CIE Flashcards
1
Q
, explain the mode of action of enzymes.
A
(shape of) U / active site, gives specificity ; A ecf from (i)
2 substrate, fits into / binds with, active site / U ; A ecf from (i)
3 complementary (shape) / matching shape ;
A ‘lock and key’ / induced fit R ‘same shape’
4 further detail of substrate binding to active site ;
5 forms, enzyme-substrate / E-S, complex ;
6 causes stress in substrate / AW ;
7 lowers activation energy / reactions occur at low(er) temperatures ;
8 not used up in reaction / remain unchanged / reusable ;
9 high turnover number / catalyse many reactions per unit time ;
2
Q
State what is meant by the term globular
A
spherical / ball-shaped / AW ;
has a tertiary structure ;
hydrophilic / polar, groups on outside ;
water soluble ;
3
Q
Explain why DNA replication is described as semi-conservative
A
each strand, of DNA acts as a template (for the synthesis of a complementary strand) ;
A described in terms of base pairing
new DNA (molecule) has one, old / parental / original, strand and one, new / daughter
strand ;
4
Q
The enzyme that catalyses the replication of DNA checks for errors in the process and corrects them. This makes sure that the cells produced in mitosis are genetically identical.
Explain why checking for errors and correcting them is necessary
A
(errors are) mutations / named type of mutation ;
ora if corrected there are no mutations
(may lead to) production of altered proteins, so, impaired / loss, of function ;
A altered amino acid in, protein / primary structure
(may lead to) different antigens, so cells are rejected (by immune system) ;
idea that cells cannot function together / impaired coordination ;
ref. to cancerous cells / cancer(s) / tumours / sickle cell anaemia or other named monogenic
condition ;
further detail ;
e.g. uncontrolled, division / mitosis / cell replication / cell growth
e.g. lack of contact inhibition / no apoptosis or described / (proto)oncogene(s
5
Q
role of the Golgi apparatus
A
processing/modification/AW/ packaging, of, proteins/ molecules ; A description of modification e.g. glycosylation A production of, secretory/ Golgi, vesicles A production of lysosome
6
Q
Explain what is meant by the term primary structure
A
(describes the) sequence of amino acids (in a polypeptide chain)
7
Q
describe the primary structure
A
regular order/pattern, based on H-bonds ;
2 between CO– group of one amino acid and NH– group of another ;
3 alpha-helix and β-pleated sheet ;
8
Q
describe the secondary structure
A
1 folding coiling ;
2 interactions between, R groups side chains ;
3 two correctly named bonds ; e.g. hydrogen bonds, disulfide, bonds/bridges, ionic
bonds, hydrophobic interactions
4 further description of bonds ; e.g. disulfide between cysteine (S–H) groups
hydrogen between polar groups (NH– and CO–)
ionic between ionised amine and carboxylic acid groups
hydrophobic interactions between non-polar side chains
5 ref. active site, specific/precise, shape ;
6 ref. globular/AW, shape ; A spherical/ball
7 ref. amino acids with, hydrophilic/polar, R groups facing to outside
9
Q
State why it is important for enzymes, to possess a tertiary structure.
A
enables (protein to) function/AW ; A enables antimicrobial action/AW
A biological catalyst, qualified
provides active site ;
qualified ref. to specificity ;
10
Q
Explain why ribosomes cant be seen using a light microscope
A
resolution/resolving power, low(er) ; ora
200 nm compared to 0.5 nm ; A resolution quoted in range 100-300 to 0.2-1.0 nm
ref. to visibility of structure C ; e.gs.
wavelength of light longer than size of, ribosomes/membrane
ribosomes/membrane, cannot be seen as less than 200nm diameter
ribosomes only 20–30 nm diameter A 15–20 nm
membranes 7–10 nm thick
small size linked to explanation of resolution
11
Q
Suggest one disadvantage of the electron microscope compared to the light microscope for the study of cells
A
only dead specimens can be viewed ;
mounted in vacuum/pre-treatment, may distort delicate structures ; A artefacts
expensive, qualified ; e.g. to buy, maintain, increased cost electricity, costs associated with,
time/training
requires, more electrical power ;
requires stable, high voltage supplies/currents ;
sensitive to external magnetic fields ;
difficult to operate/requires technical training ;
samples more difficult to prepare ; A examples e.g. thin sections
lengthy preparation time ;
monochrome/black and white only ;
not portable/can only be used in specific locations (e.g. with voltage supplies)
12
Q
Describe the changes that occur within the cell between the beginning of prophase and the end of metaphase.
Describe the changes that occur within the cell between the beginning of prophase and the end of metaphase.
A
rks can be taken from labels / annotations
1 chromatids / chromosomes / chromatin, condense / become shorter / become thicker /
coil / supercoil / AW ; A ‘become (more) visible’
2 centrioles, move to / reach, opposite poles ; R ends
3 nucleolus disappears ;
4 spindle is formed ; A ‘more developed’ A description in terms of spindle fibres
5 ref to assembly of microtubules ; A ‘makes’ microtubules R 9+2
6 nuclear envelope, disintegrates / breaks down / destroyed / AW ; A membrane
7 chromosomes, move to / at, equatorial plate / equator / metaphase plate / AW ; ignore
middle / centre
8 centromeres attach to, spindle / fibres ;
9 ref to random arrangement of chromosomes ; A ‘not in pairs’
13
Q
Describe the role of mRNA after it leaves the nucleus and enters the cytoplasm of a eukaryotic cell.
A
1 translation ; R if transcription given as well, unless in correct context
A use of, nucleotide / base, sequence, to make, amino acid chain / polypeptide / protein
I protein / polypeptide, synthesis
2 moves towards / combines with, ribosome ;
3 ref to small and/or large sub-units ; I small / large ribosome
4 codon(s) ; only accept in correct context
5 transfer / t, RNA, bringing, amino acid(s), to mRNA / ribosome ;
6 anticodon(s) ; only accept in correct context
7 (complementary) base pairing ;
8 any e.g. of codon:anticodon base pairing ; need six bases
9 ref to polyribosome(s) / used by many ribosomes ;
10 (mRNA short-lived) ref to production of protein for short period of time
14
Q
Explain how active immunity differs from passive immunity.
A
immune response ; A ‘immune system responds’
to antigen ;
clonal selection occurs / ref to B cells or T cells activated ;
antibodies made ; A ora for passive
memory cells produced ;
long-lived / long-term effect / permanent ;
not immediate / slow ; one week minimum
passive only – antibodies removed from circulation ;
15
Q
Explain why the vaccine for measles is not given in the first few months of a child’s life.
A
antibodies from, mother / colostrum / across placenta ; R ‘immunity from mother’
interact with, antigen / measles antigens / virus / pathogen ;
(so) prevents an (active) immune response ; A no immune response
too early for immune response to occur / T cells or B cells not mature ;
A not immunocompetent / immune system not developed
16
Q
Explain why the term ‘resting stage’ is not an appropriate description for cells in interphase.
A
cells metabolically active / AW ;
protein synthesis ;
transcription ;
translation ;
gene expression ;
DNA / semi-conservative, replication ;
respiration ;
synthesising, organelles / named organelle(s) ; e.g. A centrioles replicate
synthesising, macromolecules / named macromolecule ;
17
Q
State three features of prokaryotes.
A
DNA not surrounded by, nuclear, envelope / membrane ; AW
A no (true) nucleus
circular DNA ; A loop
DNA not complexed with histone proteins ; A naked DNA
(only) 70S / smaller / 18nm, ribosomes ; A ribosomes not attached to membranes
no double membrane-bound organelles ; A no, mitochondria / chloroplasts
absence of named organelle ; e.g. Golgi apparatus, ER / RER / SER
if previous mp not given, A no membrane-bound organelles
capsule / slime layer ;
very small diameter / 0.5 to 5.0µm ;
cell wall of, murein / peptidoglycan ;
examples of other relevant points pili / pilus ; no 9+2 microtubule arrangement ; flagellum not covered by cell surface membrane ; presence of plasmids ;
18
Q
State how the structure of a phospholipid differs from a triglyceride
A
2, fatty acid / hydrocarbon, chain / tails ;
(third fatty acid replaced by a) phosphate group ;
AVP ; (most) contain, nitrogen / choline (attached to phosphate in, head / polar portion
19
Q
Explain how a phospholipid is suited to its role in cell membranes.
