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exam quesitons Flashcards

1
Q

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule (2)

A
  1. Condensation (reaction)/loss of water;
  2. (Between) phosphate and deoxyribose;
  3. (Catalysed by) DNA polymerase;
    Reject if DNA polymerase joins AT/GC OR
    complementary nucleotides/bases OR forms
    hydrogen bonds
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2
Q

differences between DNA in the nucleus of a plant cell and DNA in a prokaryotic cell. (3)

A
  1. (Associated with) histones/proteins v no histones/proteins;
  2. Linear v circular;
  3. No plasmids v plasmids;
  4. Introns v no introns;
  5. Long(er) v short(er);
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3
Q

Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome. (2)

A
  1. DNA that does not code for protein/polypeptides
    OR
    DNA that does not code for (sequences of) amino acids
    OR
    DNA that does not code for tRNA/rRNA;
  2. (Positioned) between genes;
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4
Q

Give three ways in which the DNA in a chloroplast is different from DNA in the nucleus. (3)

A

In chloroplasts
1. DNA shorter;
2. Fewer genes;
3. DNA circular not linear;
4. Not associated with protein/histones, unlike nuclear DNA;
5. Introns absent but present in nuclear DNA;

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5
Q

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. (2)

A
  1. Triplets code for same amino acid
  2. Occurs in introns /non-coding sequence;
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6
Q

Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells. (5)

A

Comparisons
1. Nucleotide structure is identical;
2. Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;

Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones,
prokaryotic DNA is not;

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7
Q

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance, why?

A

Differences in base sequences
OR
Differences in histones/interaction with histones
OR
Differences in condensation/(super)coiling;

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8
Q

Messenger RNA (mRNA) is used during translation to form polypeptides.
Describe how mRNA is produced in the nucleus of a cell. (6)

A
  1. Helicase;
  2. Breaks hydrogen bonds;
  3. Only one DNA strand acts as template;
  4. RNA nucleotides attracted to exposed bases;
  5. (Attraction) according to base pairing rule;
  6. RNA polymerase joins (RNA) nucleotides together;
  7. Pre-mRNA spliced to remove introns.
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9
Q

Describe the structure of proteins. (5)

A
  1. Polymer of amino acids;
  2. Joined by peptide bonds;
  3. Formed by condensation;
  4. Primary structure is order of amino acids;
  5. Secondary structure is folding of polypeptide chain due to hydrogen
    Accept alpha helix / pleated sheet
  6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds;
  7. Quaternary structure is two or more polypeptide chains
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10
Q

Describe how proteins are digested in the human gut. (4)

A
  1. Hydrolysis of peptide bonds;
  2. Endopeptidases break polypeptides into smaller peptide chains;
  3. Exopeptidases remove terminal amino acids;
  4. Dipeptidases hydrolyse / break down dipeptides into amino acids
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11
Q

State three comparisons of genetic diversity

A
  1. The (base) sequence of DNA;
  2. The (base) sequence of mRNA;
  3. The amino acid sequence (of proteins);
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12
Q

Describe how breeding experiments could determine whether two
populations are from the same species.

A
  1. Breed the two mice together;
  2. (if Same species) produce fertile offspring.
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13
Q

Give two differences between mitosis and meiosis

A
  1. One division, two divisions in meiosis;
  2. (Daughter) cells genetically identical, daughter cells genetically different in
    meiosis;
  3. Two cells produced, (usually) four cells produced in meiosis;
  4. Diploid to diploid/haploid to haploid, diploid to haploid in
    meiosis,
  5. Separation of homologous chromosomes only in meiosis;
  6. Crossing over only in meiosis;
  7. Independent segregation only in meiosis;
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14
Q

Explain the advantage for larger animals of having a specialised system
that facilitates oxygen uptake. (2)

A
  1. Large(r) organisms have a small(er) surface area:volume (ratio);
    OR
    Small(er) organisms have a large(r) surface area:volume (ratio);
  2. Overcomes long diffusion pathway
    OR
    Faster diffusion;
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15
Q

Suggest and explain how a reduced tidal volume affects the exchange of
carbon dioxide between the blood and the alveoli.

A
  1. Less carbon dioxide exhaled/moves out (of lung)
    OR
    More carbon dioxide remains (in lung);
  2. (So) reduced diffusion/concentration gradient (between blood and
    alveoli);
  3. Less/slower movement of carbon dioxide out of blood
    OR
    More carbon dioxide stays in blood;
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16
Q

(a) Describe the gross structure of the human gas exchange system and how
we breathe in and out.(6)

A
  1. Named structures – trachea, bronchi, bronchioles, alveoli;
  2. Above structures named in correct order
    OR
    Above structures labelled in correct positions on a diagram;
  3. Breathing in – diaphragm contracts and external intercostal muscles
    contract;
  4. (Causes) volume increase and pressure decrease in thoracic cavity
    (to below atmospheric, resulting in air moving in);
    For thoracic cavity accept ‘lungs’ or ‘thorax’.
    Reference to ‘thoracic cavity’ only required once.
  5. Breathing out - Diaphragm relaxes and internal intercostal muscles
    contract;
    Accept diaphragm relaxes and (external) intercostal
    muscles relax and lung tissue elastic (so recoils).
  6. (Causes) volume decrease and pressure increase in thoracic cavity
    (to above atmospheric, resulting in air moving out);
    For thoracic cavity accept ‘lungs’ or ‘thorax’.
17
Q

Explain three ways in which an insect’s tracheal system is adapted for
efficient gas exchange.

