Cells 2 Flashcards

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1
Q

Optical microscope

A

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

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2
Q

SEM

A

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

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3
Q

TEM

A

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

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4
Q

Disadvantages of optical microscope

A

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

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5
Q

Disadvantages of SEM

A

Vacuum so can not see living organisms
lower resolution than TEM

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6
Q

Disadvantages of TEM

A

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

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7
Q

Advantages of TEM, SEM and Optical microscopes

A

Optical - can see living organisms

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

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8
Q

Magnification

A

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

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9
Q

Resolution

A

The ability to distinguish between 2 points

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10
Q

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

A

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

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11
Q

How to prepare a temporary mount

A

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

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12
Q

Cell fractionation

A

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

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13
Q

How to distinguish between a cell artefact and organelle

A

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

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14
Q

Cell cycle

A

Eukaryotic cells that are able to divide

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15
Q

Interphase

A

Is for growth and repair of the cell

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16
Q

S phase

A

DNA replicates semi conservatively leading to 2 sister chromatids

17
Q

G1 and G2

A

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

18
Q

Mitosis

A

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

19
Q

Prophase

A

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

20
Q

Metaphase

A

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

21
Q

Anaphase

A

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

22
Q

Telophase

A

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

23
Q

Cytokinesis

A

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

24
Q

The importance of mitosis

A

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

25
Q

Binary fission

A

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