A
can form a bilayer ;
link between, hydrophobic core / AW, and barrier to water-soluble substances ; A polar
/ ionic
idea of, hydrophilic / phosphate, head, forming H bonds with water ;
A facing, water / watery environment / aqueous environment / cytoplasm / cytosol
ref. contribution to fluid nature of membrane ;
further detail ; e.g. mainly saturated fatty acids, less fluid e.g. mainly unsaturated fatty
acids, more fluid
ref. to control over membrane protein orientation ; e.g. hydrophobic – hydrophobic
interaction for ‘floating’ proteins
20
Q
State three features which are characteristic of the metaphase
A
chromosomes / (sister) chromatids, line up at the, equator / equatorial plate / metaphase
plate ; A move to I middle / centre
centromeres attached to, spindle / spindle fibres ;
A (spindle) microtubules A kinetochore
centrioles, reach / located at / AW, poles ; R ends
ref. spindle fully formed ; A spindle fibres extend from poles / AW
21
Q
Explain the importance of mitosis in organisms
A
replacement of cells ;
repair of tissue ; R repair of cells
growth / increase in cell numbers ;
asexual reproduction / vegetative propagation ; R cloning
maintains / same, number of chromosomes ; A two sets of chromosomes / diploid / 2n
genetically identical to parents ;
A produces daughter cells that are genetically identical A ref. clone(s)
ref to rejection / self vs non-self ;
22
Q
In many multicellular organisms, such as mammals, the time taken for the mitotic cell cycle varies considerably between different tissues, but is very carefully controlled in each cell.
Suggest the importance of this control in mammals
A
ref. coordination of growth / limiting growth ;
ref. minimising exposure to mutations / alterations to DNA (during replication) / AW ;
prevent tumour formation ; A prevent, cancer / uncontrollable growth
effect of, tumour / cancer ; e.g. compress other organs / invades other tissues or organs
AVP ; e.g. example of timing of cell cycle linked to cell function / idea of producing cells when
required
23
Q
For Examiner’s Use
(d) Describe the role played by tRNA in polypeptide synthesis.
A
(tRNA) carries amino acid to ribosome ;
2 ref. to specificity of amino acid carried ; A role in ensuring correct primary structure
3 ref. anticodon (on tRNA): codon (on mRNA) binding ;
4 ref. complementary / base pairing ; A A-U, C-G
5 ref to tRNA binding sites within ribosome ;
6 two tRNAs bound to, mRNA / ribosome, at same time ;
7 amino acids held close to each other / AW ;
8 (for) peptide bond formation ;
9 (tRNA) can be reused / binds another amino acid ;
24
Q
Phosphate is an example of an ion transported in this way. State one use for this ion in plant cells.
A
ATP / ADP / DNA / RNA / nucleic acid / NADP / phospholipid ;
A nucleotide / named nucleotide / nucleoside A phospholipid bilayer
25
Explain why the shape of the active site of an enzyme, such as penicillinase, is important.
1 complementary shape ;
2 substrate, fits into / enters / binds to / with, active site ;
A enzyme-substrate complex / ESC
3 ref. to specificity ;
4 lock and key / induced fit ; A description of induced fit
5 ref. to temporary bonds form with, active site / R groups (of amino acid residues) ;
26
State what is meant by the term reduction division and explain why this division is
necessary in a life cycle,
chromosome number is halved / 2n n / diploid haploid ;
A 2 sets of chromosomes 1 set of chromosomes
explanation to max 1
2 restore diploid number on fusion ; R restore full set if not qualified
3 avoids number doubling with each generation ;
4 allows expression of (recessive) alleles / AW ;
5 allows variation / new combinations of chromosomes
27
State the importance of hydrogen bonding in DNA structure
hydrogen bonds hold (two), polynucleotides / strands / chains, together ;
A hold, (complementary) nucleotides / base pairs, together
A ora e.g. prevents, unwinding / strand separation
2 (many hydrogen bonds) give stability / DNA is stable molecule / DNA is long lasting /
AW ; ignore ref. to strength
3 can be broken for, transcription / replication ;
4 ref. to (double) helix ;
28
Explain what is meant by the term fluid mosaic.
fluid
idea of phospholipid (and protein) molecules, move about/ diffuse (within their
monolayer) ;
mosaic to max 1
protein (molecules), interspersed/ scattered/not a complete layer/AW ;
different/AW, proteins (molecules) ;
29
Explain how uncontrolled cell division can result in cancer
ref. to mutation(s) ;
in context of initiating uncontrolled mitosis OR as a consequence of uncontrolled
mitosis
proto-oncogenes convert to oncogenes / oncogenes switched on/ tumour suppressor
genes switched off ;
(cell division is by) mitosis ;
formation of, tumour/mass of (unspecialised) cells ;
no response to (extracellular/ intracellular) signals to control mitosis /AW ;
no contact inhibition/AW ;
no cell death/ no apoptosis ;
immune system does not recognise the cells as foreign and destroys them ;
A reference to, not non-self/ self
metastasis / described ;
30
Describe the role of the spindle during mitosis.
microtubules / spindle (fibres), attach to centromere/ kinetochore
(of chromosome during prophase) ; I metaphase
arranging/aligning/ orienting/AW, chromosomes at the equator/
metaphase plate ; R centre
fibres, shorten/ contract/retract ; A microtubules disassemble/AW
move/ pull, (sister) chromatids /(daughter) chromosomes, to opposite poles
/ centrioles ;
idea that equal number of chromosomes in each daughter, nucleus / cell ;
31
State two roles of mitosis in plants and animals other than growth.
maintaining number of chromosomes ;
ensuring genetic stability / maintaining genetically identical cells /AW ;
asexual reproduction ; A vegetative reproduction/ cloning
cloning/ clonal expansion, of (named) lymphocytes ; A B/T cells
replacement of (worn out/ dead/damaged) cells ;
regeneration, of (named) tissues /organs ;
(wound) repair (of tissues) ; R repair of cells
ref. to production of gametes ;
e.g. mitosis in gametogenesis / gamete production in plants
32
explain the difference between the two ways in which enzymes interact with their substrates. the lock and key model and the inmducted model
enzyme A uses ‘lock and key’ and enzyme B uses induced fit ;
A enzymes work by ‘lock and key’ and induced fit
enzyme A/ lock and key, (shape of) active site is complementary /AW, to
(shape of) substrate (molecule) ;
enzyme B/ induced fit, has an active site that, moulds around/ AW, the
substrate ;
33
explain the term secondary
| structure.
β-pleated sheet,
α-helix ;
determined by, coiling/ folding/ sequence, of amino acids / polypeptide ;
A primary structure for sequence of amino acids
3 stabilised/held/AW, by hydrogen bonds ;
4 between C = O and H–N (of peptide bonds) ;
A carbonyl/ carboxyl group, and, amine/ amino group
5 ref to, parallel/ anti-parallel, nature of β-pleated sheet ;
34
2, explain how enzymes that are secreted by cells in the pancreas
are packaged into vesicles and exported.
1 vesicles, form from/ ‘pinch off’, Golgi (apparatus /body / complex) ;
2 vesicles moves, through cytoplasm/ to cell (surface) or plasma membrane ;
3 role of cytoskeleton/ microtubules in movement of vesicles ;
4 energy /ATP, is required (movement of vesicles / fusion with membrane) ;
5 vesicle fuses with/AW, cell (surface)/ plasma, membrane ;
I bind/ attach A join/ merge/ becomes part of
6 exocytosis / vesicle ‘opens up’ so that enzyme molecules are released ;
7 ref to fluid nature of, membranes / phospholipid bilayer, that makes this
possible ;
35
stating the property of water that allows each of the following to
take place.
solvent for glucose and ions
polar
36
stating the property of water that allows each of the following to
take place.
movement in xylem
hydrogen bonding
37
stating the property of water that allows each of the following to
take place.
helps to decrease body
temperature in mammals
high latent heat of vapourisation/
high specific heat (capacity)/
high enthalpy heat of vapourisation/
lots of energy required for evaporation ;
38
Describe the role of the mRNA molecule in post transcrioption to translation
copy of the, DNA/ gene, (coding) for a, polypeptide/ globin ; A protein
2 travels from, DNA/ nucleus / chromosome, to ribosome ;
A mRNA made in nucleus, attached to ribosome so movement is
implied
3 for translation/ for (haemo)globin production ;
4 mRNA codes for, sequence/ order, of amino acids ; A for primary structure
5 idea that (nucleotide/base) sequence is a series of codons ;
6 base pairing/AW, between codon on mRNA and anticodon on tRNA ;
e.g. of AW
hydrogen bonds between bases
examples of base pairing: A–U/C–G
39
(b) State the thickness of a cell surface membrane.
