary Question
If a nucleus measures 100mm on a diagram, with a magnification of x10000, what is the actual size of the nucleus?
micrometers = 100 mm / (magnification) = 10 micrometers

14. Homework Questions 1-5 p34 purple book
Or Flipped learning – Fill in organelle work sheet in folder.