II. Biological Sciences

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

6. New Model Concept — Bio Fuel

Past paper practice

Practise physiology, disease and cell answers alongside the other syllabus areas; distinguish a five-mark subpart from a full twenty-mark question.

Past Paper Questions (FPSC GSA Paper 7, 2015–2026, incl. 2023 Special)

The year-wise bank below now contains complete model answers aligned with the topic pages. Suggested coverage is a planning guide, not an official marking scheme. Historical wording/year labels retain the evidence limits recorded below. Where 2.5 marks were inferred from a combined part, use the actual paper’s allocation.

2026 — Q3(c) [5] Structural Diversity of Lipids; Fatty Acids, Membrane Fluidity and Cell Signalling

Suggested coverage: diversity 1.5; fluidity 2; signalling 1.5.

Model answer

Lipids are a diverse group of largely hydrophobic or amphipathic molecules involved in energy storage, membranes and signalling.

Structural diversity: Triglycerides contain glycerol joined to three fatty acids and store energy. Typical glycerophospholipids have two fatty-acid tails and a polar phosphate-containing head, allowing bilayer formation. Waxes contain long-chain fatty acids linked to alcohols; steroids, including cholesterol, have four fused rings. Glycolipids carry carbohydrate groups.

Membrane fluidity: Cis-unsaturated tails have bends that reduce close packing and generally increase fluidity. Saturated tails pack more closely; longer chains have stronger intermolecular interactions and generally reduce fluidity. Cholesterol restrains phospholipid movement at higher temperatures and limits tight packing at lower temperatures, buffering fluidity.

Signalling: Membrane organisation affects receptor mobility, clustering and interaction with signalling proteins. Cholesterol-rich domains can organise some signalling complexes. Cleavage of membrane phospholipids generates messengers such as diacylglycerol; arachidonic acid supplies precursors for eicosanoids.

Thus, lipid composition changes both the membrane’s physical properties and the availability and organisation of signalling molecules.

Diagram: Compare straight saturated and bent cis-unsaturated tails; label polar heads and cholesterol.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2026 — Q4(c) [5] Dengue Virus: Agent, Transmission, Life Cycle, Role of Aedes

Suggested coverage: agent/transmission 1; cycle 2; vector contribution 2.

Model answer

Dengue is caused by dengue virus, which has four principal serotypes, DENV-1 to DENV-4. Its main vectors are infected female Aedes aegypti mosquitoes; Ae. albopictus also transmits it.

Human–mosquito cycle: An infected mosquito introduces virus in saliva during a bite. Virus replicates in human cells and enters the bloodstream. Another mosquito feeding during viraemia acquires it. Virus replicates in the mosquito’s midgut, disseminates and reaches its salivary glands. At subsequent bites, the mosquito can infect another person. Viral replication inside cells involves entry, RNA translation and replication, assembly and release.

Vector contribution: Aedes breeds in water-holding containers near homes, often feeds during daylight and may bite several people. Its close association with humans sustains urban transmission. Dry-resistant eggs help populations persist between wet periods.

Diagram: viraemic person → feeding mosquito → midgut replication → salivary glands → next human. The mosquito’s egg–larva–pupa–adult development is distinct from the viral transmission cycle.

CDC dengue transmission.

2025 — Q3(a) [5] Effect of Temperature and Light Intensity on Photosynthesis

Suggested coverage: definition/equation 1; light response 2; temperature response and limiting factors 2.

Opening

Photosynthesis converts light energy into chemical energy stored in organic compounds.
Its overall equation is: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂.

Effect of light intensity

At low intensity, light limits the supply of energy for the light-dependent reactions.
Increasing light generally increases the rate.
At higher intensity, the rate reaches a plateau when another factor—such as CO₂ supply—becomes limiting.
Very intense light can cause photoinhibition; the rate does not increase indefinitely.

Effect of temperature

Photosynthesis includes enzyme-controlled reactions, especially carbon fixation.
Increasing temperature from a low level usually raises the rate towards an optimum.
The optimum depends on species, acclimation and growing conditions.
Beyond it, the rate can decline because of heat stress, stomatal closure, increased photorespiration and, at sufficiently high temperatures, enzyme damage.

Conclusion

The factor most constraining the process sets the rate; improving a non-limiting factor alone may have little effect.

Figures to draw

Light intensity on x-axis, photosynthesis rate on y-axis: rising curve then plateau.
Temperature on x-axis, rate on y-axis: rise to an optimum then decline.
Label the plateau “another factor limiting”; do not assign a universal temperature optimum.

2025 — Q3(b) [5] Structure and Functions of Capillaries

Suggested coverage: definition and structure 2; functions linked to adaptations 3.

Model answer

Capillaries are microscopic blood vessels that connect arterioles with venules and form the main exchange surface between blood and tissues.

Structure: Their walls consist of a single layer of endothelial cells supported by a thin basement membrane. They lack the thick muscular coat of arteries. Their narrow lumen often allows red blood cells to pass in single file. Extensive branching forms networks with a large exchange surface. The networks’ large total cross-sectional area produces slow average blood flow, allowing time for exchange.

Functions:

Oxygen and nutrients pass from blood to tissues, while carbon dioxide and metabolic wastes enter the blood.
Pulmonary capillaries exchange oxygen and carbon dioxide with alveolar air.
Intestinal capillaries absorb water-soluble nutrients, including glucose and amino acids.
Specialised glomerular capillaries filter water and small solutes during urine formation.
Skin capillary blood flow contributes to heat exchange.

Thus, thin walls, extensive networks and slow flow make capillaries efficient exchange vessels.

Diagram cue: arteriole → capillary network beside tissue cells → venule; show oxygen/nutrients moving out and carbon dioxide/wastes moving in.

CDC hepatitis overview, WHO hepatitis.

2025 — Q3(c) [5] Hepatitis

Suggested coverage: definition 0.5; types/routes 2; prevention 1.5; treatment 1.

Model answer

Hepatitis is inflammation of the liver. Causes include viruses, alcohol, medicines and autoimmune disease; viral hepatitis has five major types.

Type	Principal route / distinguishing feature
A	Faecal–oral; contaminated food/water; usually acute
B	Blood, sexual exposure and mother-to-child; may become chronic
C	Mainly infected blood; often chronic
D	Requires hepatitis B infection; chiefly blood/body-fluid exposure
E	Commonly contaminated water; foodborne zoonotic transmission also occurs

Possible symptoms include fatigue, nausea, abdominal discomfort, dark urine and jaundice; infection may be asymptomatic. Chronic B and C can lead to cirrhosis and liver cancer.

Prevention: Safe water, sanitation and food hygiene reduce A/E transmission. Screened blood, sterile injection equipment and safer sex reduce blood/body-fluid transmission. Vaccines prevent A and B; B vaccination also prevents D by preventing B.

