Methods of studying cells

Question 1

Principles of optical microscope

Answer 1

-Use light to form 2D image
-Visible light has longer wavelength so Lower resolution
-Low magnification 1500X

Question 2

Advantage of optical

Answer 2

Can see living orgnisms
In colour

Question 3

– of optical

Answer 3

-2D image
-requires thin specimen
-low resolution so cant see internal structures or organelles
- Low magnification

Question 4

Principles of Scanning Electron microscope

Answer 4

-use electrons to form 3D image
-Beams of electrons scan the surface, knocking of electrons from the specimen which are gathered in a cathode ray tube to form an image.
-electrons have a shorter wavelength so higher resolution
-High magnification X15000000

Question 5

Advantage of SEM

Answer 5

3D image
High resolution can see internal organelles
High magnification
Used on thick specimen

Question 6

Limitation off SEM

Answer 6

Vacuum so doesn’t let u see living organisms
Lower resolution than TEM

Question 7

principles of transmission electron microscope

Answer 7

Use electrons to form a 2D image
Electromagnets focus beam of electrons onto specimen
more dense=more absorbed = darker apperance
Electrons shorter wavelength
High magnification

Question 8

Advantage of TEM

Answer 8

High res so can see internal organelles
High mag

Question 9

Limitation off TEM

Answer 9

may contain artefacts
complex staining process
2d image
requires vacuum so cannot see living organisms
only used on thin specimen

Question 10

Define magnification

Answer 10

how much bigger the image of a sample is compared to the real size

Magnification= Image size / Actual size

Question 11

Define resolution

Answer 11

how well distinguished an image is between 2 points; shows amount of detail

Question 12

Explain how you would measure the size of an object viewed with an optical microscope

Answer 12

1)Line up eyepiece graticule with stage micrometer

2)Use stage micrometer to calculate the size of divisions on eyepiece graticule at a
particular magnification

3)Take the micrometer away and use the graticule to measure how many divisions make up the object

4)Calculate the size of the object by multiplying the number of divisions by the
size of division

5)Recalibrate eyepiece graticule at different magnifications

Question 13

Explain how you would prepare a ‘temporary mount’ of a specimen on a slide

Answer 13

1)Use tweezers to place a thin section of specimen

2)Add a drop of a stain

3)Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles

Question 14

Cell fractionisation

Answer 14

1)Homogenise tissue using a blender to break open the cell to release its contents
2)Place in a cold, isotonic, buffered solution
Cold- reduces enzyme activity so organelles arent broken
Isotonic so water doesn’t move in/out of organelles by osmosis so they don’t burst / shrivel
Buffered keeps pH constant so enzymes don’t denature
3) filter homogenate to Remove large, unwanted debris

Question 15

Ultracentrifugation

Answer 15

Centrifuge homogenate in a tube at a low speed

Remove pellet of heaviest organelle and spin supernatant at a higher speed

Repeated at higher and higher speeds until organelles separated out, each time pellet is made of lighter organelles

Separated in order of mass/density: nuclei → chloroplasts → mitochondria → lysosomes →
endoplasmic reticulum → ribosomes

Question 16

How can you distinguish between an artefact and cell organelle

Answer 16

Repeatedly prepared specimens in different ways

If an object could only be seen with one preparation technique, but not another it
was more likely to be an artefact than an organelle