Cells: Methods of studying cells

Question 1

What type of microscope would be used to see a living water flea specimen? Why?

Answer 1

• Optical microscope
• Specimen has to be living

Question 2

What type of microscope would be used to see a pollen grain surface? Why?

Answer 2

• Scanning electron microscope
• Provides a 3D scan of the surface

Question 3

What type of microscope would be used to view cristae in a mitochondrion? Why?

Answer 3

• Transmission electron microscope
• High resolution allows detail to be seen

Question 4

What type of microscope would be used to view the stages of mitosis in a root cell? Why?

Answer 4

• Optical microscope
• Sample needs to be alive

Question 5

What are the three types of microscopes?

Answer 5

• Optical microscope
• Scanning electron microscope
• Transmission electron microscope

Question 6

What is the equation for mitotic index?

Answer 6

Mitotic index = Cells in mitosis / Total number of cells

Question 7

What is the equation for magnification?

Answer 7

Magnification = size of image/size of real object

Question 8

How do you convert mm (millimetre) into um (micrometre)?

Answer 8

x 1000

Question 9

How do you convert um (micrometre) into nm (nanometre)?

Answer 9

x 1000

Question 10

Give the three microscopic units in order of their size:

Answer 10

Millimetre (mm)
Micrometre (um)
Nanometre (nm)

Question 11

How do you convert nanometre (nm) into micrometre (um)?

Answer 11

/ 1000

Question 12

How do you convert micrometre (um) into milimetre (mm)?

Answer 12

/ 1000

Question 13

Define resolution:

Answer 13

How detailed an image is.

Question 14

How do transmission electron microscopes work?

Answer 14

Use electromagnets to focus a beam of electrons, which is then transmitted through the specimen.

Question 15

Why do denser parts of a specimen appear darker through transmission electron microscopes?

Answer 15

Denser parts of the specimen absorb more electrons.

Question 16

Give 1 advantage of TEM:

Answer 16

High resolution = so shows small objects

Question 17

Give 2 disadvantages of TEM:

Answer 17

• Can only be used on thin specimens
• Can only be used on non-living specimens

Question 18

Give 2 advantages of SEM:

Answer 18

• Can be used on thick specimens
• Can produce a 3D image

Question 19

Give 2 disadvantages of SEM:

Answer 19

• Lower resolution than TEM
• Can only be used on non-living specimens

Question 20

What are the three steps of cell fractionation?

Answer 20

1) Homogenisation
2) Filtration
3) Ultracentrifugation

Question 21

What is the purpose of homogenisation in cell fractionation?

Answer 21

Breaks up plasma membrane and releases organelles into solution.

Question 22

Why must the solution be kept ice-cold?

Answer 22

Prevent enzyme activity

Question 23

Why must the solution be isotonic?

Answer 23

So the concentration of chemicals in the solution and organelles are same, to prevent the organelles being damaged.

Question 24

Why must the solution contain a buffer?

Answer 24

To maintain the pH.

Question 25

Explain the first step of cell fractionation, homogenisation:

Answer 25

1) Cell is broken up (e.g. in a blender) so plasma membrane is broken up.
2) Organelles are released into an ice-cold, isotonic, buffer solution.

Question 26

Explain the second step of cell fractionation, filtration:

Answer 26

1) Homogenised cell solution is filtered through gauze to remove debris.

Question 27

Explain the third step of cell fractionation, ultracentrifugation:

Answer 27

1) Cell fragments are poured into a tube. Tube is put into a centrifuge and is spun at a low speed.
2) Densest organelles (e.g. nuclei) sink first forming pellets and are removed.
3) Tube is spun again at a higher speed - process is repeated.