(2nd Year Syllabus) Test-2

Explanation: A
Two α decays give A → A – 8 and Z → Z – 4. To get Z → Z – 2, add two β^– decays (each β^– : Z → Z + 1, A unchanged).

Explanation: D

Explanation: C

Explanation: A
Current through a capacitor depends on how fast the voltage changes.
X_C = 1/ωC
• DC: ω = 0 ⇒ X_C → ∞ ⇒ open circuit.
• AC: ω > 0 ⇒ X_C finite ⇒ current flows (larger at higher f).
Hint: Capacitor passes change, blocks constant. DC (no change) → blocks; AC (keeps changing) → passes.

Explanation: B
KE of electrons is directly proportional to frequency of photon, but no photons will be released before threshold frequency therefore line will not start from zero but after threshold frequency.

Explanation: C
Fringing is the bending of field at the top and bottom end of the sheet, to avoid this size of the sheet is taken as infinite so that there is no top and bottom end.
• To use Gauss’s law neatly, we choose a Gaussian pillbox that cuts through the sheet.
• If the sheet is treated as infinite, the situation has planar symmetry: the electric field is perpendicular to the sheet and uniform (same magnitude) on both sides, and there’s no fringing (no bending of field lines near edges).
• Then the side surface of the pillbox gets zero flux, and only the two flat faces contribute:
Φ = 2EA,  Q_enc = σA,  2EA = σA/ε₀ ⇒ E = σ/2ε₀.
For a finite sheet, edges cause fringing, the field isn’t perfectly uniform or strictly perpendicular everywhere, and flux through the side isn’t zero—so the simple derivation breaks.
Why not A or B (or D)?
• We don’t make the sheet “infinite” to “make charges/area sufficient.” Gauss’s law works for any enclosed charge; the infinity assumption is purely to ensure symmetry and eliminate edge (fringing) effects. Hence only C is correct, not “All of these.”

Explanation: B

Explanation: A
Radioiodine scan: This test can detect thyroid cancer and determine if cancer has spread. You swallow a pill containing a safe amount of radioactive iodine (radioiodine). Over a few hours, the thyroid gland absorbs the iodine.

Explanation: C
Power loss during quarter cycle = either Positive or negative
Power during half and full cycle = 0
Energy viewpoint
In the first quarter-cycle, the capacitor stores energy (W – 1/2 CV²); in the next quarter, it returns the same energy to the source. Over the half cycle, gains and returns cancel.

Explanation: B
Photon momentum p = h/λ = hv/e. Shorter λ (higher v) = Larger p.
Why other are wrong:
Changing intensity alters photon number, not p per photon (C).
Polarization rotation doesn’t change p (D).
Longer wavelength reduces p (A).

Explanation: A
Electrical energy = KE
Ve = 1/2 mv², if V and e are same, velocity is inversely proportional to mass, so lesser the mass more the velocity.
As electron have less mass than proton its velocity will be more.

Explanation:  A

Explanation: A
Know the spectrum
• EM spectrum (low → high frequency): radio → microwaves → infrared → visible → UV → X-rays → gamma.
Why satellites use microwaves
Penetrate the Ionosphere, High bandwidth, Tight beams, Practical antenna sizes.

Explanation: D
• Quantum of electromagnetic radiation; travels at speed c.
• Rest mass: m₀ = 0 (Option A is correct).
• Charge: q = 0 (Option C is correct).
• It travels at the speed of light in vacuum.  Correct
. Energy-momentum of a photon
• Energy: E = hν = hc/λ
• Momentum: p = E/c = h/λ ≠ 0
• So, photons do carry momentum.

Explanation: D
The speed of charging/discharging of an RC circuit is set by the time constant
τ = RC.
• Charging: V_C (t) = V(1 – e^–t/RC)
• Discharging: V_C (t) = V₀ e^–t/RC
A small capacitance C and a small resistance R make τ small, so both the rise (charging) and decay (discharging) curves reach their target values rapidly.
Rule: smaller R or C ⇒ smaller τ ⇒ faster response (Small time constant means that a capacitor charges and discharges quickly)
larger R or C ⇒ slower response.

Explanation: D
Magnetic force F = qv × B is perpendicular to v ⇒ it does no work.
It can (and does) change the direction of the velocity and hence the momentum → options A and C are changeable.
• The motion is uniform circular (or helical), so there is continuous centripetal acceleration → B is changeable.
• The angular velocity (cyclotron frequency) of the circular motion is

ω = |q|B/m,
which is constant for given q/m and B and independent of the particle’s speed. Thus, it is not changed by the magnetic force → D.
(Note: The magnetic force also does not change the speed/kinetic energy, but “speed” isn’t among the options here).

Explanation: D
For fixed P, raising V lowers I. Cable heating depends on I²R, so the low-current plan (X) wastes less energy as heat. Equal power transfer does not imply equal losses; losses depend on current, not on P alone.