7 nm ; A any size or range within 6nm and 10nm
40
List four features of cell surface membranes of eukaryotic cells
) cholesterol ;
unsaturated fatty acids ; A phospholipid tails
carbohydrate chains added to protein(s)/ glycoproteins ;
A oligosaccharides for carbohydrate chains
carbohydrate chains added to lipids /glycolipids ;
glycocalyx ;
channel protein(s)/AW ; A aquaporin(s) ;
carrier proteins /AW ;
peripheral/ extrinsic, proteins ;
attachment to, cytoskeleton/ microfilaments ;
receptor(s) ;
antigen(s) ;
AVP ;
41
The molecule formed from a condensation reaction between fructose and glucose.
sucrose
42
The name of the bond broken when two amino acids are separated by hydrolysis.
peptide ;
43
The unbranched polymer consisting only of β-glucose molecules
cellulose
44
The reagent used to test for the presence of proteins.
biuret ;
45
The molecule produced, in addition to fatty acids, when a triglyceride is hydrolysed
glycerol ;
46
Describe the structure of a nucleus.
spherical/ spheroid/AW ;
(nuclear) envelope/ two (nuclear) membranes /double membrane ;
(containing) nuclear pores ;
(contains) chromatin/ chromosomes ;
DNA and, proteins / histones ;
contains, nucleolus / nucleoli
or
nucleolus is / nucleoli are, dark(er) staining/ spherical/ defined ;
AVP ; e.g. outer membrane continuous with RER
heterochromatin and euchromatin
contains nucleoplasm
47
outline the process of exocytosis
vesicles move to, cell (surface)/ plasma, membrane (via cytoskeleton) ;
(vesicles) fuse/merge, with cell (surface) membrane ;
exocytosis (occurs) ;
(movement of vesicle/ exocytosis) requires, energy /ATP ;
A active (process)
48
Suggest and explain how large glycoproteins eg EPO acts on target cells and why other cells are not affected.
i) EPO, binds to/ combines with/AW, receptors ;
receptors, complementary to/ specific shape for, EPO ;
A EPO fits into receptors
cell signalling/EPO binding leads to (specific) responses within the (target)
cells /AW ;
I cells respond to EPO
only, target/ bone marrow, cells, have receptors, for EPO/ specific to EPO ;
ora
A binding triggers responses only within, target/ bone marrow, cells
49
Explain why a particular amino acid needs to be linked to a specific tRNA molecule.
ref. tRNA role in translation ;
e.g. amino acid carried by tRNA molecule to ribosome
anticodon on tRNA (with specific amino acid) binds to codon on
mRNA
tRNAs bring amino acids, adjacent to each other/ for peptide bond
formation
idea that mRNA (sequence of) codons dictate which amino acids will be
added (to polypeptide chain)/AW ;
ref. correct, sequence of amino acids / primary structure (of, polypeptide/
protein) ;
50
Explain how the structure of an enzyme such as aminoacyl tRNA synthetase would be
altered if the pH of the cytoplasm became too acidic.
hydrogen/ ionic, bonds, break / disrupted ; A electrovalent for ionic
R if other bonds named
charges at the active site may be affected ;
changes, shape/(tertiary) structure, of active site ;
A changes, shape/ tertiary structure, of enzyme
51
Explain the induced fit mechanism.
substrate enters the active site ;
active site, (partially) flexible/ changes shape slightly ;
ref. provides a better fit/ moulds around ;
allows interaction of R groups (of active site) with substrate ;
52
nucleus ;function
ref. gene(s) / genetic information / genetic
material / DNA, (coding) for, antibody /
protein / polypeptide ;
transcription (occurring) / mRNA synthesis ;
AW (ref. antibodies)
53
mitochondrion
provides / synthesises / produces / makes,
ATP (for antibody synthesis / exocytosis) ;
treat as neutral other uses of ATP
54
rough endoplasmic
| reticulum
synthesis / modification / processing /
| transport, of, antibody / protein / polypeptide ;
55
Outline the role of transfer RNA (tRNA) in the production of a polypeptide.
collects / attaches to, specific amino acid
or ;
takes specific amino acid / activated tRNA, to ribosome
idea of, adjacent / two, amino acids and codon-anticodon binding ;
peptide bond formation / ref. elongation, (to form polypeptide) ;
56
how does a competitive inhibitor
binding / AW, to, active site
2 further detail / consequence of, binding ;
if binds to active site
complementary shape to active site
similar shape to substrate A same shape A similar structure
competes with substrate for active site
3 substrate unable, to enter / bind to, active site ;
A fewer / no, enzyme-substrate / ES, complexes form
4 AVP ; e.g.
ref. to decreased enzyme activity, qualified e.g. less ATP produced /
lower respiration rate
preference for, permanent / irreversible, inhibitor (to maximise effect)
correct ref. to concentration of inhibitor and effect
57
how does a competitive inhibitor
if binds to other site
changes shape of active site
shape of substrate no longer complementary to active site
enzyme-substrate / ES, complex (already in active site)
cannot make product
for both types of binding
3 substrate unable, to enter / bind to, active site ;
A fewer / no, enzyme-substrate / ES, complexes form
4 AVP ; e.g.
ref. to decreased enzyme activity, qualified e.g. less ATP produced /
lower respiration rate
preference for, permanent / irreversible, inhibitor (to maximise effect)
correct ref. to concentration of inhibitor and effect
58
mitosis vs meiosis
diploid / two chromosome sets / 2n haploid / one chromosome set /n
same number of chromosomes as
parent / AW
half the number of chromosomes as
parent / AW
two, copies / alleles / forms, of each one, copy / allele / form, of each ;
```
(cells) genetically identical (to, each
A (cells have) same / AW, DNA /
A no genetic variation
(cells) genetically different
A (cells have) different / AW, DNA /
genetic material
A genetic variation
```
59
Explain why the organism produces cells by meiosis.
for sexual reproduction ; A for, gamete / sperm and egg / pollen and ovum,
formation or A gametogenesis
2 to produce, haploid cells / cells with one set of chromosomes, for, fertilisation /
fusion ; A to form zygote
A cells with half the number of chromosomes for, fertilisation / fusion
3 restores / AW, diploid / original, number when, fertilisation / fusion (of gametes)
occurs ; only need ref. to fertilisation / zygote once
4 idea of ploidy consequences at fertilisation if not ;
e.g. ref. to doubling of chromosome number of original
5 ref. genetic variation, linked to evolution / natural selection;
60
State the advantages of using the light microscope, rather than using the electron
microscope, in studies of tissues.
can observe living tissue ; A observing processes (e.g. like mitosis)
2 ref. portability ; e.g. ref. to size, easy to move, no requirement for special room (e.g.
vibration-free )
3 ease of use, qualified ; e.g. no technical training required, slide preparation
easier, takes less time
4 see (actual / natural / real-life) colour ;
5 ref. to, differential staining / staining particular types of tissue ;
6 fewer problems with artefacts ;
7 lower cost of, purchase / maintenance / running / AW ;
61
Explain the importance of the cell surface membrane to cells.
idea of separation / barrier / AW, from surroundings / external environment ;
2 regulates / controls / AW, entry / exit, substances / named substances ;
3 enables recognition of self (antigens) / cell recognition / avoids cell destruction / act as
antigens / AW ;
4 allows binding of / receptors for, hormones / signal molecules / neurotransmitters / antigens ;
5 cell to cell adhesion ;
6 location for enzymes / multi-enzyme systems / enzyme pathways ;
7 AVP ; e.g. idea of flexibility (for some cells,
ref. glycoproteins / glycolipids, form H bonds with water for stability
62
Suggest how the molecular structure of the enzyme changes during ‘cold
denaturation’.
1 loss of tertiary structure / hydrogen bonds broken / ionic bonds broken ;
R if include disulfide or peptide bonds
2 changes shape / substrate unable to fit, active site; A enzyme changes shape so
alters active site
3 loss of / AW, globular structure ;
4 hydrophobic groups to outside of molecule ;
5 hydrophilic groups no longer interact with water / AW ;
63
Explain the mode of action of enzymes.
1 active site has, specific / particular, shape ;
2 complementary to substrate ; A substrate fits into active site
3 ref. to (some enzymes) induced fit mechanism ; A described
4 formation of enzyme-substrate complex ; AW
5 lowering, activation energy / Ea ; A detail of how activation energy lowered
e.g substrates held close together for bond formation
facilitates transfer of electrons
places strain on bond(s) to be broken
64
three differences between DNA replication and DNA
| transcription.
