Exchange Exam Qs

Question 1

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

Answer 1

1. Micelles contain bile salts and fatty acids/monoglycerides;
   Ignore other correct components of micelles
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’

Question 2

Describe how the structure of a protein depends on the amino acids it contains.

Answer 2

1. Structure is determined by (relative) position of amino acid/R group/interactions;
   Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobic-hydrophilic interactions
2. Primary structure is sequence/order of amino acids;
3. Secondary structure formed by hydrogen bonding (between amino acids);
   Accept alpha helix/β-pleated sheet for ‘secondary structure’
4. Tertiary structure formed by interactions (between R groups);
   Accept for ‘interactions’, hydrogen bonds / disulfide bridges / ionic bonds / hydrophobichydrophilic interactions
5. Creates active site in enzymes
   OR
   Creates complementary/specific shapes in antibodies/carrier proteins/receptor (molecules);
6. Quaternary structure contains >1 polypeptide chain
   OR
   Quaternary structure formed by interactions/bonds between polypeptides;
   Accept for ‘intereactions’, hydrogen bonds/ disulfide bridges/ionic bonds/hydrophobic-hydrophilic interactions
   Accept prosthetic (group)

Question 3

Figure 1 shows a cell from the lining of the ileum specialised for absorption of
products of digestion.
SGLT1 is a carrier protein found in the cell-surface membrane of this cell, it transports glucose and sodium ions (Na+) into the cell.

(a) The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase. (2 marks)

Answer 3

1. (ATP to ADP + Pi ) Releases energy;
   Reject ‘produces/makes/creates energy’.
2. (energy) allows ions to be moved against a concentration gradient
   OR
   (energy) allows active transport of ions;
   For ‘ions’ accept Na+ or K+.
   Do not accept if this movement is of glucose not ions.

Question 4

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how. (2 marks)

Answer 4

1. (Maintains/generates) a concentration/diffusion gradient for Na+ (from ileum into cell);
   Accept ‘(Maintains/generates) a lower concentration of Na+ inside the cell compared with outside the cell’.
2. Na+ moving (in) by facilitated diffusion, brings glucose with it
   OR
   Na+ moving (in) by co-transport, brings glucose with it;
   Accept ‘co-transporter’ for ‘co-transport’.

Question 5

To study lipid digestion, a scientist placed a tube into the gut of a healthy 20-year-old man. The end of the tube passed through the stomach but did not reach as far as the ileum.
The scientist fed the man a meal containing triglycerides through the tube. The scientist also used the tube to remove samples from the man’s gut at intervals after the meal.
The scientist measured the type of lipid found in the samples. Some of her results are shown in the table below.

After collecting the samples, the scientist immediately heated them to 70 °C for 10 minutes.
Explain why. (2 marks)

Answer 5

1. To denature the enzymes/lipase;
   Accept description of denaturation in terms of change in tertiary structure.
2. So no further digestion/hydrolysis/catalysis occurred;
   Accept ‘break down’ for digestion.

Question 6

Describe the role of micelles in the absorption of fats into the cells lining the ileum. (3 marks)

Answer 6

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);
   OR
   Fatty acids increase because of hydrolysis (of triglycerides);
5. Triglycerides decrease because of digestion of ester bonds (between fatty acid and glycerol)
   OR
   Fatty acids increase because of digestion of ester bonds (between fatty acid and glycerol);
6. Fatty acids (absorbed) by diffusion;
   Reject if absorbed by facilitated diffusion
   Ignore if micelles themselves are being absorbed.
   Ignore references to monoglycerides.

Question 7

Describe the role of enzymes in the digestion of proteins in a mammal. (4 marks)

Answer 7

1. (Reference to) hydrolysis of peptide bonds;
2. Endopeptidase act in the middle of protein/polypeptide
   OR
   Endopeptidase produces short(er) polypeptides/ increase number of ends;
3. Exopeptidases act at end of protein/polypeptide
   OR
   Exopeptidase produces dipeptides/amino acids;
4. Dipeptidase acts on dipeptide/between two amino acids
   OR
   Dipeptidase produces (single) amino acids;

Accept chain/chain of amino acids/peptide for polypeptide
Accept digest/breakdown/ break for ‘act’
Mark points 2, 3 and 4 reject answers where substrate or product is incorrect eg ‘Endopeptidase produces dipeptides’
Ignore references to source and location of enzymes

Question 8

The food eaten by a rabbit is digested mainly by microorganisms in its caecum. The caecum is a section of intestine attached between the ileum and the large intestine. The resulting semi-digested material leaves the anus of a rabbit as soft, caecal droppings. The rabbit then eats these caecal droppings.
Use this information and Figure 2 to suggest how eating its own caecal droppings helps a rabbit’s digestion and absorption of dietary protein. (3 marks)

