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A- Level Biology > Unit 2 > Flashcards

Unit 2 Flashcards

1
Q

Define the terms eukaryotic and
prokaryotic cell. 2

A

Eukaryotic: DNA is contained in a
nucleus, contains membrane-bound
specialised organelles.

Prokaryotic: DNA is ‘free’ in cytoplasm,
no organelles e.g. bacteria & archaea

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2
Q

State the relationship between a system and specialised cells.

A

Specialised cells → tissues that perform
specific function → organs made of
several tissue types → organ systems

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3
Q

State an equation to calculate the actual size of a structure from microscopy

A

actual size

image size
/
magnification

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4
Q

Define magnification and resolution 2

A

Magnification: factor by which the
image is larger than the actual specimen.

Resolution: smallest separation
distance at which 2 separate structures
can be distinguished from one another

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5
Q

what is the structure 1 and function2 of a cell surface membrane

plus tails strucutre

A

f: control which substances enter and leave the cell
- involved in rapid signaling ad cell recognition
-partially permeable

s:phospholipid bilayer with intrinsic proteins embedded

hydrophilic phosphate head facing outside, hydrophobic fatty acid tails inside

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6
Q

Explain the role of cholesterol,glycoproteins & glycolipids in the cellsurface membrane.
3

A

Cholesterol: steroid molecule connects phospholipids & reduces fluidity.

Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together.

Glycolipids: cell signalling & cell recognition

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7
Q

Describe the structure of the nucleus. 4

A

● nuclear envelope, a
semi-permeable double membrane (control in and out)

● Nuclear pores mRNA/ ribosomes to
enter/exit.

● nucleolus made of RNA & proteins
assembles ribosomes.

*nucleoplasm

chromatin : squiggle of DNA = chromosomes made wound around proteins called histones

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8
Q

Describe the function of the nucleus 2-3

A

*site of DNA replication and transcription

*contains genetic code for each cell

● Controls cellular processes: gene
expression determines specialization & site
of mRNA transcription, mitosis,
semiconservative replication.

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9
Q

Describe the structure of a mitochondrion
2

function site of aerobic respiration in
eukaryotic cells
site of ATP production
(dna code for enzymes needed in respiration)

A

● Surrounded by double membrane folded
inner membrane forms folds cristae (increase sarea)

● Fluid matrix: contains mitochondrial DNA,
respiratory enzymes, lipids, proteins

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10
Q

Describe the structure of a chloroplast.2

Chloroplasts: site of photosynthesis
to convert solar energy to chemical
energy.

A

s:double membrane
Thylakoids: stack to form grana; contain photosystems with chlorophyll

Stroma: fluid-filled matrix

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11
Q

Describe the structure and function of the Golgi apparatus 2

A

f= make lysosomes, modifies proteins by adding carbohydrates (glycoproteins), make lipids

molecules are processes in cisternae

s=Flattened sacs of membrane with vessicles circles

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12
Q

describe the structure and function of the golgi vessicle

A

s= fluid filled sac in cytoplasm
produced in the golgi apparatus

f= stores lipids and proteins made by the golgi apparatus and transports them out of the cell

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13
Q

Describe the structure and function of a
lysosome.

A

-vessicle containing hydrolytic enzyme (enzymes which hydrolyase enzymes)

-hydrolayse bacteria, viruses, damage cells

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14
Q

Describe the structure and function of a ribosome 2

A

formed by protein and rRNA
-free in cytoplasm or attached to (R)ER
site of protein synthesis via translation

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15
Q

Describe the structure and function of the
endoplasmic reticulum (ER).
2

A

Cisternae: folded cell membrane through cytoplasm &
connects to nuclear envelope:

Rough ER: many ribosomes attached for protein synthesis & transport.
● Smooth ER: lipid synthesi

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16
Q

State the srtucture and functions of the cell wall 4 bacteria and plants

A

-structural strength and support

● Bacteria:
Made of the polysaccharide murein.

● Plants:
Made of cellulose microfibrils= high tensile strength
-lots of hydrogen bonds between straight chains

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17
Q

Describe the structure and function of the cell
vacuole in plants.
2

A

Surrounded by single membrane: tonoplast
contains cell sap

Controls turgor pressure.
● Absorbs and hydrolyses potentially harmful
substances to detoxify cytoplasm.

