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Biological Molecules Exam Qs Flashcards

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1
Q

Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5 Marks)

A
  1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum;
  2. (Calcium ions) cause movement of tropomyosin (on actin);
  3. (This movement causes) exposure of the binding sites on the actin;
  4. Myosin heads attach to binding sites on actin;
  5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend;
  6. (Bending) pulling actin molecules;
  7. Attachment of a new ATP molecule to each myosin head causes myosin
    heads to detach (from actin sites).
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2
Q

ATP is an energy source used in many cell processes.

Give two ways in which ATP
is a suitable energy source for cells to use. (2 marks)

A
  1. Releases relatively small amount of energy / little energy lost as heat;
    Key concept is that little danger of thermal death of cells
  2. Releases energy instantaneously;
    Key concept is that energy is readily available
  3. Phosphorylates other compounds, making them more reactive;
  4. Can be rapidly re-synthesised;
  5. Is not lost from / does not leave cells.
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3
Q

Write a simple equation to show how ATP is synthesised from ADP. (1 mark)

A

ADP + Pi → ATP

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4
Q

Give two ways in which the properties of ATP make it a suitable source of energy in biological processes. (2 marks)

A
  1. Energy released in small / suitable amounts;
  2. Soluble;
  3. Involves a single / simple reaction
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5
Q

Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2 marks)

A
  1. ATP cannot be stored / is an immediate source of energy;

2. ATP only releases a small amount of energy at a time;

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6
Q

Describe the part played by the inner membrane of a mitochondrion in producing ATP. (3 marks)

A

Electrons transferred down electron transport chain;
Provide energy to take protons / H+
into space between membranes;
Protons / H+
pass back, through membrane / into matrix / through
ATPase

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7
Q

A scientist investigated ATP production in a preparation of isolated mitochondria.
He suspended the mitochondria in an isotonic solution and added a suitable
respiratory substrate together with ADP and phosphate. He bubbled oxygen through
the preparation.
(i) Why was the solution in which the mitochondria were suspended isotonic? (1 mark)

A

Prevent damage to mitochondria caused by

water / osmosis / differences in water potential;

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8
Q

In anaerobic respiration, what is the net yield of ATP molecules per molecule
of glucose? (1 mark)

A

2 (molecules)

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9
Q

Give two advantages of ATP as an energy-storage molecule within a cell. (2 marks)

A

Cannot pass out of cell;

Quickly / easily broken down (hydrolysed)

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10
Q

Mitochondria in muscle cells have more cristae than mitochondria in skin cells.
Explain the advantage of mitochondria in muscle cells having more cristae. (2 marks)

A

(more cristae / larger surface area) for electron transport chain /
more enzymes for ATP production / oxidative phosphorylation;
muscle cells use more ATP (than skin cells)(not just more respiration);

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11
Q

Substance X enters the mitochondrion from the cytoplasm. Each molecule of
substance X has three carbon atoms.
Name substance X. (1 mark)

A

Pyruvate

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12
Q

When glucose is respired what happens to the energy which is not incorporated into ATP? (1 mark)

A

Released as heat

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13
Q

When one mole of glucose is respired anaerobically, only 2 moles of ATP are produced. Explain why less energy is released in anaerobic respiration. (1 mark)

A

Glucose only partly broken down / only broken down to lactate;

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14
Q

At the end of a sprint race, a runner continues to breathe rapidly for some
time. Explain the advantage of this. (2 marks)

A

lactate / lactic acid has built up / been produced;
oxygen used to break down lactate / convert it back to
pyruvate / glucose / glycogen;

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15
Q

Name the substance that muscles use as their immediate energy source.