Treatment: A and many E infections resolve with supportive care. Chronic B can be suppressed with antivirals; modern antivirals cure most C infections. Treatment is type-specific; “rest cures every hepatitis” is incorrect.

6. New Model Concept — Bio Fuel

2025 — Q3(d) [5] Biomass vs Biogas; Methods of Energy from Biomass

Suggested coverage: distinction/examples 2; production methods and products 3.

Model answer

Biomass is organic material of recent biological origin, such as crop residues, wood, manure and food waste. Biogas is a combustible gas mixture formed when microorganisms digest suitable organic matter without oxygen.

Feature	Biomass	Biogas
Nature	Feedstock or organic resource	Fuel gas derived from a feedstock
Form	May be solid, liquid or slurry	Mainly methane and carbon dioxide
Example	Cattle dung or crop residue	Gas from an anaerobic digester

Energy-conversion methods:

Combustion: Burning biomass produces heat; steam can drive turbines for electricity.
Anaerobic digestion: Microbes convert wet organic matter into methane-rich biogas and digestate.
Fermentation: Microorganisms convert sugars into ethanol, which is separated for fuel use.
Transesterification: Oils react with an alcohol to form biodiesel and glycerol.
Gasification: Partial oxidation at high temperature produces combustible synthesis gas.
Pyrolysis: Heating without oxygen produces bio-oil, gas and biochar.

Choice of method depends on feedstock moisture, composition and desired fuel. Biogas is one biomass-derived fuel, not a synonym for all biomass energy.

2024 — Q2(a) [5] Tuberculosis and Hepatitis

Suggested coverage: balanced coverage of the two diseases; approximately 2.5 each is a planning guide.

Model answer

Tuberculosis: TB is an infectious disease caused mainly by Mycobacterium tuberculosis. It usually affects the lungs and spreads through the air from people with infectious pulmonary TB. Symptoms include a persistent cough, fever, night sweats and weight loss. Diagnosis uses clinical assessment and appropriate microbiological tests. Treatment combines several antibiotics selected according to susceptibility and clinical eligibility. Early diagnosis, effective treatment, ventilation and respiratory protection reduce spread; BCG particularly protects children against severe TB.

Hepatitis: Hepatitis means liver inflammation, commonly due to viruses A–E. A/E commonly spread through contaminated food or water; B spreads through blood, sex and birth exposure; C is mainly bloodborne; D requires B. Symptoms may include jaundice, dark urine and fatigue. Prevention combines sanitation, safe injections, screened blood and A/B vaccination. Many acute cases receive supportive care; chronic B is suppressible and most C is curable with antivirals.

Key distinction: TB is a bacterial infection, whereas viral hepatitis is caused by viruses and cannot be treated with routine antibacterial drugs.

WHO TB, NIH viral hepatitis.

2024 — Q4(b) [5] Functioning of Liver and Pancreas

Variant B: Discuss the functioning of liver and pancreas. — 5-mark practice answer

The liver and pancreas are accessory digestive organs that also regulate metabolism.

Liver: It produces bile, whose salts emulsify fat and aid absorption. It regulates blood glucose through glycogen storage and breakdown, converts ammonia into urea, metabolises drugs and alcohol, synthesises albumin and clotting factors, and stores vitamins and iron.

Pancreas—exocrine role: It releases pancreatic juice into the duodenum. Bicarbonate neutralises acidic chyme; amylase digests starch; lipase digests fat; protease precursors support protein digestion. Trypsinogen is activated to trypsin in the small intestine.

Pancreas—endocrine role: Beta cells release insulin, promoting glucose uptake and storage and lowering blood glucose. Alpha cells release glucagon, increasing hepatic glucose production when blood glucose falls.

Together, these organs support digestion, nutrient processing and glucose homeostasis.

Suggested balance: approximately half the answer on each organ; include both pancreatic roles.

2024 — Q5(a) [5] Plant Nutrition Elements

Suggested coverage: definition/classification 1; complete enumeration 2; representative functions 2.

Definition

Essential elements are required for normal plant growth, development and completion of the life cycle.
The standard higher-plant list contains 17 elements.
“Macro” and “micro” refer to required quantities, not importance.

Macronutrients — nine

Elements	Principal roles
Carbon, hydrogen, oxygen	Form the framework of organic molecules; obtained mainly from CO₂ and water
Nitrogen	Amino acids, proteins, nucleic acids and chlorophyll
Phosphorus	ATP, nucleic acids and phospholipids
Potassium	Enzyme activation, osmotic balance and stomatal regulation
Calcium	Cell-wall structure, membrane function and signalling
Magnesium	Central component of chlorophyll; enzyme cofactor
Sulphur	Sulphur-containing amino acids and proteins

Micronutrients — eight

Iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel.
They support processes such as enzyme activity, electron transport and growth.
Example: nickel is required for the enzyme urease.

Closing point

Deficiencies may cause chlorosis, poor growth or impaired reproduction.
Symptoms vary with the deficient element; yellow leaves alone do not identify a single deficiency.

Common omission: N, P and K are important fertiliser nutrients, but they are not the complete essential-element list.

2023 Special — Q4(c) [5] Food Cycle in Our Body

Suggested coverage: introduction and pathway 1; five stages with correct mechanisms 4.

Model answer

The food cycle is the processing of food through ingestion, digestion, absorption, assimilation and egestion.

Ingestion: Food enters the mouth, where teeth break it into smaller pieces. Saliva moistens it, and salivary amylase begins starch digestion. Swallowing and oesophageal peristalsis move it to the stomach.
Digestion: The stomach churns food; hydrochloric acid provides an acidic medium for pepsin to digest proteins. In the duodenum, bile emulsifies fats, while pancreatic amylase, proteases and lipase digest carbohydrates, proteins and fats. Intestinal brush-border enzymes complete carbohydrate and protein digestion.
Absorption: Small-intestinal villi and microvilli provide a large surface. Glucose and amino acids enter blood capillaries and travel to the liver through the hepatic portal vein. Most long-chain dietary fats enter lacteals as chylomicrons and later reach the blood.
Assimilation: Cells use absorbed nutrients for energy, growth and repair; surplus nutrients may be stored as glycogen or fat.
Egestion: The large intestine absorbs remaining water and salts. Faeces are stored in the rectum and expelled through the anus.

Diagram cue: mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus; add liver, gallbladder and pancreas beside the duodenum.

Precision: Egestion removes undigested material; excretion removes metabolic wastes.

NIDDK diabetes types, NIDDK causes.

2023 Special — Q5(a) [5] Diabetes: Concept, Causes, Classification

Suggested coverage: definition/mechanism 1; classification and causes 3; consequences 1.

