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Biology A Level > Substance Exchange Exam Qs > Flashcards

Substance Exchange Exam Qs Flashcards

1
Q

Which organ produces amylase? (1 mark)

A

The pancreas

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2
Q

Which organ produces maltase? (1 mark)

A

The intestine

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3
Q

What is the purpose of amylase? (1 mark)

A

Amylase is an enzyme that helps to break down starch into simpler sugars

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4
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;
  2. (Only) maltose can bind / fit;
  3. To form enzyme substrate complex.
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5
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.
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6
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;
  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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7
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.
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8
Q

What is the purpose of pepsin? (1 mark)

A

Pepsin is an endopeptidase that breaks down proteins into smaller amino acids.

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9
Q

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

A
  1. Add iodine / potassium iodide solution to the food sample;
  2. Blue / black / purple indicates starch is present;
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10
Q

The concentration of glucose in the blood rises after eating a meal containing
carbohydrates.
The rise is slower if the carbohydrate is starch rather than sucrose. Explain why. (3 marks)

A
  1. Starch digested to maltose / by amylase;
  2. Maltose digested to glucose / by maltase;
  3. Digestion of sucrose is a single step / only one enzyme / sucrase;
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11
Q

Describe a method you could use to find the surface area of a leaf. (3 marks)

A
  1. Draw around leaf on graph paper;
  2. Count squares
  3. Multiply by 2
  4. Cut out and weigh;
  5. Multiply by 2 (for upper and lower leaf surface).
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12
Q

Give two features of leaves of xerophytes. (2 marks)

A
  1. Thick(er) cuticle so increase in diffusion distance / slower (rate of) diffusion;
  2. Hairs on leave so reduction in air movements/increase in humidity/decrease in water potential gradient;
  3. Sunken stomata so reduction in air movements / increase in humidity / decrease in water potential gradient.
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13
Q

The stomata close when the light is turned off.

Explain the advantage of this to the plant. (2 marks)

A
  1. (Because) water is lost through stomata;
  2. (Closure) prevents / reduces water loss;
  3. Maintain water content of cells.
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14
Q

Breathing out as hard as you can is called forced expiration.

(a) Describe and explain the mechanism that causes forced expiration. (4 marks)

A
  1. Contraction of internal intercostal muscles;
  2. Relaxation of diaphragm muscles / of external intercostal muscles;
  3. Causes decrease in volume of chest / thoracic cavity;
  4. Air pushed down pressure gradient.
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15
Q

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required. (4 marks)

A
  1. Trachea and bronchi and bronchioles;
  2. Down pressure gradient;
  3. Down diffusion gradient;
  4. Across alveolar epithelium.
    Capillary wall neutral
  5. Across capillary endothelium / epithelium.
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16
Q

Describe and explain how the countercurrent system leads to efficient gas exchange across
the gills of a fish. (3 marks)

A
  1. Water and blood flow in opposite directions;
    Accept: diagram if clearly annotated
  2. Maintains concentration / diffusion gradient / equilibrium not reached / water always next to blood with a lower concentration of oxygen;
  3. Along whole / length of gill / lamellae;
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17
Q

Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. The disease causes the lamellae to become thicker and to fuse together.
AGD reduces the efficiency of gas exchange in fish. Give two reasons why. (2 marks)

A
  1. (Thicker lamellae so) greater / longer diffusion distance / pathway;
    Q Neutral: ‘thicker’ diffusion pathway
  2. (Lamellae fuse so) reduced surface area;
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18
Q

The volume of water passing over the gills increases if the temperature of the water increases. Suggest why. (1 mark)

A
  1. Increased metabolism / respiration / enzyme activity;

2. Less oxygen (dissolved in water);

19
Q

Name the process by which oxygen passes from an alveolus in the lungs into the blood.
(1 mark)

A

(Simple) diffusion

20
Q

Describe two adaptations of the structure of alveoli for efficient gas exchange. (2 marks)

A
  1. Thin walls / cells;
  2. ‘Short diffusion pathway’ alone is an explanation not a description
  3. Accept squamous epithelia / one cell thick
  4. (Total) surface area is large;
21
Q

What is the function of the coronary arteries? (2 marks)

A
  1. (Carry) oxygen / glucose;
    Accept: oxygenated blood
    Ignore references to removing waste products
    Ignore references to arteries ‘pumping’ blood
  2. (To) heart muscle / tissue / cells / myocytes.
22
Q

The rise and fall in blood pressure in the aorta is greater than in the small arteries.Suggest why (3 marks)

A
  1. (is) close / directly linked to the heart / ventricle / pressure is higher / is very high;
  2. (Aorta has) elastic tissue;
    Accept elasticity
  3. (Aorta has) stretch / recoil.
23
Q

Although the speed of blood flow in an arteriole is greater than speed of blood flow
in a capillary, blood does not accumulate in the arterioles.
Explain why. (1 mark)

A
  1. Many / more capillaries (than arterioles);

2. (Cross-sectional) area of capillaries (much) greater (than of arterioles).

