LAB #
OBSERVING ONION CELLS UNDER THE MICROSCOPE
HIPOTHESIS: ………………………………………………………………………………………………………………
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Problem. What structures can you observe in an onion cell when using a compound light
microscope?
MATERIALS
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1 compound light microscope
1 slide
1 cover slip
1 pair of tweezers
1 eye dropper
a few drops of water
1 paper towel
1 small piece of onion
METHILENE BLUE
Procedure.
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Have one partner take a microscope from the back of the room. Remember to carry it
with one hand on the arm and one hand on the base. Find an outlet to plug in your
microscope. Then this same partner can pick up the eye dropper.
The other partner should pick up a slide, cover slip, onion, paper towel, and tweezers
from the front counter. Pick up the slide and the cover slip by the edges to avoid
fingerprints as well.
Now you are going to make a wet mount. Use your tweezers to peel off a small thin
section of onion from the concave side of the onion. Place this thin section on your
slide. Remember to hold the slide by the edges!
Put one drop of methilene blue on the onion and wait one minute.
Wash the excess of blue using water.
Dry the slide gently using the filter paper. Don’t touch the onion.
Use the tweezers or your fingers to gently pick up the cover slip. Line up the edge of
the cover slip with the edge of the onion on your slide. Place the cover slip at a 45°
angle to the slide, and then slowly lower it over the onion (see Figure 1 below).
Figure 1. Making a wet mount slide.
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Carefully press down on the cover slip with the tweezers to remove as many bubbles
as possible. You are now finished making your wet mount slide.
Turn on your microscope.
Lower the stage all the way using the coarse focus knob.
Put your slide on the stage and use the clip to secure it in place. Make sure the light is
shining through the onion.
Rotate the lenses so that you are using the lowest power lens.
Slowly rotate the coarse focus knob so that the stage rises and the onion cells come
into focus. One partner can peer through the microscope and turn the coarse focus
knob while the other partner can watch that the stage does not crash into the lens.
Stop when the cells come into focus. Make sure both partners get a look through the
microscope.
Carefully rotate the lenses so that the next highest power lens is being used.
Use the coarse focus knob to focus the cells, and then try using the fine focus knob to
get an even clearer picture. Make sure both partners get a look.
Rotate the lenses to the next highest power.
On your lab report, make a new section called “Observations”. In this section of your
report, draw a detailed sketch of what you see in the field of view. Remember to label
the parts of your drawing and to draw to scale. See the scientific drawing criteria
below to remind yourself what else is important when making a scientific drawing.
Throw your cover slip and onion in the garbage. Put your slide into the soapy water.
Then put your slide into the rinse water.
Dry off your slide using the paper towel. Put the paper towel in the garbage.
Wrap up the cord of your microscope and replace the microscope cover. Do not put
the microscope away yet.
Questions. Answer these questions in complete sentences, ensuring that you re-word the
question in your answer.
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What parts of the onion cell could you see? You might want to review section 1.2 in
your textbook to refresh your knowledge of cells.
2. A) What difficulties did you have performing this lab?
B) What would you do differently in a future lab to avoid this same problem from
occurring?
3. What is one thing you learned or discovered or realized from doing this lab?
Conclusion. Write a conclusion that includes the following:
- a sentence that answers the Problem
- a sentence saying whether the observations support or do not support the hypothesis
- a sentence that uses your observations as evidence to back up the previous sentence that
you just wrote
- a future lab that you could do that would build on the knowledge you gained by doing
this lab
Lab Report Criteria. . You will be graded according to those criteria.
General
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organized (not smushed, neat, in proper order)
accurate information
headings stand out
includes all sections (e.g. Problem, Hypothesis, Observations, Questions, and
Conclusion)
writing is in pen or typed
effort is apparent
name, date, block
full sentences
title that pops, first letters capitalized, descriptive not creative
Hypothesis
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“if…then” statement
proper and full sentence
must be clear
comes from knowledge of previous experience or an educated guess
a statement, not a prediction or a question
related to the problem
Questions
o question should be reworded in answer
o full sentences with proper grammar
o detailed answers, explained well
o answers correct or logical
o use examples from results to back up what you’re saying
o be sure to answer what the question is asking you
Conclusion
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paragraph
full sentences
overall summary of what was done
answers problem, and re-word the problem when you’re answering it
state whether hypothesis was correct
results from observations are used to support the statement of whether or not
hypothesis was correct
to the point
suggests a future lab to study based on the findings from this lab
Science 8 Scientific Drawing Criteria
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done in pencil
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instead of shading, use dots (stippling)
label lines are straight, horizontal, and to the right (unless it is too squishy)
labels are lower-case
everything is labeled
drawing is accurate; it looks as close to what is actually seen as possible
lots of detail
detailed, specific, descriptive title of what the drawing is
Title should have capital letters
should be neat as possible
has to have name, date, block
should be about half a page
make the lines definite and not “sketched out”
colouring is optional, but colours must be accurate
label lines touch the object they are pointing to