End Year Exam Marking Scheme (sec 3 - 2007)

Biology 5100 Marking Scheme Sec 3 End-of-Year Exams 2007 Qn 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

MCQ Answers D A D B A D B A C D C D C A B B C C A B D C C A B C B D A D

Remarks

Marker’s Comments

Marks

Q 31 (a) (b) (c) (d)

Marking Scheme Photosynthesis; Nitrogen; Contains all conditions necessary for photosynthesis;

(e)

Jar L: Ref. Plants carry out photosynthesis and uses up carbon dioxide; Ref. Rate of photosynthesis is greater than rate of respiration;

Remarks

Marker’s Comments

A: Rare gases;

Marks [1] [1] [1] [3]

[6]

Jar M: Ref. Carbon dioxide produced through respiration and present in the air; All carbon dioxide is absorbed by the substance;

Q 32 (a)(i)

Jar N: No photosynthesis occurs; Only respiration has occurred to increase the percentage of carbon dioxide; Marking Scheme Production of bile;

Remarks R: secretes bile

Any 1 of: Bile emulsifies fats; Breaks them down into smaller fat globules to increase surface area to volume ratio;

R: digests fats

Marker’s Comments

Marks [2]

Ref. more rapid breakdown by enzyme/lipase; (a)(ii)

Production of pancreatic juice; Ref. enzymes such as amylase, protease and lipase, which break down remaining starch, proteins and fats respectively;

(b)

A: specific enzymes are named (pancreatic amylase/ pancreatic lipase/trypsin)

Region 1: Stomach;

[2]

[2] R: small intestine

Region 2: Duodenum; (c)

Region 1:

[4]

Presence of HCl in gastric juice; Provides an acidic environment, Ref. optimum pH for efficient breakdown of proteins by pepsin; Region 2: Bile, pancreatic and intestinal juices are all alkaline; Provides an alkaline environment, Ref. Breakdown of proteins to polypeptides by protease/trypsin and then to amino acids by protease/erepsin;

A: neutralize acidic chyme

Q 33 (a)

Marking Scheme

(b)

Optimum temperature of enzyme 1 is at 30°C while optimum temperature of enzyme 2 is higher at approximately 95°C / AW;

Remarks R: Point marked at 60°C

Marker’s Comments

Marks [1]

[2]

From 0°C to 20°C, rate of enzyme action increases at a much faster rate for enzyme 1 compared to enzyme 2 / AW;

(c)(i)

Ref. rate of reaction increase is much slower from 40°C to 90°C; Enzyme 1;

Ref. Optimum temperature for enzyme 1 is closest to human body temperature; (c)(ii) Hot springs; (c)(iii) Enzymes are denatured; Shape of active sites has changed; Ref. Enzymes cannot combine with substrate to form enzymesubstrate complex anymore;

[2]

R: enzymes killed/died A: Three-dimensional shape of enzymes changed

[1] [2]

Q 34 (a)

Marking Scheme Epithelium cells;

Remarks

Marker’s Comments

Marks [2]

Cells line the trachea, bronchus and bronchioles; (b)

Production of mucus;

[2]

Ref. mucus trap dust particles that enters the respiratory system from trachea to bronchus and bronchioles; (c)

R: mucus removes dust particles [2]

Cilia;

Cilia sweeps dust particles trapped in mucus upwards towards the pharynx;

R: cilia moves upwards / Peristalsis

Q 35 (a)

Marking Scheme Allows some/smaller molecules to pass through but not others/bigger ones;

Remarks

(b)

Osmosis;

(c)

Sugar solution of equal concentration to that inside the membrane;

Marker’s Comments

Marks [1] [1]

R: equal concentration not mentioned

[1]

(d)

Ref. equal water potential due to same concentration of solute,

[1]

Ref. no net movement of water across the selectively-permeable membrane; Q 36

Marking Scheme Temperature receptors in the skin sends impulses to the hypothalamus;

Remarks R: Pituitary glands

(Vasodilation): Arterioles leading to blood capillaries near the skin dilates;

R: arterioles widens / capillaries dilates or widens

More warm blood flows though the blood capillaries near the skin; More heat lost from the skin though radiation; Sweat glands become more active; More sweat produced; Evaporation of sweat brings about heat loss and cools body; Any 3 of: Hypothalamus regulates body temperature by corrective mechanisms; Ref. Metabolic processes of body slows down; Less heat is produced; Hair erector muscles relaxes;

Marker’s Comments

Marks [10]

Q 37 (a)

Marking Scheme

Diagram: max [2]; Ref. patient’s blood in the coiled cellophane tubule bathed in a dialysis fluid, which collects the waste molecules; Ref. cellophane tubule acts as a selectively permeable membrane allowing urea, nitrogenous waste and mineral salts to pass through, prevents the passage of blood cells and large proteins;

Remarks R: Diagrams where entry and exit points are not clearly stated/ counterflow direction of dialysis fluid wrt blood flow within tubule / movement of substances not labelled.

Marker’s Comments

Marks [8]

Ref. concentration gradient set up and nitrogenous wastes, excess mineral salts and other toxins diffuse from the patient’s blood across the cellophane into the dialysis fluid; The dialysis fluid changed regularly to remove the waste substances and to maintain the diffusion gradient between the patient’s blood and the dialysis fluid; The patient’s blood is led from an artery in his forearm through the coiled cellophane tube in the dialysis machine and then re-enters the body via a vein in the same arm; Ref. blood prevented from clotting in the machine by addition of an anti-clotting chemical; Ref. temperature of the dialysis fluid is maintained at body temperature; (b)

Excretion is the removal of metabolic waste products that are formed in chemical reactions in the cells; Ref. removal of faeces as the removal of undigested / indigestible substances from the alimentary canal through the anus, Ref. faeces are not produced by metabolism, thus removal of faeces cannot be considered as excretion.

[2]

Q 38 (a)

Marking Scheme No fat digestion in the mouth,

Remarks

Marker’s Comments

Marks [2]

Ref. no lipase present in saliva; Fat digestion starts only in the duodenum; (b)

In the duodenum, bile, which is produced by the liver, emulsifies fats;

R: ref. ileum

[4]

Ref. gall bladder releases bile which pass through bile duct and into duodenum; It breaks fats into minute fat globules/droplets (suspended in water to form a stable emulsion); The emulsion enlarges the surface area of the fats for faster digestion; Allows the enzymes lipase to act on fats, converting them into fatty acids and glycerol; (c)

In the ileum, fatty acids and glycerol are absorbed by the lacteals of the numerous villi projecting from the walls of the small intestine; Ref. Fatty acids and glycerol recombine inside the lacteal to form fat globules; The fat globules are mixed with lymph; Transported by the lymphatic vessels to the thoracic duct where the mixture discharges into the blood stream;

[4]