Model answer

Diabetes mellitus is a metabolic disorder characterised by persistent high blood glucose caused by inadequate insulin secretion, impaired insulin action, or both. Insulin normally promotes glucose uptake and storage.

Type	Main mechanism and causes
Type 1	Autoimmune destruction of pancreatic beta cells produces severe insulin deficiency; genetic susceptibility and environmental factors contribute
Type 2	Insulin resistance with progressive beta-cell dysfunction; risk involves genetics, excess adiposity, inactivity and ageing
Gestational	Diabetes diagnosed during pregnancy in someone without previously recognised diabetes; pregnancy-related insulin resistance contributes
Other specific types	Monogenic disorders, pancreatic disease or certain medicines, among other causes

Common symptoms include frequent urination, excessive thirst, fatigue and unexplained weight loss, although type 2 may initially be silent. Persistently high glucose can damage blood vessels, kidneys, nerves and eyes.

Precision: Eating sugar alone is not a complete explanation of diabetes. Type 1 is not caused by poor lifestyle, and diabetes mellitus differs from diabetes insipidus.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2023 Special — Q5(c) [5] Enzymes: Definition, Types, Functions

Suggested coverage: definition and action 1; classes with examples 2.5; functions 1.5.

Model answer

Enzymes are biological catalysts that accelerate reactions by lowering activation energy without being consumed. Most are proteins, but catalytic RNAs called ribozymes also exist. An active site binds suitable substrates; temperature, pH and inhibitors influence activity.

Class	Reaction and example
Oxidoreductases	Electron transfer; dehydrogenases
Transferases	Transfer functional groups; kinases
Hydrolases	Break bonds using water; lipase
Lyases	Non-hydrolytic bond cleavage/addition; decarboxylases
Isomerases	Rearrange atoms within a molecule; phosphoglucose isomerase
Ligases	Join molecules coupled to energy use; DNA ligase
Translocases	Move ions or molecules across membranes; sodium–potassium ATPase

Functions: Amylase, pepsin and lipase digest food. Respiratory enzymes support ATP production. DNA polymerases and ligases enable genome replication and repair. Kinases regulate signalling, and enzyme cascades contribute to blood clotting.

Revision note: Older books list six classes; the current classification includes translocases as class seven. IUBMB enzyme classification.

2023 Special — Q5(d) [5] Cell Structure and 7 Functions of a Cell

Suggested coverage: structure 2; seven functions 3.

Model answer

The cell is the basic structural and functional unit of life. A typical human cell has a plasma membrane, cytoplasm containing organelles, and a nucleus.

Structure: The selectively permeable phospholipid membrane regulates exchange and communication. Cytoplasm contains mitochondria for ATP production, ribosomes for protein synthesis, ER for synthesis and transport, Golgi apparatus for modification and packaging, and lysosomes for intracellular digestion. The nucleus contains DNA; its nucleolus assembles ribosomal subunits.

Seven functions:

Support: Cells form the tissues and organs of the body.
Energy production: Cells convert energy from nutrients into ATP.
Metabolism: Cellular enzymes build and break down molecules.
Protein synthesis: Ribosomes make structural proteins, enzymes and other proteins.
Growth and repair: Cell growth and division replace damaged cells.
Heredity and reproduction: DNA stores information and is passed to daughter cells.
Defence: Specialised immune cells recognise and eliminate pathogens.

These functions are distributed among specialised cells; mature human red cells, for example, lack a nucleus and mitochondria.

Diagram: Draw a typical animal cell and label membrane, cytoplasm, nucleus, mitochondria, ribosomes, ER and Golgi.

2023 — Q3(a)(i) [2.5] Why Bat and Whale Are Mammals

Suggested coverage for a short part: classification and defining traits first, followed by supporting traits. The 2.5-mark allocation is a planning assumption unless printed.

Bats and whales belong to class Mammalia, despite their different habitats and locomotion.
Females possess mammary glands and feed young with milk.
Both possess hair at some life stage; it is sparse in whales.
Both breathe with lungs; whales must surface for air.
They are endothermic, have four-chambered hearts and give birth to live young.
Therefore: classification follows inherited anatomical and physiological characters, not the ability to fly or swim.

Strongest evidence: milk and hair. Endothermy and a four-chambered heart are supporting traits also found in birds.

2023 — Q3(a)(ii) [2.5] Bile

Short-part model answer: Bile is a yellowish-green fluid produced by the liver and stored and concentrated in the gallbladder. Released into the duodenum, its bile salts emulsify fat into small droplets and support micelle formation, assisting lipase action and fat absorption. Bile also carries bilirubin and excess cholesterol for excretion. It contains no digestive enzymes; pancreatic bicarbonate is the main neutraliser of incoming gastric acid.

Coverage: source/storage, fat-processing role and excretory role. The saved 2.5-mark allocation must be checked against the original paper.

2023 — Q3(b) [5] Urine Formation and Role of Kidney

Suggested coverage: kidney functions 2; urine formation and outflow 3.

Model answer

The kidneys maintain the internal environment by filtering blood and producing urine. Their functional units are nephrons.

Functions: They remove urea and other metabolic wastes, regulate water and electrolyte balance, and maintain acid–base balance. They also help regulate blood pressure through renin, stimulate red-cell production through erythropoietin, and activate vitamin D.

Urine formation:

Glomerular filtration: Blood pressure forces water and small dissolved substances from glomerular capillaries into Bowman’s capsule. Blood cells and most large proteins remain in the circulation.
Selective reabsorption: Useful substances, including glucose, amino acids, much of the filtered salts and most water, return from the tubules to blood. The loop of Henle helps establish the concentration gradient needed to conserve water.
Tubular secretion: Substances such as hydrogen ions, potassium and certain drugs move from blood into tubular fluid, helping regulate pH and composition.
Final concentration: ADH increases collecting-duct water permeability, allowing more water to return to blood when water must be conserved.

Urine passes through collecting ducts to the renal pelvis, then ureter → bladder → urethra.

Diagram cue: label glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule and collecting duct; distinguish blood flow from filtrate flow.

2023 — Q3(c)(i) [2.5] Bacterial Cell vs Plant Cell

Suggested coverage: one direct distinction followed by four paired differences.

Model answer

A bacterial cell is prokaryotic, whereas a plant cell is eukaryotic.

Feature	Bacterial cell	Plant cell
DNA	Nucleoid without a nuclear envelope; usually a circular chromosome	Linear chromosomes enclosed in a nucleus
Organelles	No membrane-bound organelles	Mitochondria, ER, Golgi and, in photosynthetic cells, chloroplasts
Wall	Usually peptidoglycan; wall-less exceptions exist	Mainly cellulose
Ribosomes	70S	80S in cytosol; organelle ribosomes differ
Division	Usually binary fission	Mitosis; meiosis during sexual reproduction

Both possess a cell membrane, cytoplasm, DNA and ribosomes.