DNA replication DNA transcription
1 DNA, formed / AW vs mRNA / pre-mRNA (transcript) , (formed)
2 two (identical) DNA molecules formed vs one mRNA molecule (formed)
3 product double-stranded DNA product single stranded (m)RNA
4 all of DNA molecule, replicated / unwinds
/ involved
part of DNA molecule / gene, involved
5 both strands involved one strand (involved)
treat ref. to sense / antisense strands as
neutral
6 (involves / uses) DNA polymerase RNA polymerase
7 (free) DNA nucleotides, required / used RNA nucleotides
8 (process involves complementary) base
pairing A–T
ignore C–G
(complementary) base pairing A–U
9 takes place in late interphase / S-phase /
synthesis phase
takes place throughout interphase
10 important in, cell division / mitosis /
meiosis
for, polypeptide / protein, synthesis
65
List two cell structures that could be present in animal cells that are not present in plant leaf
cells.
microvillus / microvilli
centriole/ centrioles
cilium / cilia
flagellum/ flagella
66
State one role of magnesium ions in the leaf cell.
(part / used in synthesis, of) chlorophyll (molecule) ;
R gives chlorophyll green colour
in translation/ joining of large and small subunits (of ribosomes) ;
enzyme, cofactor/ activator/ described ; idea of role in enzyme catalysis
A correctly named enzymes, e.g. DNA polymerase
AVP ;
e.g. stabilizing, cell wall/ proteins /nucleic acids / membranes ;
important in energy transfers /ATP synthesis ;
DNA, synthesis /replication ;
ref. to role in, light absorption/ capture (for photosynthesis) ;
67
Explain how the tertiary structure of the protein results in one being globular
folding / coiling (to form tertiary structure) ;
ref. interaction of, side chains / R groups (of amino acids) ; R react
two of ionic / electrovalent, bond
hydrogen bond
disulfide bonds
hydrophobic interaction
Van der Waal's (forces) ; one mark only for any two
hydrophobic, side chains / R-groups / amino acids, in centre / AW ;
A hydrophobic region faces, towards centre / AW
or
amino acids with hydrophilic R groups face, outwards / watery environment / AW ;
A hydrophilic amino acids for hydrophilic R groups
68
Outline the stages occurring in transcription.
DNA/ gene/ MUC5AC, unwinds /AW ; I unzips
2 H-bonds break between, (complementary) bases / base pairs / strands ;
I unzips
3 one / a, strand, acts as template/(complementary) copied ;
I ref. to, sense/ coding and antisense/non coding
4 ref. to (involvement of) RNA polymerase ;
I ref. to direction of, movement/ strand formation
5 (free) complementary RNA nucleotides added ;
A described in terms of correct base-pairs (C with G and A with U minimum)
6 step-by-step/ sequentially /AW ;
7 sugar phosphate backbone sealed/ phosphodiester bonds formed ;
A sugar phosphate backbone formed
8 (product is) messenger RNA/ mRNA ; A primary transcript
9 AVP ; e.g. transcription factors required to initiate transcription
RNA polymerase binds to promoter (sequence)
helicase unwinds
ref. to activated (RNA) nucleotides
ref. to proof reading
(transcription ends at) transcription terminator
69
a) Explain why red blood cells can be maintained in an intact state by keeping them in a normal
saline solution.
same, water potential/Ψ(inside + outside)/ no water potential gradient ;
A same solute potential I osmotic potential
(so) no, net/ overall, movement of water (molecules) ;
A osmosis does not occur
70
Suggest one component of blood plasma that could enter red blood cells and describe
how it would cross the cell surface membrane.
```
oxygen
carbon dioxide
steroids / steroid
hormones. moved by (passive) diffusion
A movement from high
to low concentration through the
to low concentration
(phospho)lipid bilayer/
hydrophobic core (of
membrane)
```
```
or
glucose
amino acid(s)
named amino acid
mineral/ inorganic, ions
named ion e.g.
sodium ions /Na+
,
magnesium ions / Mg2+
chloride ions /Cl ,
hydrogen ions
hydrogen carbonate
ions /HCO3
phosphate ions /HPO4
2
potassium ions (K+
)
facilitated
diffusion ;
A active transport
A cotransport
```
```
how it cross the membrane
transport(er)/ carrier/
integral/ intrinsic /
transmembrane, protein ;
A channel protein for
facilitated diffusion
A pump protein for active
transport
```
71
Outline briefly how a tumour forms.
uncontrolled/AW, mitosis /(mitotic) cell division/ cell replication/ cell cycle ;
either
2 one example of a change occurring in a healthy cell
e.g. proto-oncogene to oncogene
mutation of/ switching of, tumour suppressor gene
uncontrolled growth
increase in growth proteins
shorter interphase (of cell cycle)
(rapid) DNA replication
cells do not respond to signals (from other cells)
or
further detail of tumour formation ;
e.g. cells immortal/ no apoptosis / no programmed cell death
no contact inhibition/ cells continue to grow when they contact other cells
cell cycle checkpoints not controlled
abnormal/AW, mass of cells formed
undifferentiated/unspecialised, cells / tissue/ mass
cells do not function (as tissue of origin)
72
Outline the features of facilitated diffusion of glucose molecules.
transport/ transporter/ carrier, protein ; R pump protein
specific protein ;
glucose, binding site / AW ; I glucose binds R glucose receptor
specific binding site (in protein) = 2 marks
(glucose binding causes) conformational change ; AW, e.g. changes shape
passive / no energy required/ no ATP required ;
movement is, down the concentration gradient/ from high to low
concentration ; must be in context of through the membrane protein
73
Outline what occurs during early prophase so that chromosomes become visible in late
prophase.
coiling/ supercoiling/ condenses / condensation ;
| A become shorter and thicker
74
Describe the structure of the chromosome in late prophase.
```
accept from labelled diagram
two chromatids ;
identical/ sister, chromatids ;
joined by a centromere ; A kinetochore
one from
(reach chromatid) DNA complexed with protein
histone proteins / histones ;
telomeres at end of chromatids
```
75
State two differences between the chromosome at metaphase and the chromosome at late
anaphase.
metaphase versus anaphase
idea of single chromosome of two chromatids versus two separated
chromatids / daughter chromosomes
e.g. two chromatids versus, one chromatid/one daughter chromosome ;
sister chromatids joined at centromere versus chromatids separated
distance between sister chromatids zero versus increasing distance between
chromatids
share a centromere versus do not share a centromere/ centromere divides
two DNA molecules versus one DNA molecule ;
at, equator/ metaphase plate versus towards / at, poles ; R centre R ends
linear/ straight versus V shape/AW ;
76
One of the functions of a plant hormone known as cytokinin is to act as a cell signalling
molecule and promote cytokinesis.
Suggest how cytokinin acts as a cell signalling molecule.
acts at target cell ;
binds to receptor ; R receptor cells allow ecf for other mps
R trapped/ caught
ref. specificity ; A receptor complementary (shape) for cytokinin
A cytokinin fits into receptor this is also mp2
A recognition of cytokinin by receptor
receptor (located) in, cell surface/ plasma, membrane ;
A cell membrane A phospholipid bilayer A transmembrane receptor
sets off/AW, response in the cell/ described response(s) ; e.g.
triggers secondary messenger
activates enzyme(s)
I signals / causes / stimulates, cell to divide/ cytokinesis
(acts) extracellularly / extracellular signal or (acts) intracellularly / intracellular
signal ; must be in context of candidate’s answer
77
glycogen branching enzyme is another enzyme that is required for glycogen synthesis.
Suggest why glycogen branching enzyme is needed in addition to glycogen synthase
to form / has, (glycosidic α) 1–6, bonds / links (to make branches) ;
ref. to different shaped/ specific / complementary, active site required to form
bonds (for branching) ;
78
Explain why the hydrogen bonding between the two strands of DNA is important for it to
carry out its functions.
