BPSC Biology — Batch 1 Q191–Q240 · 50 Questions
Cell Biology
Q191EasyBPSC Prelims
The basic structural and functional unit of life is:
ATissue
BOrgan
CCell
DMolecule
Show Answer
✔ C — Cell
Cell is the basic structural and functional unit of all living organisms.
- Proposed by Matthias Schleiden (plants, 1838) and Theodor Schwann (animals, 1839) → Cell Theory
- Robert Hooke (1665): First observed cells in cork using a primitive microscope
- All living organisms are made of one or more cells
- All cells arise from pre-existing cells (Virchow, 1855)
Cell Theory: (1) All living organisms are composed of cells; (2) The cell is the basic unit of life; (3) All cells arise from pre-existing cells.
*Why A is wrong:* Tissue = group of similar cells performing the same function — tissues are made of cells.
*Why B is wrong:* Organ = group of tissues working together — organs are above the cell level.
*Why D is wrong:* Molecules are non-living chemical units — cells are the smallest living unit.
Q192EasyBPSC Prelims
The powerhouse of the cell is:
ANucleus
BRibosome
CMitochondria
DGolgi apparatus
Show Answer
✔ C — Mitochondria
Mitochondria = "powerhouse of the cell" — site of cellular respiration and ATP production.
- Double membrane organelle (outer + inner with cristae folds)
- Contains its own DNA and ribosomes (semi-autonomous organelle)
- Site of Krebs cycle (matrix) and oxidative phosphorylation (inner membrane)
- ATP (adenosine triphosphate) = energy currency of cells
Functions of organelles:
- Nucleus: Control centre (DNA storage, gene expression)
- Ribosome: Protein synthesis (translation)
- Mitochondria: Energy production (ATP)
- Golgi apparatus: Packaging and secretion of proteins/lipids
- Chloroplast (plants): Photosynthesis
*Why A is wrong:* Nucleus = control centre/brain of the cell, not energy production.
*Why B is wrong:* Ribosome = protein synthesis site.
*Why D is wrong:* Golgi apparatus = packages and modifies proteins for secretion.
Q193EasyBPSC Prelims
Which of the following is found in plant cells but NOT in animal cells?
AMitochondria
BRibosome
CCell wall and chloroplast
DNucleus
Show Answer
✔ C — Cell wall and chloroplast
Plant cells have structures ABSENT in animal cells:
1. Cell wall (made of cellulose) — provides rigidity, shape, and support
2. Chloroplasts — site of photosynthesis (contain chlorophyll)
3. Large central vacuole — for water storage and turgor pressure
4. Plasmodesmata — channels connecting adjacent plant cells
Animal cells have structures ABSENT in plant cells:
1. Centrioles — involved in cell division (MTOC)
2. Lysosomes — more prominent in animal cells
*Why A is wrong:* Mitochondria are present in BOTH plant and animal cells.
*Why B is wrong:* Ribosomes are present in ALL cells (prokaryotes + eukaryotes).
*Why D is wrong:* Nucleus is present in all eukaryotic cells (plant AND animal).
Q194MediumBPSC Prelims
Prokaryotic cells differ from eukaryotic cells in that prokaryotes:
AHave no cell membrane
BHave no nucleus (no membrane-bound organelles)
CHave no ribosomes
DAre always multicellular
Show Answer
✔ B — Have no nucleus (no membrane-bound organelles)
Prokaryotes (pro = before, karyon = nucleus): do NOT have a membrane-bound nucleus or membrane-bound organelles.
Examples: Bacteria, Archaea, Cyanobacteria (blue-green algae)
Key differences:
| Feature | Prokaryote | Eukaryote |
|---------|-----------|-----------|
| Nucleus | Absent (nucleoid region) | Present (membrane-bound) |
| Size | 1–10 μm | 10–100 μm |
| Ribosomes | 70S | 80S |
| Organelles | None (membrane-bound) | Present |
| DNA | Circular, naked | Linear, with histones |
| Cell wall | Present (peptidoglycan) | Varies |
*Why A is wrong:* All cells (including prokaryotes) have a cell membrane — it's essential for life.
*Why C is wrong:* Prokaryotes DO have ribosomes (70S), just smaller than eukaryotic (80S).
*Why D is wrong:* Prokaryotes are UNICELLULAR; eukaryotes can be uni- or multicellular.
Q195MediumBPSC Prelims
The process of cell division where the chromosome number is halved is called:
AMitosis
BMeiosis
CAmitosis
DBinary fission
Show Answer
✔ B — Meiosis
Meiosis (reductional division): chromosome number is halved (2n → n).
- Occurs in: gonads (testes, ovaries) — produces gametes (sperm, eggs)
- Two divisions: Meiosis I (separation of homologous chromosomes) + Meiosis II (sister chromatid separation)
- Products: 4 haploid (n) cells from one diploid (2n) cell
- Crossing over during Prophase I → genetic variation
Mitosis (equational division): chromosome number maintained (2n → 2n).
- Occurs in: somatic (body) cells — growth, repair, asexual reproduction
- Products: 2 diploid cells from one diploid cell (genetically identical)
*Why A is wrong:* Mitosis = equal division, no reduction in chromosome number.
*Why C is wrong:* Amitosis = direct (simple) cell division without spindle formation — occurs in some lower organisms.
*Why D is wrong:* Binary fission = prokaryotic cell division — not meiosis.
Q196MediumBPSC Prelims
DNA replication is said to be "semiconservative" because:
AOnly half the DNA is replicated each time
BEach new DNA double helix contains one original strand and one newly synthesized strand
CDNA is replicated in a semicircular pattern
DOnly the coding strand is conserved
Show Answer
✔ B — Each new DNA double helix contains one original strand and one newly synthesized strand
Semiconservative replication (Watson & Crick, 1953; confirmed by Meselson-Stahl experiment, 1958):
After replication, EACH new DNA double helix contains:
- ONE original (parent) strand (conserved)
- ONE newly synthesized strand
So from ONE double helix → TWO double helices, each "semi" (half) conserved.
Alternative models (proven wrong by Meselson-Stahl):
- Conservative: both parental strands stay together in one helix; new double helix is entirely new
- Dispersive: parental DNA is fragmented and dispersed throughout both daughter helices
*Why A is wrong:* The ENTIRE DNA is replicated, not just half.
*Why C is wrong:* "Semicircular" has no relevance to DNA replication mechanism.
*Why D is wrong:* Both strands (template and coding) serve as templates for new synthesis.
Q197HardBPSC Prelims
Programmed cell death (apoptosis) is important because:
AIt is a type of cell death that only occurs due to injury
BIt controls normal development, removes damaged cells, and maintains tissue homeostasis
CIt always leads to inflammation and immune response
DIt only occurs in cancer cells
Show Answer
✔ B — It controls normal development, removes damaged cells, and maintains tissue homeostasis
Apoptosis (programmed cell death): controlled, orderly process of cell self-destruction.
- Occurs through intrinsic (mitochondrial) or extrinsic (death receptor) pathways
- Caspase proteases execute the program
Biological importance:
1. Embryonic development: shaping fingers (removing interdigital webbing), brain development
2. Immune system: elimination of self-reactive T-cells (prevents autoimmunity)
3. Cancer suppression: removes cells with DNA damage → tumour suppressor mechanism
4. Tissue homeostasis: balancing cell division with cell death to maintain organ size
Apoptosis vs. Necrosis:
- Apoptosis: programmed, orderly, no inflammation, cell shrinkage, nuclear fragmentation
- Necrosis: uncontrolled cell death from injury/toxins → inflammation, cell swelling, lysis
*Why A is wrong:* Apoptosis is PROGRAMMED — it occurs during normal development, not just due to injury.
*Why C is wrong:* Apoptosis is "clean" — it does NOT cause inflammation (unlike necrosis).
*Why D is wrong:* Apoptosis occurs in normal cells throughout life; cancer cells often EVADE apoptosis.
