Topic 2a- Analysis of cell components

Question 1

What is magnification?

Answer 1

Size of image divided by size of real object.

Question 2

Differences between optical (light) and electron microscope.

Answer 2

Light- use light to form an image, maximum resolution of about 0.2 micrometres, maximum useful magnification is about x 1500.

Electron- use electrons to form an image, higher resolution then light so give more detailed image, maximum resolution of about 0.0002 micrometres, maximum useful magnification about x 1500000.

Question 3

Difference between Transmission electron microscopes and Scanning electron microscopes.

Answer 3

Transmission- use electromagnets to focus a beam of electrons, give high resolution images so can see internal structure of organelles like chloroplasts, but they can only be used on thin specimens.
Scanning- scan a beam of electrons across the specimen, images can be 3D, can be used on thick specimens, but they give lower resolution images then transmission.

Question 4

Cell Fractionation separates organelles.
What is homogenisation, filtration and ultracentrifugation?

Answer 4

Homogenisation- Breaking up the cells. E.g. vibrating the cells or by grinding the cells up in a blender.
Filtration- getting rid of the big bits.
Ultracentrifugation- separating the organelles.

Question 5

Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.
Do not include details of how you would prepare the tissue observed with an optical microscope.

Answer 5

• 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.