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18
Q

Explain some common cell adaptations. 3

A

● Folded membrane or microvilli increase
surface area e.g. for diffusion.
● Many mitochondria = large amounts of ATP for
active transport.
● Walls one cell thick to reduce distance of
diffusion pathway.

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19
Q

State the role of plasmids in prokaryotes.2

A

● Small ring of DNA that carries non-essential genes.
● genes that aid in survival of bacteria ( has enzymes that break down antibodies>

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20
Q

State the role of flagella in prokaryotes 2

A

-aids movement of bacteria (RiGID COHESION SHAPE+ROTATING BASE)
-helps cell spin through fluids

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21
Q

State the role of the capsule in prokaryotes 2

A

polysaccharide layer
-extra protective layer]helps groups of bacteria stick together

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22
Q

Compare eukaryotic and prokaryotic cells
3

A

both have:
● Cell membrane.
● Cytoplasm.
● Ribosomes (don’t count as an
organelle since not membrane-bound).

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23
Q

Contrast eukaryotic and prokaryotic cells 3-4 compare

A

Prokaryotic
-small cells, unicellular
-no membrane-bound organelles & no nucleus
-circular DNA not associated with proteins
-small ribosomes (70S)
-binary fission - always asexual reproduction
-capsule, sometimes plasmids & cytoskeleton
-murein cell walls

Eukaryotic
- larger cells,often multicellular
- always have organelles & nucleus
-linear chromosomes associated with histones
-larger ribosomes (80S)
-mitosis & meiosis - sexual and/or asexual
-cellulose cell wall (plants)/ chitin (fungi)
-no capsule, no plasmids, always cytoskeleton

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24
Q

describe the strucutre of viruses 2-4

invade ad replicate in other host cells

A

-Acellular
-nucleic acids surrounded by protein coat (capsid)

-no cell membrane, ribosomes, plasmid, flagella, cell wall

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25
Q

Describe the structure of a viral particle 2

A

● Linear genetic material (DNA or RNA) &
viral enzymes e.g. reverse transcriptase.

● Surrounded by capsid (protein coat
made of capsomeres).

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26
Q

describe viral replication 4

A

-attachment proteins on its surface bind to complementary receptor proteins on the surface of a host cell

-genetic material is released into host cell

-gentic material and protein are replicated by host cell ribosomes to synthesize viral proteins/ nucleic acid

Replicated viruses burst from host cell

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27
Q

structure of HIv 5

A

-two RNA strands
-capsid (protein coat)
-attachment proteins on surface
-reverse transcriptase (viral enzymes surrounded by capsid)
-viral envelope (lipid bilyaer and glycoproteins)

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28
Q

State the role of the capsid on viral
particles 2

A

● Protect nucleic acid from degradation

● Surface sites enable viral particle to
bind to & enter host cells or inject their
genetic material

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29
Q

State the role of attachment proteins on
viral particles

A

-Enable viral particle to bind to
complementary sites on host cell : entry
via endosymbiosis.

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30
Q

Outline how a student could prepare a temporary
mount of tissue for an optical microscope 4

A
  1. Obtain thin section of tissue
  2. Place plant tissue in a drop of water.
  3. Stain tissue iodine on a slide to make structures visible.
  4. Add coverslip using mounted needle at 45° to
    avoid trapping air bubbles
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31
Q

Suggest the 3advantages and 2limitations
of using an optical microscope

A

+ colour image
+ can show living structures
+ affordable apparatus
- 2D image
- lower resolution than electron microscopes =
cannot see ultrastructures

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32
Q

Suggest the 2 advantages and 2limitations
of using a TEM

-electrons pass through specimen
-detected as more dense structures= darker
=absorb more electrons
-Focus image onto fluorescent screen or
photographic plate using magnetic lenses.

A

+ electrons have shorter wavelength than light = high resolution,(small) ultrastructure visible
+ high magnification (x 500000)
- 2D image
- requires a vacuum = dead structures
- extensive preparation may introduce artefacts
- no colour image

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33
Q

Suggest the 2 advantages and 2 limitations
of using an SEM.

