3.1 Methods of studying cells

Question 1

What is magnification?

Answer 1

How many times bigger an image is comparing to the actual object.

Question 2

What is resolution?

Answer 2

The ability of a microscope to distinguish (區分) details of a sample / how clear an image is.

Question 3

What is the formula for calculating magnification?

Answer 3

magnification = size of image / size of real object

Question 4

How does an optical microscope work?

Answer 4

They use visible light and convex glass lenses acting as a magnifying glass to generate magnified images of objects.

Question 5

Where is the source of light located at in an optical microscope?

Answer 5

At the bottom of the microscope and the light shines upwards.

Question 6

What are the limitations of optical microscope?

Answer 6

The wavelength of light is too long

Question 7

What is the maximum magnification of optical microscope?

Answer 7

x1500

Question 8

What is the maximum resolution of optical microscope?

Answer 8

0.2 μm

Question 9

How many lenses do most optical microscopes have? State the magnification of each of the lens.

Answer 9

4 lenses - x4, x10, x40, x100

Question 10

What is the formula for calculating the magnification of optical microscope?

Answer 10

magnifying power of eyepiece lens x magnifying power of selected objective lens

Question 11

How to use an optical microscope?

Answer 11

1. stain the specimen and place the specimen into the middle of a slide
2. place a cover slip on the top of the specimen
3. clip the slide onto the stage and select the suitable objective lens
4. use the coarse adjustment knob (粗調旋鈕) to move the stage just below the objective lens
5. look through the eyepiece and use the coarse focus to move the stage downwards until the image is roughly in focus
6. use the fine adjustment knob (微調旋鈕) to make the image clearer
7. if a higher magnification is needed, swap to a more powerful objective lens and refocus

Question 12

What is cell fractionation?

Answer 12

A process where cells are broken up and different organelles that they contain are separated out.

Question 13

Where are tissues placed before cell fractionation?

Answer 13

Cold and buffered solution that has the same water potential as the tissues.

Question 14

Why are tissues placed in a cold solution before cell fractionation?

Answer 14

To reduce/stop enzyme activities

Question 15

Why are tissues placed in a buffered solution before cell fractionation?

Answer 15

So that pH doesn’t fluctuate (波動)

Question 16

Why are tissues placed in a solution that has the water potential as the tissues before cell fractionation?

Answer 16

To prevent organelles bursting or shrinking

Question 17

What are the 2 stages of cell fractionation?

Answer 17

1. homogenation
2. ultracentrifugation

Question 18

What is homogenation?

Answer 18

Breaking up cells by a homogeniser

Question 19

What happens during homogenation?

Answer 19

1. organelles will be released from the cell
2. homogenate (resultant fluid) is then filtered by filtration to remove large substances

Question 20

What is ultracentrifugation?

Answer 20

A process that separates out particles of different sizes and densities by spinning them at high speed in a centrifuge.

Question 21

What happens during ultracentrifugation?

Answer 21

1. the cell fragments are placed in a centrifuge tube and spun at a low speed
2. the heaviest organelle will be at the bottom of the tube, forming a pellet/sediment
3. the supernatant (fluid at the top) is removed and transferred to a new tube to be centrifuged at a higher speed
4. the next heaviest organelle will be at the bottom of the tube, forming a pellet/sediment
5. repeat step 3 and 4 but increase the speed each time to separate the remaining organelles until all organelles have been separated

Question 22

Rearrange the organelles in terms of weight.

Answer 22

Nucleus > chloroplast > mitochondria > lysosome > ER > ribosome