Control
The variables in this investigation to keep it a fair test are:
- To have similar slides and cover-slips as not to affect the results
- To keep the measurements as accurate as possible
Safety
There are many faults which can and will occur if this investigation is not carried out as safely as can be.
Accidents which can occur include things such as
- The main risk is that of the spread of micro organisms in the mouth when swabbing the cotton bud in the cheek and also if not disposed of properly.
- Cuts from the slide/cover slip.
- Possible injury from the forceps. Stains from the Iodine and Methylene blue stain.
- And last of all eye irritation from the onions.
Apparatus
2x Slides 1x Light Microscope
2x Cover Slips 1x Iodine Solution
1x Onion 1x Mounted Needle
1x Cotton Bud 1x Pirouette
1x Forceps 1x Acetated ruler
1x OHP Pen 1x Calculator
And a beaker of disinfectant
Method
For Cheek Cell
- Take 1 cotton bud from a freshly opened pack.
- Gently wipe within the mouth ensuring that the whole cotton bud is covered.
- Smear the cotton bud over the slide and add 1 drop of methylene blue stain with the Pirouette.
- Place the cotton bud (end with your cells) into the beaker of disinfectant.
- Place the cover slip on top of the slide with the mounted needle making certain that no air bubbles are trapped inside.
- Place the slide now under the micro scope observing it at the highest objective lens.
- At the end of investigation make sure that the slide is placed into the beaker of disinfectant.
For Onion Skin Cell
- Take 1 onion and cut off a piece.
- From this using the forceps take out the inner surface (the skin).
- Place this then onto the slide and using the pirouette add 2 drops of iodine solution.
- Place after this the cover slip using the mounted needle like before ensuring there are no air bubbles.
- Place the slide then under the light microscope.
- Firstly focus on the slide with the lowest objective lens.
- Then use the highest objective lens to see the cells.
Conclusion
In the investigation I found that yes as said in Prediction that the plant cell is bigger than the animal cell.
Also I will see from the table below that the cells have 3 things the same but the plant has 3 additional inclusions within it.
I know from this that the Nucleus, Cytoplasm and Cell Membrane are essential in a cell as I shall explain:
- Nucleus- the brain of the cell. Controls what happens in the cell.
- Cytoplasm- substance in which all reactions in cell occur
- And the cell Membrane- Controls what goes in and out of cell
Also in the plant there are extras:
- Vacuole- Cell Sap which the cell feeds on (contains sugars and salt)
- Chloroplasts- inside are the chlorophyll a green pigment which absorbs sunlight for the process of photosynthesis
- And the Cell Wall- A coating of cellulose which acts as a rigid support for the plant (without this the plant if hit would burst)
We have also learnt of the Mitochondria (the dots in the cell) this is where all the energy of the cell comes from. And where the process of respiration transpires.
Also from this I have learnt how to use a microscope:
- How to prepare a slide e.g. putting on the skin and adding dye.
- How to correct and adjust the mirror of the microscope to allow maximum light in
- How to put on a cover slip and avoiding any air bubbles being trapped in the slide.
- How to focus in on the cell an then identifying the parts of a cell and how to do it without damaging or disturbing the slide
- And how to change the objective lens on the microscope in order to zoom into the cell
I learnt that a plant cell is larger then an animal cell and I think this due to what it contains as there are much more in a plant cell than there is in an animal cell.
(Mass). As you will see from the calculations that my prediction were in fact close to that of the result found.
Finally I learnt how to convert millimetres into micrometers. There is a simple method to finding this as seen below. This should be applied to the method when finding comparing the cells.
- First put your acetated ruler under the microscope and see how many lines you can observe.
For instance if you refer to Drawing and Calculations I see that there are 2 and a half millimetres.
- This then is converted to be your EPG (Eye Piece Gradient). This can be found by dividing 1 by your millimetres seen. For instance in my investigation it will be 1*2.5 which is 0.4 millimetres. Therefore my EGP is 0.4 mm.
- After this you measure the cell in my investigation I see 2 divisions.
- So we multiply the divisions by the EPG. e.g. 0.2 x 0.4
- This is 80 therefore my cheek cell is 80 µm long.
Evaluation
From this investigation I can assess that there may have and I think happened these faults are:
- Lack of experience with the microscope- this has been my first time using the microscope and there were problems. For instance when I first examined the cheek cell we thought we had some kind of wooden cell it was brown and had grooves. After consulting the teacher we discovered that the mirror in fact had not been facing the sun but at the window ledge
So I’d resolved that problem
- Lack of light- It was a cloudy day so there wasn’t much light which limited the view of the cell so might’ve disrupted the results
- Faulty Equipment- so observation of cell was distorted the lens was cracked obstructing view
- Air bubbles- In the onion skin investigation I found that I had left some air bubbles trapped in the slide so the drawing of the cell was disordered
- Too much dye- I had put in too much so this resulted in inaccuracy in drawing the cell
- Slide dirty- this obscured vision consequently caused problems in the seeing of the cell
If I was to repeat this investigation again I would take certain precautions so in future I don’t duplicate this incident again.
I would take care to guarantee that these errors are avoided and think ahead to resolve this.
Below I give a list of my resolutions:
- Light- make sure that you receive maximum light for best results but to boost this up why not include an artificial light
- Equipment- this cannot be avoided but check your apparatus before use and take care of it
- Air bubbles- This can only be solved by being vigilant when placing the cover slip on and making sure that there are no bubbles within the slide
- Dye- read the instructions before carrying out the investigation and proof reading , double checking and asking around if you are doing it right
- Dirty slide- when taking a slide pick one that is clean and to make sure wash and dry thoroughly