A
  1. Tracheoles have thin walls so short diffusion distance to cells;
  2. Highly branched / large number of tracheoles so short diffusion
    distance to cells;
  3. Highly branched / large number of tracheoles so large surface
    area (for gas exchange);
  4. Tracheae provide tubes full of air so fast diffusion (into insect
    tissues);
  5. Fluid in the end of the tracheoles that moves out (into tissues)
    during exercise so faster diffusion through the air to the gas
    exchange surface;
    OR
    Fluid in the end of the tracheoles that moves out (into tissues)
    during exercise so larger surface area (for gas exchange);
  6. Body can be moved (by muscles) to move air so maintains
    diffusion / concentration gradient for oxygen / carbon dioxide;
18
Q

Explain two ways in which the structure of fish gills is adapted for efficient
gas exchange.

A
  1. Many lamellae / filaments so large surface area;
  2. Thin (surface) so short diffusion pathway;
19
Q

Describe the processes involved in the absorption and transport of
digested lipid molecules from the ileum into lymph vessels. (5)

A
  1. Micelles contain bile salts and fatty acids/monoglycerides;
  2. Make fatty acids/monoglycerides (more) soluble (in water)
    OR
    Bring/release/carry fatty acids/monoglycerides to cell/lining (of the
    iluem)
    OR
    Maintain high(er) concentration of fatty acids/monoglycerides to
    cell/lining (of the ileum);
    Accept lipid/fat for fatty acid/ monoglyceride
  3. Fatty acids/monoglycerides absorbed by diffusion;
    Reject if absorbed by facilitated diffusion
    Ignore if micelles themselves are being absorbed
  4. Triglycerides (re)formed (in cells);
    Accept chylomicrons form
  5. Vesicles move to cell membrane;
    Accept exocytosis for ‘vesicles move’
20
Q

Describe the role of micelles in the absorption of fats into the cells lining
the ileum.

A
  1. Micelles include bile salts and fatty acids;
    Ignore other correct components of micelles.
  2. Make the fatty acids (more) soluble in water;
    For ‘fatty acids’ accept fats / lipids.
  3. Bring/release/carry fatty acids to cell/lining (of the ileum);
    For ‘fatty acids’ accept fats/lipids.
  4. Maintain high(er) concentration of fatty acids to cell/lining (of the
    ileum);
  5. Fatty acids (absorbed) by diffusion;
21
Q

Explain the advantages of lipid droplet and micelle formation

A
  1. Droplets increase surface areas (for lipase /
    enzyme action);
  2. (So) faster hydrolysis / digestion (of
    triglycerides / lipids);
  3. Micelles carry fatty acids and glycerol /
    monoglycerides to / through membrane / to
    (intestinal epithelial) cell;
22
Q

suggest how golgi apparatus is involved in
the absorption of lipids.

A
  1. Modifies / processes triglycerides;
  2. Combines triglycerides with proteins;
  3. Packaged for release / exocytosis
    OR
    Forms vesicles;
23
Q

Suggest two ways the student could improve the quality of his scientific
drawing of the blood vessels in this dissection.

A
  1. Only use single lines/do not use sketching (lines)/ensure lines are
    continuous/connected;
  2. Add labels/annotations/title;
  3. Add magnification/scale (bar);
  4. Draw all parts to same scale/relative size;
  5. Do not use shading/hatching;
24
Q

Describe two precautions the student should take when clearing away after
the dissection.

A
  1. Carry/wash sharp instruments by holding handle
    OR
    Carry/wash sharp instruments by pointing away (from body)/down;
    Accept for ‘instruments’, a suitable named example,
    eg. scalpel
  2. Disinfect instruments/surfaces;
    Accept for ‘instruments’, a suitable named example,
    eg. scalpel
    Accept for ‘disinfect’, sanitise OR use antiseptic
  3. Disinfect hands
    OR
    Wash hands with soap (and water);
    Accept for ‘disinfect’, sanitise OR use antiseptic
  4. Put organ/gloves/paper towels in a (separate) bag/bin/tray to dispose;
25
Q

Explain how an arteriole can reduce the blood flow into capillaries

A
  1. Muscle contracts;
  2. Constricts/narrows arteriole/lumen;
26
Q

(b) Name and describe five ways substances can move across the
cell-surface membrane into a cell. (5)

A
  1. (Simple) diffusion of small/non-polar molecules down a
    concentration gradient;
    If no reference to ‘small/ non-polar’ for 1.
    accept this idea from ‘large/charged’ given in
    description of 2.
  2. Facilitated diffusion down a concentration gradient via
    protein carrier/channel;
    Reject if active rather than passive
  3. Osmosis of water down a water potential gradient;
  4. Active transport against a concentration gradient via
    protein carrier using ATP;
  5. Co-transport of 2 different substances using a carrier protein;
27
Q

Describe and explain two features you would expect to find in a cell
specialised for absorption.