Q198HardBPSC Prelims
The fluid mosaic model of the cell membrane was proposed by:
AWatson and Crick
BSinger and Nicolson
CSchleiden and Schwann
DMeselson and Stahl
Show Answer
✔ B — Singer and Nicolson
Fluid Mosaic Model (1972): Singer and Nicolson proposed that the cell membrane consists of:
- Phospholipid bilayer (fluid): two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails inward
- Proteins (mosaic): embedded in or attached to the phospholipid bilayer
- Integral/transmembrane proteins: span the entire bilayer
- Peripheral proteins: attached to the surface
- Cholesterol: maintains membrane fluidity
Key properties:
- Fluid: phospholipids can move laterally (gives flexibility)
- Mosaic: proteins are scattered like tiles in a mosaic pattern
*Why A is wrong:* Watson and Crick = DNA double helix structure (1953).
*Why C is wrong:* Schleiden and Schwann = Cell Theory (1838-39).
*Why D is wrong:* Meselson and Stahl = semiconservative DNA replication (1958).
Genetics
Q199MediumBPSC Prelims
Mendel's Law of Segregation states that:
ATwo alleles for each trait segregate during gamete formation and end up in different gametes
BGenes for different traits assort independently into gametes
CAll offspring of two homozygous parents are homozygous
DDominant traits always mask recessive traits in all crosses
Show Answer
✔ A — Two alleles for each trait segregate during gamete formation and end up in different gametes
Mendel's First Law (Law of Segregation): The two alleles for any hereditary character separate (segregate) during gamete formation; each gamete carries only ONE allele for each character.
Example: Tall (TT) × Short (tt):
- F1: all Tt (Tall — T dominant over t)
- F2 (Tt × Tt): TT : Tt : tt = 1:2:1 (genotype); Tall : Short = 3:1 (phenotype)
Law of Segregation applies to ONE gene at a time.
Mendel's Second Law (Law of Independent Assortment): Alleles of different genes assort independently during gamete formation (option B describes this — not the Law of Segregation).
*Why B is wrong:* Independent assortment of different genes = Second Law, not First Law.
*Why C is wrong:* Homozygous parents give heterozygous offspring if parents differ.
*Why D is wrong:* Dominance is a separate concept, not itself the Law of Segregation.
Q200MediumBPSC Prelims
A person with blood group AB has parents with blood groups A and B respectively. This is an example of:
AIncomplete dominance
BEpistasis
CCodominance — both Iᴬ and Iᴮ alleles are expressed simultaneously
DRecessive inheritance
Show Answer
✔ C — Codominance — both Iᴬ and Iᴮ alleles are expressed simultaneously
ABO Blood Group System demonstrates codominance:
- Iᴬ and Iᴮ alleles are BOTH expressed when present together → blood group AB
- Neither is dominant over the other — both antigens (A and B) are produced on RBCs
ABO Genotypes:
- Type A: IᴬIᴬ or Iᴬi
- Type B: IᴮIᴮ or Iᴮi
- Type AB: IᴬIᴮ (codominance)
- Type O: ii (recessive — no surface antigen)
Blood group inheritance relevance:
- AB × AB: possible offspring = Type A (IᴬIᴬ), Type AB (IᴬIᴮ), Type B (IᴮIᴮ) — NOT Type O
- Universal donor: Type O; Universal recipient: Type AB
*Why A is wrong:* Incomplete dominance = blended phenotype (e.g., red + white flower → pink). ABO shows NO blending.
*Why B is wrong:* Epistasis = one gene suppresses another gene's expression — different concept.
*Why D is wrong:* AB requires both dominant alleles — not recessive.
Q201HardBPSC Prelims
Down syndrome (Trisomy 21) is caused by:
AA single gene mutation on chromosome 21
BHaving an extra copy of chromosome 21 (three instead of two)
CDeletion of part of chromosome 21
DX-chromosome inactivation
Show Answer
✔ B — Having an extra copy of chromosome 21 (three instead of two)
Down syndrome (Trisomy 21): caused by the presence of THREE copies of chromosome 21 (instead of the normal two).
- Karyotype: 47 chromosomes instead of normal 46
- Caused by non-disjunction during meiosis (usually maternal meiosis I or II) — chromosomes fail to separate properly
- Risk increases with maternal age: ~1/1500 at age 25, ~1/100 at age 40
Features: intellectual disability, characteristic facial features (flat face, upward-slanted eyes, protruding tongue), low muscle tone, heart defects (40% of cases), increased risk of leukaemia, early-onset Alzheimer's disease.
*Why A is wrong:* Single gene mutations cause conditions like sickle cell disease, cystic fibrosis — not Down syndrome (which is a chromosomal disorder, not a gene mutation).
*Why C is wrong:* Deletion of chromosome 21 material = different syndrome (e.g., monosomy causes Turner's syndrome in sex chromosomes).
*Why D is wrong:* X-chromosome inactivation (Lyon hypothesis) is normal female development — not Down syndrome.
Q202HardBPSC Prelims
Sickle cell anaemia is caused by a mutation that results in:
AAn extra chromosome 11
BSubstitution of glutamic acid by valine in the β-globin chain of haemoglobin
CDeletion of the β-globin gene
DA dominant mutation affecting red blood cell production
Show Answer
✔ B — Substitution of glutamic acid by valine in the β-globin chain of haemoglobin
Sickle cell anaemia: autosomal recessive disease caused by a POINT MUTATION in the HBB gene (chromosome 11):
- Normal Hb: position 6 of β-globin = Glutamic acid (GAG codon)
- Mutant HbS: position 6 = Valine (GTG codon) — single base change (A→T)
Result: HbS polymerizes under low O₂ → RBCs become sickle-shaped → block capillaries, break down → anaemia, pain crises (vaso-occlusive crisis), organ damage.
Genetics: autosomal recessive
- HbAHbA: normal
- HbAHbS: sickle cell trait (carrier — mostly asymptomatic, some protection against malaria)
- HbSHbS: sickle cell disease (severe)
*Why A is wrong:* Extra chromosome 11 = not the cause; sickle cell is a point mutation, not a chromosomal abnormality.
*Why C is wrong:* Deletion of β-globin gene causes β-thalassaemia (no β-globin production) — different from sickle cell.
*Why D is wrong:* Sickle cell is autosomal RECESSIVE, not dominant.
Q203HardBPSC Prelims
Which of the following correctly explains the Central Dogma of Molecular Biology?
AProtein → RNA → DNA
BDNA → RNA → Protein (DNA → mRNA → Polypeptide)
CRNA → DNA → Protein
DProtein → DNA → RNA
Show Answer
✔ B — DNA → RNA → Protein (DNA → mRNA → Polypeptide)
Central Dogma (Francis Crick, 1958):
DNA → RNA → Protein
More specifically:
1. Transcription: DNA → mRNA (in nucleus)
- RNA polymerase reads template strand; produces mRNA
2. Translation: mRNA → Protein (at ribosomes)
- Ribosome reads codons; tRNA brings amino acids
Additional flows in retroviruses (exceptions):
- Reverse transcription: RNA → DNA (HIV uses reverse transcriptase)
- RNA can also be transcribed to RNA (some viruses)
Francis Crick & James Watson: discovered DNA double helix structure (1953, Nobel 1962).
*Why A is wrong:* Protein cannot be converted back to RNA or DNA (in normal biology).
*Why C is wrong:* RNA → DNA = reverse transcription (HIV only) — not the standard Central Dogma.
*Why D is wrong:* Protein cannot create DNA or RNA — information flows FROM DNA, not into it.
Q204MediumBPSC Prelims
Sex determination in humans follows which pattern?
AFemale (XX) determines sex; males are XY by default
BMales (XY) produce two types of gametes (X or Y); the Y-bearing sperm determines male offspring
CSex is determined by environmental temperature
DSex is determined by the number of X chromosomes alone
Show Answer
✔ B — Males (XY) produce two types of gametes (X or Y); the Y-bearing sperm determines male offspring
Human sex determination (XX-XY system):
- Females: 44 autosomes + XX = 46,XX
- Males: 44 autosomes + XY = 46,XY
Females produce only X-bearing eggs (homogametic sex).
Males produce X-bearing AND Y-bearing sperm (heterogametic sex).
