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BIOLOGY > microscopy / mitosis > Flashcards

microscopy / mitosis Flashcards

1
Q

Describe how optical microscopes work.

A
  1. lenses focus rays of light + magnify the view of a thin slice of specimen.
  2. different structures absorb different amounts + wavelengths of light.
  3. reflected light is transmitted to the observer via the objective lens + eyepiece.
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2
Q

Suggest the advantages and limitations of using an optical microscope.

A
  • colour image ,
  • visualise living cells - watch behaviours like cell division in real time.
  • affordable apparatus
  • 2D image
  • lower resolution than electron microscopes = cannot see ultrastructure .
  • resolution 0.2μm - not large enough to visualise any smaller organelles
  • magnify 1500x actual size
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3
Q

Describe how a transmission electron microscope (TEM) works.

A

1) uses electromagnets - pass high energy beam of electrons through thin slice of specimen.
(e- have shorter wavelength compared to visible light so higher resolution/ detailed images produced.)

2) more dense structures appear darker since they absorb more electrons.

3) focus image onto fluorescent screen / photographic plate using magnetic lenses .

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4
Q

Suggest the advantages + limitations of using a TEM.

A
  • electrons have shorter wavelength than light = high resolution, so ultrastructure visible
  • high magnification (x500000)
  • high resolution (0.0002 μm/ 20nm)

but
- 2D image
- requires a vaccum - cannot show living structures extensive preparation may introduce artefacts // live cells cannot be used
- no colour image

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5
Q

Describe how a Scanning Electron Microscope (SEM) works.

A

1) emit a beam of electrons towards sample,, (knocking electrons off it used to build image ) onto a specimens surface electromagnetic lenses.

2) reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.

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6
Q

Suggest the advantages and disadvantages of using an SEM.

A
  • produce 3D images of cells + organelles.
  • electrons have shorter wavelength than light = high resolution.

but
- requires a vaccum = cannot show living structures
- no colour image
- only shows outer surface
- expensive

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7
Q

Define Magnification.

A
  • how enlarged the image is compared to the original object
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8
Q

Define the term Resolution.

A
  • how well a microscope distinguishes between two points that are close together.
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9
Q

Explain how to use an eyepiece graticule and stage micrometer to measure size of a structure.

A

1) place micrometer on stage to calibrate eyepiece graticule.

2) line up scales on graticule and micrometer. count how many graticule divisions are in 100um on the micrometer

3) length of 1 eyepiece division = 100um/ no. divisions

4) use calibrated values to calculate actual length of structures.

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10
Q

state an equation to calculate actual size of a structure from microscopy .

A

actual size = image size / magnification.

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11
Q

explain how to view specimens under an optical microscope .

A

1) pipette drop water onto slide then place specimen on top.

2) add drop of stain = creates contrast + enables organelles to be visualised .

3) add cover slip to protect specimen - carefully tilting + lowering down (careful no air bubbles)

4) place slide onto stage + select lowest-powered objective lens.

5) look down at eyepiece + use coarse adjustment knob to focus specimen

6) select increasingly higher magnification until visualise cell structures .

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12
Q

explain what is meant by cell fractionation.

A
  • technique - separates organelles according to their density - to visualise certain organelles under microscope separately
  • bursting cell surface membrane to release organelles + spinning cell solution at high speeds
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13
Q

outline what happens during cell fractionation and ultracentrifugation

A

1) mince and homogenise tissue to break open cells + releases organelles

2) filter homogenates to remove debris

3) perform differential centrifugation

a) spin homogenate in centrifuge
b) the most dense organelles on mixture will form a pellet
c) filter off the supernatant and spin again at higher speed

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14
Q

explain the first process of fractionation - homogenisation .

A
  • break apart the plasma membrane to release the organelles
  • vibrating the cells or by breaking them apart in a blender
    —> needs placed in solution : ice-cold, isotonic and buffered .
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15
Q

why does solution need to be ice cold ?

A
  • to slow down activity of enzymes
  • some enzymes degrade organelles so need to reduce their activity to persevere cells organelles .
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16
Q

why solution need to be isotonic ?

A
  • solute conc of solution need to be same as the cells that’s been broken down —> otherwise water would move into organelles by osmosis resulting in damage
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17
Q

why solution need to be buffered ?

A
  • ensures pH stays constant .
  • proteins are denatured by changes in pH
18
Q

why does solution need to be buffered ?

A
  • ensures the pH remains constant .
  • proteins are denatured by changes of pH
19
Q

why is the homogenised solution filtered ?

A
  • to remove any tissue debris .
  • organelles are small enough to pass through the holes of the filter paper so will be present in filtrate .
20
Q

explain the process of ultracentrifugation .

A
  • spin the filtrate at increasing speeds .
  • heaviest organelles will sink to bottom of test tube forming a pellet
  • transfer the remaining solution to a separate test tube (spun at slightly higher speed .)
  • repeated until u obtain the organelle that u want = organelles separated from solution from heaviest to lightest .
21
Q

define mitosis .