A
  1. Folded membrane/microvilli so large surface area (for absorption);
    Reject references to ‘villi’.
    Accept ‘brush border’ for ‘microvilli’.
  2. Large number of co-transport/carrier/channel proteins so
    fast rate (of absorption)
    OR
    Large number of co-transport/carrier proteins for active transport
    OR
    Large number of co-transport/carrier/channel proteins for facilitated
    diffusion;
  3. Large number of mitochondria so make (more) ATP (by respiration)
    OR
    Large number of mitochondria for aerobic respiration
    OR
    Large number of mitochondria to release energy for active transport;
  4. Membrane-bound (digestive) enzymes so maintains
    concentration gradient (for fast absorption);
28
Q

The movement of substances across cell membranes is affected by
membrane structure. Describe how.

A
  1. Phospholipid (bilayer) allows movement/diffusion of nonpolar/lipid-soluble substances;
  2. and 2. Accept correct named examples
  3. and 2. Ignore water
    Accept phospholipid (bilayer) allows movement/diffusion
    of O2/CO2
    Accept water-insoluble
  4. Phospholipid (bilayer) prevents movement/diffusion of polar/
    charged/lipid-insoluble substances
    OR
    (Membrane) proteins allow polar/charged substances to cross
    the membrane/bilayer;
    Accept water-soluble
  5. Carrier proteins allow active transport;
  6. Channel/carrier proteins allow facilitated diffusion/co-transport;
    Accept aquaporins allow osmosis
  7. Shape/charge of channel / carrier determines which
    substances move;
  8. Number of channels/carriers determines how much movement;
  9. Membrane surface area determines how much
    diffusion/movement;
  10. and 7. Accept correct reference to faster/slower/rate for
    ‘how much movement’
    Accept microvilli / Golgi (apparatus) / ER / rER
    Accept surface area to volume for ‘surface area’
  11. Cholesterol affects fluidity/rigidity/permeability;
29
Q

Describe binary fission in bacteria

A
  1. Replication of (circular) DNA;
    Accept nucleoid
    Reject chromosome
    Reject mitosis
  2. Replication of plasmids;
  3. Division of cytoplasm (to produce daughter cells);
30
Q

Suggest and explain how two environmental variables could be changed
to increase the growth rate of these cells.

A
  1. Increased (concentration of) glucose;
  2. Increased respiration;
  3. Increased (concentration of) oxygen;
  4. Increased respiration;
  5. Increased temperature;
  6. Increased enzyme activity;
  7. Increased (concentration of) phosphate;
  8. Increased ATP/DNA/RNA;
  9. Increased (concentration of) nucleotides;
  10. Increased DNA synthesis;
31
Q

(a) Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

A

Iron ions
1. Haemoglobin binds/associates with oxygen
OR
Haemoglobin transports/loads oxygen;Sodium ions
2. Co-transport of glucose/amino acids (into cells);
3. (Because) sodium moved out by active transport/Na – K pump;
4. Creates a sodium concentration/diffusion gradient;
5. Affects osmosis/water potential;
Phosphate ions
6. Affects osmosis/water potential;
Accept 5. OR 6. – not both
7. Joins nucleotides/in phosphodiester bond/in backbone of
DNA/RNA/in nucleotides;
8. Used in/to produce ATP;
Reject ‘energy produced’
9. Phosphorylates other compounds (usually) making them more
reactive;
10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;

32
Q

Explain five properties that make water important for organisms

A
  1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
  2. A solvent so (metabolic) reactions can occur
    OR
    A solvent so allowing transport of substances;
  3. High (specific) heat capacity so buffers changes in temperature;
    For ‘buffer’ accept ‘resist’.
  4. Large latent heat of vaporisation so provides a cooling effect (through
    evaporation);
    Reject latent heat of evaporation
  5. Cohesion (between water molecules) so supports columns of water
    (in plants);
    For ‘columns of water’ accept ‘transpiration stream’.
    Do not credit ‘transpiration’ alone but accept
    description of ‘stream’.
    For ‘columns of water’ accept ‘cohesion-tension
    (theory)’.
  6. Cohesion (between water molecules) so produces surface tension
    supporting (small) organisms;
33
Q

Describe the induced-fit model of enzyme action and how an enzyme acts as a
catalyst.

A
  1. Substrate binds to the active site/enzyme
    OR
    Enzyme-substrate complex forms;
  2. Active site changes shape (slightly) so it is complementary to substrate
    OR
    Active site changes shape (slightly) so distorting/breaking/forming bonds in the substrate;
  3. Reduces activation energy;

biology exam q (2 decks)

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