3.2.1.3 Studying cells

Question 1

What is magnification

Answer 1

How many times bigger the object appears

Question 2

What is resolution

Answer 2

Ability to distinguish 2 points

Question 3

Equation to calculate the ‘actual image size’

Answer 3

actual object size = image size / magnification

Question 4

What measurements are used in the magnification equation

Answer 4

1000 micro m in 1 mm
1000 nm 1 micro m

Question 5

How to measure an object using a microscope and gratitude

Answer 5

. Line up the gratitude with the object
. Count the no. Of eye piece units for the measurement
. Multiply the no. Of eye piece units by the calibration factor
. Calibrate the graticule using a stage micro m - how many micro m per eyes piece unit

Question 6

How does an optical (light) microscope work

Answer 6

• light waves are focused onto an object and then onto the eye using glass lenses

Question 7

Uses of an optical microscope

Answer 7

• study living and dead cells, cells can be stained in order to see features more easily

Question 8

Limitations of the optical microscope

Answer 8

• relatively low magnification and resolution so cannot see all the organelles in a cell

Question 9

Resolution & magnification of the optical microscope

Answer 9

RESOLUTION:
0.2 micro m

MAGNIFICATION:
X2000 to x1500

Question 10

How does a transmission electron microscope (TEM) work

Answer 10

• beams of negatively charged electrons are focused using electromagnets and pass through the cell
• image appears darker the more electrons that are absorbed

Question 11

Uses of the TEM

Answer 11

• view ultra structure of cells (all organelles can be visualised)

Question 12

Limitations of the TEM

Answer 12

. Vacuum required for microscope to function
. Specimen must be thin to allow transmission of elec.
. Staining with metals required
. Cells must be dead
. Artefacts may occur - features which aren’t part of the cell, but occur due to preparation methods

Question 13

How does a scanning electron microscope work (SEM)

Answer 13

beams of negatively charged electrons are focused using electromagnet & reflect off the surface of an object

Question 14

Uses of the SEM

Answer 14

• beam is scanned across the surface, allowing a 3-D image to be built up

Question 15

Limitations of the SEM

Answer 15

. Vacuum required for microscope function
. Specimen must be thin in order to allow transmission of electrons
. Staining with metals required
. Cells must be dead
. Artefacts may occur

Question 16

Resolution & magnitude for TEM

Answer 16

RESOLUTION:
0.1 nm

MAGNIFICATION:
X50,000,000

Question 17

Resolution & magnitude for SEM

Answer 17

RESOLUTION:
20nm

MAGNIFICATION:
X1,000,000

Question 18

2 processes used for extracting organelles

Answer 18

1. Homogenation
2. Ultracentrifugation

Question 19

Process of homogenation

Answer 19

cells & organelles are kept in a solution which is:
. PH buffered - prevent denaturation of proteins which could affect enzyme function or damage organelles
. Cold - reduce enzyme activity, so organelles are not digested
. Isotonic - prevent H20 movement osmosing into organelles & lysis of organelles

• Cells are broken up in a blender
• Fluid, homogenate is filtered to remove whole cells & large cell fragments

Question 20

Process of ultracentrifugation

Answer 20

• tube of homogenate is placed in a centrifuge & spun at low speeds
  . the heaviest organelles, nuclei, settle at the bottom of the tube
• the remaining fluid, supernatent, is removed, placed in a new tube & spun at higher speeds
  . Next heaviest organelles, mitochondria settle at the bottom of the tube
• the process of removing the supernatent to a new tube & spinning at higher speeds is repeated several more times
  . Heaviest remaining organelles settle each time