Methods Of Studying Cells (3.2.1.3)

Question 1

What is magnification?

Answer 1

• The number of times larger the image is compared to the object

Question 2

What is the resolution?

Answer 2

• The minimum distance between two points in which they can still be viewed as separate

Question 3

Describe light microscopes

Answer 3

• The preparation is quick and easy. Specimens need to be thin and stained to make structures visible
• They have lower resolution due to the long wavelength of light. Small organelles in a cell are not visible

Question 4

Describe electron microscopes

Answer 4

• Use beams of electrons focused by electromagnets
  -The shorter wavelengths of electrons provide a greater resolution

Question 5

Describe transmission electron microscopes

Answer 5

• A beam of electrons is transmitted through a thin specimen, which is stained with electron-dense substances like heavy metals
• Produces 2D images, showing internal structures of cells

Question 6

Describe scanning electron microscopes

Answer 6

• A beam of electrons scans the surface of a specimen coated with a thin layer of heavy metal such as gold
• Produces 3D images, showing surface structures of cells

Question 7

What are the differences between light microscopes and electron microscopes?

Answer 7

• Uses beam of light / Uses beam of electrons
• Lower magnification / Higher magnification
• Relatively low resolution / Much greater resolution
• Focused using glass lenses / Focused using electromagnets
• Can observe living specimens / Specimens must be dead and dehydrated
• Image in colour / Image in black and white
• Preparation of specimen is simple / Complex and time-consuming preparation of specimen

Question 8

What are the differences between scanning electron microscopes and transmission electron microscopes?

Answer 8

• Lower resolution than TEM / Higher resolution than SEM
• Produces image of surface structures / Produces image of internal structures
• Gives 3D image / Gives 2D image
• Sections can be thicker than with TEM / Sections must be very thin

Question 9

What is cell fractionation?

Answer 9

• The process of breaking up cells to separate their individual components for further study

Question 10

What is ultracentrifugation?

Answer 10

• Technique used to separate these components based on their density

Question 11

What is the process of cell fractionation?

Answer 11

• The cells are broken up using a homogeniser in an ice-cold, isotonic, buffer solution, releasing the organelles from the cells
• The solution needs to be cold to prevent enzyme activity, isotonic to prevent osmotic damage to the organelles and buffered to maintain pH and prevent protein denaturation
• The homogenate is filtered to remove cell debris
• The remaining liquid is centrifuged at low speeds. The densest organelles, such as the nuclei, form a pellet at the bottom of the tube
• The fluid on top is called the supernatant and contains the rest of the organelles. This can be spun at higher speeds for longer periods of time to isolate other organelles
• The process continues, increasing the speed and duration each time, to isolate and separate organelles from heaviest to lightest

Question 12

What is the order of density of the organelles?

Answer 12

• Nuclei → chloroplasts → mitochondria → RER → cell-surface membrane → golgi apparatus → SER → ribosomes