Biology > Microscopy and cell structure > Flashcards

Microscopy and cell structure Flashcards

(52 cards)

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1
Q

magnification

A

the number of times and image has been enlarged compared to its actual size

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2
Q

resolution

A

the minimum distance between two objects to be able to distinguish them as two separate objects

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3
Q

gram stain colours

A

gram-positive bacteria: purple/violet

gram-negative bacteria: pink/red

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4
Q

what (and what colour) does iodine stain?

A

starch grains (blue-black)

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5
Q

what colours does methylene blue stain what?

A

nucleus: dark blue (+ve charge of dye attracted to -ve charge of DNA)
cytoplasm: light blue

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6
Q

purpose of staining

A

increase contrast to identify different cell types and/or organelles

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7
Q

two types of stains

A
  • simple
  • differential
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8
Q

simple stain with example

A
  • one stain used
  • uniformly stains all structures of cell
  • used to measure cell size but not to identify organelles
  • e.g. methylene blue
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9
Q

differential stain with example

A
  • multiple stains used
  • used to differentiate different organelles
  • e.g. gram stain
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10
Q

negative stain technique

A

dye with a -ve charge repels -ve charged organelles + materials (usually stains cytoplasm so organelles stand out)

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11
Q

four advantages of electron microscopes

A
  • shoes details of organelles
  • higher resolution
  • higher magnification
  • two types (TEM + SEM)
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12
Q

six disadvantages of electron microscopes

A
  • large (not portable)
  • affected by magnetic fields
  • preparation of specimens is lengthy and require expertise
  • preparation can distort specimen
  • images are black and white
  • expensive (to buy and operate)
  • vacuum is required
  • specimens must be dead
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13
Q

what types of images do SEM and TEM each make

A

SEM: 3D images of surfaces

TEM: 2D images of cross sections

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14
Q

order of microscopes increasing in resolution and magnification

A
  • light
  • SEM
  • TEM
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15
Q

ultrastructure

A

features of a cell which can be seen using an electron microscope

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16
Q

artefacts

A

visible structural detail caused by the processing of a specimen (not part of the actual specimen) e.g. air bubble trapped under cover slip or distortion of membranes from preparation for e- microscopes

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17
Q

wet mount steps

A
  • pipette a drop of water on the middle of a slide
  • using tweezers, place specimen on top of water droplet
  • add a drop of iodine solution
  • place a cover slip over the sample by slowly lowering it from an angle with a mounted needle (to avoid air bubbles)
  • dab excess liquid from the edges
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18
Q

membrane of a permanent cell vacuole

A

tonoplast

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19
Q

nucleus vs nucleolus

A

nucleolus contains the DNA, RNA and proteins is within the nucleus (some cells have more than one nucleolus)

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20
Q

features that are present in all bacteria

A
  • cytoplasm
  • plasma membrane
  • cell wall (made of peptidoglycan)
  • 70s ribosomes
  • circular DNA
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21
Q

features that are present in some bacteria (but not all) and their purpose

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A
  • slime capsule (protection)
  • plasmid DNA
  • infold in membranes (absorb phosytnetic substrates or fix nitrogen)
  • flagellum (motion)
  • pili (attached to other cells or surfaces + sexual reproduction)
22
Q

intrinsic vs extrinsic proteins

Study These Flashcards
A

intrinsic proteins spam the whole phospholipid bilayer

extrinsic proteins only span one layer of the phospholipid bilayer OR lie on the surface

23
Q

components of a plasma membrane

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A
  • phospholipids
  • intrinsic/extrinsic proteins
  • channel proteins
  • carrier proteins
  • glycoproteins
  • glycolipids
24
Q