2023 — Q3(c)(ii) [2.5] Cold-Blooded Animals and Temperature

Suggested coverage for a short part: ectothermy → falling temperature → reduced enzyme activity and movement; add one example.

“Cold-blooded” usually refers here to ectotherms, whose body temperature depends strongly on environmental heat.
Falling environmental temperature lowers their body temperature.
Enzyme-controlled reactions and metabolism slow.
Energy supply, nerve activity and muscle performance consequently decrease, making movement sluggish.
Examples include a lizard or frog in cool conditions; some animals bask to warm themselves.

Avoid: saying low temperature necessarily destroys or denatures their enzymes.

CDC hepatitis overview, WHO hepatitis.

2023 — Q3(d) [5] Hepatitis: Types, Causes, Prevention, Cure

Suggested coverage: definition 0.5; types/routes 2; prevention 1.5; treatment 1.

Model answer

Hepatitis is inflammation of the liver. Causes include viruses, alcohol, medicines and autoimmune disease; viral hepatitis has five major types.

Type	Principal route / distinguishing feature
A	Faecal–oral; contaminated food/water; usually acute
B	Blood, sexual exposure and mother-to-child; may become chronic
C	Mainly infected blood; often chronic
D	Requires hepatitis B infection; chiefly blood/body-fluid exposure
E	Commonly contaminated water; foodborne zoonotic transmission also occurs

Possible symptoms include fatigue, nausea, abdominal discomfort, dark urine and jaundice; infection may be asymptomatic. Chronic B and C can lead to cirrhosis and liver cancer.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2023 — Q5(b) [5] Digestion of Carbohydrates, Proteins, and Fats

Suggested coverage: brief definition 0.5; balanced three-nutrient comparison 3.5; absorption 1.

Model answer

Digestion breaks large food molecules into smaller absorbable products through mechanical processing and enzymatic hydrolysis.

Nutrient	Main sites and agents	Products
Carbohydrates	Salivary amylase in mouth; pancreatic amylase and brush-border enzymes in small intestine	Glucose, galactose and fructose
Proteins	Pepsin in acidic stomach; pancreatic proteases and intestinal peptidases in small intestine	Mainly amino acids, with small peptides absorbed and further processed
Fats	Bile emulsification in duodenum; mainly pancreatic lipase in small intestine	Mainly free fatty acids and monoglycerides

Bile is not an enzyme: it increases the fat surface available to lipase. Pancreatic bicarbonate neutralises incoming gastric acid, enabling intestinal enzymes to function.

Absorption: Monosaccharides and amino acids enter villus capillaries and portal blood. Most long-chain fat products are reassembled into triglycerides and packaged as chylomicrons, entering lacteals before reaching the blood.

Diagram cue: Label mouth, stomach and duodenum with their relevant enzymes; finish with villus capillary versus lacteal.

2022 — Q3(a) [5] Vaccination: Types, Side-Effects, Effectiveness

Suggested coverage: immune mechanism 1; types/examples 2; effects and effectiveness 2.

Model answer

Vaccination exposes the immune system to an antigen or instructions for making one, inducing protective immune responses and memory without requiring the full disease.

Types with examples: Live attenuated vaccines include measles and OPV; inactivated vaccines include IPV. Subunit/recombinant vaccines include hepatitis B, conjugate vaccines include Hib, and toxoid vaccines include tetanus. Genetic platforms include mRNA and DNA vaccines.

Side effects: Temporary injection-site pain, tiredness and fever may occur. Serious allergic reactions are rare. Risks and suitability depend on the particular vaccine and recipient.

Effectiveness: Vaccines reduce the risk of infection, severe illness or transmission to varying degrees. Protection depends on the vaccine, correct dosing, time since vaccination and the pathogen. Some require boosters; no vaccine guarantees absolute protection. High coverage can reduce spread for diseases where vaccination interrupts transmission.

Example: Smallpox eradication illustrates the population benefit of coordinated vaccination.

CDC vaccine basics.

2022 — Q3(b) [5] Polio: Symptoms, Spreading, Prevention, Vaccine

Suggested coverage: cause/spread 1; symptoms 1; vaccination and prevention 3.

Model answer

Poliomyelitis is a highly infectious disease caused by poliovirus. It multiplies in the intestine and can invade the nervous system, damaging motor neurons and causing paralysis.

Spread and symptoms: Transmission is mainly faecal–oral through contaminated hands, food or water. Most infections cause no symptoms; symptomatic cases can involve fever, fatigue, headache, vomiting, neck stiffness and limb pain. About one in 200 infections causes irreversible paralysis. Respiratory-muscle involvement can be fatal.

Vaccines: Oral polio vaccine (OPV) contains live attenuated virus and induces useful intestinal immunity. Inactivated polio vaccine (IPV) is injected and strongly protects against paralysis. Their use follows immunisation programmes; vaccination requires the recommended doses.

Prevention: High routine coverage, supplementary campaigns, safe water, sanitation, hand hygiene and surveillance interrupt transmission. Reaching missed children is particularly important in eradication work.

There is no cure that reverses established paralytic polio; prevention through immunisation is essential.

WHO poliomyelitis.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2022 — Q3(c) [5] DNA and RNA

Suggested coverage: definitions/shared units 1; comparison 3; information flow 1.

Model answer

DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are nucleic acids made of nucleotides. Each nucleotide contains a sugar, phosphate and nitrogenous base. Phosphodiester bonds join the sugar–phosphate backbone.

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Typical structure	Two antiparallel complementary strands forming a double helix	Usually single-stranded, often folded
Eukaryotic location	Mainly nucleus; also mitochondria and chloroplasts	Nucleus and cytoplasm, including ribosomes
Main role	Long-term storage and transmission of genetic information	Gene expression, regulation and some catalytic functions

In DNA, A pairs with T and G with C. Messenger RNA carries a transcribed sequence to ribosomes; transfer RNA delivers amino acids; ribosomal RNA forms the structural and catalytic core of ribosomes.

Information flow: DNA → transcription → RNA → translation → protein. RNA is not merely a temporary copy: different RNAs perform distinct tasks.

2021 — Q3(a) [5] Relationship Between Cells, Tissues, and Organs

Suggested coverage: definitions 2; linked examples and hierarchy 3.

Model answer

Multicellular organisms show increasing levels of organisation: cell → tissue → organ → organ system → organism.

A cell is the basic living unit. A tissue is an organised group of cells, with any associated extracellular material, performing related functions. An organ consists of different tissues working together for a particular function.

