2A - Cell division (investigating mitosis) Flashcards
Explain the experiment that you can do to observe the stages of mitosis
Make sure you were wearing safety goggles and a lab coat before you start and you should wear gloves when using stains.
- Cut 1cm from the tip from a growing root (e.g. of an onion). It needs to be the tip because that’s where growth occurs (and so that’s where mitosis takes place).
- Prepare a boiling tube containing 1 M hydrochloric acid and put it in a water bath at 60 degrees C.
- Transfer the root tip into 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. Get read of the rest.
- 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. The stain will make the chromosomes easier to see under a microscope.
- Place a cover slip over the cells and push down firmly to squash the tissue. This will make the tissue thinner and allow light to pass through it. Don’t smear the cover slip sideways or you will damage the chromosomes.
- Now you can look at all the stages of mitosis under an optical microscope.
Explain how you can observe cells using an optical microscope
- Start by clipping the slide you’ve prepared onto the stage.
- Select the lowest-powered objective lens (the one that produces the lowest magnification).
- Use the coarse adjustment knob to bring the stage up to just below the objective lens.
- 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.
- Adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide.
- If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
What is the equation for mitotic index?
mitotic index = (number of cells with visible chromosomes) / (total number of cells observed)
What would you expect the mitotic index of a tissue that is growing to be like?
High - lots of cells
What could a high mitotic index indicate?
Growth, tissue repair or cancerous growth in some tissues.
What can you use to calculate the size of cells in a microscope?
A graticule and micrometer.
Where is an eyepiece graticule fitted?
Onto the eyepiece.
What is a graticule?
A transparent ruler with numbers but no units that is fitted on to the eyepiece.
Where is a stage micrometer placed?
On the stage.
What is a stage micrometer?
A microscope slide with an accurate scale and it’s used to work out the value of the divisions on the eyepiece graticule at a particular magnification.
Does an eyepiece graticule have units?
No
Does a stage micrometer have units?
Yes
What is the equation linking magnification, actual size and image size?
actual size = (size of image) / (magnification)
What are artefacts?
Things that you can see down the microscope that aren’t part of the cell or specimen that you’re looking at.
Give examples of artefacts
Bits of dust, air bubbles and fingerprints.
Or inaccuracies caused.by squashing and staining your sample.