three components of the cytoskeleton

Study These Flashcards
A
  • microfilaments
  • microtubules
  • intermediate fibres
25
what are microfilaments and their function?
- contractile fibres made of actin (protein) - cell movement and contraction (e.g. cytokinesis)
26
what are microtubules and their function?
- globular tubulin proteins polymerise to form tubes - maintain cell structure and shape - move organelles and vesicles around cells (e.g. spindle fibres)
27
what is the function.of intermediate fibres?
- give mechanical strength to cells and maintain integrity (e.g. skin cells)
28
what theory shows the plasma membrane structure and why?
- fluid mosaic model - fluid because the phospholipid molecules are flexible and free to move around each other - mosaic because the embedded proteins vary in size, shape and position
29
are channel and carrier proteins active/passive?
channel: passive carrier: passive or active
30
function of glycolipids
cell markers/antigens
31
functions of glycoproteins
- receptors for neurotransmitters or drugs - receptors for peptide/non-steroid hormones
32
where does cholesterol go in the membrane?
- lipid with a hydrophilic end and a hydrophobic end - hydrophilic end interacts with hydrophilic phosphate heads - hydrophobic end interacts with the hydrophobic fatty acid tails
33
how does cholesterol maintain fluidity?
- sits in between phospholipids to prevent them from grouping too closely and crystallising - also sits in between phospholipids to hold them together in high temperatures etc (prevent gaps)
34
roles of plasma membranes
- separates cell's components from external environment - partially permeable (regulates movement of materials into and out of cell) - transport (facilitated diffusion, active/cotransport, endo/exocytosis) - cell recognition - cell attachment - cell signalling (cytokines, non-steroid hormones, drugs)
35
roles of membranes within cells (around organelles)
- improve reaction efficiency - compartmentalisation - enzymes embedded in membrane (e- carriers etc) - increase SA (thylakoid/cristae) - isolates nuclear DNA - pores allow RNA to leave - separates potentially harmful contents from cells (lysosomes containing lysozymes)
36
four factors affecting membrane fluidity
- temperature - cholesterol - fatty acid saturation - lipid packing
37
beta blockers
drugs that work by having a specific structure to bind to specific membrane receptors preventing first messengers from binding
38
how does temperature affect membrane permeability?
- increase in temp increases kinetic energy of phospholipids - phospholipids move more freely - membrane becomes more fluid therefore more permeable - AND proteins may denature, leaving gaps in membrane
39
how do solvents affect membrane permeability?
- solvents such as alcohol (non-polae alkyl chain and polar OH group) interact with the phospholipids - solvents dissolve/surround them leaving more bigger gaps in membranes therefore increasing permeability
40
why may plant specimens be soaked in acid before being prepared on a microscope slide?
- acid can help break down the components (e.g. pectin) of the cell wall - allows stain to penetrate easier
41
when staining multiple specimens on one plate, what should you ensure and why?
- specimens are close together but not touching - allow stain to cover all of the specimens and no overlap means the stain can fully penetrate each specimen
42
what is a limitation of using tweezers when preparing specimens for slides?
tweezers can cause damage to the cells or tissues
43
why might iodine stain be used?
- cheaper - safer (less toxic/corrosive) - increase contrast within cells under a microscope
44
why might a stained specimen be heated before placing onto a slide? and what should you be careful of when doing this?
- heat encourages staying to fully penetrate tissue - do not allow the stain to evaporate or exceed temperatures that may denature enzymes (if looking at active processes such as mitosis)
45
why might you place multiple specimens on one slide?
increase the chance of success of a specimen being visible and active
46
why should you rinse stains with distilled water before placing on slides? (when looking at mitotic cells)
stains that remain unbound to DNA can obscure the visibility of chromosomes
47
why should glycerol be placed on active cells when preparing microscopes slides? and why is too much glycerol a potential issue?
- keep cells hydrated therefore active - too much glycerol can cause pieces of tissue to drift/slip off to the side
48
why should the squashing of tissues in a microscopes slide be delayed?
- allows cells to harden - reduce risk of cells bursting upon squashing
49
why should the microscope slide be wrapped up in paper towel before squashing the specimen?
reduce the risk of fracturing the glass
50
what is important when squashing is specimen in a microscope slide? and why?
- surface that the specimen is being squashed on is flat - high pressure is applied without twisting or sideways movements which may damage the tissue or the slide
51
what could you do if cells in a microscope specimen are overlapping and obscuring view?
- wrap the slide in paper towels - resquash the specimen further
52
what can be done to remove air bubbles trapped in slides?
a drop of water can be pipetted under the corner of the cover slip in attempt to push the air bubble out
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