methods of studying cells 2

Question 1

Define magnification

Answer 1

How many times bigger an object appears

Question 2

Define resolution

Answer 2

The ability to distinguish two points next to each other

Question 3

If the resolution of a microscopic image is too low, what can be said about the light/electrons used

Answer 3

The wavelength is too long

Question 4

Magnification equation

Answer 4

Magnification = image size / actual size

Question 5

1cm = ?mm

Answer 5

10

Question 6

1mm = ?µm

Answer 6

1000

Question 7

1µm = ?nm

Answer 7

1000

Question 8

Measurement unit conversion image

Answer 8

Question 9

How to measure an object using a microscope and graticule

Answer 9

Line up graticule with object
Count how many epu for the measurement
Calibrate graticule using stage micrometer - how many µm per epu
Multiply the number of epu by the calibration factor

Question 10

Resolution of optical microscope

Answer 10

Low

Question 11

Resolution of SEM

Answer 11

Medium

Question 12

Resolution of TEM and ADVANTAGE

Answer 12

High
allows organelles to be seen in greater detail

Allows organelles to be seen in greater detail

Question 13

Magnification of optical microscope

Answer 13

Low

Question 14

Magnification of TEM

Answer 14

High

Question 15

Magnification of SEM

Answer 15

Medium

Question 16

How does a optical microscope work

Answer 16

Light ray focused onto object then onto eye using glass lenses

Question 17

How does a SEM work

Answer 17

Electrons deflected/bounce off specimen
Foccused by electromagnets

Question 18

How does a TEM work

Answer 18

Electrons transmitted/pass through specimen
Foccused by electromagnets

Question 19

Primary use of optical microscope

Answer 19

Study living cells

Question 20

Primary use of SEM

Answer 20

View 3D image

Question 21

Primary use of TEM

Answer 21

View cell ultrastructure

Question 22

Are optical microscope images in colour

Answer 22

Yes

Question 23

Are TEM images in colour

Answer 23

No

Question 24

Are SEM images in colour

Answer 24

No

Question 25

Non-limitations to optical microscopes

Answer 25

Can be dead or alive No vacuum Not too thin Stained with dye No artefacts Doesn’t take too long

Question 26

Limitations to SEM

Answer 26

Must be dead In vacuum Very thin specimin Stained with metal Artefacts may occur Time consuming

Question 27

Limitations to TEM

Answer 27

Must be dead Must be in vacuum Specimin must be very thin Stained with metal Artefacts may occur Time consuming

Question 28

In microscope images, if the resolution is high/low what can be said about the light or electrons wavelength

Answer 28

Low resolution = long wavelength High resolution = short wavelength

Question 29

Describe how to extract chloroplast from a cell sample

Answer 29

Homogenise cells in homogeniser Filter to remove unbroken cells/debris Place homogenate in test tube and spin in a centrifuge at low speed Remove nuclei pellet at bottom Respin supernatant in new test tube at higher speed Remove chloroplast pellet

Question 30

When extracting organelles from cells during ultracentrifugation, what is the order of heaviest organelles, that must be removed

Answer 30

Nuclei Chloroplast - only if plant cell Mitochondria

Question 31

When extracting organelles from cells, why must the solution be cold

Answer 31

Reduce enzyme activity, so organelles aren’t digested

Question 32

When extracting organelles from cells, why must the solution be isotonic

Answer 32

Prevent water movement into organelles by osmosis - preventing lysis

Question 33

When extracting organelles from cells, why must the solution be pH buffered

Answer 33

Maintain pH Prevent denaturations of proteins and enzymes

Question 34

How can you make specimens more visible in an optical microscope?

Answer 34

By staining the specimen with a coloured dye.

Question 35

What are the steps of using an electron microscope?

Answer 35

Fix the specimen. Dehydrate the specimen. Cut into thin slices. Stain. Mount onto a copper grid. Place in a vacuum.

Question 36

Explain why a homogenate is filtered before spinning at low speed in the centrifuge. (2)

Answer 36

removes debris / intact cells / sand; which would contaminate the 1st sediment / interfere with the results;

Question 37

Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells (6 points)

Answer 37

1. Cell homogenisation to break open cells 2. Filter to remove large debris 3. Use iostonic solution to prevent damage to organelles 4. Keep cold to prevent damage by enzymes/use buffer to prevent enzyme's denaturing 5. Centrifuge at lower speed to separate nuclei 6. Re-spin supernatant at higher speed to get mitochondria in pellet

Question 38

An optical light microscope cannot be used to see a plasma membrane. Explain why.

Answer 38

Does not have the resolution / cannot distinguish between points this close together; As light has longer wavelength;

Question 39

Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure (9 points - 4 principles, 5 limitations)

Answer 39

1. Electrons pass through thin specimen 2. Denser parts absorb more electrons 3. So denser parts appear darker 4. Electrons have short wavelength so give high resolution 5. Cannot look at living material - must be in vacuum 6. Specimen must be very thin 7. Artefacts present 8. Complex staining method/long preparation time 9. Image not 3D

Question 40

Describe how to determine size and structure with microscope of an organism

Answer 40

1- measure and divide by magnification 2- Micrometers to cm x10000 or 1- measure and divide by length of scale bar 2- Multiply by actual length of scale bar

Question 41

Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical light microscope. (4marks)

Answer 41

Add a drop of water to a glass slide Place a section of a thin tissue sample onto a glass slide Put onto drop of water Add iodine solution to stain it And add cover slip lower with mounted needle - prevents air bubbles

Question 42

Describe the limitations of a light microscope.

Answer 42

low magnification low resolution 2D

Question 43

In the preparation for cell fractionation, why is the tissue placed in a cold solution?

Answer 43

to reduce enzyme activity which may break down organelles

Question 44

In the preparation for cell fractionation, why is the tissue placed in a isotonic solution?

Answer 44

to prevent organelles bursting/shrinking due to osmosis

Question 45

Why do electron microscopes produce high resolution images?

Answer 45

the beam of electrons has a short wavelength (shorter wavelength than light)

Question 46

Why is a buffer solution used when homogenising cells?

Answer 46

keep pH the same / controls pH; prevent change to / denaturing of proteins/enzymes;

Question 47

why is the Resolution in Electron microscopes higher?

Answer 47

shorter wavelength between electrons longer wavelength In light rays

Question 48

No large lipid droplets are visible with the optical microscope in the samples from suspension A. Explain why.

Answer 48

Emulsification; (Cannot be seen) due to resolution (of optical microscope);