1 important in contributing to 3-D structure of molecule / AW ;
2 many hydrogen bonds so, gives stability / strands not easily separated / long lasting ;
AW
3 (individual) hydrogen bonds (more) easily broken (than covalent bonds) ; A
hydrogen bonds weak / hydrogen bonds can be broken
consequence
4 (so strands can be separated) for (DNA) replication ; A description
5 (so strands can be separated) for (DNA) transcription ; A description
6 hydrogen bonds only form between, specific bases / named base pairs, so, few
mistakes / faithful replication / AW ;
7 idea that hydrogen bonds can easily re-form (without chemical reaction) ;
79
Suggest the significance of:
| (i) DNA being very stable
sequence will not (spontaneously) change / AW ; A decreases chance of mutation
(so) gene products / proteins, produced will always be functional ;
maintains all, genetic information / AW, throughout life of cell ;
same, genetic information / AW, passed on to, daughter cells / offspring ;
AVP ; e.g. maintains size so still enclosed within nucleus
80
Suggest the significance of:mRNA being highly stable.
translation / protein synthesis, will stop when mRNA breaks down ;
allows re-use of nucleotides (for other mRNA) ;
ref. to control of gene expression ; A prevents too much product forming
ref. to control of cell activity / fast response to changing rquirements ;
ref. to efficiency in energy use ;
81
Describe the structure of the cell surface membrane
phospholipid bilayer ;
A lipid bilayer
2 phospholipids have, phosphate / hydrophilic, heads, and, hydrophobic tails / fatty
acid chains ;
3 ref. to, labile nature of bilayer structure / phospholipid (molecules) moving (within
their monolayer) ;
4 protein molecules, interspersed/ scattered/not a complete layer/AW ;
5 many /AW, different /AW (protein molecules) ;
6 example of type of protein ;
7 idea of (most) proteins, moving/not in fixed position ;
8 reference to cholesterol ;
82
State two differences between the cell structures used in translation in prokaryotes and
eukaryotes.
(b) different, structure/rRNA, (of ribosomes) ;
(ribosomes), larger/ 80S, in eukaryotes or smaller/ 70S in prokaryotes ;
(some) attached to/AW, (eternal surface of) RER in eukaryotes ; ora
A only found in cytoplasm in prokaryotes
83
State one use for phosphates in organisms.
```
phosphate
any one relevant ;
e.g. part of structure of
AMP/ADP/ATP
nucleotide
nucleic acid/DNA/RNA/ polynucleotide
phospholipid
A phospholipid bilayer
phosphorylation/ enzyme activation
bone tissue
```
84
State one use for nitrates in organisms.
```
nitrate
any one relevant ;
e.g. (nitrogen for) amino acids / proteins / enzymes / named (e.g. haemoglobin)
AMP/ADP/ATP
nucleotide
nucleic acid/DNA/RNA/ polynucleotide named nitrogen base (adenine/ cytosine/
thymine/ uracil/ guanine)
(some) phospholipids
```
85
Lemon juice contains citric acid. Adding even a small amount of diluted lemon juice to
apple slices slows the appearance of the brown colour.
Suggest an explanation for this observation.
enzymes work in a limited pH range / either side of optimum pH rate decreases ;
(acid so) presence of H+
ions, partially denatures / denatures (some), enzymes ;
further detail ; e.g. ref. to breaking ionic or hyrdrogen bonds
change of active site shape means substrate can no longer fit ;
AVP ; e.g. ref. to antioxidant effect of, lemon juice / citric acid / vitamin C
86
Describe the changes that occur during prophase in an animal cell.
appearance of chromosomes / condensation of chromatin/AW ;
chromosomes visible as two, sister chromatids / chromatids joined by a centromere ;
spindle formation/ spindle fibres form/ microtubules assemble/AW ;
centrioles, move to/reach, opposite poles ;
R sides / ends
disappearance of nucleolus ;
disassembly / breakdown of, nuclear envelope ;
A nuclear membrane
87
Describe the process of active transport.
b) transport is against the concentration gradient/AW ;
requirement of, energy /ATP ;
use of, membrane/ carrier/ transport/ pump, protein ;
R channel/pore, protein
ref. to conformational change (of pump protein) ;
ref. to specificity ;
88
Explain what is meant by transcription.
) (i) making a (complementary) copy of, DNA; A a gene
ref. information/AW, for production of a polypeptide ;
one (DNA) strand acts as a template ; AW
production of (pre) mRNA ;
detail of process ; e.g. assembly of nucleotides
RNA polymerase
89
Describe how proteins become denatured at high temperature and explain how this could
lead to damaging cell membranes.
loss of, tertiary structure / quaternary structure/ secondary structure ;
A loss of shape of active site in correct context
2 loss of globular, shape/ structure/ form ;
3 breakage of, ionic / hydrogen/ hydrophobic, bonds / interactions ;
to max 2
4 loss of function of (membrane) proteins ;
5/6 detail ; ;
e.g. transport of, polar molecules / ions, impaired AW
loss of cell to cell adhesion
unable to receive cell signals
loss of enzyme function
7 ref. to membranes, become leaky / lose partially permeable nature ;
A cannot regulate, entry / exit, substances
8 disrupt interaction between protein and phospholipid bilayer/ described ;
90
Suggest the differences in the cell cycle of a cancer cell compared with that of a normal
cell of the same type.
cell cycle shorter/ interphase shorter/ division more frequent ;
(cell cycle) checkpoints not controlled ;
uncontrolled (growth/division)/AW ;
AVP ; e.g. no differentiation (into epithelial cell)
A no cell death/apoptosis
91
Explain how this drug acts as a competitive inhibitor
(ACE) inhibitor/ drug, has similar shape as, substrate/polypeptide ;
2 complementary (shape) to active site (shape) ;
3 binds to/ fits into/ enters, active site (of ACE enzyme) ;
A forms enzyme-substrate complex
4 substrate cannot, enter/ bind ;
A competes with substrate for active site
A no/few/prevents formation of, ES complexes
5 reduces rate of, reaction/ formation of angiotensin/ product formation ;
92
State two properties of water which make it possible for organisms such as
Chlamydomonas to live in water.
) any two from
1 good solvent/ polar (for substances needed by the organism ) ; AW
2 transparent/ allows light through, (for photosynthesis) ;
3 liquid over wide range of temperatures ;
4 high specific heat capacity ; A description
5 high latent heat of vaporisation ;
6 ref. to density ; e.g. ice/ solid, less dense than, water/ liquid
circulation bringing nutrients to surface
7 ref. to low viscosity for locomotion ;
93
histidine, position 57
• aspartate, position 102
• serine, position 195.
In the functioning enzyme, these three amino acids are close together in the active site.
Explain how the structure of the protein makes this possible.
folding/ coiling, (of polypeptide chain) ;
tertiary structure ;
(held in position by) ref. to R group interactions ;
A two or more bond types in context
brings distant, amino acids / parts of the chain, close ; AW
94
features of phagocyte
small quantity rough endoplasmic reticulum
few ribosomes
some lysosomes
some vacuoles / vesicles / phagosomes present
lobed nucleus
absent Golgi
few mitochondria
plasma / cell (surface), membrane invaginations, inholdings
95
plasma membrane
many mitochondria
no invaginations, no infoldings plasma / cell (surface), membrane
Golgi present
round nucleus
vacuoles / vesicles / phagosomes absent
many ribosomes
large
amount of rRER
96
Explain how the hydrogen bonds between water molecules affect the properties of water and help to make water an ideal environment for many organisms.
AVP answers must be in context to a watery external environment ref to molecules held together / strong attraction / AW ; A cohesion between water molecules detail of hydrogen bonding, e.g. slight –ve charge on O, slight +ve charge on H ; A water molecules are polar high boiling point / boils at 100oC ; high latent heat of vaporisation ; so water is liquid over wide range of temperatures ; (liquid so) provides, support / buoyancy ; high (specific) heat capacity ; stable temperature / temperature of water does not change quickly ; large amount of energy needed to be transferred from water for it to freeze / high latent heat of fusion ; maximum density at 4°C / less dense at 0°C ; provides surface tension ; ref solvent ; AVP ; AVP ; e.g. ref to surface dwellers, less need for support tissue, stable habitat qualified, ref upwelling currents ice floats / insulates
97
describe how the structure of glycogen differs from the structure of amylose
branched ; 1–6 , glycosidic, links / bonds ; not, coiled / helical ;
98
describe the advantages for organisms in storing polysaccharides, such as glycogen, rather than storing glucose
compact so large quantity can be stored ; insoluble so no osmotic effect ; glucose would lower water potential ; A decrease, more negative (so) water would enter and cell volume would increase ; (so) plant cells would need thicker cell walls / animal cells might burst ; glucose reactive molecule ;
99
Explain the advantage of studying cells, such as transfer cells, with the electron microscope rather than the light microscope.
higher / greater resolution / resolving power ; ora A 0.5 nm (0.0005 µm) compared with 200 nm (0.02 µm) because of shorter wavelength ; A smaller more detail can be seen / much clearer (at the same magnification) / can see two points that are close together ; can see cell structures that are not visible in the LM ; A e.g. ribosomes / membranes can see detail of structures just visible in LM with e.g. ; A mitochondrion / chloroplast
100
Explain the importance of disulfide bonds in protein molecules, such as antibodies
(disulfide) bonds are between, cysteine(s) / cysteine residues ; A between R groups S-H S-H 2 covalent bond ; 3 strong bond / not easily broken ; 4 hold, polypeptides / chains / protein , together ; R proteins / strands 5 (in protein with) tertiary / quaternary (structure) ; 6 maintain shape / stop loss of shape / prevent deforming ; A 3D structure R structure unqualified
101
Describe three roles of the proteins in cell surface membranes.