Animal example: Cardiac muscle cells form cardiac muscle tissue. In the heart, this tissue works with connective tissue, vascular tissue and nervous tissue to pump blood. The heart and blood vessels together form the circulatory system.

Plant example: Epidermal cells form epidermal tissue. In a leaf, epidermis, mesophyll and vascular tissues cooperate in photosynthesis and gas exchange. Xylem supplies water, mesophyll fixes carbon, and the epidermis limits water loss.

Thus, cells specialise, tissues coordinate related work, and organs integrate several tissue functions.

2021 — Q3(b) [5] Cell Wall vs Cell Membrane

Suggested coverage: definitions 1; paired structural and functional differences 4.

Model answer

The cell membrane is the living cell’s selectively permeable boundary. A cell wall is an additional extracellular layer outside the membrane in plants, fungi and many prokaryotes.

Feature	Cell wall	Cell membrane
Occurrence	Plants, fungi and most bacteria; absent in animals	All cells
Composition	Cellulose in plants; chitin in fungi; peptidoglycan in most bacteria	Lipid bilayer with proteins
Position	Outside the plasma membrane	Surrounds cytoplasm; inside the wall if present
Mechanical character	Relatively rigid and supportive	Thin, flexible and dynamic
Permeability	Porous to water and many small solutes	Selectively controls movement using bilayer and transport proteins
Main roles	Shape, protection and resistance to osmotic bursting	Transport, signalling, recognition and internal regulation

The wall provides mechanical support, whereas the membrane controls the cell’s chemical exchange. A plant cell requires both structures.

2021 — Q3(c) [5] Transpiration and Leaf Structure

Suggested coverage: definition/mechanism 1.5; leaf adaptations 2.5; significance 1.

Definition

Transpiration is loss of water vapour from aerial plant parts, mainly through leaf stomata.

Mechanism

Water reaches the leaf through xylem.
It evaporates from moist mesophyll cell walls into internal air spaces.
Water vapour diffuses through stomata to the atmosphere along a concentration gradient.

Leaf structure	Contribution
Broad lamina	Provides a large surface across which exchange may occur
Mesophyll and air spaces	Provide moist evaporation surfaces and a route for vapour diffusion
Stomata	Main adjustable openings for vapour loss
Guard cells	Regulate stomatal opening, balancing CO₂ entry against water loss
Waxy cuticle	Restricts uncontrolled evaporation
Veins containing xylem	Replace water lost from the leaf

Significance

Evaporation helps drive transpiration pull, supporting upward movement of water and minerals.
It cools leaves.
Excessive loss without replacement reduces turgor and can cause wilting.

Diagram labels: cuticle, epidermis, mesophyll, air spaces, xylem, guard cells, stoma and outward water-vapour arrows.

Correction: transpiration does not automatically maintain turgor; water uptake must balance water loss.

2021 — Q3(d) [5] Double Circulation and the Heart

Suggested coverage: definition and circuits 2; adaptations linked to function 3.

Model answer

Double circulation means that blood passes through the heart twice during one complete journey through the lungs and body.

Pulmonary circuit: right ventricle → pulmonary arteries → lung capillaries → pulmonary veins → left atrium. Blood releases carbon dioxide and gains oxygen.

Systemic circuit: left ventricle → aorta → body tissues → venae cavae → right atrium. Blood supplies tissues with oxygen and nutrients and collects wastes.

Adaptations of the heart:

Four chambers and a complete septum keep oxygenated and deoxygenated blood separate.
A thick muscular left ventricle generates the high pressure required to supply the whole body.
A thinner right ventricular wall pumps through the shorter pulmonary circuit at lower pressure, protecting delicate lung capillaries.
Atrioventricular and semilunar valves prevent backflow and maintain one-way movement.
Coordinated rhythmic contraction, initiated by the sinoatrial node, allows the atria to fill the ventricles before ventricular ejection.

This arrangement supplies oxygenated blood efficiently while maintaining suitable pressures in the two circuits.

Diagram cue: body → right atrium → right ventricle → lungs → left atrium → left ventricle → body. Add the named vessels and arrows.

2021 — Q5(b) [5] Bread Decomposition Due to Fungi

Suggested coverage: cause/conditions 1; digestion sequence 3; examples and significance 1.

Cause

Airborne fungal spores can settle on exposed bread.
Bread provides nutrients; sufficient moisture and suitable warmth allow many moulds to grow.

Sequence

A spore germinates on suitable bread.
Thread-like hyphae grow and form a mycelium.
The fungus secretes digestive enzymes into the bread.
Enzymes break complex substances into smaller soluble molecules.
The fungus absorbs these products for growth and respiration.

Visible result

Fungal colonies produce the familiar fuzzy patches; colour depends on the mould and its reproductive structures.
Examples include Rhizopus and Penicillium.

Biological explanation

This is saprotrophic nutrition with extracellular digestion.
Fungi recycle nutrients in ecosystems; on stored bread, the same process causes spoilage.
Exposure alone does not guarantee rapid mould growth: moisture, temperature and storage conditions influence the rate.

Flow diagram: spores → germination → hyphae → enzymes → digestion → absorption.

Avoid: saying fungi make their food through photosynthesis or that all moulds produce the same toxins.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2020 — Q3(b) [5] Carbohydrates: Classification with Examples

Suggested coverage: definition 1; three classes with examples and functions 4.

Model answer

Carbohydrates are organic compounds containing carbon, hydrogen and oxygen. Many approximately follow the formula Cₓ(H₂O)ᵧ, although this is not universal. Their units are linked by glycosidic bonds.

Class	Structure	Examples and roles
Monosaccharides	Single sugar units; cannot be hydrolysed into simpler carbohydrates	Glucose supplies energy; ribose and deoxyribose occur in nucleic acids
Oligosaccharides	Short chains, commonly 2–10 sugar units	Disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose) and maltose (two glucose units)
Polysaccharides	Long chains of monosaccharides	Starch stores glucose in plants; glycogen stores it in animals; cellulose supports plant walls

Functions: Carbohydrates provide respiratory fuel, energy reserves and structural support. Cell-surface carbohydrates also contribute to recognition. Humans do not digest cellulose enzymatically, but it contributes dietary fibre.

Diagram cue: one sugar unit → short chain → long chain; name the glycosidic link.

2020 — Q5(a) [5] Hepatitis: Types and Preventive Measures

Suggested coverage: definition 0.5; types/routes 2; prevention 1.5; treatment 1.

Model answer

Hepatitis is inflammation of the liver. Causes include viruses, alcohol, medicines and autoimmune disease; viral hepatitis has five major types.