At fertilization:
- Egg (X) + X-sperm = XX = Female
- Egg (X) + Y-sperm = XY = Male
The SRY gene (sex-determining region on Y chromosome) triggers male development in XY embryos. Without SRY (XX), female development follows by default.
Cultural context: the male gamete determines the baby's sex — relevant to combat social myths that blame mothers.
*Why A is wrong:* Females don't "determine" sex — it's the sperm (X or Y) that does.
*Why C is wrong:* Temperature-dependent sex determination occurs in crocodiles and some reptiles — NOT humans.
*Why D is wrong:* Sex is determined by X + Y (presence of Y = male), not X count alone (though Turner's = 45,X has only one X).
Q205MediumBPSC Prelims
Haemophilia is called a "sex-linked" disorder because:
AIt affects only females
BThe gene is located on the X chromosome; affected males get it from carrier mothers
CIt is caused by the Y chromosome
DIt skips alternate generations in a random pattern
Show Answer
✔ B — The gene is located on the X chromosome; affected males get it from carrier mothers
Haemophilia (X-linked recessive disorder): gene for clotting factor VIII (Haemophilia A) or IX (Haemophilia B) is on the X chromosome.
Inheritance pattern:
- Carrier female (X^H X^h): appears normal but carries the recessive allele
- Affected male (X^h Y): has haemophilia (only one X, so recessive is expressed)
- Affected female (X^h X^h): extremely rare (needs two recessive X's)
Famous example: Queen Victoria was a carrier → passed haemophilia to European royal families (Tsarevich Alexei of Russia).
*Why A is wrong:* Haemophilia primarily affects MALES (who have only one X chromosome).
*Why C is wrong:* The haemophilia gene is on the X chromosome, not the Y chromosome.
*Why D is wrong:* X-linked disorders skip generations in a predictable pattern (sons of carrier mothers).
Human Physiology — Digestion
Q206EasyBPSC Prelims
The primary site of digestion and absorption of food in humans is:
AStomach
BLarge intestine
CSmall intestine
DMouth
Show Answer
✔ C — Small intestine
Small intestine = primary site of BOTH digestion and absorption.
- Three parts: Duodenum (digestion) → Jejunum (absorption) → Ileum (absorption)
- Digestive enzymes from pancreas (lipase, amylase, protease) and intestinal glands
- Bile from liver (emulsifies fats)
- Large surface area: villi and microvilli (brush border) = ~200 m² total
Role of each organ:
- Mouth: mechanical digestion (teeth), salivary amylase (starch → maltose)
- Stomach: protein digestion (pepsin in HCl), churning
- Small intestine: complete digestion + absorption
- Large intestine: water/electrolyte absorption, faeces formation
*Why A is wrong:* Stomach primarily digests proteins; limited absorption (alcohol, aspirin).
*Why B is wrong:* Large intestine absorbs water and electrolytes; no significant food digestion.
*Why D is wrong:* Mouth starts digestion (starch) but minimal absorption.
Q207MediumBPSC Prelims
The enzyme pepsin, found in the stomach, digests:
AStarch (carbohydrates)
BFats (lipids)
CProteins
DNucleic acids
Show Answer
✔ C — Proteins
Pepsin: protease enzyme secreted by chief cells (peptic cells) of gastric glands.
- Inactive precursor: pepsinogen → activated by HCl (stomach acid) → pepsin
- Function: begins protein digestion (proteins → polypeptides/peptones)
- Active at pH 1.5–2.5 (strongly acidic stomach environment)
Digestive enzymes by substrate:
- Proteins: pepsin (stomach), trypsin/chymotrypsin/peptidases (small intestine)
- Starch: salivary amylase (mouth), pancreatic amylase (small intestine)
- Fats: lipase (pancreas, small intestine), bile (emulsification)
- Nucleic acids: DNase, RNase (pancreas)
*Why A is wrong:* Starch is digested by amylase (salivary and pancreatic).
*Why B is wrong:* Fats are digested by lipase (pancreatic); bile salts emulsify fats first.
*Why D is wrong:* Nucleic acids are digested by nucleases (DNase, RNase).
Human Physiology — Circulation
Q208MediumBPSC Prelims
The correct pathway of blood flow through the human heart is:
ARight atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body
BLeft atrium → Left ventricle → Lungs → Right atrium → Right ventricle → Body
CRight ventricle → Left ventricle → Lungs → Right atrium → Left atrium → Body
DLeft ventricle → Lungs → Left atrium → Right ventricle → Body
Show Answer
✔ A — Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body
Human circulatory pathway (double circulation):
Pulmonary circuit (right side → lungs):
Right atrium → Right ventricle → Pulmonary artery → Lungs (oxygenation) → Pulmonary veins
Systemic circuit (left side → body):
Left atrium → Left ventricle → Aorta → Body (O₂ delivery) → Superior/Inferior Vena Cava → Right atrium
Note: Pulmonary artery carries deoxygenated blood TO lungs; Pulmonary veins carry oxygenated blood FROM lungs (exception to artery/vein oxygen rule).
*Why B is wrong:* Left side receives oxygenated blood FROM the lungs, doesn't pump TO the lungs.
*Why C is wrong:* No direct left ventricle → lungs connection; order is reversed.
*Why D is wrong:* Left ventricle pumps to the body (aorta), not directly to lungs.
Q209MediumBPSC Prelims
Which component of blood is responsible for oxygen transport?
AWhite blood cells (WBCs)
BPlatelets
CRed blood cells (RBCs) containing haemoglobin
DPlasma proteins
Show Answer
✔ C — Red blood cells (RBCs) containing haemoglobin
Red blood cells (RBCs/Erythrocytes) contain haemoglobin (Hb) — the oxygen-carrying protein.
- Haemoglobin: tetramer of 4 globin chains (2α + 2β), each with an iron-containing heme group
- Each Hb molecule carries up to 4 O₂ molecules (one per iron atom)
- Normal Hb: Adult (HbA), Fetal (HbF — higher O₂ affinity), Sickle cell (HbS)
- RBC count: 4.5-5.5 million/μL (males); 4-5 million/μL (females)
- RBCs: no nucleus (mature), biconcave disc shape (maximises surface area)
Blood components:
- RBCs: O₂ transport (haemoglobin)
- WBCs: immunity (phagocytosis, antibodies)
- Platelets: clotting (haemostasis)
- Plasma: transport of nutrients, hormones, wastes
*Why A is wrong:* WBCs (leucocytes) = immune defense, not O₂ transport.
*Why B is wrong:* Platelets = blood clotting; no oxygen transport function.
*Why D is wrong:* Plasma proteins = albumin (osmotic pressure), globulins (antibodies), fibrinogen (clotting) — not O₂ transport.
Q210HardBPSC Prelims
The normal resting heart rate in adults and its regulation involve:
AHeart rate 40-50 bpm; controlled only by circulating adrenaline
BHeart rate 60-100 bpm; sino-atrial (SA) node is the pacemaker, modulated by autonomic nervous system
CHeart rate 120-150 bpm; controlled exclusively by the cerebellum
DHeart rate 60-100 bpm; controlled only by the pituitary gland
Show Answer
✔ B — Heart rate 60-100 bpm; sino-atrial (SA) node is the pacemaker, modulated by autonomic nervous system
Normal resting heart rate: 60-100 beats per minute (bpm) in adults.
(Average ~72 bpm; well-trained athletes may have 40-60 bpm = bradycardia — physiological)
Sino-atrial (SA) node: located in the right atrium wall; natural pacemaker of the heart.
- Generates electrical impulse at ~72 bpm
- Impulse → Atrio-ventricular (AV) node → Bundle of His → Purkinje fibres → Ventricular contraction
Autonomic nervous system modulation:
- Sympathetic (fight-or-flight): increases HR (via noradrenaline → β₁ receptors)
- Parasympathetic/Vagus nerve: decreases HR (via acetylcholine → M₂ receptors)
*Why A is wrong:* Normal HR is 60-100, not 40-50; adrenaline alone doesn't control HR.
*Why C is wrong:* 120-150 bpm at rest = tachycardia (abnormal); cerebellum controls coordination, not heart rate.
