Year 10 General Science
Student Name: ____________________
/30 Marks
%
Microscopic Investigation - Calculating sizes and comparing bacteria
Background information
Robert Hooke first saw cells with a light microscope in 1665.
On the right is one of his drawings of a piece of cork and a leaf.
How big is a bacterial cell?
A typical bacterial cell is
roughly about 2 microns
in diameter. The Ecoli
in the picture is 3
microns long but only
about 1 micron wide.
2 microns means that an average bacterial cell
is two micrometres (2µm) across the cell and
5000 of them would need to be lined up to
stretch across one centimetre.
Aims of the investigation:
 To become re-acquainted with the use of a light microscope.
 To be able to calculate and compare the size of objects seen under the microscope.
 To practise drawing scientific diagrams
 To compare the sizes and features of different bacterial cells.
Equipment:
Compound Microscope
Microscope slides
Cover slips
Forceps
Absorbent paper
Pipette
Methylene blue
Onion
Iodine
Cutting Board
Prepared slides (bacteria)
Mini ruler pieces
Use the diagram above to remind yourself of the names of the parts of the compound microscope
Part A – using the microscope
6 Marks
Plug in the microscope, check that the light works and the eyepiece lenses are clean.
You can use some alcohol (hand sanitizer) to clean them if necessary.
a. Why does the stage come with “stage clips”?
b. Which part of the microscope is used to adjust the
amount of light passing through your specimen?
c. Why does the specimen you are looking at need to
be very very thin?
d. Why should the coarse adjustment knob only be
used on low power?
e. Which two things might you need to adjust when
your partner is ready to show you something that
they already have in focus?


f. Why will people who normally wear glasses NOT
need to have them on when looking down the
microscope?
Part B – calculating sizes
6 Marks
Place a small piece of plastic ruler onto the stage of the microscope so that you can see
it when you look through the eyepieces.
a. How much of the ruler can you see in the field of view? How many millimetres of the
ruler can fit across the field of view? You can use fractions/decimals in your answer.
i. On low power
ii. On Medium power
1 mark
Look at one of your hairs under the microscope.
You can use some clear tape to secure the hair onto a microscope slide.
b. Bring the hair into focus on low power and then on medium power.
Show your teacher the hair on
medium power
Student Outcome:
Proficient
Can do this with a little guidance
Struggles to achieve this
Marks
2
1
0
c. Estimate the diameter of your hair in micrometres (microns) by considering how much
of the field of view it occupies. You can also use the conversion scale printed below.
The diameter of my hair is approximately ________________ microns (μm)
1 mark
d. Complete the table
Low Power
Medium Power
Eye piece
magnification
X 10
X 10
Objective Lens
magnification
X4
Overall total
magnification power
High Power
X 40
X100
Objects appear 100
times bigger than their
actual size
2 marks
Part C – How big is an onion cell?
6 Marks
Watch the teacher
demonstration to learn how to
prepare some onion cells and
mount them onto a microscope
slide. The teacher will provide
the stained slides for you.
Use the microscope to focus on
just one onion cell in your field
of view and calculate
approximately how big this
onion cell is. Measure both the
length and width of the cell.
a. Draw a neat pencil sketch of the onion cell.
Use clean, simple, lines and shapes – it should be a clear diagram showing
accurate proportions not an artist’s drawing.
2 marks
b. Show the length or width of the
cell on your diagram (Look at the
e-coli cell on the front page).
Make sure your sketch has a title
and shows all of the detail you
can see down the microscope.
Hint: Onion cells have very large vacuoles
2 marks
c. What is the scale of your sketch?
1mm on the page = ______________ μm
1 mark
Using the same scale, draw a circle next to your onion cell with a diameter of 2µm
d. The circle represents an average bacterial cell. Estimate approximately how many
bacterial cells would fit inside your onion cell?
1 mark
Part D – looking at bacteria
6 Marks
View at least two different types of bacteria on high power, using the prepared slides.
Take care to ensure that you do not break the slides by using the high power lens
incorrectly. Please ask for help if you need it.
For two different types of bacteria, draw a neat pencil sketch of just one or two
individual bacteria - include labels and a scale.
Google some information about these bacteria to add as notes below your sketch.
Type of Bacteria: ___________________________________________
Scale:
Notes:
Type of Bacteria: ______________________________________________
Scale:
Notes:
Part E – Discussion and Conclusions:
6 Marks
Briefly discuss the procedures and outcomes of the investigation. Describe what you did.
Discuss what went well and what you found difficult. Are you confident that your work is
reliable or are there some concerns with the information and detail presented here? Are
there any questions that have arisen from this investigation that you might want to
investigate further?
Write a brief conclusion summarising your findings in relation to the aims.
a. How have you used the microscopes better now than you did in year 8 or 9?
b. What have you learned about calculating the sizes of small things?
c. What did you do to make your diagrams clear, accurate and informative?
d. What have you discovered about the sizes and features of bacteria?