A104 Biology Problem 1
6
th
Presentation-Part 1
Cell Counting
Activity owner: Cindy Chua and Zheng Yuanli Approved by: Dr. Esther Chng
Module Chair: Cherry Chan
In Today’s Problem
You are given the following information:
o Yeast is required for the production of beer.
o 0.5 gallon of yeast slurry is available to provide 1.80 × 1011 yeast cells.
o Concentration of yeast slurry must be determined to find the volume of slurry required.
o Cell counting under a microscope is conducted to determine concentration of yeast slurry.
o Each yeast cell is approximately 4 µm in diameter.
o Sample of yeast under the microscope is diluted 100× first.
o Assume that the number of yeast cells observed in all five blue clusters of the microscopic view of the yeast cells are the same.
o Each blue square has area of 0.04 mm2 and depth of 0.1 mm.
What do you Recognise?
• “× 1011” refers to a large number and “gallon” is a unit for volume.
• Concentration of the yeast slurry
o must be determined to find the volume of yeast slurry required to provide 1.80 × 1011 yeast cells.
o unknown but can be found from cell counting under a microscope.
• A 4 µm diameter is probably very small and a microscope magnifies the cells to make cell counting easier.
• Cell counting involves counting the number of cells in a fixed area. • The volume of sample in each blue cluster of the microscopic
view of the yeast cells can be computed from its area and depth. • Diluting the sample of yeast slurry involves adding water to it.
• A 100× dilution may imply some degree of dilution.
What is your Approach?
• What is the purpose of using scientific notation, e.g.
“× 10
11”?
• What does “µm” mean?
• How is “gallon” converted to other units of volume?
• What are the Units for other physical quantities?
• Why is a microscope used in cell counting?
• What is the purpose of a 100× dilution?
• How to determine concentration from cell counting?
• How to determine volume of yeast slurry required?
What is the Purpose of using Scientific
Notation?
• A quantity of “180 × 10
9” yeast cells is the same as
“180000000000” yeast cells.
• Typically, when handling very large or small numbers,
scientific notations
are used.
• The basic format is
M
10
N, where
M
is any real number
between 1 and 10
and
N
is an
integer
.
Examples: 10-2 = 0.01
10-1 = 0.1
100 = 1
101 = 10
102 = 100
108 = 100000000
• If 18 000 000 000 is to be
What does “µm” mean?
• Prefix can be added to a unit to produce a
multiple of the original unit.
Factor Name Symbol 10-9 nano- n
10-6 micro- μ
10-3 milli- m
10-2 centi- c
10-1 deci- d
103 kilo- k
106 mega- M
109 giga- G
• The size of yeast cell is
approximately 4
μ
m,
which means
o
4
10
-6m or
o
4
10
-3m
m.
How is “gallon” converted to other
Units of Volume?
• Units are required to specify the value of the physical
quantities.
• Two common unit systems used today:
1) Imperial System (E.g. inch, foot, gallon, pound, ounce)
2) Metric System (E.g. metre, litre, kilogram)
Example of conversions between the unit systems: 1 foot (ft) = 0.3048 metres
1 pound (lb) 0.454 kilograms
What are the Units for other Physical
Quantities?
• The International System of Units (known as
SI unit
) is
the modern form of metric system.
• The SI has
7 basic (fundamental) units
:
Base quantity SI base unit
Name Symbol
Length metre m
Mass kilogram kg
Time second s
Temperature kelvin K
What are the Units for other Physical
Quantities? (Continued…)
• All physical quantities and measurements can be expressed
in
derived units
of the SI system. The symbols for derived
units are obtained by multiplication and division.
o Examples:
• The symbol for "per" (meaning "divided by") is “/” (slash).
o Example: If the concentration of a salt solution is 50 particles/m3,
it means that in every 1 m3 of the solution, there are 50 particles of
the solute (salt).
Derived quantity
SI derived unit
Name Symbol
Area metre square m2
Concentration
kilogram per metre cube
or
number of particles per metre cube
kg/m3
or
What is the purpose of a 100× Dilution?
• When the yeast sample is too
concentrated, the yeast cells
observed under the microscope
will crowd the counting grid
making it difficult to count them
effectively.