-electrons focused by magnets
-reflected electrons hit collecting device and produce a image

A

+ 3D image
+ electrons have shorter wavelength than light = high resolution
- requires a vacuum = cannot show living structures
- no colour image
- only shows outer surface

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34
Q

Outline what happens during cell fractionation and
ultracentrifugation. 1-3a-c

A
  1. homogenize tissue to break open cells &
    release organelles.
  2. Filter homogenate to remove debris.
  3. Perform differential centrifugation:
    a) Spin homogenate in centrifuge.
    b) The most dense organelles in the mixture form a pellet.
    c) Filter off the supernatant and spin again at a higher speed
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35
Q

Explain why fractionated cells are kept in
a ice cold, buffered, isotonic solution. 3

A

ice cold: slow the action of enzymes so they don’t digest organelles

buffered: maintain constant pH. (protein/enzymes not damaged in 3*

isotonic: so they all have the same water potential and prevent osmosis of organelles

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36
Q

State what the cell 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)

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37
Q

Outline what happens during interphase.
G0= dormancy period 3

A

G1: making new organelles (ATP)
-cell synthesises proteins for replication e.g.
tubulin for spindle fibres & cell size doubles

S: DNA replicates = chromosomes consist of 2
sister chromatids joined at a centromere

G2: organelles divide

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38
Q

State the purpose of mitosis.

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
A

produces 2 genetically identical daughter cells
for:
● Growth
● Cell replacement/ tissue repair
● Asexual reproduction

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39
Q

what happens at prophase 2

A
  1. Chromosomes condense, becoming visible.
  2. Centrioles move to opposite poles of cell (animal
    cells) & mitotic spindle fibres form.
  3. Nuclear envelope & nucleolus break down =
    chromosomes free in cytoplasm
40
Q

Outline what happens during metaphase 2

A

-chromatids line up at cell equator

-spindle fibres attach to centromeres and pull to the end poles

41
Q

Outline what happens during anaphase 3

requires energy from ATP hydrolysis

A
  1. Spindle fibres contract (shorten)

-centromeres divide.

  • chromatids separate and pulled to opposite poles of cell (looks like ‘V’ shapes facing each other).
  1. Spindle fibres break down.
41
Q

Outline what happens during telophase 2

A
  1. Chromosomes decondense, becoming
    invisible again.
  2. New nuclear envelopes form around each
    set of chromosomes = 2 new nuclei, each
    with 1 copy of each chromosome
42
Q

difference in benign and malignant tumours

A

benign
-less likely to be life threatening
-grow more slowly
-more compact

malignant
-more likely to be life threatening
grow more rapidly
less compact

43
Q

Suggest how cancer treatments control the rate of cell division.

-Dna replication

distrupt spindle formation

A

Disrupt the cell cycle:
● prevent DNA replication
-by inibiting DNA helicase /
polymerase
-in s phase of interphase
-prevent the synthesis of enzymes needed for DNA replication
-disrupts cell cycle= forcing cell to kill itself

● disrupt spindle formation = inhibit metaphase
/ anaphase
NB: can also damage healthy cells

44
Q

how does binary fission happen in prokaryotic cells 3-4

A

-Circular DNA replicates once and plasmids replicate in any amount in the cytoplasm
-Cell elongates and cytoplasm splits by cytokinesis
*produces two daughter cells = single copy circular DNA molecule and a variable number of plasmids

45
Q

Why is it so difficult to develop effective treatments
against viruses?

A

Replicate inside living cells = difficult to kill them without killing host cells.

46
Q

Describe the fluid mosaic model of
membranes. 2

A

Fluid: phospholipid bilayer in which
individual phospholipids can move

=membrane has flexible shape.

Mosaic: extrinsic & intrinsic proteins of different sizes and shapes are embedded.

47
Q

Explain the functions of extrinsic and intrinsic proteins in membranes.

2 for each ?