Answer 8

1. More/remaining/undigested (protein) broken down;
   Accept all (protein) broken down
2. (So more) amino acids absorbed;
3. (Because) protein/food passes again through stomach/ileum;

Question 9

Tick (✔) the box by the name of the process by which fatty acids and glycerol enter the intestinal epithelial cell. (1 mark)
Active transport
Diffusion
Endocytosis
Osmosis

Answer 9

Diffusion

Question 10

Explain the advantages of lipid droplet and micelle formation. (3 marks)

Answer 10

1. Droplets increase surface areas (for lipase / enzyme action);
   Context is important
   Reject micelles increase surface area
2. (So) faster hydrolysis / digestion (of
   triglycerides / lipids);
   Ignore ‘breakdown’
3. Micelles carry fatty acids and glycerol /
   monoglycerides to / through membrane / to (intestinal epithelial) cell;
   Ignore ‘small enough’
   Accept description of membrane
   Reject any movement through membrane proteins

Question 11

Name Structure Q in the diagram above and suggest how it is involved in the absorption of lipids (4 marks)
Structure Q = Golgi Apparatus

Answer 11

2. Modifies / processes triglycerides;
3. Combines triglycerides with proteins;
4. Packaged for release / exocytosis
   OR
   Forms vesicles;
   *Ignore ‘processes and packages’ unqualified
5. Reject synthesises triglycerides
6. Accept ‘forms / are lipoproteins’*

Question 12

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. (3 marks)

Answer 12

1. Sodium ions actively transported from ileum cell to blood;
2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose);
3. Glucose enters by facilitated diffusion with sodium ions;

Question 13

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

Answer 13

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.

Question 14

The insect opens its spiracles at a lower frequency in very dry conditions.
Suggest one advantage of this. (1 mark)

Answer 14

Less / no water lost / (more) water retained;

Question 15

Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why. (2 marks)

Answer 15

1. More air / oxygen enters / air / oxygen enters quickly / quicker;

Accept: converse for carbon dioxide
Can be in any correct context eg insect, tracheoles, muscle
Neutral: air / oxygen enters

(So) maintains / greater diffusion or concentration gradient;

Question 16

Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion.
Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping. (1 mark)

Answer 16

Large(r) SA:VOL / short(er) diffusion distance (to tissues)
Accept: thin diffusion pathway

Question 17

The ends of tracheoles connect directly with the insect’s muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why. (1 mark)

Answer 17

Greater surface area exposed to air;
Neutral: shorter diffusion distance
Gases move / diffuse faster in air than through water;
2. Q Neutral: ‘harder to diffuse’
2. Accept gases diffuse directly, rather than through water
Increases volume / amount of air;

Question 18

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

Answer 18

Increased respiration so less oxygen dissolved in water

Question 19

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

Answer 19

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; Must have the idea of ‘maintaining’ or ‘always’ in reference to concentration / diffusion gradient Accept: constant concentration / diffusion gradient

3.Along whole / length of gill / lamellae; Accept: gill plate / gill filame

Question 20

Emphysema is a disease which affects the lungs. It causes a decrease in the number of alveoli. It may also cause the alveolar walls to become thickened.
Explain why people with emphysema may need to use oxygen masks to help with their breathing. (3 marks)

Question 21

Palisade mesophyll tissue is adapted for efficient photosynthesis. Describe two ways in which the cells of the tissue are adapted for
(i) maximum light absorption;
1 …………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………… …. 2 …………………………………………………………………………………………………………………. …………………………………………………………………………………………………………….. ……..
(ii) efficient uptake of carbon dioxide.

Question 22

In the lungs oxygen passes from the alveoli to the blood.
Describe and explain the features that make this process rapid and efficient

Question 23

Explain the role of the diaphragm in breathing out. (3 marks)

Question 24

High blood pressure leads to an accumulation of tissue fluid. Explain how.

Answer 24

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

Question 25

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of capillary. Explain how.

Answer 25

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)

Question 26

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. (3)

Answer 26

1. Tracheoles have thin walls so short diffusion distance to cells; 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;

Question 27

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest (3)

Answer 27

1. Oxygen used in (aerobic) respiration; 2. (so) oxygen (concentration) gradient (established); Accept description of gradient Ignore: ‘along gradient idea’ unless direction is made clear Ignore: movement through gas/water Reject: gradient in wrong direction 3. (so) oxygen diffuses in; 2 and 3. Accept: oxygen moves down a diffusion gradient for 2 marks