A
  • type of cell division where cells produce identical copies of themselves + used for growth + repair and asexual reproduction .
22
Q

state what the cel cycle is and outline its stages .

A
  • cycle of division with intermediate growth periods

1) interphase
2) mitosis or meiosis (nuclear division )
3) cytokinesis ( cytoplasmic division )

23
Q

explain why the cell cycle doesn’t occur in some cells .

A
  • after differentiation , some types of cell in multicellular organisms no longer have ability to divide.
24
Q

what’s the difference between the cell cycle and mitosis ?

A
  • cell cycle includes growth period between divisions = mitosis is only 10% of the cycle + refers only to nuclear division .
25
Q

outline what happens during interphase .

A
  • individual chromosomes not visible - 2 chromatids contain 2 identical DNA molecules produced by semi conservative replication .
  • G1: cell synthesis proteins for replication : e.g = tubulin for spindle fibres + cell size doubles
  • S: cell replicates its DNA = chromosomes consists of 2 sister chromatids joined at a centromere .
  • G2: cell keeps growing until all organelles have duplicated.
26
Q

state the purpose of mitosis .

A
  • produces 2 genetically identical daughter cells for :
  • growth
  • cell replacement / tissue repair
  • asexual reproduction
27
Q

outline what happens during prophase .

A

1) chromosomes condense : becoming visible . (X-shaped : 2 sister chromatids joined at centromere)

2) centrioles move to opposite poles of cell + mitotic spindle fibres form .

3) nuclear envelope + nucleolus disintegrates = chromosomes free in cytoplasm .

28
Q

outline what happens during metaphase .

A
  • sister chromatids line up along the middle of the cell .
  • they attach to the spindle fibres by the centromere .
29
Q

outline what happens during anaphase .

A
  • the centromere splits + chromatids pulled to opposite poles of the cell .
  • requires energy from ATP hydrolysis .

1) spindle fibres contract - centromeres divides
2) sister chromatids seperate into 2 distinct chromosomes + pulled to opposite poles of the cell
3) spindle fibres break down

30
Q

outline what happens during telophase .

A

1) chromosomes decondense - becomes invisible again

2) new nuclear envelopes reforms around them forming 2 new nuclei , each with 1 copy of each chromosome

31
Q

outline what happens during cytokinesis .

A
  • cytoplasm divides = plasma membrane pinches off to form 2 new genetically identical cells .
32
Q

describe how an uncontrolled mitosis may result to cancer .

A
  • mitosis is genetically controlled + stops once cell divided enough times to make cells you need
  • if genes that control mitosis mutate , mitosis can occur unchecked - resulting in formation of of a tumour .
    —> if invades surrounding tissue - cause cancer .
33
Q

how do some cancer cells work by disrupting the cell cycle ?

A
  • some prevent synthesis of enzymes involved in DNA replication
    —> prevents cell cycle progressing past S phase - undergo apoptosis
  • radiotherapy works by damaging DNA using radiation
  • cell cycle stalled during DNA checkpoint stages
34
Q

why is only the root tip used when calculating a mitotic index ?

A
  • meristematic cells at root tip are actively undergoing mitosis.
  • cells further from root tip are elongating rather than dividing .
35
Q

how to calculate mitotic index ?

A
  • measure of proportion of cells which are undergoing mitosis
  • mitotic index = no. cells with visible chromosomes / total number of cells
36
Q

suggest how cancer treatments control the rate of cell division .

A
  • during cell cycle :

— prevent DNA relication .
— disrupt spindle information - inhibit metaphase / anaphase.

37
Q

how do prokaryotes cells replicate ?

A

binary fission:

1) DNA loop replicates . Both copies stay attached to cell membrane . Plasmids replicate in cytoplasm .

2) cell elongates , separating the 2 DNA loops.

3) cell membrane contracts + septum forms

4) cell splits into 2 identical progeny cells: each with 1 copy of DNA loop but a variable no. plasmids.

38
Q

estimate the exponential growth of bacteria within 8 hours. assume binary fission occurs once every 20 mins + there’s 1 bacterium at the start.

A

8 x 60 = 480 mins

480 / 20 = 24 divisions

2^24

39
Q

why are viruses classified as non-living ?

A
  • they are acellular - no cytoplasm, no metabolism + cannot self replicate.
40
Q

outline how viruses replicate .

A

1) attachment proteins attach to receptors on host cell membrane .

2) enveloped viruses fuse with cell membrane or move in via endocytosis + release DNA/RNA into cytoplasm

3) host cell uses viral genetic information to synthesise new viral proteins / nucleic acid .

4) components of new viral particle assemble.

41
Q

how do new viral particles leave the host cell?

A
  • bud off + use cell membrane to form envelope .
  • cause lysis of host cell.
42
Q

why is it difficult to develop effective treatment against viruses ?

A
  • replicate inside living cells = difficult to kill them without killing host cells

BIOLOGY (14 decks)

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