Using a microscope and magnificationIB MYP Sciences: Subtopic test

1. 1
   A student in Mumbai is using a light microscope for the first time to look at a prepared slide of onion cells. The microscope has an eyepiece lens of magnification ×10, three objective lenses (×4, ×10 and ×40), a stage, a coarse focus knob and a fine focus knob.

   (a)

   Which part should the student use to bring the specimen roughly into focus when using the lowest-power objective lens?

   [1 mark]

   • AFine focus knob
   • BEyepiece lens
   • CCoarse focus knob
   • DStage

   (b)

   The student uses the ×10 eyepiece lens with the ×40 objective lens. What is the total magnification?

   [1 mark]

   • A×4
   • B×50
   • C×40
   • D×400

   (c)

   Explain why the student should start by looking at the slide with the lowest-power objective lens.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician in Cape Town prepares a temporary slide of the thin, transparent skin from the inside of an onion bulb. She has forceps, a dropper of water, iodine solution, a microscope slide and a cover slip.

   (a)

   What is the main purpose of adding a drop of iodine solution to the slide?

   [1 mark]

   • ATo stain the cell structures so they can be seen more clearly
   • BTo make the specimen larger
   • CTo stop the specimen drying out
   • DTo increase the number of cells on the slide

   (b)

   Why must the piece of onion tissue placed on the slide be very thin?

   [1 mark]

   • ASo that it is magnified more
   • BSo that light can pass through it
   • CSo that it stays alive
   • DSo that it takes up less space on the stage

   (c)

   Describe how the cover slip should be placed on the specimen, and give the reason for this.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Seoul observes cheek cells under a light microscope and makes labelled drawings. Her teacher asks her to calculate the magnification of each drawing so that other students can work out the real size of the cells.

   (a)

   One cheek cell in her drawing is 60 mm wide. Its actual width is 0.03 mm. Calculate the magnification of the drawing.

   [3 marks]

   (b)

   In a second drawing, at a magnification of ×1500, a different cheek cell is 45 mm wide. Calculate the actual width of this cell in micrometres (µm). 1 mm = 1000 µm.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A charity in Lagos supplies low-cost light microscopes to schools and rural health clinics. Teachers at a partner school want their students to use the microscopes, and the charity is deciding whether to extend the programme to more clinics.

   (a)

   A teacher wants her students to test the hypothesis that iodine stain makes the nuclei in onion cells easier to see. Plan an investigation using a light microscope. In your answer, state a hypothesis with a scientific reason, identify the variables, and describe a safe method.

   [6 marks]

   (b)

   Discuss and evaluate the charity's plan to extend its programme of low-cost microscopes to more rural health clinics. Consider social, economic and ethical implications, and finish with a justified conclusion.

   [6 marks]

   Total for question 4: 12 marks

End of questions