*Why D is wrong:* Pituitary hormones have long-term effects (thyroid stimulation → metabolism) but don't directly control moment-to-moment HR.
Human Physiology — Respiration
Q211EasyBPSC Prelims
In the lungs, the exchange of gases (O₂ and CO₂) between air and blood occurs across:
AThe bronchi
BThe trachea
CThe alveoli (air sacs)
DThe bronchioles
Show Answer
✔ C — The alveoli (air sacs)
Alveoli: tiny air sacs at the end of bronchioles — primary site of gas exchange.
- ~300 million alveoli in human lungs (total surface area ~70 m²)
- One cell thick (Type I pneumocytes) → very short diffusion distance
- Surrounded by capillaries → oxygen diffuses IN, CO₂ diffuses OUT
Gas exchange by simple diffusion (down concentration gradient):
- O₂: alveolar air → blood (pO₂ alveoli ~100 mmHg > blood ~40 mmHg)
- CO₂: blood → alveolar air (pCO₂ blood ~46 mmHg > alveoli ~40 mmHg)
Respiratory tract: Nose → Pharynx → Larynx → Trachea → Primary Bronchi → Secondary Bronchi → Bronchioles → Alveolar ducts → Alveoli
*Why A is wrong:* Bronchi are conducting airways — gas transport only, no exchange.
*Why B is wrong:* Trachea = conducting airway only; no gas exchange.
*Why D is wrong:* Bronchioles are conducting airways; terminal bronchioles lead to alveoli.
Q212MediumBPSC Prelims
The oxygen-carrying capacity of haemoglobin is reduced in the presence of carbon monoxide because:
ACO destroys red blood cells
BCO combines with haemoglobin with much higher affinity than O₂, forming carboxyhaemoglobin (COHb)
CCO decreases the pH of blood, denaturing haemoglobin
DCO blocks the alveoli, preventing oxygen from reaching blood
Show Answer
✔ B — CO combines with haemoglobin with much higher affinity than O₂, forming carboxyhaemoglobin (COHb)
CO binds to haemoglobin at the SAME SITE as O₂ (iron atom in heme) with ~240 times greater affinity than O₂.
- COHb (carboxyhaemoglobin): bright cherry-red colour (unlike normal bluish deoxygenated blood)
- COHb cannot carry O₂ → tissues are starved of O₂ (hypoxic hypoxia, but no cyanosis)
- CO also shifts the O₂-Hb dissociation curve left → remaining O₂ released less readily to tissues
Symptoms: headache (mild), dizziness, loss of consciousness, death.
Treatment: 100% O₂ (displaces CO from Hb); hyperbaric O₂ for severe cases.
*Why A is wrong:* CO doesn't destroy RBCs — RBC integrity is maintained (COHb just doesn't carry O₂).
*Why C is wrong:* CO does not significantly acidify blood at normal exposure levels.
*Why D is wrong:* CO is gaseous and does not physically block alveoli.
Human Physiology — Excretion
Q213MediumBPSC Prelims
The functional unit of the kidney is called:
AGlomerulus
BNephron
CUreter
DBowman's capsule
Show Answer
✔ B — Nephron
Nephron: structural and functional unit of the kidney.
- Each kidney contains ~1 million nephrons
- Nephron parts:
1. Bowman's capsule: cup-like structure surrounding glomerulus
2. Glomerulus: capillary knot → ultrafiltration of blood
3. Proximal Convoluted Tubule (PCT): reabsorption of glucose, amino acids, Na⁺, water
4. Loop of Henle: concentration of urine (countercurrent mechanism)
5. Distal Convoluted Tubule (DCT): hormonal regulation (ADH, aldosterone)
6. Collecting duct: final concentration of urine
Urine formation: Filtration → Reabsorption → Secretion → Excretion
*Why A is wrong:* Glomerulus = capillary knot where filtration occurs — one PART of a nephron.
*Why C is wrong:* Ureter = tube carrying urine from kidney to bladder — not a part of the nephron.
*Why D is wrong:* Bowman's capsule = one component of the nephron, not the entire functional unit.
Q214HardBPSC Prelims
Antidiuretic hormone (ADH/Vasopressin) regulates kidney function by:
AIncreasing urine production (diuresis) when water intake is high
BMaking collecting duct cells more permeable to water → more water reabsorbed → concentrated urine
CStimulating the glomerulus to filter more blood
DIncreasing Na⁺ reabsorption in the loop of Henle
Show Answer
✔ B — Making collecting duct cells more permeable to water → more water reabsorbed → concentrated urine
ADH (Antidiuretic Hormone / Vasopressin): secreted by posterior pituitary in response to:
- High blood osmolality (dehydration → osmoreceptors in hypothalamus detect high solute concentration)
- Low blood pressure/volume
Mechanism:
ADH → binds V₂ receptors on collecting duct cells → inserts aquaporin-2 (water channels) → water reabsorbed from filtrate back into blood → CONCENTRATED URINE (small volume) → body water conserved.
Absence of ADH (Diabetes Insipidus): collecting duct impermeable to water → DILUTE URINE in large volumes.
Note: Aldosterone (from adrenal cortex) increases Na⁺ reabsorption in DCT/collecting duct → water follows osmotically (separate from ADH).
*Why A is wrong:* ADH is ANTIDIURETIC (reduces urine production) — the opposite of diuresis.
*Why C is wrong:* ADH acts on collecting duct, not the glomerulus.
*Why D is wrong:* Aldosterone increases Na⁺ reabsorption in DCT/collecting duct — this is NOT ADH's primary action.
Human Physiology — Nervous System
Q215MediumBPSC Prelims
The basic functional unit of the nervous system is the:
AGanglion
BNeuron (nerve cell)
CAxon
DSynapse
Show Answer
✔ B — Neuron (nerve cell)
Neuron = structural and functional unit of the nervous system.
Neuron parts:
- Cell body (soma): contains nucleus, metabolic centre
- Dendrites: receive signals from other neurons (multiple, tree-like branches)
- Axon: transmits signals AWAY from cell body (one axon, may be long)
- Myelin sheath: insulation (Schwann cells in PNS, oligodendrocytes in CNS) → speeds conduction
- Nodes of Ranvier: gaps in myelin → saltatory conduction
- Synaptic terminals: releases neurotransmitters across synapse to next neuron/muscle
Types of neurons:
- Sensory (afferent): sense organs → CNS
- Motor (efferent): CNS → muscles/glands
- Interneurons: within CNS (most numerous)
*Why A is wrong:* Ganglion = cluster of neuron cell bodies outside the CNS — not a single unit.
*Why C is wrong:* Axon = part of a neuron (the elongated process) — not the complete unit.
*Why D is wrong:* Synapse = junction between two neurons — a connection, not a cell.
Q216HardBPSC Prelims
Myelin sheath in neurons serves the function of:
AProducing neurotransmitters for synaptic transmission
BProviding nutrition to neurons
CInsulating the axon and increasing conduction speed (saltatory conduction)
DStoring memories in the brain
Show Answer
✔ C — Insulating the axon and increasing conduction speed (saltatory conduction)
Myelin sheath: lipid-protein wrapping around axons.
- Formed by: Schwann cells (PNS) and Oligodendrocytes (CNS)
- Insulates the axon → prevents electrical signal leakage
- Saltatory conduction: action potential "jumps" from one Node of Ranvier to the next → much faster than continuous conduction
- Myelinated fibres: 70-120 m/s conduction speed
- Unmyelinated fibres: 0.5-2 m/s conduction speed
Multiple sclerosis (MS): autoimmune disease destroying myelin → slowed/disrupted nerve conduction → muscle weakness, vision problems, coordination difficulties.
*Why A is wrong:* Neurotransmitters are produced in the neuron's cell body (soma) and stored in synaptic vesicles — not myelin.
*Why B is wrong:* Nutrition comes from astrocytes and blood supply — not myelin.
*Why D is wrong:* Memory storage involves synaptic plasticity (long-term potentiation) in the hippocampus — not myelin.