(carrier / channel protein for) facilitated diffusion / described ; A action of (co-) transport protein described 2 (carrier protein for) active transport / described ; 3 cell recognition / distinguishing self from non-self / act as antigens / AW ; 4 receptor ; A binding site qualified in terms of, hormones / neurotransmitters / cytokines / cell signalling molecules ; 5 T-cell receptor / described ; 6 cell (to cell) adhesion / described ; 7 enzyme ; 8 form (hydrogen) bonds with, water / fluid surroundings, to stabilise membrane ;
102
Describe how the student would test for the presence of starch.
iodine in potassium iodide solution / I in KI solution / iodine solution ; R iodine / iodine test A if ‘solution’ not used, but clear that it is a solution
positive result = (from yellow / red brown to) blue-black / blue / black ; R blue-black precipitate
103
what happens in mitosis anaphase
1 chromosomes / chromatids, move to / at, poles / centrosomes ; 2 attached to, spindle / microtubules ; 3 by, centromeres / kinetochores ; A centromeres leading 4 pulled by, microtubules / spindle fibres / AW ; A contracting / shortening / disassembling
104
suggest the disadvantages of using an electron microscope to study mitosis
these points are independent 1 cannot follow, movement of chromosomes / AW ; e.g. ‘processes in mitosis’ 2 can only view dead material ; 3 sections have to be thin ; 4 overstaining obscures details (of chromosomes) ; A artefacts 5 cannot see, all of the chromosomes / whole chromosomes ;
105
Some cells take in bacteria by endocytosis. Explain how endocytosis occurs at a cell surface membrane.
attachment (of bacteria) to receptor(s) ; AW
ref. ability to attach to antibody (bound to antigen on bacterium)
infolding / invagination / AW, of membrane ; A membrane engulfs A pseudopodia
form (round bacterium)
fusion / AW, of membrane ;
formation of, vacuole / vesicle
106
primary structure
sequence / arrangement / order / AW, of amino acids
107
secondary structure
α, helix / helices ;
| β / pleated, sheet
108
tertiary structure
folding of, one / each, polypeptide / globin ; A coiling
(shape) held in place by interactions between, R-groups / side chains ;
A three or more named interactions
109
quaternary structure
(arrangement / interaction, of) four polypeptides / four globins / two α and two β
globins ; A chains A ref. to more than one polypeptide if specific ref. to α and β
chains
haem / prosthetic group ; A porphyrin
110
State the function of collagen in the walls of arteries.
withstands pressure ;
prevents, overstretching / AW ;
prevents, bursting / rupture / AW ;
111
lysosome
contains /storage of, hydrolytic / digestive, enzymes
112
Golgi vesicle
transfer / transport, of, protein / lipids ;
113
Golgi (body / complex /apparatus)
modification of protein glycosylation / described modification of lipid pack(ag)ing (of), protein / lipids production of, (Golgi / secretory) vesicles / lysosomes ignore synthesis of protein
allow ecf if smooth endoplasmic reticulum
114
rough endoplasmic reticulum
protein / polypeptide, synthesis translation modification of protein / described (e.g. folding, glycosylation) protein transport (to Golgi)
115
smooth endoplasmic reticulum
lipid / sterol / cholesterol / steroid, synthesis ;
116
mitochondrion
one from ; aerobic respiration ATP synthesis/ production / AW link reaction Krebs cycle oxidative phosphorylation
117
nucleolus
production of, ribosomes / rRNA / tRNA ;
118
cell surface membrane
control of movement of substances into and out of the cell
119
Describe the molecular structure of glycogen and explain how this structure makes it suitable for storage.
polysaccharide ;
chains of α-glucose (residues) ; only need α once α1–4 glycosidic bonds / links ;
branches ; (because of) α 1–6 glycosidic bonds ; only need glycosidic once
idea that many ‘ends’ to easily, add / remove, glucose ; compact / AW ; insoluble ; will not affect, water potential / ψ ; AW AVP ;
120
Suggest why cholesterol is packaged into lipoproteins before release from liver cells into the blood.
lipoproteins are soluble ;
cholesterol is not water-soluble ; cholesterol surrounded by / lipoproteins have, phospholipid heads / proteins, that are hydrophilic ; AW
allows transport in blood ;
121
Explain why cells of the body need to be supplied with cholesterol
cholesterol needed for making / components of, membranes ; membrane stability ; regulating the fluidity of, membranes / phospholipid bilayer ; production of, steroid hormones / named steroid hormone ; AVP ; e.g. helps prevent entry of, ions / polar molecules
122
State one function of the Golgi apparatus other than the packaging of substances into vesicles for transport
glycosylation / adding sugar molecules to proteins / making glycoproteins ; A modifying proteins
phosphorylating proteins ; cutting / folding, proteins ; assembly of polypeptides into proteins (with quaternary structure) ;
AVP ; e.g. lipid synthesis
ref. lysosome formation
123
ions cross cell surface membranes using facilitated diffusion or active transport. Explain why ions cross cell surface membranes by these mechanisms and not by simple diffusion.
(sodium ions are) charged / hydrophilic ; I ref. to size / polar cannot pass through hydrophobic, core / interior, (of phospholipid bilayer) ;
(so) must pass through, transport proteins / carrier proteins / channel proteins (facilitated diffusion) ;
ref. to hydrophilic (amino acids lining) channels ; ref. to active transport only way to move sodium ions against concentration gradient
124
Suggest why a student would not be able to see a microtubule using a good quality light microscope
resolving power, not high enough / poor / low / 250 nm / 0.25 µm / half the wavelength of light (used) ; A resolution for resolving power resolution limited by wavelength of light ; microtubule (diameter) too small to interfere with light waves / AW ;
125
Outline the role of microtubules in mitosis.
forms part of, spindle / spindle fi bres ; attachment to centromeres / chromosomes / chromatids ; detail ; e.g. movement of, sister chromatids / (daughter) chromosomes, to (opposite) poles / spindle fi bres shortening at anaphase
126
Describe how the structure of starch makes it suitable for its function
amylose, spiral / spiralled / helix / helical ; R α-helix R coiled amylopectin branched ; compact / AW ; qualifi ed ; e.g. for maximum storage (so) insoluble / osmotically inactive / inert ; amylopectin, many free ends (so easily supplies glucose) ; (amylose / amylopectin / starch) contain glucose for immediate use as respiratory substrate (on hydrolysis) ;
127
o outline the process of cell signalling
chemicals released are circulating hormones ; hormones combine with cell surface receptors ; on target cells / cells where transcription is triggered ; action of kinases and phosphatases (within the cell) lead to (specifi c) response ; specifi c response = transcription / production of mRNA ;
128
Compare the structure of an ATP molecule with DNA nucleotide
similarities both have, pentose / 5C sugar ; both have, organic / nitrogenous, base ; A both have purine (base) both have phosphate ; differences (ATP) ribose not deoxyribose ; (ATP) adenine not guanine ; (ATP) three phosphates, not one
129
Explain why it is important that the daughter cells produced during a mitotic cell cycle in humans are genetically identical.
so they have the same number of chromosomes (as parent cell) ;
idea that cells would be rejected (if genetically different) ; ref. to role of the immune system in removing genetically different cells ;
130
what happens in cytokenisis
chromosomes, uncoil / become diffuse / decondense / AW ; A chromosomes unwind / become long and thin A chromosomes become chromatin A cell enters interphase spindle breaks down / microtubules disassemble / AW ; R disappears
nuclear envelope, reforms / forms / forming ; A nuclear membrane R (re)appears nucleolus / nucleoli, reform(s) / forms / forming ; R (re)appears
cell membrane, drawn together / furrows / AW ; idea of role of, microfilaments / AW, in ‘drawstring’ effect ;
division of cytoplasm / cell separation / cleavage / cleavage furrow develops ; A cytokinesis if not credited in (i) cell membrane fuses ; [3 max]
131
Describe the process of exocytosis.
vesicle / vacuole, moves towards, cell, surface / membrane ;
A plasma membrane R if lysosome
2 fusion / described, of vesicle with membrane ; R attach / bind / combine
3 ref. to (fluid nature of) phospholipids ;
4 contents / AW, secreted / released / exported / removed / emptied / excreted ;
A waste material / digested material
5 active process / energy-requiring / ATP used / AW ;
R ‘active transport’ R endocytosis
132
Suggest two other ways in which the polypeptide chain is modified to produce the
functioning protein.
the removal of the first amino acid, methionine,
from a newly formed polypeptide chain to make a functioning protein.