A

ATP (End of ATP Questions)

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16
Q

Monosaccharides and disaccharides taste sweet.
The lactose-free milk made after hydrolysis with lactase tastes sweeter than the
cow’s milk containing lactose.
Suggest why. (2 marks)

A
  1. (Lactose hydrolysed to) galactose and glucose;
  2. (So) more sugar molecules;
  3. Idea of more sugars essential
  4. (So) more / different receptors stimulated / sugars produced are sweeter
    (than lactose). (Start of Carbohydrates)
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17
Q

Give two ways in which the structure of starch is similar to cellulose. (2 marks)

A
  1. Are polymers / polysaccharides / are made of monomers / of
    monosaccharides;
  2. Contain glucose / carbon, hydrogen and oxygen;
  3. Contain glycosidic bonds;
  4. Have 1−4 links;
    Neutral: references to ‘unbranched’, insoluble, formed by
    condensation, flexible and rigid
    Are made of the monomer glucose = MP 1 and 2 = 2 marks
  5. Hydrogen bonding (within structure).
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18
Q

Give two ways in which the structure of starch is different from cellulose. (2 marks)

A

(Starch)

  1. Contains α / alpha glucose;
  2. Helical / coiled / compact / branched / not straight;
  3. 1,6 bonds / 1,6 branching;
  4. Glucoses / monomers same way up;
  5. No H-bonds between molecules;
  6. No (micro / macro) fibres / fibrils.
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19
Q

Explain one other way in which sieve cells are

adapted for mass transport (2 marks)

A

1) No / few organelles / very little cytoplasm / cytoplasm at edge / more room / hollow / large vacuole / large space / thick walls
2) (So) easier / more flow / (thick / strong walls) resist pressure. Easier flow may be expressed in other ways e.g. lower resistance to flow

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20
Q

Suggest and explain one other way in which companion cells are adapted for the transport of sugars between cells (2 marks)

A

Mitochondria release energy / ATP / site of respiration;

  1. For active transport/uptake against a concentration gradient.
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21
Q

Explain the difference in the structure of the starch molecule and the cellulose
molecule (2 marks)

A
  1. Starch formed from α-glucose but cellulose formed from β-glucose;
  2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
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22
Q

Explain one way in which starch molecules are adapted for their function in plant
cells. (2 marks)

A

Starch is insoluble so doesn’t affect water potential.

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23
Q

Explain how cellulose molecules are adapted for their function in plant cells (3 marks)

A
  1. Long and straight chains;
  2. Become linked together by many hydrogen bonds to form fibrils;
  3. Provide strength (to cell wall).
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24
Q

In humans, the enzyme maltase breaks down maltose to glucose.
This takes place at normal body temperature.
Explain why maltase:
• only breaks down maltose
• allows this reaction to take place at normal body temperature. (5 marks)

A
  1. Tertiary structure / 3D shape of enzyme (means);
    Accept references to active site
  2. Active site complementary to maltose / substrate / maltose fits into active
    site / active site and substrate fit like a lock and key;
    Idea of shapes fitting together
  3. Description of induced fit;
  4. Enzyme is a catalyst / lowers activation energy / energy required for reaction;
    Accept “provides alternative pathway for the reaction at a
    lower energy level”
  5. By forming enzyme-substrate complex;
    Accept idea that binding stresses the bonds so more easily
    broken
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25
Q

Scientists have investigated the effects of competitive and non-competitive
inhibitors of the enzyme maltase.
Describe competitive and non-competitive inhibition of an enzyme. (5 marks)

A
  1. Inhibitors reduce binding of enzyme to substrate / prevent formation of
    ES complex;
    Max 3 if only one type of inhibition dealt with. Accept maltase and maltose as examples of enzyme and substrate (and others)
    Only once, for either inhibitor
    (Competitive inhibition),
  2. Inhibitor similar shape (idea) to substrate;
  3. (Binds) in to active site (of enzyme);
    Accept allows max rate of reaction to be reached / max
    product will eventually be formed
    Accept complementary to active site
  4. (Inhibition) can be overcome by more substrate;
    (Non-competitive inhibition),
  5. Inhibitor binds to site on enzyme other than active site;
  6. Prevents formation of active site / changes (shape of) active site;
  7. Cannot be overcome by adding more substrate;
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26
Q

