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Biology /3.3: Microscope Measurements and Required Practical

3.3: Microscope Measurements and Required Practical

Biology10 CardsCreated 17 days ago

This deck covers key concepts related to microscope measurements and practical laboratory techniques, including the use of eyepiece graticules, calibration, and methods for calculating the mitotic index.

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What is an eyepiece graticule?

An glass disc that is placed in the eyepiece of a microscope. A scale is etched on the glass disc.
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Key Terms

Term
Definition
What is an eyepiece graticule?
An glass disc that is placed in the eyepiece of a microscope. A scale is etched on the glass disc.
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Why can’t the scale be directly used to measure the size of objects under an objective lens?
Because each objective lens will magnify to a different degree
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How do you calibrate the eyepiece graticule?
Use a stage micrometer

Describe a method to calculate the mitotic index of cells

1. Heat 1 mol dm​-3 H​ Cl at ​60​​°C​​ in a water bath.
2. C​ut a small sample of the ​root tip​​ using a ​scalpel​​.
3. Transfer root tip to...

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What is the equation for mitotic index?
Mitotic index=number of cells with visible chromosomes÷total number of cells in sample
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Why do cells need to be taken from the root tip?
Because this is the region of cells undergoing mitosis
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3.3: Microscope Measurements and Required Practical
TermDefinition
What is an eyepiece graticule?
An glass disc that is placed in the eyepiece of a microscope. A scale is etched on the glass disc.
Why can’t the scale be directly used to measure the size of objects under an objective lens?
Because each objective lens will magnify to a different degree
How do you calibrate the eyepiece graticule?
Use a stage micrometer

Describe a method to calculate the mitotic index of cells

1. Heat 1 mol dm​-3 H​ Cl at ​60​​°C​​ in a water bath.
2. C​ut a small sample of the ​root tip​​ using a ​scalpel​​.
3. Transfer root tip to ​HCl​​ and ​incubate​​ for 5 minutes.
4. Remove from HCl and wash sample in cold distilled water and ​remove the very
tip ​​using a scalpel.
5. Place tip on a microscope slide and add a few drops of ​stain​​
This makes the ​chromosomes visible​​ and will therefore show which cells
are undergoing mitosis.
6. Lower the cover slip down carefully onto the slide. Make sure there are ​no air
bubbles ​​in the slide which may distort the image, and that the​ coverslip doesn’t
slide sideways which could damage the chromosomes.
7. Place under a microscope and set the ​objective lens​​ ​​on the lowest
magnification.
8. Use the ​coarse adjustment knob​​ ​​to move the lens down to just above the slide.
9. Use the ​fine adjustment knob​​ ​​to carefully re-adjust the focus until the image is clear​​
10. To calculate ​mitotic index​​, ​​cells ​undergoing mitosis​​ must be counted (cells with ​chromosomes visible​​), as well as the​ total number of cells​​.

What is the equation for mitotic index?
Mitotic index=number of cells with visible chromosomes÷total number of cells in sample
Why do cells need to be taken from the root tip?
Because this is the region of cells undergoing mitosis
Why does the root tip need to be firmly squashed?
In order to get a thin layer of cells which light can pass through
Why was a stain used?
To make chromosomes visible
Why were the root tips placed in hydrochloric acid?
In order to soften the tissues and separate the cells
Why were the root tips heated at 60 degrees for 5 mins
To increase the kinetic energy of the molecules, increasing the rate of reaction with the acid, denaturing proteins, softening cells and stopping mitosis