A

extrinsic:
● binding sites/ receptors
e.g. for hormones
● antigens (glycoproteins)
● bind cells together
● involved in cell signalling

intrinsic:
● electron carriers
(respiration/photosynthesis)
● channel proteins (facilitated
diffusion)
● carrier proteins (facilitated
diffusion/ active transport)

48
Q

what is mitotic index

A

mitotic index = number of cells with visible chromosomes ÷ total number of cells

49
Q

(extra info )
Explain the functions of membranes within cells

A

● Provide internal transport system.
● Selectively permeable to regulate passage
of molecules into / out of organelles.
● Provide reaction surface.
● Isolate organelles from cytoplasm for
specific metabolic reactions

50
Q

Explain the functions of the cell-surface
mebrane 3

A

● Isolates cytoplasm from extracellular
environment.
● Selectively permeable to regulate
transport of substances.
● Involved in cell signalling/cell recognition.

51
Q

Name and explain 3 factors that affect
membrane permeability.

A

● Temperature:
-high temperature denatures membrane (carrier/channel) proteins / phospholipid molecules
- have more kinetic energy & move further apart / can change shape
● pH: changes tertiary structure of membrane
proteins.
● Use of a solvent: may dissolve membrane.

52
Q

Define osmosis

A

net movement of water across a partially permeable membrane from an area of higher water potential to a area of lower water potential

-(untik dynamic equilibrium is reached

53
Q

What is water potential (ψ)? 3

A

● pressure created by water molecules
measured in kPa
● Ψ of pure water at 25℃ & 100 kPa: 0
● more solute = ψ more negative

54
Q

How does osmosis affect plant and
animal cells?

A

● osmosis INTO cell:
plant: protoplast swells = cell turgid
animal: lysis (hypotonic)

● osmosis OUT of cell:
plant: protoplast shrinks = cell flaccid
animal: crenation (hypotonic)

55
Q

Suggest how a student could produce a desired
concentration of solution from a stock solution

A

● volume of stock solution = required concentration x final volume needed / concentration of stock
solution.
● volume of distilled water = final volume needed -volume of stock solution.

56
Q

Define simple diffusion 2

A

-net movement of small/non polar molecules down a concentration gradient (high to low)

-passive

57
Q

define facilitated diffusion

A

-diffusion large/ polar lolecules/ ions via carrier/ channel proteins down a concetration gradient
(has complementary binding sites)

-passive

58
Q

Explain how channel and carrier proteins
work 2

A

Channel: hydrophilic channels bind to specific ions =
one side of the protein closes & the other opens

Carrier: binds to complementary molecule =
conformational change releases molecule on other side of membrane;

( in active transport, requires energy from ATP hydrolysis)

59
Q

Name 5 factors that affect the rate of
diffusion.

A

● Temperature= more KE
● Diffusion distance
● Surface area= more channel/carrier, lipid soluble
● Size of molecule
● Difference in concentration (how steep the
concentration gradient is)

60
Q

State Fick’s law.rate of diffusion proprtional to

A

surface area x difference in
concentration / diffusion distance

61
Q

How are cells adapted to maximise the
rate of transport across their
membranes? 2

A

● many carrier/ channel proteins
● folded membrane increases surface
area

62
Q

Explain the difference between the shape of a graph of concentration (x-axis) against rate (y-axis) for simple vs facilitated diffusion. 2

A

Simple diffusion: straight diagonal line; rate of
diffusion increases proportionally as concentration increases.

Facilitated diffusion: straight diagonal line later levels off when all channel/ carrier proteins are saturated

63
Q

Define active transport. 2

A

against a concentration gradient via carrier proteins using ATP

ATP hydrolysed and attached tocarrier protein= protein changes shape

Specific carrier protein transports molecules/ ions from area of low concentration to area of higher concentration
(i.e. against concentration gradient).

64
Q

Compare and contrast active transport and facilitated diffusion 3

A

● Both may involve carrier proteins.
● Active transport requires energy from ATP
hydrolysis; facilitated diffusion is a passive
process.
● Facilitated diffusion may also involve channel
proteins.

65
Q

Define co-transport.

A

co-transport of 2 different substances using a carrier protein

Substances bind to complementary intrinsic protein:
symport: transports substances in same direction
antiport: transports substances in opposite direction e.g.
sodium-potassium pump.