Explain how a sports drink could provide an energy boost when running. (3 marks)

(End of carbohydrates)

A

1) (Drink) contains carbohydrates / sugars so High GI / (drink) contains carbohydrates / sugars so raises blood glucose concentration quickly;
2. Contains salt so glucose more rapidly absorbed;
3. Increases glucose to muscles for respiration;
4. More / faster respiration so more / faster energy release;

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27
Q

Describe how you could use the emulsion test to show the presence of oil in a
sample of fish. (3 marks)

(Start of Lipids)

A
  1. (Shake with) ethanol/alcohol;
  2. Then add (to) water;
  3. White/milky/cloudy (layer indicates oil).
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28
Q

Describe how you would test a piece of food for the presence of lipid. (2 mark)

A
  1. Dissolve in alcohol, then add water;

2. White emulsion shows the presence of lipid.

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29
Q

Newborn babies can be fed with breast milk or with formula milk. Both types of milk contain
carbohydrates, lipids and proteins.
• Human breast milk also contains a bile-activated lipase. This enzyme is thought to
be inactive in milk but activated by bile in the small intestine of the newborn baby.
• Formula milk does not contain a bile-activated lipase.
Scientists investigated the benefits of breast milk compared with formula milk.
(a) The scientists used kittens (newborn cats) as model organisms in their laboratory
investigation. Other than ethical reasons, suggest two reasons why they chose to use cats as model organisms (2 marks)

A
  1. (Are mammals so) likely to have same physiology / reactions as humans;
  2. Small enough to keep in laboratory / produce enough milk to extract;
  3. (Can use a) large number.
30
Q

Some seeds contain lipids. Describe how you could use the emulsion test to show
that a seed contains lipids. (3 marks)

A
  1. Crush/grind;
  2. With ethanol/alcohol;
  3. Water must be added after ethanol for third mark
  4. Then add water / then add to water;
  5. Forms emulsion / goes white / cloudy;
31
Q

A triglyceride molecule is formed by condensation. From how many molecules is this triglyceride formed? (1 mark)

A

4 molecules

32
Q

The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different (2 marks)

A
  1. Phosphate / PO4;
    “It” refers to phospholipid.
  2. Instead of one of the fatty acids / and two fatty acids;
33
Q

What is meant by an unsaturated fatty acid. (1 marks)

A

Double bonds (present) / some / two carbons with only one hydrogen / (double bonds) between carbon atoms / not saturated with hydrogen

34
Q

Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid?

A

1) Double bond

2 between carbon

35
Q

Hydrogen bonds are important in cellulose molecules. Explain why (2 marks)

A
  1. Holds chains / cellulose molecules together / forms cross links
    between chains / cellulose molecules / forms microfibrils, providing
    strength / rigidity (to cellulose / cell wall);
  2. Hydrogen bonds strong in large numbers;x
    Principles here are first mark for where hydrogen bonds are
    formed and second for a consequence of this.
    Accept microfibres
36
Q

A starch molecule has a spiral shape. Explain why this shape is important to its function in cells. (1 mark)

A

Compact / occupies small space / tightly packed;

37
Q

Explain two ways in which fatty acids are important in
the formation of new cells. (4 Marks)

(End of lipids)

A

Fatty acids used to make phospholipids;
Phospholipids in membranes;
More phospholipids more membranes made;

Fatty acids respired to release energy;
More triglycerides more energy released;
Energy used for cell production / production of named cell component

38
Q

Describe how you would test a piece of food for the presence of lipid. (2 marks)

(Start of monomers and polymers)

A
  1. Dissolve in alcohol, then add water;

2. White emulsion shows the presence of lipid.

39
Q

Suggest one advantage of the different percentage of cholesterol in red blood cells compared with cells lining the ileum. (1 mark)

A

Red blood cells free in blood / not supported by other cells so cholesterol helps
to maintain shape;

40
Q

Explain the difference in the structure of the starch molecule and the cellulose (1 mark)

A
  1. Starch formed from α-glucose but cellulose formed from β-glucose;
  2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted.
41
Q

Explain one way in which starch molecules are adapted for their function in plant
cells. (2 marks)

A
  1. Insoluble;
  2. Don’t affect water potential;
    Or
  3. Helical;
  4. Compact;
42
Q

Explain how cellulose molecules are adapted for their function in plant cells. (2 marks)

A
  1. Long and straight chains;
  2. Become linked together by many hydrogen bonds to form fibrils;
  3. Provide strength (to cell wall).
43
Q 
Messenger RNA (mRNA) is used during translation to form polypeptides.
Describe how mRNA is produced in the nucleus of a cell. (6 marks)
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
44
Q

Describe the structure of proteins. (5 marks)

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
    bonding;
    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.
45
Q

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

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.
46
Q

Name the type of reaction that joins monosaccharides together. (1 mark)

A

Condensation reaction

47
Q

Some cells lining the bronchi of the lungs secrete large amounts of mucus. Mucus contains protein.
Name one organelle that you would expect to find in large numbers in a mucus-secreting cell and describe its role in the production of mucus. (2 marks)

(End of monomers and polymers)

A
  1. Golgi (apparatus);
  2. Package / process proteins;
    OR
  3. Rough endoplasmic reticulum / ribosomes;
  4. Make polypeptide / protein / forming peptide bonds;
    OR
  5. Mitochondria;
  6. Release of energy / make ATP;
    OR
  7. Vesicles;
  8. Secretion / transport of protein;
48
Q

Describe the role of DNA polymerase in DNA replication (1 mark)

(Start of nucleic acids)

A

Joins nucleotides (to form new strand).

49
Q

Other than being smaller, give two ways in which prokaryotic DNA is different
from eukaryotic DNA. (2 marks)

A
  1. Circular / non-linear (DNA);
  2. Not (associated) with proteins / histones;
    Accept does not form chromosomes / chromatin
  3. No introns / no non-coding DNA.
50
Q

The events that take place during interphase and mitosis lead to the production of two
genetically identical cells. Explain how. (4 marks)

A
  1. DNA replicated;
    Reject: DNA replication in the wrong stage
  2. (Involving) specific / accurate / complementary base-pairing;
    Accept: semi conservative replication
  3. (Ref to) two identical / sister chromatids;
  4. Each chromatid / moves / is separated to (opposite) poles / ends of cell.
51
Q

In a study, a student cut thin sections of tissue to view with an optical microscope.
Explain why it was important that the sections were thin. (2 marks)

A
  1. To allow (more) light through;
    Accept: transparent
  2. A single / few layer(s) of cells to be viewed.
    Accept: (thin) for better / easier stain penetration
52
Q

Scientists determined that a sample of DNA contained 18% adenine.
What were the percentages of thymine and guanine in this sample of DNA? (2 marks)

A
  1. Thymine 18 (%);

2. Guanine 32 (%).

53
Q

Why do the arrows during DNA replication during the splitting of the original stand point opposite ways? (2 mark)

A
  1. (Figure 1 shows) DNA has antiparallel strands / described;
  2. (Figure 1 shows) shape of the nucleotides is different / nucleotides
    aligned differently;
  3. Enzymes have active sites with specific shape;
  4. Only substrates with complementary shape / only the 3’ end can bind
    with active site of enzyme / active site of DNA polymerase.
54
Q

Like many other viruses, HSV can remain inactive inside the body for years.
When HSV becomes active, it causes cold sores around the mouth.

HSV can remain inactive inside the body for years. Explain why thisvirus can be described as inactive. (2 marks)

A
  1. No more (nerve) cells infected / no more cold sores form;

2. (Because) virus is not replicating

55
Q

Human cells infected with a virus may undergo programmed cell death

Suggest one advantage of programmed cell death (1 mark)

A

Prevents replication of virus.