Explanation: C
Compton wavelength shift Δλ = h/mc(1–cosθ) depends only on the scattering angle θ (and the scatterer’s mass). It’s maximal for backscatter θ=180° :Δλ_max = 2h/(mc), regardless of the photon’s frequency or wavelength. (A photon’s “velocity” isn’t adjustable-it’s c in vacuum.)

Explanation: D
Time required to charge a capacitor to 100%= infinite
For a charging RC circuit,
V_C (t) = V(1 – e^–t/τ), τ = RC
To reach 100% of the supply voltage, we would need
1 – e^{–t /τ} = 1 ⇒ e ^–t/τ = 0
which happens only as t → ∞. So, a capacitor never reaches exactly 100% in finite time-it approaches it asymptotically.
Useful benchmarks for MCQs (“practically full”):
• t = 1τ : ~63.2%
• t = 2τ : ∼86.5%
• t = 3τ : ∼95.0%
• t = 4τ : ~98.2%
• t = 5τ : ~99.3% (often taken as “fully charged” in practice, but not mathematically 100%).

Explanation: A

Explanation: B
For a capacitor, current is proportional to the rate of change of voltage, so current reaches its peak before voltage does. Hence, current leads voltage by 90⁰.

Explanation: A
Dark lines on bright bg = line absorption spectrum
Bright lines on dark bg = line emission spectrum.

Explanation: C
I = Q / t
Q = ne {where n is the number of electrons, e is the charge of an electron}
I = ne / t
16 × 10^–3 = n × 1.6 × 10^–19 / 1
n = 16 × 10^–3 / 16 × 10^-20
n = 1 × 10¹⁷ electrons. 

Explanation: A
State Lenz’s law
• The induced emf/current in a circuit opposes the change in magnetic flux that produces it.
• Mathematically: ε =− Δ Φ/ Δ t. The negative sign encodes the opposition.
2. Energy meaning behind the opposition
• Because the induced current opposes the change, you must do extra mechanical work (push/pull harder) to keep the change happening.
• That mechanical work doesn’t vanish—it is converted into electrical energy of the induced current (then typically into heat i²R or stored as magnetic energy).
Conceptual example
• Push a bar magnet into a coil. The coil’s induced current produces a magnetic field that repels the magnet’s motion.
• Your hand supplies mechanical energy → coil has induced emf and current → electrical energy (often dissipated as heat).
What Lenz’s law is NOT claiming
• B. Electrical → Mechanical happens in motors (Lorentz force) but that’s not what Lenz’s law is asserting.
• C. Mechanical → Chemical is about batteries/electrochemistry; not Lenz’s law.
5. Energy-conservation hook
• Lenz’s law enforces conservation of energy: the opposition ensures the electrical energy comes from the mechanical work you do.

Explanation: B
1. What full-wave rectifiers do:
They flip the negative half-cycles to positive, so both halves of each AC cycle appear as output pulses.
2. Cycle vs pulses:
• Input: 1 cycle –1 positive half +1 negative half.
• After full-wave: both halves become positive pulses → 2 pulses per input cycle.
3. Frequency relation:
If the input frequency is f_in, the output pulse (ripple) frequency is
f_out = 2f_in. 
4. Quick example:
Mains 50 Hz → full-wave ripple 100 Hz.
Mains 60 Hz → full-wave ripple 120 Hz.
Memory hook: Full-wave uses full cycle → two pulses per cycle →2f.

Explanation: C

Explanation: C
Ohm’s law V = IR holds only if the resistance R (and hence resistivity ρ) stays essentially constant while current flows. But current heats a conductor, changing its temperature T, and most materials have a temperature coefficient of resistivity α defined by
ρ(T) = ρ₀ (1 + α ΔT).
• If α is near zero, ρ changes very little with temperature → R is nearly constant → the V – I graph is linear → Ohm’s law applies.
• If α is large positive or large negative, ρ changes a lot as the conductor warms/cools → R is not constant → non-ohmic behavior.
• “Infinite” is unphysical here.
Note: All real conductors approximate Ohm’s law over limited conditions. Alloys like nichrome have a small α, which is why they’re used where a stable resistance is needed.

Explanation: A
As north side is moving Away, according to Lenzs law side facing the magnet will behave as south pole, meaning clockwise current will flow through it.

Explanation: B
Voltage at which current rises= breaking voltage
Breaking of bonds = Zenner effect
Rise of current = Avalanche effect.

Explanation: B
The energy drop is larger from n = 5 to n = 2 than from n = 3 to n = 2. Since E = hf, a larger energy difference means higher frequency (shorter wavelength).

Explanation B
Because I=E/R_L+r, increasing r (with E, R_L fixed) makes the denominator larger ⇒ I decreases.
Terminal voltage across the load is V_t = IR_L (also = E – Ir ). Since I drops (and R_L is fixed), V_t decreases.
Load power P_RL= I² R_L = (V_t²/R_L) therefore also decreases.

