Cells 2

Question 1

Optical microscope

Answer 1

uses light from a 2D image
Visible light
longer Wavelength so slower resolution 200nm
Lower magnification x 1500

Question 2

SEM

Answer 2

uses electrons to form a 2d image
beams of electrons can surface knocking off electrons from a thin specimen which are gathered by a cathode ray tube to form an image
Higher resolution as electrons have a shorter wavelength
High magnification

Question 3

TEM

Answer 3

uses electrons to form a 3d image
electromagnets focus beam of electrons onto specimen, transmitted more dense = more absorbed = darker appearance
electrons shorter wavelength so higher resolution 0.2nm
high mag - x 1500000

Question 4

Disadvantages of optical microscope

Answer 4

2D image
Only used on thin specimens
low resolution ( can’t see internal structures or organelles e.g. ribosomes)
low mag

Question 5

Disadvantages of SEM

Answer 5

Vacuum so can not see living organisms
lower resolution than TEM

Question 6

Disadvantages of TEM

Answer 6

2d image
only used on thin specimens
vacuum so can not see LO

Question 7

Advantages of TEM, SEM and Optical microscopes

Answer 7

Optical - can see living organisms

SEM
- 3D image
High resolution
High magnification
used on thick specimens
TEM
High Resolution and magnification

Question 8

Magnification

Answer 8

how much bigger is the image is compared to the actual size

Question 9

Resolution

Answer 9

The ability to distinguish between 2 points

Question 10

Steps for measuring the size of an object with an eye piece graticule

Answer 10

Line up eyepiece graticule with stage micrometer
- Use stage micrometer to calculate the size of divisions on eyepiece graticule at a particular magnification
- Take the micrometer away and use the graticule to measure how many divisions
make up the object
- Calculate the size of the object by multiplying the number of divisions by the size of division
- Recalibrate eyepiece graticule at different magnifications

Question 11

How to prepare a temporary mount

Answer 11

Use tweezers to place a thin section of specimen e.g. tissue on a water drop on a microscope slide
- Add a drop of a stain e.g. iodine in potassium iodide solution used to stain starch grains in plant cells
- Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles

Question 12

Cell fractionation

Answer 12

Homogenise tissue using a blender
- Disrupts cell membrane / break open cell
- Release contents / organelles
2. Place in a cold, isotonic, buffered solution
- Cold reduces enzyme activity so organelles aren’t broken down
- 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
- Remove large, unwanted debris e.g. whole cells, connective tissue
4. Ultracentrifugation
a) Centrifuge homogenate in a tube at a low speed
b) Remove pellet of heaviest organelle and spin supernatant at a higher speed
c) Repeated at higher and higher speeds until organelles separated out, each time pellet is made of lighter organelles
d) Separated in order of mass/density: nuclei → chloroplasts → mitochondria → lysosomes → endoplasmic reticulum → ribosomes

Question 13

How to distinguish between a cell artefact and organelle

Answer 13

repeatedly prepared specimen 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

Question 14

Cell cycle

Answer 14

Eukaryotic cells that are able to divide

Question 15

Interphase

Answer 15

Is for growth and repair of the cell

Question 16

S phase

Answer 16

DNA replicates semi conservatively leading to 2 sister chromatids

Question 17

G1 and G2

Answer 17

Number of organelles and volume of cytoplasm increases; protein synthesis; ATP content increased

Question 18

Mitosis

Answer 18

Parent cell divides = two genetically identical daughter cells, containing identical/exact copies of DNA of the parent cell.
- Stages - ‘PMAT

Question 19

Prophase

Answer 19

Chromosomes condense, becoming shorter and thicker = appear as two sister chromatids joined by a centromere
- Nuclear envelope breaks down and centrioles move to opposite poles forming spindle network

Question 20

Metaphase

Answer 20

Chromsomes align at the equator
Spindle fibres attach to chromosomes by centromeres

Question 21

Anaphase

Answer 21

Spindle fibres contract, pulling sister chromatids to opposite poles of the cell
- Centromere divides

Question 22

Telophase

Answer 22

Chromosomes uncoil, becoming longer and thinner
- Nuclear envelope reforms = two nuclei
- Spindle fibres and centrioles break down

Question 23

Cytokinesis

Answer 23

The division of the cytoplasm, usually occurs, producing two new cells

Question 24

The importance of mitosis

Answer 24

Parent cell divides to produce 2 genetically identical daughter cells for…
- Growth of multicellular organisms by increasing cell number
- Repairing damaged tissues / replacing cells
- Asexual reproduction

Question 25

Binary fission

Answer 25

Circular DNA and plasmids replicate Cytoplasm expands (cell gets bigger) as each DNA molecule moves to opposite poles of the cell
- Cytoplasm divides
- = 2 daughter cells, each with a single copy of DNA and a variable number of plasmids