56
Q

The scientists concluded that production of this microRNA allows HSV to remain in
the body for years
Explain how this microRNA allows HSV to remain in the body for years. (4 marks)

A

MicroRNA binds to cell’s mRNA (no mark)

  1. (Binds) by specific base pairing;
  2. (So) prevents mRNA being read by ribosomes;
  3. (So) prevents translation / production of proteins;
  4. (Proteins) that cause cell death.
57
Q

In a piece of DNA, 34% of the bases were thymine.

What percentage were adenine thymine and cyctosine

A

Thymine 34
Cytosine 16
Adenine 34
Cytosine 16

58
Q

A polypeptide has 51 amino acids in its primary structure. What is the minimum number of DNA bases required to code for the amino
acids in this polypeptide? (1 mark)

(End of Nucleic acids)

A

153

59
Q

What organ produces insulin? (1 mark)

A

The pancreas

60
Q

What organ produces amylase? (1 mark)

A

The pancreas which secretes it into the small intestine

61
Q

What organ produces maltase? (1 mark)

A

The small intestine

62
Q

Maltose is hydrolysed by the enzyme maltase.

Explain why maltase catalyses only this reaction. (3 marks)

A 
1. Active site (of enzyme) has (specific) shape / tertiary structure / active
site complementary to substrate / maltose;
Reject active site on substrate.
Must have idea of shape
Assume “it” = maltase
Accept (specific) 3D active site
Reject has same shape
2. (Only) maltose can bind / fit;
Accept “substrate” for “maltose”
3. To form enzyme substrate complex.
63
Q

Describe and explain how centrifuging the culture allowed the scientists to obtain a
cell-free liquid. (3 marks)

A
  1. Large / dense / heavy cells;
  2. Form pellet / move to bottom of tube (when centrifuged);
  3. Liquid / supernatant can be removed.
64
Q

Give one function of lysosomes. (1 mark)

A

Break down cells / cell parts / toxins.

65
Q

H. pylori cells produce an enzyme that neutralises acid.

Suggest one advantage to the H. pylori of producing this enzyme.

A
  1. To stop / reduce them being damaged / destroyed / killed;
    Reject (to stop) bacteria being denatured.
  2. By stomach acid.
66
Q

A principle of homeostasis is the maintenance of a constant internal environment. An
increase in the concentration of carbon dioxide would change the internal environment
and blood pH.
Explain the importance of maintaining a constant blood pH. (3 marks)

A

1) Named protein / enzyme (in blood) sensitive to / affected by change in
pH;
2)(Resultant) change of charge / shape / tertiary structure;
3)Described effect on named protein or enzyme.
e.g. less oxygen binds with haemoglobin / less transport across membranes /
fewer substrates can fit active site / fewer enzyme-substrate complexes.

67
Q

A technician investigated the effect of temperature on the rate of an enzyme-controlled
reaction. At each temperature, he started the reaction using the same volume of substrate
solution and the same volume of enzyme solution.

Give one other factor the technician would have controlled. (1 mark)

A

Concentration of substrate solution / of enzyme solution / pH.

68
Q

What is the hexagonal structure in a DNA molecule (1 mark)

A

A deoxyribose

69
Q

Scientists determined that a sample of DNA contained 18% adenine.
What were the percentages of thymine and guanine in this sample of DNA? (2 marks)

(End of proteins and enzymes)

A
  1. Thymine 18 (%);

2. Guanine 32 (%).

70
Q

Give two properties of water that are important in biology. Explain the
importance of each property you identify. (4 marks)

A 
Cohesion 
Adhesion
Waters Specific heat capacity 
Ability to expand when frozen
Ability to dissolve many substances
71
Q

Explain the meaning of the terms hydrophilic and hydrophobic (2 marks)

A

Hydrophobic - dislikes water

Hydrophilic - likes water

Biology A Level (63 decks)

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