Q228HardBPSC Prelims
Reflex actions bypass the brain because:
AThe brain is too slow to process quick responses
BThe spinal cord directly coordinates reflex arcs without waiting for brain input
CReflexes are controlled by the cerebellum, not the main brain
DPeripheral nerves function independently without any nervous system control
Show Answer
✔ B — The spinal cord directly coordinates reflex arcs without waiting for brain input
Reflex arc: the neural pathway for a reflex action:
Receptor (stimulus) → Sensory neuron → Spinal cord (integration centre) → Motor neuron → Effector (muscle/gland)
The spinal cord integrates the reflex response WITHOUT sending the signal to the brain first. This allows FASTER response times:
- Example: withdrawing hand from hot object — complete in ~0.03-0.05 seconds
- If brain involvement required: ~0.1-0.5 seconds (awareness + decision + motor command)
Types of reflexes:
- Monosynaptic (patellar/knee-jerk reflex): ONE synapse in spinal cord
- Polysynaptic (withdrawal reflex): multiple interneurons
The brain IS informed AFTER the reflex occurs (you feel the pain after your hand moves away).
*Why A is wrong:* The brain processes rapidly, but bypassing it speeds up reflexes even more — it's about optimisation, not brain inadequacy.
*Why C is wrong:* Cerebellum coordinates voluntary movement (balance, fine motor) — not reflexes.
*Why D is wrong:* Peripheral nerves are part of the reflex arc — they are crucial components of it.
Human Physiology — Endocrine System
Q217EasyBPSC Prelims
Insulin is produced by which organ?
ALiver
BPancreas (beta cells of Islets of Langerhans)
CAdrenal gland
DThyroid gland
Show Answer
✔ B — Pancreas (beta cells of Islets of Langerhans)
Insulin: produced by β (beta) cells of the Islets of Langerhans in the pancreas.
- Function: lowers blood glucose → promotes glucose uptake by cells (especially liver, muscle, adipose tissue)
- Mechanism: insulin binds receptor → GLUT4 transporters move to cell surface → glucose enters cells
- Discovery: Frederick Banting and Charles Best (1921, University of Toronto) — Nobel Prize 1923
Other pancreatic hormones:
- α (alpha) cells: glucagon (raises blood glucose — opposite of insulin)
- δ (delta) cells: somatostatin (inhibits insulin and glucagon)
Diabetes Mellitus:
- Type 1: autoimmune destruction of β-cells → no insulin production
- Type 2: insulin resistance + inadequate insulin production
*Why A is wrong:* Liver produces glucose (glycogenolysis, gluconeogenesis) and responds to insulin — doesn't produce insulin.
*Why C is wrong:* Adrenal gland produces adrenaline (medulla) and cortisol/aldosterone (cortex) — not insulin.
*Why D is wrong:* Thyroid gland produces T₃, T₄ (regulate metabolism) and calcitonin — not insulin.
Q218MediumBPSC Prelims
Goitre (thyroid enlargement) is caused by deficiency of:
AVitamin A
BIodine
CIron
DCalcium
Show Answer
✔ B — Iodine
Goitre = enlarged thyroid gland, commonly caused by iodine deficiency.
- Thyroid hormones (T₃ = triiodothyronine, T₄ = thyroxine) require iodine for synthesis
- Iodine deficiency → thyroid cannot make enough T₃/T₄ → low blood thyroid hormone
- Pituitary detects low T₃/T₄ → releases more TSH (thyroid-stimulating hormone) → TSH causes thyroid to ENLARGE (compensatory hypertrophy) → GOITRE
- Severe deficiency in pregnancy: CRETINISM in fetus (mental retardation, stunted growth)
Prevention: iodized salt (NaI or KI added to salt)
Bihar and iodine deficiency:
- Bihar is in the "Himalayan goitre belt" — hilly areas of northern Bihar (Champaran, Sitamarhi) have iodine-deficient soil and water.
- National Iodine Deficiency Disorders Control Programme (NIDDCP).
*Why A is wrong:* Vitamin A deficiency → night blindness, xerophthalmia — not goitre.
*Why C is wrong:* Iron deficiency → anaemia — not goitre.
*Why D is wrong:* Calcium deficiency → rickets (with vitamin D deficiency), tetany — not goitre.
Q219HardBPSC Prelims
The "flight or fight" response is triggered by which hormone?
AInsulin
BCortisol
CAdrenaline (Epinephrine)
DOxytocin
Show Answer
✔ C — Adrenaline (Epinephrine)
Adrenaline (Epinephrine): secreted by adrenal medulla (inner core of adrenal glands, above kidneys).
Released in response to: acute stress, danger, exercise, hypoglycaemia.
"Fight or flight" responses:
- Heart rate ↑ (tachycardia)
- Blood pressure ↑ (vasoconstriction in skin/gut; vasodilation in muscles)
- Blood glucose ↑ (glycogenolysis in liver)
- Bronchial dilation ↑ (more O₂ to lungs)
- Pupils dilate (better vision)
- Blood redirected to muscles (away from digestion)
- Sweating ↑
Noradrenaline (norepinephrine): from adrenal medulla AND sympathetic nerve endings — primarily vasoconstriction.
*Why A is wrong:* Insulin lowers blood glucose — the opposite of fight-or-flight (stress raises glucose).
*Why B is wrong:* Cortisol (adrenal cortex) is the "chronic stress hormone" — manages long-term stress (anti-inflammatory, raises blood glucose) — NOT the acute fight-or-flight response.
*Why D is wrong:* Oxytocin = "love hormone" — bonding, childbirth contractions, breastfeeding.
Human Physiology — Reproduction
Q220MediumBPSC Prelims
In human females, the site of fertilisation of the egg by sperm is:
AUterus (womb)
BOvary
CFallopian tube (oviduct) — usually the ampulla
DCervix
Show Answer
✔ C — Fallopian tube (oviduct) — usually the ampulla
Fertilisation occurs in the Fallopian tube (oviduct), specifically in the ampulla (upper wider portion).
- Sperm travel: vagina → cervix → uterus → fallopian tube
- Ovulated egg released from ovary → picked up by fimbriae → enters fallopian tube
- Sperm meets egg in the ampullary-isthmic junction of fallopian tube
- Fertilization: acrosome reaction → one sperm penetrates zona pellucida → zygote formed
- Zygote undergoes cleavage → morula → blastocyst while travelling to uterus (3-5 days)
- Implantation: blastocyst implants in uterine endometrium
*Why A is wrong:* Uterus = site of implantation and fetal development — NOT fertilisation.
*Why B is wrong:* Ovary = site of egg production/ovulation — not fertilisation.
*Why D is wrong:* Cervix = gateway between vagina and uterus — sperm passes through but fertilisation does not occur here.
Human Physiology — Immunity
Q221MediumBPSC Prelims
Vaccines work by:
AKilling all bacteria in the body
BDirectly providing antibodies (passive immunity)
CStimulating the immune system to produce antibodies and memory cells (active immunity)
DReplacing damaged white blood cells
Show Answer
✔ C — Stimulating the immune system to produce antibodies and memory cells (active immunity)
Vaccines = preparations of antigens (weakened/killed pathogens, or their proteins) that stimulate the immune system.
Active immunity (from vaccines):
1. Antigen enters body (vaccine)
2. B-lymphocytes recognize antigen → differentiate into plasma cells
3. Plasma cells produce antibodies → neutralise antigen
4. Memory B-cells and memory T-cells formed → long-lasting immunity
5. On future exposure to real pathogen → rapid secondary immune response
Types of vaccines:
- Live attenuated: BCG (TB), OPV (polio), MMR
- Inactivated: IPV (polio), hepatitis A
- Subunit/protein: hepatitis B, HPV
- Toxoid: DPT (diphtheria, pertussis, tetanus)
- mRNA: COVID-19 (Pfizer, Moderna)
*Why A is wrong:* Vaccines don't kill bacteria — antibiotics do.
*Why B is wrong:* Providing READY-MADE antibodies = passive immunity (e.g., anti-rabies immunoglobulin, snake antivenom).
*Why D is wrong:* Vaccines don't replace WBCs; they educate existing immune cells.
