Cell Structure and Division- Analysis of Cell Components

Question 1

What is magnification?

Answer 1

How much bigger the image is than the specimen

Question 2

How is magnification calculated?

Answer 2

Magnification= image size/actual size

Question 3

What is resolution?

Answer 3

How detailed the image is and how well a microscope distinguishes between two points that are close together

Question 4

How do optical microscopes form an image?

Answer 4

By using light

Question 5

What is the maximum resolution of an optical microscope?

Answer 5

About 0.2 micrometers so optical microscopes can’t be used to view organelles smaller than this such as ribosomes, the endoplasmic reticulum, lysosomes, mitochondria in detail

Question 6

What is the maximum useful magnification of an optical microscope?

Answer 6

About x1500

Question 7

How do electron microscopes view an image?

Answer 7

By using electrons

Question 8

How does the resolution of electron microscopes compare to optical microscopes?

Answer 8

Electron microscopes have a higher resolution so give a more detailed image

Question 9

What is the maximum resolution of electron microscopes?

Answer 9

About 0.0002 micrometers- about 1000 times higher than optical microscopes

Question 10

What is the maximum useful magnification of an electron microscope?

Answer 10

About x1500000

Question 11

What are the two types of electron microscope?

Answer 11

Transmission electron microscope and scanning electron microscope

Question 12

How do TEMs view an image?

Answer 12

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

Question 13

Which parts of the specimen will absorb more electrons in TEMs?

Answer 13

Denser parts of the specimen absorb more electrons which makes these areas look darker on the image

Question 14

What is an advantage of TEMs?

Answer 14

They give high resolution images so that you can see the internal structure of organelles

Question 15

What is a disadvantage of TEMs?

Answer 15

They can only be used on thin specimens

Question 16

How do SEMs view images?

Answer 16

Scan a beam of electrons across the specimen which knocks off electrons from the specimen and are gathered in a cathode ray tube to form an image

Question 17

How are images shown from SEMs?

Answer 17

Show the surface of the specimen and they can be 3D

Question 18

What is an advantage of SEMs?

Answer 18

Can be used on thick specimens

Question 19

What is a disadvantage of SEMs?

Answer 19

Give lower resolution images than TEMs

Question 20

How do you prepare a ‘temporary mount’ of a specimen on a slide?

Answer 20

1. Pipette a drop of water onto the slide
2. Use tweezers to place a thin section of specimen on top of water drop
3. Add a drop of a stain which is used to highlight objects in a cell
4. Add cover slip- stand slip upright on slide next to water droplet, carefully tilt and tower it to cover specimen, try not to get any air bubbles as they’ll obstruct view of specimen

Question 21

What is the purpose of cell fractionation?

Answer 21

Separate organelles from the rest of the cell

Question 22

What are the three steps in cell fractionation?

Answer 22

Homogenisation (breaking up the cells), filtration (getting rid of big parts), ultracentrifugation (separating organelles)

Question 23

How can homogenisation be done?

Answer 23

Vibrating the cells or grinding cells up in a blender

Question 24

What happens in homogenisation?

Answer 24

Breaks up the plasma membrane and releases organelles into solution

Question 25

Why must the solution be kept ice-cold?

Answer 25

Reduce the activity of enzymes that break down organelles

Question 26

Why must the solution be isotonic?

Answer 26

Should have the same concentration of chemicals as cells being broken down to prevent damage to organelles by osmosis

Question 27

Why should a buffer solution be added?

Answer 27

To maintain the pH

Question 28

What happens in filtration?

Answer 28

Homogenised cell solution is filtered through a gauze to separate any large cell debris or tissue debris from organelles

Question 29

How does filtration work?

Answer 29

Organelles are much smaller than the debris so they pass through the gauze

Question 30

What is the process of ultracentrifugation?

Answer 30

1. Cell fragments are poured into a tube which is put into a centrifuge and spun at a low speed. Heaviest organelles form pellet at bottom of tube and rest of organelles form supernatant at top of tube
2. Supernatant is drained off, poured into another tube and spun in centrifuge at a higher speed. Heaviest organelles form pellet, supernatant is drained off and spun at an even higher speed in centrifuge
3. Process repeated at higher and higher speeds until all organelles are separated out

Question 31

What is the order of organelles from heaviest to lightest?

Answer 31

Nuclei, mitochondria, lysosomes, endoplasmic reticulum, ribosomes