Explanation: C
What happens in an air-core transformer?
• Air has no magnetic domains and is a poor conductor.
⇒ No hysteresis loss (no domains to realign).
⇒ Negligible eddy currents (no conducting core to host circulating currents).
 Introduce a ferromagnetic core (e.g., steel): what changes?
• High permeability → larger flux density B for the same magnetizing current.
• The core is conductive and ferromagnetic, so two core losses appear.
Eddy-current loss increases
• Time-varying flux induces circulating currents in the conductive core.
Hysteresis loss appears/increases
• Ferromagnets have magnetic domains; each AC cycle forces domains to realign.
Design note (to avoid confusion)
• Engineers laminate the core and use high-resistivity, grain-oriented silicon steel to reduce these losses, but they are still greater than in air (where they were essentially absent).
Hint: Air core a no core losses; ferromagnetic core ⇒ eddy + hysteresis losses show up → both increase.

Explanation: B
Connecting P to + and N to − lowers the barrier, narrows the depletion region, and allows large current dominated by majority carriers.

Explanation: A

Explanation: A

Explanation: D
Compare penetration (external exposure):
• Alpha (α): very low penetration-stopped by paper/skin.
• Beta (β): moderate-stopped by a few mm of Al/plastic.
• X-rays: high-need lead shielding.
• Gamma (γ): highest-require thick lead/concrete.
Why “most harmful”?
For whole-body external exposure, the greater the penetration and energy, the deeper and wider the damage. Gamma rays (highest frequency/energy EM) penetrate most, damaging internal organs and tissues → most hazardous in this context.

Explanation: B
When two or more genes are located on the same chromosome and inherited together, the phenomenon is called linkage.

Explanation: B
Carbon monoxide (CO) binds with haemoglobin to form carboxy haemoglobin, which prevents oxygen from binding. Hence, oxygen supply to tissues decreases.

Explanation: C
1. A nerve impulse is an electrochemical wave caused by the movement of ions (Na⁺, K⁺) across the neuron’s membrane.
• It involves depolarization → repolarization → hyperpolarization.
• This is the actual signal traveling along the axon.
2. Check options:
• A. Reflex arc → pathway involving receptor, sensory neuron, interneuron, motor neuron, effector. It’s not the wave itself.
• B. Reflex action → automatic, involuntary response (e.g., knee jerk).
• C. Nerve impulse → correct term for the electrochemical wave.
• D. Influx → refers to entry of ions (like Na⁺ influx), part of the process but not the whole wave.
Correct Answer: C. Nerve impulse
A nerve impulse is the traveling wave of depolarization and repolarization along the neuron membrane, allowing transmission of information.

Explanation: B
1. Genotype Tt meaning:
• T = dominant allele (tallness).
• t = recessive allele (shortness).
• Together, Tt shows the organism is heterozygous for the height gene.
2. Check options:
A. Allele has at least 2 genes (Wrong). An allele is a version of a single gene, not multiple genes.
B. There are at least two different alleles of the gene (Correct). The genotype shows that the height gene exists in two forms: T and t.
C. Two different genes for height (Wrong). Only one gene for height, but it has two alleles.
D. One allele with 2 forms  Slightly misleading. It’s the gene that has two forms (alleles), not the allele itself.
Correct Answer: B. There are at least two different alleles of the gene
Genotype Tt proves that the height gene exists in more than one form (alleles). The capital T (dominant) codes for tallness, and small t (recessive) codes for shortness. Having Tt shows heterozygosity → two different alleles for the same gene.

Explanation: D
1. Ovulation timing: occurs around day 14 of a 28-day cycle, triggered by the LH surge.
2. After ovulation (luteal phase):
• The ruptured follicle transforms into the corpus luteum.
• The corpus luteum secretes large amounts of progesterone and some oestrogen.
• Progesterone prepares the endometrium for possible implantation.
3. Check options:
A. FSH Highest before ovulation to stimulate follicle growth, then decreases.
B. LH Surge occurs at ovulation, then drops quickly.
C. Oestrogen Peaks before ovulation, then shows only a slight rise again, not the main hormone after ovulation.
D. Progesterone This is the hormone that increases significantly after ovulation.
Correct Answer: D. Progesterone
Three days after ovulation (early luteal phase), progesterone levels rise sharply due to secretion from the corpus luteum. This differentiates the luteal phase from the follicular phase.

Explanation: B
1. Darwin’s theory of evolution (1859, On the Origin of Species):
• Populations show variation.
• More offspring are produced than can survive (struggle for existence).
• Individuals with favorable traits survive and reproduce more.
• Over generations, these advantageous traits become common.
• This process = natural selection.
2. Check options:
A. Mutation in genes → Mutations create variation, but Darwin did not know about genes or mutations.
B. Natural selection → Darwin’s main principle.
C. Use and disuse of organs → This was Lamarck’s theory, not Darwin’s.
D. Inheritance of acquired characteristics → