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 = 33.333. Q asks for whole cells so 33.

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)

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.

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

Practicing magnification maths There are: 1 000 000 nanometres (nm) in a millimetre (mm) 1000 micrometres (mm) in a millimetre 1000 millimetres in a metre (m) 1 000 000 micrometres in a metre 1 000 000 000 nanometres in a metre.

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

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 (15 000 mm) 15 000/2.6 = 5769 times

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)

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.

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)

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.

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

Plenary Question If a nucleus measures 100mm on a diagram, with a magnification of x10000, what is the actual size of the nucleus? 100 000 micrometers = 100 mm. 100 000/ 10 000 (magnification) = 10 micrometers

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