methods of studying cells

Question 1

cells can be studied using ?

Answer 1

optical microscope
transmission electron microscope
scanning electron microscope
cell fractionation and ultracentrifugation

Question 2

explain how to use a optical microscope

Answer 2

-thin layer of tissue is cut and mounted onto a slide with a cover slip
-light is passed through the sample and wither absorbed or transmitted
-the image is magnified using a lens
-stain may be added to highlight certain structures

Question 3

advantages of optical microscope

Answer 3

-quick
-inexpensive
-colour and living tissue can be seen

Question 4

disadvantages of optical microscope

Answer 4

-magnification and resolution is limited
-smaller wavelength than light will not be able to be seen
-two object separated by a gap smaller than a wavelength of light cannot be resolved

Question 5

explain how a transmission electron microscope is used

Answer 5

-thin sample is prepared and place in a vacuum chamber
-a beam of electrons is passed through and either absorbed or transmitted
-transmitted electrons are detected by a sensor
-a computer builds up a 2d image

Question 6

advantages of transmission electron microscope

Answer 6

-magnification and resolution is high

Question 7

disadvantages of transmission electron microscope

Answer 7

-only dead tissue can be examined
-only 2d images
-only black and white

Question 8

explain how a scanning electron microscope works

Answer 8

-electrons are fired at the sample and are detected as the are scattered
-sample can be prepared eg by spraying gold
-3d image is produced

Question 9

advantages of scanning electron microscope

Answer 9

-3d image
-magnification and resolution= high

Question 10

disadvantages of scanning electron microscope

Answer 10

-only dead tissue can be seen
-artifacts may be produced in the prep

Question 11

explain hoe cell fractionation and ultracentrifugation works

Answer 11

-separates parts of cell for study
-tissue is homogenised to break open cells and release content
-carried out in a solution- ice cold isotonic buffer
>ice cold- to stop enzyme released damaging cell components
>isotonic- has same water potential as cell to stop osmosis and cell bursting
>buffer- prevents pH from changing so strong acid/ alkali released from the tissue doesn’t damage the cell

-mixture is centrifuged and produced a pellet containing cell walls and supernatant containing other cell components- supernatant is removed and centrifuged at high speeds
-this produces a pellet containing nuclei and chloroplasts as these are organelles with the highest density
-centrifuging the supernatant at high speeds for longer with produce pellets with other organelles in