OBSERVING CELLS

Question 1

What is a light microscope (optical microscope)?

Answer 1

Toll that uses a beam of light and optical lenses to magnify specimens up to 1500x life size.

Question 2

What is an electron microscope?

Answer 2

Tool that uses a beam of electrons and magnetic lenses to magnify specimens up to 500,000x life size.

Question 3

What is magnification?

Answer 3

Measure of how much bigger the image you can see is than the real image.

Question 4

What is resolution (resolving power)?

Answer 4

Measure of how close together two objects can be before they are seen as one.

Question 5

What are transmission electron micrographs (TEMs)?

Answer 5

Micrographs produced by the electron microscope, give 2D images like those from a light microscope, but magnified 500,000x.

Question 6

What are scanning electron micrographs (SEMs)?

Answer 6

Micrographs produced by the electron microscope, have a lower magnification than TEMs, but produce a 3D image.

Question 7

What does cell theory state?

Answer 7

Cells are fundamental units of structure, function and organisation in all living organisms.

Question 8

How do you calculate total magnification?

Answer 8

Magnification of objective lens x magnification of eyepiece lens = total magnification

Question 9

What image does the objective lens produce?

Answer 9

Magnified and inverted.

Question 10

Why is staining used?

Answer 10

To make it easier to identify particular types of cells, or particular parts of cells.

Question 11

What does haematoxylin stain?

Answer 11

Nuclei of plants & animal cells purple, blue or brown.

Question 12

What does methylene blue stain?

Answer 12

Nuclei of animal cells blue.

Question 13

What does acetocarmine stain?

Answer 13

chromosomes in dividing nuclei (plant & animal cells).

Question 14

What does iodine stain?

Answer 14

Starch-containing material in plant cells blue-black.

Question 15

What are the advantages of the light microscope?

Answer 15

• Can see living plants & animals directly, allows you to compare prepared slides with living tissue.
• Relatively cheap.
• Relatively light & portable.

Question 16

What are the disadvantages of the light microscope?

Answer 16

• Limited powers of resolution & magnification.
• Staining/preservation tissue can produce artefacts. What we may see may not be a true representation of the living tissue.

Question 17

What are the advantages of the electron microscopes?

Answer 17

• Huge powers of magnification & resolution.

- Many details of cell structure can be seen.

Question 18

What are the disadvantages of the electron microscope?

Answer 18

• All specimens examined in a vacuum, air would scatter electrons.
• Specimens undergo severe treatment, likely to produce artefacts.
• Extremely expensive.
• Large, have to be kept at constant temp/pressure and need to maintain internal vacuum.

Question 19

Why are heavy metal ions used to stain specimens for electron microscopy?

Answer 19

To improve the scatter of electrons and make greater contrast in image.

Question 20

What is the correlation between wavelength and resolution?

Answer 20

Resolving power increases as the wavelength gets smaller.

Question 21

How are images displayed in an electron microscope?

Answer 21

On a screen or monitor.