2.1 - Cells

Question 1

What are the main aspects of cell theory?

Answer 1

1. Cells are the units of structure and functions in all organisms.
2. New cells arise form pre-existing cells.
3. Cells require and use energy.
4. Cells contain DNA which is passed onto daughter cells –> the genetic information.
5. Some organisms are unicellular eg. Thy are made up of one cell, while others are multicellular and consist of a large number of cells of different types that have a hierarchical organisational structure.

Question 2

What is a light microscope?

Answer 2

• A compound microscope which incorporates more than one lens.
• The image is magnified by the objective lens and further magnified by the ocular lens (eye piece)

Question 3

What factors determine the quality of the image seen through the microscope?

Answer 3

• Focus
• Brightness
• Contrast
• Resolution

Question 4

How does focus affect the image quality?

Answer 4

• Related to the focal length and can be controlled with focus knobs.

Question 5

How does the contrast of the image affect its quality?

Answer 5

• Related to the illumination system and can be adjusted by changing the intensity of the light and the diaphragm /pinhole.

Question 6

What is the reason for applying chemical stains to biological specimens?

Answer 6

• Applying a chemical stain to a biological specimen can enhance the contrast. Contrast is related to the illumination system and can be adjusted by changing the intensity of the light and the diaphragm/pinhole.

Question 7

How does the brightness of the image affect its quality?

Answer 7

• How light or dark is the image?
• Related to the illumination system and can be adjusted by changing the voltage of the lamp and adjusting the pinhole apertures.

Question 8

How does the resolution of the image affect its quality?

Answer 8

• How close can two points be before they are no longer seen as two separate points?
• Related to the numerical aperture of the objective lens and therefore is a relatively fixed characteristic on a microscope.

Question 9

Scanning Electron Microscopes have a smaller resolution than light microscopes. What do you think this means for the quality of the images they produce?

Answer 9

Due to the higher maximum magnification of the SEM, the resolution is much lower. This is because the further the image is magnified, the resolution of the image is decreased and therefore the quality of the image is lesser than the higher resolution of a light microscope.

Question 10

What is the maximum magnification of each type of microscope?

Answer 10

• The Light Microscope has a maximum magnification of x1500
• The Transmission Electron Microscope has a magnification of more than x100,000
• The Scanning Electron Microscope has a magnification of x100,000.