1 secondary structure / α-helix / β-(pleated) sheet ;
2 tertiary structure / description / folding / complex 3D shape ;
3 formation of named bond(s) ; R if peptide bond in list
4 quaternary structure / description (e.g. assembly of polypeptides) ;
5 glycosylation / formation of glycoproteins / addition of carbohydrate(s) or sugar(s) ;
R hydrocarbon chain
6 addition of, non-protein portion(s) / prosthetic group(s) / named example ;
A haem / iron / Fe / copper / Cu / magnesium / Mg / AW
7 removal of some amino acids ; R one amino acid
8 polypeptide(s) cut into two or more pieces ;
9 AVP ; e.g. ref. to exposure to water molecules and folding
R ref. to amino acids coded for by stop codons
133
Any cell containing one complete set of chromosomes.
haploid
134
Describe the structural differences between amylopectin and amylose
1 amylopectin branched / AW; ora
2 amylose, spiral /spiralled / helix / helical; ora
R α – helix
R coiled
allow ecf from mps 1 and 2 to award mp 3
3 amylose (α) 1 – 4 linkages but 1 – 4 and 1 – 6 linkages in amylopectin / amylose
has 1 – 4 linkages only;
accept from clearly labelled diagram(s)
135
State one role of magnesium ions within chloroplasts
any one valid; e.g.
1 for chlorophyll, structure / synthesis / formation / AW
2 for ATP functioning A required for energy transfers
3 for enzyme, functioning / cofactor
4 signalling ion / regulates carbon fixation
5 for, DNA / RNA, synthesis
6 stabilises, DNA / RNA, structure
7 required in, translation / joining, small and large subunits (of ribosomes)
136
c State the structural features of DNA that make it a stable molecule
complementary bases / base pairing, hold(s) strands together / AW;
2 (because of) many hydrogen bonds;
R if between adjacent nucleotides
if mp 1 and 2 not awarded
1/2 hydrogen bonds hold strands together;
3 sugar-phosphate backbone / AW, with covalent / phosphodiester, bonds;
4 double helix structure protects bases;
5 AVP; coiling protects from, chemical / enzyme, attack
137
DNA has been described as a ‘carrier of coded information’.
| Explain this statement.
1 (information is) ref. (different) sequence / order of bases / nucleotides (in the
polynucleotide strand);
A described in terms of sequence of bases
2 DNA / gene, contains / AW, information for the synthesis of a, polypeptide / protein /
enzyme;
3 idea that (coded because) information becomes sequence of amino acids;
4 idea that information passed on (cell to cell / parent to offspring);
138
i) State the role of mitosis in cell division of somatic cells.
oduce genetically identical daughter epithelial cells for)
1 (for tissue) repair ;
R cell repair
2 idea of replacing, dead / destroyed / damaged / worn-out / AW, cells ;
A replacement of cells, unqualified if mp 1 gained
3 ref. protection of, underlying tissue / muscle and elastic layer /
tunica media / AW ;
4 meiosis produces, haploid cells / cells with n chromosomes / cells with one set of
chromosomes ;
A cells with half the number of chromosomes
5 meiosis for gamete formation ;
A sex cells
R meiosis in gametes
139
Explain why the somatic cells undergo mitosis and not meiosis.
(mitosis to), maintain genetic stability / produce genetically identical cells /
produce clones ora
or
meiosis produces genetically different cells ;
(mitosis), ensures cells retain function / cells function as tissue / AW ;
(mitosis) maintains chromosome number ;
A maintains, diploid number / 2n
meiosis produces, haploid cells / cells with n chromosomes / cells with one
A cells with half the number of chromosomes
meiosis for gamete formation ;
A sex cells
R meiosis in gametes
140
Suggest and explain what would happen to bacteria placed in a solution with a water
potential more negative than their cell contents.
cell contents shrink / cytoplasm shrinks ; AW
R cell shrinks unless clear that the cell wall remains, intact / same size
2 cell (surface) membrane / plasma membrane, peels away / AW, from cell wall ;
A plasmolysis occurs / cell becomes flaccid
3 (movement of) water out by osmosis ;
4 down water potential gradient / from high to low water potential / to lower
water potential /from less negative to more negative water potential ;
A ψ for water potential
141
Explain the effects of a non-competitive inhibitor on the rate of enzyme activit
1 reduces (rate of enzyme activity) ;
2 binds at a site on the enzyme other than at the active site/allosteric site ;
3 change in tertiary structure ;
4 change in shape/ conformation/ configuration of active site ;
5 substrate unable to bind/ product unable to form/ES complexes do not form/ fewer
ESC ;
6 AVP ; e.g. Vmax not reached/ increasing substrate concentration no effect
142
Explain how the tertiary and quaternary levels of protein structure of the haemoglobin
molecule contribute to its role in the transport of oxygen.
1 globular (shape) ; A rounded/ spherical R circular
2 hydrophilic, amino acids /R-groups, face cytosol
or
hydrophobic, amino acids /R-groups, to the interior ; AW
3 (so) soluble or dissolved in cytoplasm/ cytosol ;
4 ref. to haem/ prosthetic (group)/porphyrin (ring)/Fe2+/
ferrous ion/iron (ion), binding
oxygen ; R forms bonds with
5 four polypeptides / haems /AW, so 4 oxygen molecules / 8 oxygen atoms ;
A four polypeptides, each carrying an oxygen molecule/O2
6 cooperative binding/allostery / described ;
7 AVP ; e.g. tertiary structure allows association of prosthetic group
143
Double membrane-bound organelle, absent in animal cells, that produces ATP.
A = chloroplast
144
Partially permeable membrane surrounding the large permanent vacuole of plant cells
tonoplast
145
Formed from microtubules during mitosis
/ spindle fibre(s
146
Has peptidoglycan as one of its major component
(bacterial / prokaryotic) cell wall
147
Site of assembly of 80S ribosomes
nucleolus
148
State two structural differences between fructose and sucrose.
fructose no glycosidic bondmonosaccharideone ring (structure) fewer/ less, C and H and O atoms. powder
sucrose
glycosidic bondglycosidic bond sucrose is a disaccharide made from the monosaccharides glucose and fructose two rings crystalline
149
Outline how the properties of water make it ideal as the largest component of plasma.
1 (good) solvent ; R organic solvent
2 statement linking solvent properties to role of plasma ; e.g.
standalone statements do not need mp1
polar molecules /ions /ionic compounds /named substance(s),
dissolve in, water/ plasma R blood cells
ions dissociate, in water/ plasma
many /AW, substances dissolve in, water/ plasma R blood cells
water is attracted to (many different) substances
water/ plasma, is the transport medium for substances /transports substances
presence of solutes to maintain (constant) water potential
3 cohesion between water molecules /water is cohesive ;
A water molecules are sticky
4 so, continuous /uninterrupted /AW, blood flow ; in context of mp3
5 high specific heat (capacity) ;
6 statement linking high specific heat capacity to role of plasma ;
allow ecf for high heat capacity / specific heat capacity
e.g. helps, stabilise /(body to) regulate, temperatures
helps maintain constant (blood) temperature
water resists changes to temperature
7 high (latent) heat of, vaporisation / evaporation ;
8 in body temperatures, plasma stays liquid /water does not evaporate ; AW 9 low compressibility ; A incompressible
10 maintains efficient blood flow/ helps to push blood through vessels ; AW
11 low viscosity ;
12 allows efficient circulation of blood /AW ;
13 pH 7 / neutral ;
14 ref. to stability proteins ; A prevents denaturation
150
E. carotovora is a rod-shaped bacterium.
| Explain why two of the bacterial cells in do not appear rod-shaped in pictures
cells not sectioned in LS ; ora
| A cross-section shown / depends on angle of cut / cut in different planes / end view
151
Describe how a DNA molecule replicates.