Q222HardBPSC Prelims
HIV (Human Immunodeficiency Virus) causes AIDS by:
AProducing toxins that kill all white blood cells
BSpecifically destroying CD4⁺ T-helper cells, crippling the immune response
CBlocking antibody production by plasma cells
DDirectly infecting and killing red blood cells
Show Answer
✔ B — Specifically destroying CD4⁺ T-helper cells, crippling the immune response
HIV specifically targets and destroys CD4⁺ T-helper cells (T lymphocytes):
- HIV binds to CD4 receptor + CCR5/CXCR4 co-receptors on T-helper cells
- Uses reverse transcriptase to convert its RNA genome → DNA → integrates into host cell DNA (provirus)
- Eventually kills T-helper cells → CD4 count drops
AIDS: CD4 count falls below 200 cells/μL (normal: 800-1200 cells/μL) → immune system severely compromised → opportunistic infections (PCP pneumonia, Cryptococcal meningitis, TB, CMV retinitis, Kaposi's sarcoma).
Treatment: Antiretroviral therapy (ART) — combination of reverse transcriptase inhibitors + protease inhibitors + integrase inhibitors. ART does not cure but suppresses viral load → CD4 count recovers.
*Why A is wrong:* HIV doesn't produce toxins that kill ALL WBCs; it specifically targets CD4⁺ T-cells.
*Why C is wrong:* Plasma cell function is indirectly impaired (as they need T-helper cells for activation) but HIV doesn't directly block antibody production.
*Why D is wrong:* HIV targets T-lymphocytes, not red blood cells.
Human Physiology — Nutrition
Q223MediumBPSC Prelims
Night blindness is caused by deficiency of:
AVitamin C
BVitamin D
CVitamin A
DVitamin B₁₂
Show Answer
✔ C — Vitamin A
Night blindness (Nyctalopia): inability to see in dim light or at night.
Cause: Vitamin A (retinol) deficiency.
Mechanism:
- Rod cells in retina contain rhodopsin (visual purple) = opsin + retinal (a form of Vitamin A)
- In dim light → rhodopsin breaks down → sends signal to optic nerve → vision in low light
- Vitamin A deficiency → insufficient rhodopsin → rod cells cannot function → night blindness
Progressive vitamin A deficiency:
1. Night blindness (early)
2. Bitot's spots (white foamy patches on conjunctiva)
3. Xerophthalmia (dry cornea)
4. Keratomalacia (corneal ulceration, melting) → permanent blindness
Sources of Vitamin A: carrots, dark leafy greens, egg yolk, liver, fish oil.
*Why A is wrong:* Vitamin C deficiency → Scurvy (bleeding gums, poor wound healing).
*Why B is wrong:* Vitamin D deficiency → Rickets (children — soft bones), Osteomalacia (adults).
*Why D is wrong:* Vitamin B₁₂ deficiency → Pernicious anaemia, nerve damage (subacute combined degeneration of spinal cord).
Q224EasyBPSC Prelims
Which vitamin is synthesised in the human body on exposure to sunlight?
AVitamin A
BVitamin B
CVitamin C
DVitamin D
Show Answer
✔ D — Vitamin D
Vitamin D (cholecalciferol) is synthesised in the skin upon exposure to UVB radiation from sunlight.
- Precursor: 7-dehydrocholesterol (in skin) + UVB → cholecalciferol (Vitamin D₃)
- Cholecalciferol → liver (25-hydroxylation) → kidneys (1-hydroxylation) → calcitriol (active form, 1,25-dihydroxyvitamin D₃)
Function: promotes calcium and phosphorus absorption in the intestine → bone mineralisation.
Deficiency: Rickets (children — soft, deformed bones), Osteomalacia (adults — soft bones, fractures).
Dietary sources: fish liver oil (cod liver oil), fatty fish, egg yolk, fortified milk.
*Why A is wrong:* Vitamin A (retinol) from diet (animal sources) or converted from beta-carotene (plant sources) — not made from sunlight.
*Why B is wrong:* B vitamins (B₁, B₂, B₃, etc.) from diet — not synthesised from sunlight.
*Why C is wrong:* Vitamin C (ascorbic acid) from fruits and vegetables — not synthesised in humans (humans lack gulonolactone oxidase enzyme).
Q225MediumBPSC Prelims
Scurvy is caused by deficiency of vitamin C. Which of the following is a key symptom?
ANight blindness and xerophthalmia
BSoft bones and rickets
CBleeding gums, poor wound healing, and skin haemorrhages
DBeri-beri and nerve damage
Show Answer
✔ C — Bleeding gums, poor wound healing, and skin haemorrhages
Scurvy (Vitamin C / Ascorbic acid deficiency):
Vitamin C is essential for collagen synthesis — the main structural protein in connective tissue.
Without Vitamin C → collagen is weak → connective tissue breaks down:
- Bleeding gums (gingival haemorrhage) — most classic sign
- Poor wound healing (old wounds reopen — "re-opening of ancient scars")
- Petechiae and ecchymoses (skin haemorrhages)
- Perifollicular haemorrhages (bleeding around hair follicles)
- Corkscrew hairs (twisted, fragile)
- Swollen, painful joints
- Anaemia (as Vitamin C aids iron absorption)
- Historical: killed sailors on long voyages (James Lind, 1747 — citrus prevents scurvy)
*Why A is wrong:* Night blindness/xerophthalmia = Vitamin A deficiency.
*Why B is wrong:* Soft bones/rickets = Vitamin D deficiency (children).
*Why D is wrong:* Beri-beri = Vitamin B₁ (thiamine) deficiency — dry beri-beri (nerve damage), wet beri-beri (heart failure, oedema).
Human Physiology — Endocrine/Misc
Q226HardBPSC Prelims
The hormone responsible for regulating the sleep-wake cycle is:
ACortisol
BMelatonin
CSerotonin
DDopamine
Show Answer
✔ B — Melatonin
Melatonin: secreted by the pineal gland in the brain.
- Regulated by light: darkness → pineal gland secretes melatonin → promotes sleep; light → melatonin suppressed → wakefulness
- Circadian rhythm: melatonin levels peak at 2-4 AM, lowest midday
- Mechanism: melatonin binds MT₁/MT₂ receptors → lowers body temperature, reduces alertness → induces sleep
Uses of melatonin:
- Treatment of jet lag (reset circadian rhythm)
- Shift-work sleep disorder
- Insomnia in elderly (melatonin production decreases with age)
Serotonin (option C): precursor to melatonin; produced in gut (90%) and brain raphe nuclei; mood regulation, appetite, gut motility.
Dopamine (option D): reward, motivation, movement (Parkinson's disease = dopaminergic neuron loss).
*Why A is wrong:* Cortisol = "morning hormone" — rises before waking (cortisol awakening response), regulates energy and immune response, not the primary sleep regulator.
*Why C is wrong:* Serotonin = mood/happiness, precursor to melatonin — not the direct sleep-wake regulator.
*Why D is wrong:* Dopamine = reward/motivation neurotransmitter — promotes wakefulness and alertness (opposite role).
Human Physiology — Blood
Q227MediumBPSC Prelims
Which blood group is called the "universal donor"?
ABlood group A
BBlood group B
CBlood group AB
DBlood group O
Show Answer
✔ D — Blood group O
Blood group O (Type O): Universal donor — can donate RED BLOOD CELLS to any blood group recipient.
- Type O RBCs have NO A or B antigens → no immune reaction in any recipient
- But Type O individuals have BOTH anti-A and anti-B antibodies in plasma
Blood group AB: Universal recipient — can receive blood from any donor
- Type AB plasma has NEITHER anti-A nor anti-B antibodies → no reaction against any donor's antigens
ABO compatibility (for whole blood/packed RBCs):
| Donor | Can donate to |
|-------|--------------|
| O | O, A, B, AB (universal donor) |
| A | A, AB |
| B | B, AB |
| AB | AB only (universal recipient) |
*Why A is wrong:* Type A can donate to A and AB only — not universal.
*Why B is wrong:* Type B can donate to B and AB only — not universal.
*Why C is wrong:* Type AB can only donate to AB — universal RECIPIENT, not donor.
Human Physiology — Reproductive System
Q229MediumBPSC Prelims
Colostrum (the first milk secreted after childbirth) is important because:
AIt is high in fat and calories to prevent weight loss in the newborn
BIt contains maternal antibodies (especially IgA) providing passive immunity to the newborn
CIt stimulates the baby's digestive system to produce enzymes
DIt prevents jaundice in the newborn
Show Answer
✔ B — It contains maternal antibodies (especially IgA) providing passive immunity to the newborn
Colostrum: thick, yellowish fluid secreted by mammary glands for 2-4 days after delivery.
Rich in:
- Secretory IgA (antibodies): provides passive immunity to newborn's mucosal surfaces (gut, respiratory tract)
- Lactoferrin: antimicrobial protein
- Leukocytes (white blood cells): immune protection
- Growth factors: promote gut development
- Lower in fat than mature milk but HIGHER in protein and immunoglobulins
Why colostrum matters:
- Newborns have immature immune systems → cannot produce antibodies effectively
- Maternal antibodies in colostrum: protect against infections during first months of life
- Also called "liquid gold"
*Why A is wrong:* Colostrum is actually LOW in fat compared to mature breast milk — it's primarily an immune protection fluid.
*Why C is wrong:* Colostrum's main role is immune, not triggering enzyme production.
*Why D is wrong:* Colostrum doesn't prevent jaundice — physiological jaundice from neonatal bilirubin is a separate issue.
Q230HardBPSC Prelims
Luteinizing hormone (LH) surge during the menstrual cycle causes:
AMenstruation (shedding of uterine lining)
BDevelopment and maturation of the primary follicle
COvulation (rupture of the mature follicle and release of the egg)
DImplantation of the fertilised egg
Show Answer
✔ C — Ovulation (rupture of the mature follicle and release of the egg)
Menstrual cycle regulation (28-day average):
Day 1-5: Menstruation (uterine lining sheds)
Day 1-13: Follicular phase
- FSH (Follicle-Stimulating Hormone): stimulates follicle development → growing follicle produces oestrogen
Day 13-14: LH Surge (massive spike in LH):
- Triggers OVULATION on day ~14 (rupture of dominant follicle → egg released)
Day 14-28: Luteal phase
- Ruptured follicle → corpus luteum (produces progesterone)
- Progesterone: maintains uterine lining for potential implantation
- If no fertilisation: corpus luteum degenerates → progesterone drops → menstruation
*Why A is wrong:* Menstruation = progesterone drop when corpus luteum degenerates (day 28); NOT LH surge.
*Why B is wrong:* Follicle maturation = FSH (follicular phase, days 1-13).
*Why D is wrong:* Implantation requires progesterone (from corpus luteum) — not LH.
Plant Biology
Q231EasyBPSC Prelims
Photosynthesis can be summarised as:
AC₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (glucose broken down)
B6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ (glucose made from CO₂ and water)
CProteins → amino acids + energy (protein digestion)
DC₂H₅OH + 3O₂ → 2CO₂ + 3H₂O (ethanol combustion)
Show Answer
✔ B — 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ (glucose made from CO₂ and water)
Photosynthesis: process by which green plants convert light energy into chemical energy (glucose).
6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂
Two stages:
1. Light reactions (in thylakoid membranes): light captured → ATP and NADPH produced; water splits → O₂ released (photolysis)
2. Calvin cycle / Dark reactions (in stroma): CO₂ fixed into glucose using ATP and NADPH from light reactions
Chlorophyll: green pigment in chloroplasts; absorbs red and blue light most, reflects green (hence plants look green).
*Why A is wrong:* Option A = cellular respiration (the REVERSE of photosynthesis — glucose BROKEN DOWN).
*Why C is wrong:* Protein digestion → hydrolysis by proteases — not photosynthesis.
*Why D is wrong:* Ethanol combustion = chemistry, not biology/photosynthesis.
Q232MediumBPSC Prelims
Transpiration in plants is the process of:
AAbsorption of water from soil through roots
BMovement of water from roots to leaves via xylem (water transport)
CLoss of water vapour from leaves (mainly through stomata)
DPhotosynthesis requiring water as a raw material
Show Answer
✔ C — Loss of water vapour from leaves (mainly through stomata)
Transpiration: evaporation of water from plant surfaces, primarily through stomata (pores on leaves).
- ~90% of water absorbed by plants is transpired
- Creates a "transpiration pull" (negative pressure) that draws water upward from roots through xylem (cohesion-tension theory)
- Regulates plant temperature (cooling effect — like sweating)
- Enables mineral transport (water carries dissolved minerals from soil to leaves)
Stomata: guard cells control opening/closing based on light, CO₂ concentration, water stress.
- Light: stomata OPEN (for photosynthesis gas exchange)
- Drought/ABA (abscisic acid): stomata CLOSE (to conserve water)
*Why A is wrong:* Water absorption by roots = osmosis (root hair cells absorb water from soil when soil water potential > root water potential).
*Why B is wrong:* Water movement from roots to leaves = translocation via xylem — the process driving this is transpiration pull, but the movement itself isn't called "transpiration."
*Why D is wrong:* Photosynthesis uses water as a raw material (photolysis) — separate from transpiration.
Q233MediumBPSC Prelims
Auxins are plant hormones that primarily function in:
APromoting seed germination
BPromoting fruit ripening
CPromoting cell elongation and phototropism (plants bending towards light)
DInhibiting plant growth during drought
Show Answer
✔ C — Promoting cell elongation and phototropism (plants bending towards light)
Auxins (e.g., IAA — Indole-3-Acetic Acid): discovered by Frits Went (1926).
Primary functions:
- Cell elongation: auxins stimulate cells to elongate (increase plasticity of cell wall)
- Phototropism: light → unequal auxin distribution → shaded side grows faster → plant bends toward light
- Gravitropism: gravity → auxins accumulate on lower root/shoot side → differential growth
- Apical dominance: auxins from apical bud inhibit lateral bud growth
- Root formation: low concentrations promote root growth; high concentrations inhibit
Other plant hormones:
- Gibberellins: stem elongation, seed germination, bolting
- Cytokinins: cell division, delay senescence
- Ethylene: fruit ripening, leaf abscission
- Abscisic acid (ABA): dormancy, stomatal closure in drought
*Why A is wrong:* Seed germination = gibberellins (break dormancy).
*Why B is wrong:* Fruit ripening = ethylene (C₂H₄) — commercial ripening chambers use ethylene gas.
*Why D is wrong:* ABA (abscisic acid) inhibits growth during drought and promotes dormancy.
Q234HardBPSC Prelims
C4 plants (like maize and sugarcane) are more photosynthetically efficient than C3 plants because:
AC4 plants have more chlorophyll per leaf area
BC4 plants have a CO₂ concentrating mechanism that reduces photorespiration
CC4 plants perform photosynthesis at night (CAM pathway)
DC4 plants do not require water for photosynthesis
Show Answer
✔ B — C4 plants have a CO₂ concentrating mechanism that reduces photorespiration
C4 photosynthesis: named for the 4-carbon compound (oxaloacetate) formed when CO₂ is first fixed.
CO₂ concentrating mechanism:
- C4 plants fix CO₂ initially in MESOPHYLL CELLS (into 4C compound using PEP carboxylase — high CO₂ affinity)
- 4C compound transported to BUNDLE SHEATH CELLS → decarboxylated → releases CO₂ at HIGH CONCENTRATION for Calvin cycle (Rubisco)
- High CO₂ in bundle sheath → Rubisco doesn't react with O₂ → NO PHOTORESPIRATION
Photorespiration (in C3 plants): Rubisco reacts with O₂ instead of CO₂ (wasteful) → reduced photosynthetic efficiency at high temperatures.
Result: C4 plants are MORE efficient at high temperatures and high light intensities (tropical conditions).
*Why A is wrong:* Chlorophyll content is not significantly different between C3 and C4 plants.
*Why C is wrong:* CAM (Crassulacean Acid Metabolism) plants (cacti, pineapple) open stomata at NIGHT — this is a THIRD pathway, separate from C4.
*Why D is wrong:* All photosynthesis requires water (for photolysis in light reactions).
