2.1 Summary Questions

Question 1

Outline the basic concepts of the cell theory. (3 marks)

Answer 1

1 Both plant and animal tissue is composed of cells
1 Cells are the basic unit of all life
1 Cells only develop from existing cells

Question 2

Explain why staining is used in microscopy. (2 marks)

Answer 2

1 Staining provides contrast as different structures/organelles absorb stains differently
1 allowing identification

Question 3

Compound microscopes led to new discoveries essential for cell theory to be fully explained. Explain the benefit of having two lenses in a microscope. (4 marks)

Answer 3

Objective lens and eyepiece lens (1); objective lens magnifies the specimen (1); eyepiece lens
magnifies image (from objective lens) (1); higher magnification (produced than with just one
lens) (1)

Question 4

Calculate the low and high power magnifications of a microscope with the following lenses:
i Eyepiece lens x10
ii Objective lenses x10 and x40

Answer 4

i 0 × 10 = 100 (1)

ii 10 × 40 = 400 (1)

Question 5

You are observing a specimen of squamous tissue under high power. The individual cells have an average diameter of 60 μm and the diameter of the field of view of the objective lens is 2 mm. Calculate the maximum number of whole cells that are visible in the field of view. (3 marks)

Answer 5

area of field of view =
2
 1000
= 3.141 × 106 μm2 (1)
average area of cell =
2
  30
= 2.827 × 103 μm2 (1)
3
6
2.827 ×10
3.141×10
= 1111.11 = 1111 whole cells (1)