Looking into the microscope

 

 

As part of the Year 7 Science curriculum, students learn how to prepare a slide and use a light microscope to view cells at different magnifications. Students are required to answer questions as they perform tasks using the microscopes.

 

 

Below is a piece of outstanding work from Kara Perilli that she presented for her Year 7 Microscope Prac. 

 

microscope prac

 

aim:To effectively use the microscope to determine the size of the field of view, to examine the letter “e” while viewing at 40x and 100x and to have our first look at a plant (onion) cell.

 

hypothesis:The microscope will allow me to see the letter e and onion cell up to 100x magnification. I predict I will be able to see some organelles in the onion cell.

 

materials:

  • Microscope
  • Slide
  • Coverslip
  • Letter ‘e’
  • Red onion

method:

1. Set up the microscope with the letter ‘e’ on the slide with the coverslip.

    a. view letter “e” at 40x moving slide backwards, forwards and to each slide describing what you see. 

    b. view the letter “e” at 100x. Describe what you see.

 

2. The Field Of View (F.O.V.) is the area you can see through the microscope’s ‘window’. 

    a. use the grid paper provided and explain how you could ascertain the diameter of the field of view         when the microscope is on 40x and 100x (state your answers in millimetres and micrometres).

    b. calculate the area of the field of view when on 40x and 100x in mm and cm squared.

 

3. Draw or provide a photo of the letter e. Show a scale below this as determined by the FOV.

 

4. Look at page 39/41 of your textbook. Follow instructions to prepare slide of thin onion membrane. If we are using white onion we will need to stain the cell.

 

questions:

  1. When making your slide, what did you find difficult?

    Although i didn’t make a slide, I saw one of the main difficulties when making the slide is peeling the membrane so that it’s only one cell thick. This is essential to be sure that you can clearly see cells under the microscope (if there’s any more than one layer of cells you cannot see them, no matter what; eg your skin). When making the slides, it is also quite difficult to apply the dye in an even manner- while this makes the cell features easier to see, you must make sure there is consistently dye through the onion, otherwise the clumps of ink will disable you from seeing anything.

  2. Draw a diagram of what you saw at 40x or label a picture from your phone. Describe this in words in

      your results table.

      See under results table.

 

  3. Try to isolate one cell at 100x. Draw a diagram or label a pic from your phone. Describe what you see          in  your results table

      See under results table.

 

results (with pictures):

Article

40x

100x


Letter ‘e’

I saw all the little ink splotches and imperfections in and around the main body of the letter. Everything is backwards- when i move the slide left, it moves right, when i move it up it goes down.

At 100x, i can see everything i saw at 40x, but a clear difference is that i can plainly see splatters of oil in the paper around the ‘e’. I assume this ink is oil-based.


Field of View

I can ascertain the diameter of the field of view by positioning the grid paper so that one of the (bigger) squares starts right on the edge of the F.O.V. I then can count the number of (millimetres) across and convert to micrometres if required.

D= 4.5mm or 4500 micrometres

A= 15.9mm squared, or 0.159cm squared

A= 2.5mm squared, or 0.025cm squared

D= approx 1.8mm or 1800 micrometres


 
 

 

Onion cells

The cells are mismatched and squashed together, and I can faintly see nuclei in some of the cells. The nuclei are dyed pale pink and look like they’re randomly distributed within the cell. There are some (brown) imperfections on the slide or lens which are not to be mistaken for nuclei- they are most probably dirt. I can also see a thick, dark line going across the FOV, which is probably where the onion membrane has folded over, or there is a higher concentration of dye in that area. I can clearly see cell walls around each cell, the purpose of which is to resist turgor, or water pressure, coming from the vacuole. (See Figure 1)

I can now see more imperfections and see a lot more nuclei, getting a closer look at them. I cannot see any other organelles due to the fact that nuclei are the biggest in size. Unlike viewing the same onion piece at 40x, i can get a closer look at the vacuoles (which store the cell’s nutrients and waste) and the cell walls that surround and protect them. However, the cell membrane, which surrounds, protects and controls what goes in and out of the cell, is not visible even under 100x magnification. Next to some of the cell walls, you can see a thin line only slightly lighter than the cell wall. This is not to be mistaken for the cell membrane, as it’s just a variation in the ink.

(See Figure 2)

 

 

discussion:

 

In this practical, I aimed to learn how to use a light microscope, examine a printed letter and onion skin cell under it and learn how to make an dyed onion slide.

As anticipated, I was able to observe the letter ‘e’ and the stained onion skin cells from 40 and 100x

magnification. 


While viewing the printed letter ‘e’ (see Figure 3), I saw that at higher magnification the ink appeared splattered and imperfect, not displaying a sharp edge as can be seen by the naked eye. We were also able to examine the paper that the letter was printed on more closely. The paper does not appear smooth or flat; the edges of the ink display small bubbles. Due to their appearance and their proximity to the main body of the letter, I can guess that the bubbles are oil, and the ink used is oil-based. Like the case of water and oil, the oil has formed bubbles because the pigment is denser than the oil and won’t mix because the oil/ink molecules are more attracted to one another. The resulting mixture is a suspension.

 

In the case of the onion specimen, the cell wall and nucleus of each cell were visible and appeared pink in colour (after dying the slide for means of contrast). The cell wall is a protective layer that resists the water pressure (turgor) inside a cell (or vacuole), providing structural support to the cell and giving the plant its shape. The nucleus has two main functions. It stores the cell’s genetic material (DNA) and coordinates the cell’s activities. However, the other organelles were not visible. It is likely that a higher magnification and another dye are needed to see these intracellular

structures. 

 

The Field of View  (FOV) is the amount of specimen one can see through the microscope.  

While viewing these objects, I also found that increasing the magnification also shortens the FOVs diameter. At 40x magnification the FOV was determined to be 4.5mm, while at 100x magnification the FOV was 1.8mm.

We also found that, when looking through a microscope, the image of the specimen is inverted. This is because of the properties of the convex, objective lens, which enlarges the image you’re seeing but also inverts it.

 

conclusion:

In conclusion, the light microscope we used is a useful tool to help magnify specimens and determine their structural detail. At the magnifications used in this practical, we were able to see the cell walls and nuclei of onion cells, but not other intracellular structures.



 

BPC What's On!

BPC Music presents 
A Christmas Eve at The Spotted Mallard. 


Monday, 17 December - 7PM
Dinner and drinks menu available at venue.

Last year's performance was a sell out, so get your booking in fast!

 

$15 Tickets at door, table bookings are essential call 9380 8818