Q235MediumBPSC Prelims
Nitrogen fixation by Rhizobium bacteria occurs in the:
ASoil directly around plant roots (rhizosphere)
BRoot nodules of leguminous plants (peas, beans, lentils, gram)
CLeaves of all plants
DSoil independently of any plant association
Show Answer
✔ B — Root nodules of leguminous plants (peas, beans, lentils, gram)
Rhizobium: soil bacteria that form symbiotic associations with leguminous plants (Fabaceae family).
- Bacteria infect root hair cells → plant forms root nodules
- Inside nodules: Rhizobium fixes atmospheric N₂ → NH₃ (ammonia) using the enzyme nitrogenase
- N₂ + 8H⁺ + 8e⁻ + 16 ATP → 2NH₃ + H₂ + 16 ADP + 16 Pi
- Leguminous plants get fixed nitrogen (amino acids, nucleotides); Rhizobium gets carbohydrates
- Leghemoglobin (pink colour in nodules) = O₂ scavenger (protects nitrogenase from O₂ damage)
*Why A is wrong:* Rhizobium lives in soil rhizosphere only BEFORE infecting the plant; fixation occurs inside root NODULES.
*Why C is wrong:* Rhizobium does not infect leaves; root nodule association is root-specific.
*Why D is wrong:* Free-living nitrogen fixers exist (Azobacter, Clostridium) but Rhizobium's primary fixation is INSIDE nodules.
Ecology
Q236EasyBPSC Prelims
A food chain describes:
AThe process of photosynthesis by plants
BThe sequence of organisms through which energy and nutrients pass in an ecosystem
CThe circular flow of nutrients between living organisms and the environment
DThe competition between species for the same food resource
Show Answer
✔ B — The sequence of organisms through which energy and nutrients pass in an ecosystem
Food chain: a linear sequence showing energy and material transfer from one organism to the next through feeding relationships.
Example: Grass → Grasshopper → Frog → Snake → Hawk
- Grass = Producer (makes own food via photosynthesis)
- Grasshopper = Primary consumer (Herbivore)
- Frog = Secondary consumer (Carnivore)
- Snake = Tertiary consumer
- Hawk = Apex predator (top of chain)
Energy flow: ~10% of energy passes from one trophic level to the next (90% lost as heat, waste) — 10% Rule or Lindeman's Efficiency.
*Why A is wrong:* Photosynthesis = energy capture at producer level only; food chain shows transfer THROUGH the system.
*Why C is wrong:* Circular flow of nutrients = biogeochemical cycles (carbon cycle, nitrogen cycle, water cycle) — different concept.
*Why D is wrong:* Competition between species = interspecies competition — a type of ecological interaction, not a food chain.
Q237MediumBPSC Prelims
Which of the following best defines "biodiversity"?
AThe total number of plant species in a given area
BThe variety of life on Earth at all levels — genetic, species, and ecosystem diversity
CThe number of endangered species in a country
DThe total biomass of living organisms in an ecosystem
Show Answer
✔ B — The variety of life on Earth at all levels — genetic, species, and ecosystem diversity
Biodiversity (biological diversity): encompasses THREE levels:
1. Genetic diversity: variation in genes within a species (e.g., different varieties of rice — basmati, Sona Masuri, Pusa Basmati; varieties of mango)
2. Species diversity: variety of species in an area (e.g., number of bird species in Valmiki Tiger Reserve)
3. Ecosystem diversity: variety of habitats, ecosystems, and ecological processes (e.g., mangroves, grasslands, rivers, forests)
India: megadiverse country (one of 17) with ~7-8% of world's species on 2.4% of land area.
Bihar's biodiversity: Valmiki National Park (Bengal tigers, gharials, one-horned rhinos), Ganga river (Gangetic dolphins, fresh water turtles, gharials).
*Why A is wrong:* Only plant species = too narrow; biodiversity includes all life forms and multiple levels.
*Why C is wrong:* Endangered species list is a conservation metric — a subset of biodiversity consideration.
*Why D is wrong:* Biomass = total mass of organisms — not the same as diversity.
Q238HardBPSC Prelims
The Ganga river dolphin (Platanista gangetica) was declared India's national aquatic animal in:
A1956
B1972
C2009
D2019
Show Answer
✔ C — 2009
Gangetic River Dolphin (Susu): declared India's National Aquatic Animal in 2009 (by Government of India, as part of Ganga conservation efforts).
Key facts:
- Found in: Ganga, Brahmaputra, Meghna, Karnaphuli river systems
- Bihar has the largest population: ~500 dolphins in the Ganga stretch between Sultanganj and Kathihar
- Vikramshila Gangetic Dolphin Sanctuary (Bihar, Bhagalpur district): only dolphin sanctuary in India
- Critically endangered: IUCN Vulnerable; Schedule I (Wildlife Protection Act, 1972)
- Threats: Hunting, fishing net entanglement, river pollution, sand mining, habitat fragmentation from barrages
*Why A is wrong:* 1956 = Indian Wildlife Board formed; national aquatic animal not designated.
*Why B is wrong:* 1972 = Wildlife Protection Act passed — Ganga dolphin got Schedule I protection, but "national aquatic animal" designation came in 2009.
*Why D is wrong:* 2019 = various environmental policy announcements, not the dolphin declaration.
Ecology & Environment
Q239HardBPSC Prelims
Which is the correct sequence in ecological succession from bare rock to forest?
AForest → Shrubs → Herbs → Lichen/Moss → Bare rock
BBare rock → Lichen/Moss → Herbs → Shrubs → Forest
CBare rock → Herbs → Forest → Lichen → Shrubs
DLichen → Bare rock → Shrubs → Herbs → Forest
Show Answer
✔ B — Bare rock → Lichen/Moss → Herbs → Shrubs → Forest
Primary succession on bare rock (xerarch succession):
1. Bare rock (Pioneer stage)
2. Lichen/Crustose lichens (first colonisers — break down rock via acids; build thin soil layer)
3. Mosses (slightly more soil needed; further weathering)
4. Herbs/Annual grasses (colonise as soil develops)
5. Shrubs (woody plants establish)
6. Forest (Climax community — stable final state)
Each stage modifies the environment → enables next stage to establish.
Secondary succession: occurs on previously vegetated land (after fire, flood, clearing) — faster than primary succession because soil remains.
Climax community: stable, final stage of succession — self-sustaining ecosystem.
*Why A is wrong:* Option A is BACKWARDS — it shows retrogressive succession (forest → bare rock = human destruction).
*Why C is wrong:* Order is incorrect — herbs before lichens doesn't happen in primary succession.
*Why D is wrong:* Lichen can't colonise before the bare rock stage — lichen IS the first coloniser of bare rock.
Disease & Health
Q240MediumBPSC Prelims
Malaria is caused by which organism?
ABacterium — Mycobacterium malaria
BVirus — Malaria virus
CProtozoan — Plasmodium (P. vivax, P. falciparum, P. malariae, P. ovale)
DFungus — Malaria fungus
Show Answer
✔ C — Protozoan — Plasmodium (P. vivax, P. falciparum, P. malariae, P. ovale)
Malaria: caused by Plasmodium (protozoan parasite), transmitted by female Anopheles mosquito.
Plasmodium species infecting humans:
- P. falciparum: most dangerous (cerebral malaria, blackwater fever, drug-resistant strains)
- P. vivax: most common worldwide; relapsing (dormant hypnozoites in liver)
- P. malariae: quartan malaria (fever every 72 hours)
- P. ovale: rare; relapsing
Life cycle:
- In mosquito (sexual stage): gametocytes → sporozoites
- In humans: sporozoites → liver (schizogony) → merozoites → RBCs (erythrocytic cycle) → fever cycle
- Fever pattern: P. vivax = tertian (48-hour cycle); P. malariae = quartan (72-hour cycle)
*Why A is wrong:* Malaria is NOT bacterial (Mycobacterium = TB bacteria family).
*Why B is wrong:* Malaria is NOT viral (unlike dengue, chikungunya, COVID-19 which ARE viral).
*Why D is wrong:* Malaria is NOT fungal (fungi cause candidiasis, aspergillosis, dermatophytosis).