Type	Principal route / distinguishing feature
A	Faecal–oral; contaminated food/water; usually acute
B	Blood, sexual exposure and mother-to-child; may become chronic
C	Mainly infected blood; often chronic
D	Requires hepatitis B infection; chiefly blood/body-fluid exposure
E	Commonly contaminated water; foodborne zoonotic transmission also occurs

Possible symptoms include fatigue, nausea, abdominal discomfort, dark urine and jaundice; infection may be asymptomatic. Chronic B and C can lead to cirrhosis and liver cancer.

CDC hepatitis overview, WHO hepatitis.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2019 — Q2(a) [5] Vitamin Deficiency Diseases (matching table)

Structured model answer (5 marks):

Vitamins are essential organic compounds needed in small amounts for normal body function, and their deficiency causes specific diseases: Vitamin A deficiency causes night blindness (xerophthalmia); Vitamin B1 (thiamine) deficiency causes beriberi; Vitamin B2 (riboflavin) deficiency causes cracked lips/skin lesions (ariboflavinosis); Vitamin B3 (niacin) deficiency causes pellagra; Vitamin B12 deficiency causes megaloblastic anaemia; pernicious anaemia is an autoimmune cause of B12 malabsorption; Vitamin C deficiency causes scurvy (bleeding gums, joint pain); Vitamin D deficiency causes rickets in children and osteomalacia in adults (weak/soft bones); Vitamin K deficiency causes poor blood clotting (excessive bleeding).

2019 — Q2(b) [5] Cholesterol and Cardiovascular Disease

Suggested coverage: definition/functions 2; level qualification 1; harmful mechanism 2.

Model answer

Cholesterol is a sterol lipid synthesised mainly in the liver and also obtained from animal foods. Because it is poorly soluble in water, lipoproteins carry it in blood.

Importance: It helps regulate cell-membrane properties and is a precursor of steroid hormones, bile acids and vitamin D.

Blood levels: A commonly quoted adult desirable total-cholesterol value is below 200 mg/dL. This is a population reference, not a universal treatment target; LDL goals depend on overall cardiovascular risk. LDL carries cholesterol to tissues, while HDL participates in its return towards the liver.

Why excessive LDL is harmful: LDL-containing particles can accumulate in arterial walls and promote inflammation and atherosclerotic plaque formation. Plaques may narrow coronary arteries, reducing oxygen supply and causing angina. Plaque rupture can trigger a clot that blocks blood flow, producing a myocardial infarction. Similar disease in cerebral arteries can cause stroke.

Genetics, diets high in saturated or trans fats, smoking and some metabolic disorders influence risk. Prevention includes appropriate diet, physical activity, tobacco avoidance and risk-based medical management.

Exam focus: Explain plaque rupture and thrombosis; “fat blocks the heart” is insufficient.

2019 — Q3(d) [5] Vaccines vs Antibiotics

Suggested coverage: definitions 1; four paired distinctions 3; resistance qualification 1.

Model answer

Vaccines prepare immune defences against a specific disease; antibiotics kill bacteria or inhibit bacterial growth.

Feature	Vaccines	Antibiotics
Main purpose	Prevention and immune preparation	Treatment of susceptible bacterial infections; selected preventive uses
Mechanism	Antigen-specific immune responses and memory	Act on bacterial targets such as walls or ribosomes
Target	Certain viral or bacterial diseases	Bacteria, not viruses
Timing	Usually before exposure; some post-exposure uses	Usually during infection
Duration	Protection may persist, sometimes needing boosters	Drug effect requires an appropriate regimen; does not itself create immune memory

For example, hepatitis B vaccine prevents infection, while an appropriate antibiotic regimen treats bacterial TB. Antibiotics do not treat influenza or dengue. Resistance arises in microbes, not because the patient’s body becomes resistant.

CDC antibiotic use.

2019 — Q4(c) [5] Egg-Laying Mammals

Suggested coverage: reproductive exception 1; examples/distribution 2; defining mammalian traits 2.

Direct answer

No. Most mammals give birth to live young, but monotremes lay eggs.

Examples and distribution

Example	Natural distribution
Platypus	Eastern Australia, including Tasmania
Echidnas	Australia and New Guinea; distribution varies by species

Why they remain mammals

They have hair.
Females produce milk for their young.
They possess mammalian skeletal and physiological characteristics.
Monotremes lack nipples; milk is released through mammary openings onto skin/hair.
Egg laying is a reproductive exception within mammals, not evidence that they are birds or reptiles.

Comparison

Monotremes: egg-laying mammals.
Marsupials: live young born relatively undeveloped.
Placental mammals: prolonged development supported by a complex placenta.

Conclusion

Live birth is common among mammals but is not a universal defining feature.

Avoid: calling living monotremes an “intermediate species” between reptiles and mammals.

2019 — Q5(c) [5] Danger of Antibiotic Misuse

Suggested coverage: misuse examples 1; selection and spread 2; consequences/prevention 2.

Model answer

Antibiotic misuse includes unnecessary treatment of viral illness, use without proper assessment, incorrect drug selection, and inappropriate dose or duration.

Resistance mechanism: Bacterial populations may contain resistant variants or acquire resistance genes. Antibiotic exposure kills susceptible bacteria while resistant bacteria survive and multiply. Resistance genes may also spread between bacteria. Unnecessary or inappropriate exposure increases selection pressure.

Consequences: Resistant infections become harder to treat, may require more toxic or expensive medicines, prolong illness and increase the risk of complications and death. Unnecessary antibiotics can also cause adverse effects and disturb normal microbiota.

Prevention: Use antibiotics only when indicated and exactly as prescribed. Do not share them or use leftovers. Prescribers should select appropriate agents and durations, supported by testing when relevant. Infection prevention, vaccination and surveillance reduce the need for antibiotics.

Precision: Resistance develops in bacteria; it is not immunity acquired by the patient.

CDC antibiotic use.

2018 — Q3(a) [5] Polio

Suggested coverage: cause/spread 1; symptoms 1; vaccination and prevention 3.

Model answer

Poliomyelitis is a highly infectious disease caused by poliovirus. It multiplies in the intestine and can invade the nervous system, damaging motor neurons and causing paralysis.

There is no cure that reverses established paralytic polio; prevention through immunisation is essential.

WHO poliomyelitis.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2018 — Q3(c) [5] Digestion of Carbohydrates

Suggested coverage: definition 1; sites, enzymes, products and absorption 4.

Model answer

Carbohydrates include sugars and polymers such as starch; digestible carbohydrates provide an important source of glucose.

