BIOLOGY MARCH 2020 PAPER 12



Q1: The diagram shows an eyepiece graticule and cell viewed through a microscope. When the eyepiece graticule was calibrated at this magnification, the whole length of the graticule shown covered 12 divisions of a stage micrometer scale. There were 100 divisions in 10 mm of the stage micrometer.









 What is the actual length of the cell?
 A 2.5µm
 B 3.6µm
 C 360µm
 D 3 mm

ANSWER C

In this question, you need to make use of the data given in the question. To begin with, find the magnitude of one division of the stage micrometer. If 100 divisions occupy 10mm, then 1 division of the stage micrometer would be ((1*10))/100) = 0.1mm. Since 100 divisions of a graticule covered 12 divisions of a stage micrometer, then 100 divisions would be equal to 12*0.1mm = 1.2mm. Therefore, 1 division of an eyepiece graticule would be equal to 0.012mm.

In the picture shown above, the cell covers 29 divisions of a graticule, so the length of the cell is 29*0.012mm = 0.348mm. 

The dimensions of cells are usually given in micrometers. So to change mm to micrometer, we simply multiply the answer in mm by 1000 since 1mm is equal to 1000 micrometers. The answer is actually 0.348mm*1000 = 348 micrometers = approximately 360 micrometers.
 

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