Cellular Structures: Microscopic Examination of Onion Cells
Studying Cells with a Microscope – Lesson 3
Task 1 – Practical skills: making a slide of onion cells and viewing it with a microscope
Watch the video below to show you how to make a microscope slide to
view onion cells. (from 2:43 to (9:00).
Use the video to write a method on how to prepare a slide to view onion
cells observe under a microscope.
Task 1 – Practical skills: making a slide of onion cells and viewing it with a microscope
•
Cut a section of onion and then peel a thin layer of onion.
•
Place the thin layer of onion onto a glass slide (be careful to only hold the
slide by the edges to avoid fingerprints).
•
Make the piece of onion skin as flat as you can on the slide to avoid cells
overlapping.
•
Add a few drops of iodine to
stain
your onion cells. This will make them easier
to see.
•
Carefully lower the coverslip over the onion at an angle. You can use a
mounted needle to help with this. This reduces the chance of air bubbles
forming.
Check your method and self assess!
Task 2 – Numeracy - Magnification
1.
Use the information given to work out the magnification.
No calculators!
Magnification = eye piece lens x objective lens
100
800
3000
175
660
Task 2 – Numeracy - Magnification
Actual size =
image size
magnification
Image size = actual size x magnification
Magnification =
image size
Actual size
Actual size = image size ÷ magnification
or
or
Magnification = image size ÷ actual size
Actual size = how big the cell is in real life (without being magnified)
Image size = The size of the cell in a drawing or what you can now see down the microscope
Magnification = How much bigger you’ve made the cell look on your microscope
If an onion cell was observed through a x100 magnification and it measured 17mm, what would be the actual size of the
cell?
Actual size =
17mm
= 0.17 mm
100
2.
Apply what you know to work out the actual size of the following.
a.
An animal cell measures 10mm under magnification x250.
a.
A piece of muscle tissue measures 25mm under magnification x100.
A red blood cell measures 5mm under magnification x40.
Task 2 – Numeracy - Magnification
10
Actual size = image size ÷ magnification
250
= 0.04 mm
the size of the cell in real life (actual size)
Actual size = image size ÷ magnification
25
100
= 0.25 mm
Actual size = image size ÷ magnification
5
40
= 0.125 mm
Light microscope
1.
2.
Eye piece lens
objective lens
How to calculate total magnification?
Eye piece magnification x objective lens magnification
What is the main limitation of a light
microscope?
Maximum magnification is quite low (x1000) compared to an
electron microscope (x500 000 or more).
What is the main limitation of an electron
microscope?
Can only be used to view dead tissues.
Preparing a slide to view cells
Why do we use substances like iodine solution and
methylene blue?
They act as a stain to make the cells more visible.
Why is a mounted needle used when preparing a glass
slide?
Prevents the formation of air bubbles.
Learn how to prepare a microscope slide with onion cells for observation. Follow step-by-step instructions, including cutting and peeling onion sections, staining cells with iodine, and using a coverslip. Additionally, understand how to calculate magnification in microscopy to determine actual cell sizes.
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Presentation Transcript
Studying Cells with a Microscope Lesson 3 Task 1 Practical skills: making a slide of onion cells and viewing it with a microscope A piece of onion A pair of forceps A microscope A coverslip Iodine solution A microscope slide A mounted needle Safety goggles Watch the video below to show you how to make a microscope slide to view onion cells. (from 2:43 to (9:00). https://www.youtube.com/watch?v=SX6mow1AExI Use the video to write a method on how to prepare a slide to view onion cells observe under a microscope.
Task 1 Practical skills: making a slide of onion cells and viewing it with a microscope Check your method and self assess! Cut a section of onion and then peel a thin layer of onion. Place the thin layer of onion onto a glass slide (be careful to only hold the slide by the edges to avoid fingerprints). Make the piece of onion skin as flat as you can on the slide to avoid cells overlapping. Add a few drops of iodine to stain your onion cells. This will make them easier to see. Carefully lower the coverslip over the onion at an angle. You can use a mounted needle to help with this. This reduces the chance of air bubbles forming.
Task 2 Numeracy - Magnification 1. Use the information given to work out the magnification. No calculators! Magnification = eye piece lens x objective lens Eye piece lens (x) Objective lens (x) Magnification (x) 10 40 100 25 55 10 20 30 7 12 100 800 3000 175 660
Task 2 Numeracy - Magnification Actual size = image size magnification or Actual size = image size magnification Image size = actual size x magnification Magnification = image size actual size Magnification = image size or Actual size Actual size = how big the cell is in real life (without being magnified) Image size = The size of the cell in a drawing or what you can now see down the microscope Magnification = How much bigger you ve made the cell look on your microscope
Task 2 Numeracy - Magnification If an onion cell was observed through a x100 magnification and it measured 17mm, what would be the actual size of the cell? Actual size = 17mm = 0.17 mm 100 2. Apply what you know to work out the actual size of the following. a. An animal cell measures 10mm under magnification x250. Actual size = image size magnification = 0.04 mm the size of the cell in real life (actual size) 10 250 a. A piece of muscle tissue measures 25mm under magnification x100. Actual size = image size magnification 25 100 = 0.25 mm A red blood cell measures 5mm under magnification x40. Actual size = image size magnification = 0.125 mm 40 5
Light microscope How to calculate total magnification? Eye piece lens 1. Eye piece magnification x objective lens magnification objective lens 2. What is the main limitation of a light microscope? Maximum magnification is quite low (x1000) compared to an electron microscope (x500 000 or more). What is the main limitation of an electron microscope? Can only be used to view dead tissues.
Preparing a slide to view cells Why do we use substances like iodine solution and methylene blue? They act as a stain to make the cells more visible. Why is a mounted needle used when preparing a glass slide? Prevents the formation of air bubbles.