• Diluting the sample would
reduce
this
crowding effect
.
• To dilute a solution means to add
more solvent (usually water)
without the addition of more
solute.
Cells in a diluted sample Crowded cells in the original sample
Image from:
What is the purpose of a 100× Dilution?
(Continued…)
• Dilution
refers to the
reduction in concentration
of a solution.
• Dilution factor
tells us the
magnitude through which a solution
is diluted by
.
• By comparing the concentration, C
initial, of the initial
(concentrated) solution to the concentration, C
final, of the final
(dilute) solution:
o For example,
Di𝑙𝑢𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 = 𝐶𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝐶𝑓𝑖𝑛𝑎𝑙
Cinitial 200 particles/L
Cfinal
20 particles /L
• The compound microscope
has two
systems of lenses for greater
magnification:
o The oculars, or eyepiece lenses, that the user looks into. They are usually 10× or 15× power.
o The objective lenses, or the lenses closest to the object. They are usually 4×, 10×, 40× and 100× power.
Why is Microscope used in Cell Counting?
• Microscope is used to observe small objects at
higher
magnification
. It uses visible light that is magnified and
concentrated by glass lenses.
• Specimens must be thin enough for light to pass through.
Ocular / Eyepiece lenses
Objective lenses
• For example, a combination of
10× ocular and 100× objective
lenses will produce a total
magnification of 1000×.
o An actual specimen of 1 µm
placed under such a microscope will hence be magnified 1000× and appear as 1 mm.
Why is Microscope used in Cell Counting?
(Continued)
• A specimen placed under the microscope using different
combination of ocular and objective lenses will produce a
different total magnification.
Ocular / Eyepiece lenses
Objective lenses
Why is Microscope used in Cell Counting?
(Continued)
• The smallest particle which can be seen by an
unaided human eye is about 0.01 mm.
• Given that a yeast cell is about 4 µm, which is
0.004 mm, without magnification, yeast cells cannot be
seen by an unaided human eye.
• The figure below shows a sample of yeast cell under
different magnifications in a microscope.
100× 400× 1000×
A104 Biology Problem 1
6
th
Presentation-Part 2
Cell Counting
Activity owner: Cindy Chua and Zheng Yuanli Approved by: Module Chair
How to Determine Concentration from
Cell Counting?
Area 0.04 mm2
Depth 0.1 mm
Grid in the hemocytometer
Yeast cells observed in one blue cluster under the microscope
1. Volume of each blue cluster
= 0.04 × 0.1 = 0.004 mm3
2. 1000 mm3 = 1 mL
1 mm3 = 0.001 mL
0.004 mm3 = 4 × 10-6 mL
3. By counting the number of yeast cells observed in one blue cluster, the concentration of the yeast slurry can be computed. For
example, if 66 yeast cells were counted,
Concentration = 66 cells / (4 × 10-6) mL
= 1.65 × 107 cells/mL
Image from:
http://www.bfz.biz/tag/cell-counting Image from:
4. Assuming that the number of yeast cells observed in all five blue clusters is the same, the approximate concentration of the yeast cell sample that is placed on the hemocytometer is also 1.65 × 107 cells/mL
5. Since the yeast sample in the hemocytometer has been diluted 100×,
Initial concentration = (1.65 × 107) × 100
=
1.65 × 10
9cells/mL
Hemocytometer (to be viewed under the microscope)
Initial sample
100× dilution
Diluted sample
1.65 × 107 cells/mL
How to Determine Concentration from
Cell Counting? (Continued…)
Image from:
How to Determine Volume of Yeast
Slurry required? (Continued…)
6. Since 1.80 × 1011 yeast cells are required,
Volume of yeast slurry required = (1.80 × 1011) / (1.65 × 109)
= 109.09 mL required (2 d.p)
7. 1 gallon 3.79 L = 3790 mL
8. Since 0.5 gallon is available, 0.5 gallon 0.5 × 3790
= 1895 mL available
What You Have Learnt
• Recognize and use units found in the Metric and Imperial System
• Identify SI (metric) measurement symbols
• Use prefixes and their symbols to indicate decimal sub-multiples and multiples of the SI units
• Perform unit conversions
• Recognize the purpose of magnification and dilution factors in experiments
