FA 22.214.171.124- measure cell sizes using a microscope Name__________________________ TASK 1: Calibration and calculation of actual size using an eyepiece graticule. Steps to follow to calibrate your microscope. Before a microscope can be used to determine the actual size of cells it needs to be calibrated. 1 Switch on you microscope and make sure it is set on the lowest objective (4x). 2. Look through the eyepiece and find the eyepiece graticule scale. From 0 to 1 you can see 10 graticule units. How many graticule units from 3 to 5?_______ 3. Place your ruler on the stage. Look through the eyepiece and locate 1mm on your ruler. (the lines are very thick). Your ruler represents the stage micrometer as our microscopes are not fitted with them. 4. 1mm = ___________ µm 5. Count how many eyepiece graticule units fit into 1 mm (1000 µm) on your ruler. (Count from the middle of the one line to the middle of the next line) ______________graticule unit fits. 6. _______graticule units fits into 1000 µm therefore 1 graticule unit will equal _______ µm. 7. Place the onion epidermis slide (60 or 1) on the stage. 8. Determine the actual length of 1 cell. (Take note of which cell you use) Count how many graticule units the cell consists of and then multiply it by the length of one graticule unit. (as you calculated in step 6) __________________________________________________________________________ Length of onion epidermis cell ______________ 9. To calibrate the next objective lens, set your microscope on the middle objective (10x). 10 Place your ruler on the stage and locate 1mm on your ruler. (the lines are even thicker). 11 Count how many eyepiece graticule units fit into 1 mm (1000 µm) on your ruler. (Count from the middle of the one line to the middle of the next line) ______________graticule unit fits. 12 Why do more graticule units fit into a mm on your ruler now? ___________________________ _____________________________________________________________________________ 13 So now 1000 µm = ______________ graticule units so 1 graticule unit will equal _______µm. 14 Place the onion epidermis slide on the stage again. 15 Determine the actual length of 1 cell (USE THE SAME CELL AS STEP 8). Count how many graticule units it consists of and then multiply it by the length of one graticule unit (step 13) __________________________________________________________________________ Length of onion epidermis cell = _______________ 17 Are the lengths of your cells as calculated in step 8 and 15 the same? ______________ 18 Should they be the same? _____________________ 19 Explain your answers in 17 and 18.____________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ 20. To accurately DETERMINE the actual size (length and width) of a cell at least 5 cells should be measured and an average calculated. Choose any five epidermis cells and determine their lengths and widths. Complete the table below showing you measurements. (Also add a heading) You can use either the 4X OR 10x objective lens Heading:____________________________________________________________________________ Cell Number Length (µm) Width (µm) 1 2 3 4 5 Average TASK 2 – Compare the cell lengths of different types of cells in plants and animals. (use the middle objective lens) 21. Use slides 54, 24, 20, 22 and 60 to complete the table below. Only calculate the length of one cell (step 6). For slide 60 use the average length of the onion cell that you calculated in question 21. Heading:____________________________________________________________________________ Slide number 20 22 24 54 60 Type of cell Adipose (fat) cell Squamous epithelium cell Length (µm) ACHIEVED: Students answer questions 9 to 15 correctly and shows understanding when asked about the steps. EXTENSION WORK – Draw a biological drawing of one onion epidermis cell. Add three labels.