3.2.1.3 Studying Cell Flashcards
Describe how you could make a temporary mount?
Put two drops of water on the slide
Obtain thin section of plant cell
Place the plant tissue flat
Add three drops of iodine in potassium iodide
Carefully lower, the covers slip on the top with mounted Needle
Additional
Use tissue to absorb excess liquid
Place the slide on the platform of the microscope
How to measure the main diameter of starch grain present-in cell viewed in temporary mound
Measure the diameter of grain, using the eyepiece graticule
Calibrate the eyepiece gratitude using a stage micrometre at the same magnification
Randomly sample, 10+ grains and use to calculate the mean
Equation for image size
Image size = actual size x magnification
Cell fractionation process (used to isolate organelles)
Preparation: tissue is placed in cold, buffered solution with the same water potential as the organelles (isotonic)
Homogenisation: This brakes, open, the cell usually done, either by vibrating the cell or grinding them in the homogeniser/ blender. This release the organelles from the cell.
Filtration : the resulting fluid (homogenate) is filtered to remove any debris (whole cell / large tissue)
Ultracentrifugation : (exam )
-Centrifuge at low speed and remove supernatant
- Centrifuge supernatant at high speed
the fragment in the filtered homogenate are separated in the centrifuge at increasing speed
Why the tissue has to be placed in cold buffered solution with the same potential organelles?
Cold : reduce enzyme activity to preferred digestion of organelle/mitochondria , inactivated
Buffered : maintain pH , stop enzyme/protein denatured
Same water potential : the organelle will not shrink or lysis. Stop net movement of water by osmosis.
Compare and contrast, how optical, TEM and SEM work and cell being study
Lightbeam vs electron beam
Glass lens vs electromagnetic
Living cell vs dead cell (vacuum)
Less preparation vs more preparation (time-consuming/ thinner Spciesman (TEM))
Lower resolution vs higher resolution (smaller, organelle, can be observed) vs lower than TEM
Coloured image (natural colour) vs black and white
2D vs 2D vs 3D
Less chance of artefacts vs higher chance of artefacts due to complicated preparation [tem]
The resolution of image obtained using electron microscope is higher than the resolution of an image obtained using an optical microscope. WHY?
Shorter wavelength between electron
longer wavelength in light rays
how the student can use a ruler and a caculater to determined the size of the structure from photograph obtain using a microscope and give answer in um
- Measure (length of structure) and divide by magnification;
- Correct conversion from measured length to μm, either
× 10 000 from cm
OR
× 1000 from mm; - Measure (length of structure) and divide by
(image) length of scale bar; - Multiply by actual length of scale bar;
Describe the principles and the limitations of using a transmission electron
microscope to investigate cell structure.
Principles:
1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
Principles:
Allow maximum of 3 marks
Limitations:
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex / long preparation time;
9. Image not in 3D / only 2D images produced.
describe how you would determined a reliable mitotic index from tissue observed with an optical microscope
- Count cells in mitosis in field of view;
- Divide this by total number of cells in field of view;
- Repeat many/at least 5 times
OR
Select (fields of view) at random;
“Push down hard on the cover slip, but do not push the cover slip sideways.”
Explain why she was given this instruction.
- Push hard – spread / squash tissue;
- Not push sideways – avoid rolling cells together / breaking chromosomes.