24
Q

Other than causing slow blood flow, explain one advantage of capillaries being narrow. (2 marks)

A
  1. Short pathway / short distance between blood and outside of capillary;
  2. Large surface area (of blood) in contact with walls of capillaries;
  3. Fast exchange / fast diffusion / fast osmosis.
25
Q

What factor limits the minimum internal diameter of the lumen of a capillary? (1 mark)

A

Width / size / diameter of blood cell.

26
Q

The volume of blood leaving the capillary network into the veins is less than the volume of blood entering from the arteries.
Explain why. (1 mark)

A

(Fluid) in tissue fluid / (fluid) in lymph.

27
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.
28
Q

High blood pressure leads to an accumulation of tissue fluid. Explain how. (3 marks)

A
  1. High blood pressure = high hydrostatic pressure;
  2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary;
  3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.
29
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;
  5. Hydrogen bonding (within structure).
30
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.
31
Q

Explain one 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.
32
Q

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

A
  1. Mitochondria release energy / ATP / site of respiration;
  2. For active transport / uptake against concentration gradient.
  3. Ribosomes / rough endoplasmic reticulum produce(s) proteins;
  4. (Proteins) linked to transport e.g. carrier proteins / enzymes.
33
Q

One theory of translocation states that organic substances are pushed from a high
pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves (3 marks)

A
  1. Water potential becomes lower / becomes more negative (as sugar enters
    phloem) ;
  2. Water enters phloem by osmosis;
  3. Increased volume (of water) causes increased pressure.
34
Q

Contrast the processes of facilitated diffusion and active transport. (3 marks)

A
  1. Facilitated diffusion involves channel or carrier proteins whereas active transport
    only involves carrier proteins;
  2. Facilitated diffusion does not use ATP / is passive whereas active
    transport uses ATP;
  3. Facilitated diffusion takes place down a concentration gradient whereas
    active transport can occur against a concentration gradient.
35
Q

Describe the mass flow hypothesis for the mechanism of translocation in plants. (4 marks)

A
  1. In source / leaf sugars actively transported into phloem;
  2. By companion cells;
  3. Lowers water potential of sieve cell / tube and water enters by osmosis;
  4. Increase in pressure causes mass movement (towards sink / root);
  5. Sugars used / converted in root for respiration for storage.
36
Q

Explain how tissue fluid is formed (2 marks)

A
  1. (Overall) outward pressure of 3.2 kPa;

2. Forces small molecules out of capillary.

37
Q

The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why. (1 mark)

A

Loss of water / loss of fluid / friction (against capillary lining).

38
Q

High blood pressure leads to an accumulation of tissue fluid. Explain how. (3 marks)

A
  1. High blood pressure = high hydrostatic pressure;
  2. Increases outward pressure from (arterial) end of capillary / reduces
    inward pressure at (venule) end of capillary;
  3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.
39
Q

The water potential of the blood plasma is more negative at the venule end of the
capillary than at the arteriole end of the capillary. Explain why. (3 marks)

A
  1. Water has left the capillary;
  2. Proteins (in blood) too large to leave capillary;
  3. Increasing / giving higher concentration of blood proteins (and thus wp).
40
Q

Breathing out as hard as you can is called forced expiration.
(a) Describe and explain the mechanism that causes forced expiration. (4 marks)

A
  1. Contraction of internal intercostal muscles;
  2. Relaxation of diaphragm muscles / of external intercostal muscles;
  3. Causes decrease in volume of chest / thoracic cavity;
  4. Air pushed down pressure gradient.
41
Q

One theory of translocation states that organic substances are pushed from a high
pressure in the leaves to a lower pressure in the roots.
Describe how a high pressure is produced in the leaves. (3 marks)

A
  1. Water potential becomes lower / becomes more negative (as sugar enters
    phloem) ;
  2. Water enters phloem by osmosis;
  3. Increased volume (of water) causes increased pressure.
42
Q

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs.
Details of breathing are not required. (4 marks)

A
  1. Trachea and bronchi and bronchioles;
  2. Down pressure gradient;
  3. Down diffusion gradient;
  4. Across alveolar epithelium.
    Capillary wall neutral
  5. Across capillary endothelium / epithelium.
43
Q

The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise.
Explain the advantage of this shift. (3 marks)

A
  1. Lower affinity for oxygen/releases more oxygen/oxygen is released quicker /oxygen dissociates/unloads more readily;
  2. (To) muscles / tissues / cells
  3. (For) high/rapid respiration;

Biology A Level (63 decks)

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