Mouth: Chewing increases surface area. Salivary amylase begins starch hydrolysis, forming maltose and shorter carbohydrate chains.
Stomach: Salivary action may continue briefly inside a food bolus, but gastric acidity subsequently inactivates amylase. The stomach secretes no major carbohydrate-digesting enzyme.
Small intestine: Pancreatic amylase continues starch digestion. Brush-border maltase, sucrase and lactase convert disaccharides into absorbable monosaccharides.
Absorption: Glucose, galactose and fructose enter intestinal epithelial cells and then villus blood capillaries. Portal blood carries them to the liver for processing, storage or distribution.
Residue: Undigested carbohydrate, including much fibre, reaches the colon; some is fermented by microbes.

Flow: starch → smaller sugars → monosaccharides → intestinal blood → liver.

The endpoint is absorbable monosaccharides, not absorption of intact starch.

2018 — Q3(d) [5] Cell Structure: Animal vs Plant

Suggested coverage: basic structure 2; comparison 3.

Model answer

A cell is the basic unit of life. Plant and animal cells are eukaryotic: their DNA is enclosed in a nucleus, while their cytoplasm contains mitochondria, ribosomes, ER and Golgi apparatus. The cell membrane regulates entry and exit; organelles perform specialised metabolic tasks.

Feature	Plant cell	Animal cell
Wall	Cellulose wall outside the membrane provides support	No cell wall
Plastids	Chloroplasts in photosynthetic cells	No chloroplasts
Vacuole	Usually a large central vacuole maintaining turgor	Usually smaller vesicles/vacuoles
Shape	Often relatively fixed because of the wall	Often flexible or irregular
Centrioles	Absent from most higher-plant cells	Usually present

Both cell types respire; plant cells do not rely on photosynthesis instead of respiration. Chloroplasts are generally absent from root cells.

Diagram: Draw two simple labelled cells; highlight wall, chloroplast and central vacuole in the plant cell.

2017 — Q3(a) [5] Common Causes of Heart Attack

Suggested coverage: definition 1; direct mechanism 2; risk factors with explanation 2.

Model answer

A heart attack, or myocardial infarction, occurs when prolonged inadequate coronary blood supply causes death of heart muscle.

Main mechanism: Atherosclerotic plaque develops in a coronary artery. If a plaque ruptures or erodes, platelets and clotting factors form a thrombus. The clot may obstruct blood flow, depriving myocardium of oxygen and nutrients. Coronary spasm and other mechanisms can also cause infarction.

Major risk factors:

Elevated LDL cholesterol contributes to plaque formation.
Hypertension injures arterial walls and increases cardiac workload.
Smoking promotes vascular injury and thrombosis.
Diabetes accelerates vascular disease.
Physical inactivity and excess adiposity worsen metabolic risk.
Age and family history indicate non-modifiable susceptibility.

Thus, distinguish the immediate cause—loss of coronary perfusion—from factors that increase its probability.

Diagram cue: coronary artery → plaque rupture → clot → reduced oxygen → myocardial cell death.

NIDA prescription drug report.

2017 — Q3(b) [5] Drug Addiction vs Drug Abuse

Suggested coverage: definitions 1; paired distinctions 3; dependence qualification/example 1.

Model answer

Drug abuse is older terminology for harmful or inappropriate substance use. Addiction is characterised by compulsive use despite harm and impaired control. Modern clinical assessment generally uses “substance use disorder.”

Aspect	Harmful use / abuse	Addiction
Pattern	Use causes risk or harm; may be episodic	Persistent compulsion and difficulty controlling use
Control	Loss of control need not be established	Impaired control is central
Priorities	Harm can occur without drug seeking dominating life	Substance use may displace responsibilities and relationships
Continuation	May occur without a sustained compulsive pattern	Use continues despite adverse consequences

Tolerance and withdrawal may occur, but neither alone defines addiction. Physical dependence can develop during appropriate prescribed treatment without compulsive misuse. Conversely, addiction can exist without prominent withdrawal.

For example, a single episode of dangerous misuse is harmful but does not by itself establish addiction. Repeated compulsive use despite serious harm warrants assessment for a substance use disorder.

2017 — Q3(c) [5] Structure and Functions of the Human Ear

Suggested coverage: labelled anatomical diagram 2; structure and functions 3. The split is a practice guide.

Model answer

The ear detects sound and helps maintain balance. It consists of outer, middle and inner regions.

Outer ear: The pinna collects sound waves and directs them through the auditory canal to the tympanic membrane (eardrum).

Middle ear: Eardrum vibrations pass through the malleus, incus and stapes to the oval window. The ossicles increase pressure at the oval window for effective transmission into inner-ear fluid. The Eustachian tube connects the middle ear with the pharynx and equalises pressure across the eardrum.

Inner ear—hearing: Vibrations create waves in cochlear fluid, moving the basilar membrane and bending hair cells in the organ of Corti. These cells convert mechanical stimulation into electrical signals carried through the cochlear nerve to the brain.

Inner ear—balance: Semicircular canals detect rotational acceleration. The utricle and saccule detect linear acceleration and head position relative to gravity, supporting posture and equilibrium.

Required diagram: Use the anatomical ear figure later on this page as a drawing reference. Label pinna, auditory canal, eardrum, malleus, incus, stapes, oval window, cochlea, semicircular canals, vestibule, auditory nerve and Eustachian tube. A flowchart alone does not satisfy “draw the structure.”

2017 — Q3(d) [5] Significance of Vitamins; Fat-Soluble Vitamins

Vitamins are organic micronutrients needed in small amounts for metabolism, immunity and growth. Fat-soluble: A (vision, night blindness), D (calcium absorption, rickets), E (antioxidant, muscle weakness), K (clotting, bleeding). Covered in detail under IV. Food Science.

2016 — Q4(a) [5] Vaccines and DNA Vaccines

Suggested coverage: general mechanism 1.5; DNA mechanism 2; benefits/limitations 1.5.

Model answer

A vaccine stimulates adaptive immunity by presenting antigens or genetic instructions for their production. Antigen recognition activates immune cells and creates memory, allowing a faster protective response upon later exposure.

DNA vaccine mechanism:

A manufactured plasmid contains a gene encoding a pathogen antigen.
Delivery introduces the plasmid into some host cells.
In the nucleus, the gene is transcribed into mRNA.
Ribosomes translate the mRNA into antigen.
Antigen presentation stimulates antibody and T-cell responses and immune memory.

Potential benefits: No live pathogen is required, the platform is adaptable, and production and storage may offer practical advantages.

Limitations: Efficient delivery and sufficient immune responses can be challenging. Safety, effectiveness, cost and approval must be evaluated for each product. DNA vaccines should not be described as automatically cheaper, completely risk-free or equivalent to mRNA vaccines.

Diagram: plasmid DNA → host-cell transcription → mRNA → antigen → immune response.

2016 — Q4(b) [5] Dengue

Suggested coverage: agent/vector 1; practical prevention linked to transmission 4.

