Investigating mitosis Flashcards
When preparing a sample of a plant root in order to observe mitosis, why is it important to take the sample from the root tip?
because that is where growth and mitosis occurs
2) Why should you add a stain to your sample when trying to observe mitosis?
the stain will make chromosomes easier to see under a microscope
In microscopy, what are artefacts? Give three examples.
Artefacts are things you can see down the microscope that are not part of the cell or specimen you’re looking at. They’re usually made during the preparation of the specimen. Examples include dust, air bubbles and fingerprints.
When using an optical microscope, should you start with the lowest- or highest-powered objective lens?
You should start with the lowest-powered objective lens and swap to a higher-powered objective lens if you need to see the slide with greater magnification.
5) Describe how to prepare and stain a root tip to observe the stages of mitosis.
Methods may vary: e.g. cut 1 cm from the tip of a growing root. Prepare a boiling tube containing 1 M hydrochloric acid and put it in a water bath at 60 °C. Transfer the root tip to the boiling tube and incubate for about 5 minutes. Use a pipette to rinse the root tip well with cold water. Leave the tip to dry on a paper towel. Place the root tip on a microscope slide and cut 2 mm from the very tip of it. Use a mounted needle to break the tip open and spread the cells out thinly. Add a few drops of stain and leave it for a few minutes. Place a cover slip over the cells and push down firmly to squash the tissue.
What is a mitotic index?
the proportion of cells undergoing mitosis
A scientist is observing a sample of cells under the microscope.
Out of 105 cells, 46 have visible chromosomes. Calculate the mitotic index of this sample. Give your answer to 2 decimal places.
0.44. Mitotic index = number of cells with visible chromosomes total number of cells observed. 46 105 0.438… = 0.44 to 2 decimal places.
A sample of tissue from an adult kidney is found to have a high mitotic index. What might this indicate?
A high mitotic index could indicate that tissue repair is currently taking place or that there is a tumour forming in the tissue. (It’s an adult kidney, so it’s not likely to be growing normally.)
How do you use an optical microscope?
1) Start by clipping the slide you’ve prepared onto the stage.
2) Select the lowest-powered objective lens
(i. e. the one that produces the lowest magnification).
3) Use the coarse adjustment knob to bring the stage up to just below the objective lens.
4) Look down the eyepiece (which contains the ocular lens). Use the coarse adjustment knob to move the stage downwards, away from the objective lens until the image is roughly in focus.
5) Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide.
6) If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
What equipment can you use to calculate the size of cells?
a graticle and a micrometer
What is an eyepiece graticule?
It’s like a transparent ruler with numbers, but no units. An eyepiece graticule is fitted onto the eyepiece.
What is a stage micrometer?
It is a microscope slide with an accurate scale (it has units) and it’s used to work out the value of the divisions on the eyepiece graticule at a particular magnification.
The stage micrometer is placed on the stage
How do you use a graticle and micrometer to measure the size of a cell?
e.g. when one divsion on the micrometer (of 0.1mm) is the same a s 4.5 divisions on the eyepiece graticule?
Each division on a stage micrometer is 0.20 mm. At a certain magnification, 1 division on the stage micrometer is equivalent to 6.5 divisions on the eyepiece graticule. A cell viewed under the microscope is 5 eyepiece divisions long. How long is the cell in mm?
0.15 mm (to 2 s.f.). 1 division on the eyepiece graticule is 0.20 ÷ 6.5 = 0.030… mm. So the cell is 0.030… x 5 = 0.153… mm.
How do you calculate the size of cells when you’re given an image of the cells under a microscope?
If the image of a cell measures 5 mm and the magnification is x 100. What is the actual size?
actual size = image size / magnification
Example: If the image of a cell measures 5 mm and the magnification is x 100, then the actual size of the cell will be: 5 / 100 = 0.05 mm.