DNA (double helix), unwinds / AW ; A uncoil
2 hydrogen bonds between (complementary) bases broken ;
ignore DNA unzips
3 complementary, base / nucleotide, pairing ; A A-T and C-G
4 phosphodiester bonds ;
5 both strands used as templates ; A both strands are copied
6 produces two identical DNA molecules ; A ‘DNAs’
7 semi-conservative / each new DNA = one ‘old’ and one ‘new’ strand ;
8 ref to DNA polymerase ;
9 correct ref to other named enzyme ; e.g. helicase (unwinds), topoisomerase (cuts
backbone), ligase (formation of phosphodiester bonds)
10 ref to Fig. 5.1 ; e.g. described dotted lines as H bonds that need to be broken
look for annotations on Fig. 5.1
11 AVP ; e.g. replication fork(s), replication bubble(s), antiparallel nature,
Okazaki fragments, activated nucleotides (3 phosphate groups)
152
chloroplast
```
name chloroplast(s) ;
function (site of) ; photosynthesis
light-dependent, reactions / stage (of photosynthesis)
light, absorption / AW
light-independent, reactions / stage (of photosynthesis)
Calvin cycle
carbon fixation
photophosphorylation
A ATP synthesis
ignore (treat as neutral) ref. to, glucose / oxygen, synthesis
ignore chlorophyll
R light / dark, stage / reactions
```
153
lysosome function
n = contains / storage of hydrolytic / digestive, enzymes
154
Golgi / secretory, vesicles =
transport, protein / lipids
155
name rough endoplasmic reticulum ;
R RER or rough ER R endoplastic
function (site of) ; protein / polypeptide, synthesis
translation
modification of protein / described (e.g. folding)
protein transport (to Golgi)
(incorrect name)
156
) Describe what is meant by the term competitive inhibitor.
binds with / fits into / AW, active site ; R collides with / reacts with
complementary shape to active site / similar shape to substrate ;
A same shape as substrate / same or similar structure as substrate
fewer, enzyme-substrate / E – S, complexes ;
A no ESC in context of one enzyme
A fewer successful collisions between enzyme and substrate
A prevents formation of E – S complexes
reduces rate of / slows (enzyme) reaction ;
A reduced enzyme activity / A less product formed
157
Describe the role of the ribosome in translation.
) all points except mp3 may be taken from a labelled/annotated diagram
1 ref. to, attachment / AW, to mRNA ;
2 idea of two codon attachment, sites / space, for six bases or nucleotides ;
3 mRNA has code for sequence of amino acids (in a polypeptide) ;
4 (ribosome) provides sites for attachment of two tRNA (molecules) ;
A implied
5 each tRNA has a specific amino acid / AW ;
6 (mRNA) codon – anticodon (tRNA), binding ;
A description in terms of complementary base pairing
A ‘matching’
7 formation of peptide bonds (catalysed by peptidyl transferase) ;
8 idea of ribosome moving along mRNA one codon at a time ;
158
Describe the structure of a cellulose molecule and explain how cellulose is a suitable
material for the cell walls of plants.
1 (polymer / polysaccharide of) β-glucose ; allow glucose if β given for bond
2 (1-4, β) glycosidic, bonds / linkages ; A glucosidic
R if 1-6 also given
3 ref. to (β) glucose units, linked at 180° to each other / alternately orientated / AW ;
4 many –OH groups projecting out (in different directions) ;
5 unbranched (polymer) / straight chain / linear ;
6 many hydrogen bonds between molecules ;
7 (straight chain allows) molecules lie parallel to each other ;
8 (form) microfibrils ;
9 many microfibrils form (cellulose) fibres ;
10 ref. to fibres at angles / criss-cross / AW ;
11 (cellulose) cell wall is permeable ;
A idea of many gaps, in wall / between fibres, allowing passage of water / (named)
substances
12 ref. to strength to, prevent cell bursting / withstanding (turgor) pressure / AW ;
159
State two similarities and two differences between facilitated diffusion and active
transport.
similarities
use, membrane / integral / intrinsic / transmembrane / transport / carrier, proteins ;
R channel proteins
are specific / have specific binding site ;
involve conformational / shape, change of protein ;
(movement of (named)), ions / polar molecules / water soluble molecules / hydrophilic
molecules / lipid insoluble molecules ;
I large molecules A charged
(movement) across membranes / into or out of the cell ; [max 2]
differences A ora
facilitated diffusion is (movement from), high(er) to low(er) concentration /
down concentration gradient ; ora A diffusion gradient
I ‘along a concentration gradient’
facilitated diffusion, is passive process / does not require energy and / or ATP (from the cell) ;
R ATP energy
R the cell makes energy for active transport
160
Some enzymes are found in phloem tissue.
| Describe how enzymes catalyse reactions.
) answers may be general or in the context of phloem transport
active site (with shape) complementary to substrate ;
A description in terms of lock and key (either way round)
I structure
induced fit / described ;
substrate binds to active site / enzyme-substrate complex forms / ESC forms ;
ref. to specificity of enzymes ;
activation energy of reaction is lowered ;
example of how activation energy lowered ;
e.g. reactants held close together for bond formation
transfer of electrons
strain on bonds
alternative pathway
holding the substrate in such a way that the bonds needed to be broken are exposed
product released from, enzyme / active site ;
A enzyme can be used again / enzyme unchanged at end of reaction
161
Explain how the structure of a phospholipid molecule makes it suitable for its function in cell
membranes. You may label and annotate F
1 ref. to hydrophilic / polar, phosphate, head / group
and
hydrophobic / non polar, hydrocarbon / fatty acid, tails / chains ;
R if labelled correctly but incorrectly described in the text
2 ref. to forms part of a bilayer ;
3 (fatty acid) tails / chains, may be saturated or unsaturated ;
max 2 for function – mp4 to mp7
head
4 forms hydrogen bonds with water/ interacts with water/AW ;
5 stabilises the membrane ;
tails
6 idea that unsaturated fatty acids contribute to fluidity (of membrane) ;
7 barrier to, hydrophilic substances /water soluble substances /polar
substances /ions /AW ; ora
A movement of, non-polar/AW, substances
162
State two components of a cell surface membrane other than phospholipid molecules and
describe their function.
glycoprotein ;
one of
antigen /markers /tags / described in terms ‘self’ ;
receptor (for signalling molecule)/AW ;
cell recognition ;
cell adhesion ;
interacts /AW, with water to stabilise the membrane ;
cholesterol ;
one of
stabilises membrane ;
regulates /maintains /AW, fluidity of membrane ;
A in low temperatures increases fluidity / in high temperatures decreases fluidity
prevents passage of ions /polar molecules, through membrane ;
glycolipid ;
antigen /markers /tags / described in terms ‘self’ ;
cell adhesion ;
interacts /AW, with water to stabilise the membrane ;
protein ; I any qualification of component e.g. channel / carrier/ transport
receptor (for signalling molecule)/AW ;
enzyme / co-enzyme ;
anchoring cytoskeleton ;
for cell to cell adhesion /any named type e.g. desmosome, tight junction ;
channel / carrier, allows facilitated diffusion /description ;
A for, protein / carrier protein / channel protein /transport protein
carrier, for active transport / description ;
A for protein / carrier protein /transport protein
163
Explain how enzymes lower the activation energy needed to allow reactions to proceed
```
two from
1 provide an alternative pathway ;
2 brings reactants close together (in active site /to form ESC) ;
3 put a strain on the reactant(s) ;
4 so bonds, break /form, more easily ;
5 transfer of, charges /groups ;
6 AVP ; e.g. involvement of R groups
```
164
More mRNA molecules than tRNA molecules are synthesised in cells.
Suggest a reason for this
mRNA, less stable / broken down sooner / used only for a short time / does not last long /
is temporary / has short (half-) life ; I ‘used up’
tRNA is re-used (for a longer time); no ora
unless correct ref. to mRNA ‘shelf life’
165
tRNA molecules are synthesised inside the nucleus of eukaryotic cells.
Outline the process by which tRNA molecules are synthesised in the nucleus
1 gene for each tRNA (molecule) is transcribed ;
2 hydrogen bonds in DNA are broken ;
I unwinding /unzipping
3 one strand of DNA is the template ;
4 RNA polymerase ;
5 (free RNA) nucleotides joined together/ formation of phosphodiester bonds ;
I complementary base pairing
6 AVP ; e.g. correct ref. to helicase in breaking hydrogen bonds
