Microscopes and measuring cellsIB MYP Biology: Subtopic test

1. 1
   A student prepares a slide of onion skin cells and views it with a light microscope. The eyepiece lens is marked ×10 and the objective lens she selects is marked ×40.

   (a)

   What is the total magnification of the image?

   [1 mark]

   • A×50
   • B×4
   • C×400
   • D×4000

   (b)

   Which part of the microscope should she use to make the final small adjustments to the focus?

   [1 mark]

   • AThe fine focus knob
   • BThe coarse focus knob
   • CThe objective lens
   • DThe light source

   (c)

   Outline how the student should use the objective lenses and the focus knobs to obtain a clear image.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student photographs a human cheek cell through a microscope. The cell in the photograph is 45 mm long. The actual length of the cell is 0.03 mm.

   (a)

   What is the magnification of the photograph?

   [1 mark]

   • A×150
   • B×15 000
   • C×0.0007
   • D×1500

   (b)

   What is the actual length of the cell in micrometres (µm)?

   [1 mark]

   • A3 µm
   • B30 µm
   • C300 µm
   • D30 000 µm

   (c)

   A second diagram of the same cell is drawn at a magnification of ×400. Calculate the length of this diagram in millimetres.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student wants to compare the size of onion skin cells with human cheek cells. She prepares a slide of each, views both at the same magnification (×400) and makes a labelled drawing of one cell from each. She then measures the length of each drawing in millimetres.

   (a)

   State a testable hypothesis for the student's investigation, with a scientific reason, and identify the dependent variable.

   [3 marks]

   (b)

   The drawing of the onion skin cell is 48 mm long. Calculate the actual length of the cell, in millimetres and then in micrometres (µm).

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A research team has discovered a new rod-shaped bacterium about 2 µm long. Using a light microscope they can see its shape but cannot make out its ribosomes or plasmids. Their university must decide whether to spend a large part of its science budget on an electron microscope, which gives much more detail but costs many times more than a light microscope and needs specially trained staff.

   (a)

   Explain why an electron microscope would show the research team more about the bacterium than a light microscope.

   [6 marks]

   (b)

   Discuss whether the university should spend its budget on an electron microscope.

   [6 marks]

   Total for question 4: 12 marks

End of questions