Methods Of Studing Cells (Microscopes)

Question 1

Define magnification

Answer 1

Tells you how many times bigger the image produced by the microscope is that the real life object

Question 2

Define resolution

Answer 2

The ability to distinguish between two objects that are close together

Question 3

How to convert millimetres to micrometres (mm - um)

Answer 3

x1000

Question 4

How to convert micro meters into nanometres

Answer 4

x1000

Question 5

Magnification equation

Answer 5

Magnification = Size of image / Size of real object
I
A M

Question 6

What optical microscopes use to form an image

Answer 6

Light

Question 7

What is the maximum resolution of a light microscope

Answer 7

0.2 micrometers (um)

Question 8

What is the maximum magnification of an optical microscope

Answer 8

x 1500

Question 9

What organelles can’t be seen with an optical microscope

Answer 9

Ribosomes, endoplasmic reticulum, lysosomes

Question 10

What do electron microscope is used for an image

Answer 10

Electrons

Question 11

Which has higher resolution TEM or SEM

Answer 11

TEM

Question 12

Which has greater magnification electron or light microscope

Answer 12

Electron

Question 13

What does the images that electron microscopes produce look like

Answer 13

Black and white
(Can be coloured by computer) 

Question 14

What are the two types of electron microscope

Answer 14

Transmission electron microscope’s (TEMs)
Scanning electron microscope’s (SEMs)

Question 15

How does a transmission electron microscope work

Answer 15

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

Question 16

Advantages of TEMs

Answer 16

High resolution
Can see internal structures

Question 17

Disadvantages of TEMs

Answer 17

Thin specimens only
Can’t view living organisms - uses vacuum so no water
No coloured image

Question 18

What is an artefact in microscopy

Answer 18

Looks like a real structure but is the result of preserving or staining a specimen

Question 19

What does the image from TEM look like and WHY?

Answer 19

Denser parts absorb more electrons- look darker 

Question 20

How does a scanning electron microscope work

Answer 20

They scan a beam of electrons across the specimen
The electrons knock off the specimen and collected by cathode to form an image

Question 21

Advantages of SEM

Answer 21

Can be used as thick specimens
Produce 3-D image

Question 22

Disadvantages of SEM

Answer 22

Lower resolution than TEM
Cannot be used to observe live specimens

Question 23

What are the steps of cell fractioning (3)

Answer 23

Homogenisation
Filtration + cold ionic buffer etc
Ultracentrifugation

Question 24

What does Homogenisation mean

Answer 24

Breaking up of cells

Question 25

What is done to the sample of the tissue in homogenisation

Answer 25

Placed in an cold,isotonic, buffer solution.

Question 26

Why is the solution ice-cold

Answer 26

To reduce the activity of enzymes which break down organelles

Question 27

Why is the solution isotonic

Answer 27

Same water potential as the cell to prevent osmosis/lysis

Question 28

Why is the solution of buffer

Answer 28

To prevent organelle proteins from becoming denatured

Question 29

What is done with the solution once prepared ( homogenisation)+ what does this achieve /do

Answer 29

Added to a homogeniser which grinds up the cell Breaks the plasma membrane releases the organelles into the homogenate ( solution)

Question 30

What is done during filtration

Answer 30

The homogenate is filtered through a gauze separate large debris organelles passed through

Question 31

What is the pellet

Answer 31

The heavy organelles which settle at the bottom forming a thick sediment

Question 32

What happens during ultracentrifugation

Answer 32

Put in a tube Spun in a centrifuge Supernatant is put in a new tube spin again Repeat

Question 33

What is a supernatant

Answer 33

The remaining organelles which are suspended in the fluid above the sediment

Question 34

Describe how you’d make a temporary mount of a piece of plant tissue to observe the position of the starch grains in the cell when using an optical microscope

Answer 34

Add drop of water to slide Add thin section of cell onto slide Stain with iodine Lower cover slip using mounted needle

Question 35

Order of cell separation in cell fractioning 5 layers

Answer 35

1) nuclei 2) mitochondria 3) Lysosomes 4) ERs + Golgi apparatus 5) ribosomes

Question 36

Why do you A) push B)not push sideways On a microscopic slide

Answer 36

A- spread tissue B- avoid cells rolling together

Question 37

Why would an optical microscope not be able to identify an organelle (2 marks)

Answer 37

Low resolution Light has longer wavelength

Question 38

Give an example of why you may not be able to see the structure inside a cell

Answer 38

Not stained

Question 39

How can chloroplasts be isolated from leaves

Answer 39

Homogenisation and filter leaves Place in cold, isotonic, buffer solution solution Spin in centrifuges and remove cell debris Spin at higher speed and remove chloroplasts

Question 40

Suggest why you cannot see a nucleus in a image The image is clear and fairly magnified

Answer 40

Not stained

Question 41

Benefits of TEMs over SEMs

Answer 41

Higher resolution see internal structures

Question 42

Write out unit conversion from mm to nm

Answer 42

Look on posit for answer

Question 43

How to use graticule x3

Answer 43

Measure using eyepiece Calibrate eyepiece gratified against stage ruler Take number of measurements to calculate mean