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Understanding Magnification and Size in Biology: A Student Guide

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This resource focuses on calculating and understanding the relative sizes of biological molecules, viruses, cells, and bacteria using SI units. Students will learn to compute magnification from scale bars and determine the actual size of biological specimens through practical calculations. Engaging activities such as group work with the Magnification Revision poster will solidify these concepts. By working through examples involving animal and plant cells, students will enhance their skills in measuring and interpreting biological structures.

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Understanding Magnification and Size in Biology: A Student Guide

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  1. Magnify-cent Biology!! IB Biology Topic 2

  2. LearningOutcomes Everyoneshould: • Compare relativesizes of biologicalmolecules, viruses, cells and bacteria usingappropritate SI units Mostwill: • Calculatemagnificationfrom a scale bar Somemight • Calculatemagnification and actual size of biologicaldrawings and specimens

  3. Now try the Magnification Revision poster as a group!

  4. Answersforthe animal cell Calculate the magnification factor The line 5 m is 20 mm long. So 20 000 m = 5 m Magnification is 20 000/5 = x 4 000. Calculate the length of structure G Length of G is 12 mm = 12 000 m Magnification is x 4 000 Real size is 12 000/4000 = 3 m Calculate the diameter of structure B Diameter is 8 mm = 8 000 m Magnification is x 4 000 Real size is 8 000/ 4 000 = 2m Calculate the diameter of the nucleus Diameter is 36 mm = 36 000 m Magnification is x 4 000 so real size is 36 000/4 000 = 9 m Calculate the diameter of the cell at its widest point 109 mm = 109 000 m = 109 000/4 000 = 27–25 m For all the answers above there is a tolerance limit of + or – 0.5mm, so + or – 0.1 – 0.2 m There are other perfectly correct ways of doing the calculation, so if your method is different, but arrives at the correct answer, then that is fine.

  5. Answersfortheplantcell Calculate the magnification factor. The line representing 40 m is 25 mm or 25 000 m long Therefore, magnification factor is 25 000/40 = x 625. Calculate the thickness of the cellulose cell wall. Wall is 3.0 mm = 3 000 m Magnification is x 625 Actual thickness of wall is 3 000/625 = 4.8 m Calculate the length of the cell. 120 mm = 120 000 m magnification factor is x 625 Actual length is 120 000/625 = 192 m Calculate the length of structure C. 29 mm = 29 000 m magnification is x 625 Actual length is 29 000/625 = 46.4 m Calculate the length of the vacuole. 80 mm = 80 000 m magnification is x 625 Actual length is 80 000/625 = 128 m.

  6. LearningOutcomes Everyoneshould: • Compare relativesizes of biologicalmolecules, viruses, cells and bacteria usingappropriate SI units Mostwill: • Calculatemagnificationfrom a scale bar Somemight • Calculatemagnification and actual size of biologicaldrawings and specimens

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