Methods Of Studying Cells

Question 1

What is the difference between magnification and resolution?

Answer 1

Magnification: is the increase in the apparent size of the object-the extent to which it has been enlarged
Resolution: is the ability to distinguish between 2 points that are closer together

Question 2

How does a light microscope work?

Answer 2

Eyepiece lens:
Magnifies and focuses the image

Objective lens:
Collects light passing through the specimen and produces and magnified image

Condenser lens: focuses light onto the specimen

Question 3

Advantages and disadvantages of TEM and SEM

Answer 3

+ TEM: give high resolution images and shows small objects
-TEM: can only be used on thin specimens and only dead

+SEM: can be used on thick specimens and 3D
-SEM: lower resolution than TEM. Is also only dead specimens
-SEM: artefacts are present

Question 4

What is an artifact?

Answer 4

Something that is seen under a microscope that isn’t part of a specimen- can be dust, air bubble, fingerprints- common in electron microscopes because they need a lot of preparation
To overcome this problem by repeatedly preparing specimens in different ways

Question 5

How can the size of an object using a optical(light) microscope be found/measured

Answer 5

1) line up scale of eyepiece with stage micrometer l

2) calibrate eyepiece using stage micrometer to calculate size of divisions on eyepiece graticule

3) using graticule measure how many dodging make up the object

4) calculate size of object by multiplying number of divisions by size of division

5) recalibrate eyepiece graticlue at different magnifications

Question 6

Securing and explain steps of cell fractionation

Answer 6

1)homogenise tissue using a blender-disrupts cell membrane, breaking open cells to release the organelles

2) place in cold isotonic buffer solution- cold to reduce enzyme activity (no organelles being broken down), isotonic so water won’t move in or out via osmosis (no bursting), buffer to keep pH constant (no denaturing of enzymes)

3) filter homogenate - removing large unwanted debris

4) ultracentrifugation, low speed first to remove heaviest first then increasing to get to lighter organelles (nuclei-chloroplast/mitochondria- lysosomes “- ER- ribosomes)