66
Q

Explain how co-transport is involved in
the absorption of glucose / amino acids
in the small intestine. 5

A

1.Na+ions leave epithelial cell and enter blood;.
2. (Transport out is by) active transport / pump / via carrier protein using ATP.
3. So, Na+conc. in cell is lower than in lumen (of gut)
4.Sodium/Na+ions enter by facilitateddiffusion
5.Glucose absorbed with Na+ions against their concentration

67
Q

what is a pathogen 2

A

Organisms that cause disease

-they have antigens on their surface

-bacteria
-fungi
-viruses

68
Q

What is a antigen

A

(foreign)
-cell surface molecule/(glyco)protein/(glyco)lipid/
polysaccharide.

-which stimulates a immune response

69
Q

Explain how phagocytosis destroys pathogens?
(non-specific response, carried out by macrophages)

A
  1. Phagocyte recognises foreign antigen

2.Phagocyte moves round and engulfs pathogen by endocytosis to form phagosome

3.Phagosome fuses with lysosome and is enclosed in vacoule (phagolysosome)

  1. Lysoszymes digest pathogen (hydrolysed)
  2. Presents antigen on surface = antigen presenting cell (APC)
70
Q

explain the role of antigen-presenting cells (APC) in the cellular response

A

-Macrophage displays antigen from the pathogen on its surface (after hydrolysis in phagocytosis).

Enhances recognition by THelper cells, which cannot directly interface with pathogens/ antigens in body fluid.

71
Q

Give 2 differences between specific and nonspecific immune responses
(2for each)

A

-nonspecific (inflammation, phagocytosis) = same for all pathogens

-specific (B & T lymphocytes) = complementary pathogen

-nonspecific = immediate
-specific = time lag

72
Q

Name 2 types of specific immune response

2

A

-Cell-mediated immunity= T lymphocytes
(responds to foreign material inside body cell= responds to own cells altered by (cancer, viruses, organ transplanted)

Humoral immunity= B lymphocytes
(responds to foreign material outside body cells)= responds to bacteria and viruses by producing antibodies

73
Q

explain cell mediated response (t cells) 3

A

-Complementary T h cells bind to foreign antigen on APC (after phagocytosis has happened)

-T h cells produce a clone of daughter cells that release cytokines

-clonal selection of complementary T h cells (rapid mitosis) become
*memory T cells
*Cytotoxic T cells
*T helper cells= secrete cytokines that stimulate B cells to divide and form….

-

74
Q

explain the role of t helper cells 2

A

-secrete cytokines that stimulate B cells to divide by rapid mitosis and clonal selection and differentiate to

*plasma cells
*memory B cells

75
Q

Outline the process of the humoral response B cells

3

A

-Complementary T H cells bind to foreign antigens on antigen-presenting T cells

-Release cytokines that stimulate clonal selection and rapid mitosis of complementary B cells

-B cells differentiate into plasma cells and memory cells

-plasma cells secret antibodies with complementary variable region to antigen

76
Q

define antibody 2

describe levels of protein strucutre

structure

A

-protein specific to antigen, produced by B cells

-s=Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen.
-The rest of the molecule is known as the constant region

1* proteins with chains of amino acids
3Unique 3D shape with further folding and H, ionic bonds,Disulfide bridge in hinge region
4 4 polypeptide chains

77
Q

How do antibodies lead to the
destruction of a pathogen? 2

A

-Formation of antigen-antibody
complex

-results in agglutination, which
enhances phagocytosis.

78
Q

What are monoclonal antibodies?

A

Antibodies produced from a single clone of B cells

78
Q

What are memory cells?

A

● Specialised TH/ B cells produced from
primary immune response.

● Remain in low levels in the blood.

● Can divide very rapidly by mitosis if
organism encounters the same pathogen
again.

79
Q

Contrast the primary and secondary immune response 3

A

secondary response:
● Faster rate of antibody production.
● Shorter time lag between exposure & antibody production.
● Higher concentration of antibodies.
● Antibody level remains higher after the secondary response.
● Pathogen usually destroyed before any symptoms.