Model answer

Dengue is caused by dengue virus. Its principal vector is the infected female Aedes aegypti mosquito; Ae. albopictus can also transmit it.

Prevention:

Empty, scrub or remove water-holding containers, tyres and discarded objects to destroy breeding sites.
Keep water-storage vessels tightly covered and maintain gutters and drains.
Use suitable repellents, long sleeves and window or door screens to reduce bites.
Protect daytime sleepers with nets, because Aedes commonly bites during daylight.
Prevent mosquitoes from biting infected people, reducing onward transmission.
Support surveillance, community clean-up and targeted larval/adult mosquito control by public-health services.

Control should focus on sustained source reduction; fogging alone is temporary and does not remove eggs or breeding containers. Vaccination eligibility depends on the vaccine and local programme.

Exam focus: This question asks prevention; a long account of symptoms and treatment would displace relevant points.

CDC dengue prevention.

2016 — Q5(a) [5] Liver as the "Chief Chemist" of the Body

Variant A: “Liver is the chief chemist in the human body.” Comment. — 5-mark practice answer

The liver is called the chief chemist because it carries out numerous reactions essential for metabolism, storage, detoxification and excretion.

Carbohydrate metabolism: It stores glucose as glycogen, breaks glycogen down when required and forms glucose from non-carbohydrate sources, helping maintain blood glucose.
Protein metabolism: It removes amino groups from excess amino acids and converts toxic ammonia into urea for renal excretion. It also synthesises albumin and many clotting factors.
Fat metabolism: It processes fatty acids and synthesises cholesterol and lipoproteins.
Detoxification: It metabolises many drugs, alcohol and other potentially harmful substances.
Bile formation: It produces bile, supporting fat digestion and absorption and providing a route for bilirubin and excess cholesterol excretion.
Storage: It stores glycogen, iron and vitamins such as A and B12.

These coordinated functions explain its central role in maintaining the chemical balance of blood.

2. Biomolecules — Proteins, Lipids, Carbohydrates and Enzymes

2016 — Q5(b) [5] Cholesterol

Suggested coverage: definition/functions 2; level qualification 1; harmful mechanism 2.

Model answer

Cholesterol is a sterol lipid synthesised mainly in the liver and also obtained from animal foods. Because it is poorly soluble in water, lipoproteins carry it in blood.

Importance: It helps regulate cell-membrane properties and is a precursor of steroid hormones, bile acids and vitamin D.

Exam focus: Explain plaque rupture and thrombosis; “fat blocks the heart” is insufficient.

2015 — Q3(b) Kidney Function

Suggested coverage: kidney functions 2; urine formation and outflow 3.

Model answer

The kidneys maintain the internal environment by filtering blood and producing urine. Their functional units are nephrons.

Urine formation:

Glomerular filtration: Blood pressure forces water and small dissolved substances from glomerular capillaries into Bowman’s capsule. Blood cells and most large proteins remain in the circulation.
Selective reabsorption: Useful substances, including glucose, amino acids, much of the filtered salts and most water, return from the tubules to blood. The loop of Henle helps establish the concentration gradient needed to conserve water.
Tubular secretion: Substances such as hydrogen ions, potassium and certain drugs move from blood into tubular fluid, helping regulate pH and composition.
Final concentration: ADH increases collecting-duct water permeability, allowing more water to return to blood when water must be conserved.

Urine passes through collecting ducts to the renal pelvis, then ureter → bladder → urethra.

Diagram cue: label glomerulus, Bowman’s capsule, proximal tubule, loop of Henle, distal tubule and collecting duct; distinguish blood flow from filtrate flow.

2015 — Q7(a) Pollen Allergy

Suggested coverage: definition/trigger 1; mechanism 2; manifestations and control 2.

Model answer

Pollen allergy is an inappropriate immune response to proteins in pollen from plants such as grasses, weeds and trees. It commonly causes seasonal allergic rhinitis, or hay fever.

Mechanism: During sensitisation, the immune system produces pollen-specific IgE antibodies that attach to mast cells. On later exposure, the allergen cross-links this IgE, triggering release of histamine and other mediators. These produce inflammation of nasal and eye tissues.

Manifestations: Sneezing, a runny or blocked nose, itchy nose and watery, itchy eyes are typical. Susceptible people may also develop asthma symptoms. Timing depends on local plants and pollen seasons.

Control: Reduce exposure during high pollen periods, keep outdoor pollen out of living spaces where practical, and use appropriate clinician-guided allergy treatment. Selected patients benefit from allergen immunotherapy.

Distinction: Pollen allergy is neither a contagious infection nor a reaction to every kind of pollen.

2015 — Q7(b) Antibiotics, Hormones, and Greenhouse Effect (short notes)

Suggested coverage: use only the space allocated to each note; the original mixed prompt also includes greenhouse effect.

Model answer

Antibiotics: These medicines kill or inhibit susceptible bacteria by targeting processes such as cell-wall formation or protein synthesis. Penicillins are an example. Antibiotics do not act against viruses. Their selection depends on the infection and susceptibility; inappropriate use favours resistance.

Hormones: Hormones are chemical messengers secreted by endocrine cells. They reach target cells, often through blood, and act through specific receptors. Insulin from pancreatic beta cells lowers blood glucose by supporting uptake and storage; thyroid hormones influence metabolic activity. Feedback mechanisms regulate secretion, helping maintain homeostasis.

Exam scope: If the paper also asks for the greenhouse effect, answer that separately: atmospheric gases absorb and re-emit outgoing terrestrial infrared radiation, warming the surface and lower atmosphere. Increased greenhouse gases strengthen the natural effect. Do not allocate the entire mixed question’s marks to these two biology notes.

2015 — Q9(a) Anemia

Suggested coverage: definition 1; causes 2; symptoms/mechanism 2.

Model answer

Anaemia is a haemoglobin concentration below the appropriate reference range for a person’s age and physiological state. It reduces the oxygen-carrying capacity of blood.

Causes:

Reduced production: Iron deficiency limits haemoglobin synthesis; vitamin B12 or folate deficiency impairs red-cell production. Kidney disease can reduce erythropoietin.
Blood loss: Heavy menstrual bleeding, gastrointestinal bleeding or injury can cause anaemia.
Increased destruction: Haemolytic disorders, including some inherited conditions such as sickle-cell disease and thalassaemia, shorten red-cell survival.

Symptoms and signs: Fatigue, weakness, pallor, dizziness, breathlessness and palpitations result from reduced oxygen delivery and compensatory cardiovascular activity. Mild or slowly developing anaemia may produce few symptoms.

Anaemia is not synonymous with iron deficiency. Management requires identifying its cause; iron is appropriate for iron deficiency rather than automatically for every anaemia.