80
Q

What causes antigen variability? 4

A
  1. Random genetic mutation changes DNA base sequence.
  2. Results in different sequence of codons on mRNA (
  3. Different primary structures of antigen = H-bonds,ionic bonds & disulfide bridges form in different places in tertiary structure.
  4. Different shape of antigen.
81
Q

Explain how antigen variability affects the incidence of disease 2

A

● Memory cells no longer complementary to
antigen = individual not immune = can catch
the disease more than once.

● Many varieties of a pathogen = difficult to
develop vaccine containing all antigen types

82
Q

Compare 2 and contrast passive 4 and active 4 immunity. Give
examples of both types.

passive natural: antibodies in breast milk/ across placenta
passive artificial: anti-venom, needle stick injections
active natural: humoral response to infection
active artificial: vaccination

A

● both involve antibodies
● can both be natural or artificial

active= exposure to antigen, take while for protection to develop, memory cells produced
-long term protection as antibodies produced complementary to antigen

pass= doesn’t require exposure to antigen, protection immediate, memory cells not produced
-short term protection as antibodies broken down

83
Q

Explain the principles of vaccination 4

A
  1. Vaccine contains dead/ inactive form of a pathogen or antigen.
  2. Triggers primary immune response (B plasma cells).
  3. Memory cells are produced and remain in the
    bloodstream, so secondary response is rapid &
    produces higher concentration of antibodies.
  4. Pathogen is destroyed before it causes symptoms.
84
Q

What is herd immunity?

A

Vaccinating large proportion of population reduces available carriers of the pathogen.

Protects individuals who have not been
vaccinated e.g. those with a weak immune
system.

85
Q

Suggest some ethical issues surrounding the use of vaccines 4

A

● production may involve use of animals= animal tested
● potentially dangerous side-effects
● clinical tests may be fatal
● compulsory vs opt-out ( may not be able to get vaccine)

86
Q

Suggest the clinical applications of monoclonal antibodies 3

A

● Pregnancy tests by detecting HCG hormones in urine.
● Diagnostic procedures e.g. ELISA test
● Targeted treatment by attaching drug to antibody so that
it only binds to cells with abnormal antigen e.g. cancer
cells due to specificity of tertiary structure of binding
site.

87
Q

Explain the principle of the a direct ELISA test 5

A

detects presence of a specific antigen

  1. Monoclonal antibodies bind to bottom of test plate.
  2. Antigen molecules in sample bind to antibody. Rinse excess.
  3. Mobile antibody with ‘reporter enzyme’ attached binds to
    antigens that are ‘fixed’ on the monoclonal antibodies. Rinse
    excess.
  4. Add substrate for reporter enzyme. Positive result: colour
    change.
88
Q

Explain the principle of an indirect ELISA
test 5

A

detects presence of an antibody against a specific antigen

  1. Antigens bind to bottom of test plate.
  2. Antibodies in sample bind to antigen. Wash away excess.
  3. Secondary antibody with ‘reporter enzyme’ attached binds
    to primary antibodies from the sample.
  4. Add substrate for reporter enzyme. Positive result: colour
    change.
89
Q

Suggest some ethical issues surrounding the use of monoclonal antibodies.

A

● Production involves animals. (Animals are often used to produce cells from which monoclonal antibodies are produced)
● Drug trials against arthritis & leukaemia resulted in multiple organ
failure.

90
Q

How does HIV result in the symptoms of AIDS?

A
  1. Attachment proteins bind to complementary CD4
    receptor on TH cells.
  2. HIV particles replicate inside TH cells, killing or damaging them.
  3. AIDS develops when there are too few TH cells for the
    immune system to function.
  4. Individuals cannot destroy other pathogens & suffer from
    secondary diseases/ infections.
91
Q

Why are antibiotics ineffective against viruses?
2
antibiotics destroy murein cell wall (bacteria), viruses have no cell wall

A

Antibiotics often work by damaging murein cell
walls to cause osmotic lysis. Viruses have no
cell wall.

Viruses replicate inside host cells = difficult to
destroy them without damaging normal body
cells.

92
Q

two ways pathogens cause disease 2

A

release toxins
kill cells

93
Q

two ways pathogens cause disease 2

A

release toxins
kill cells

A- Level Biology (9 decks)

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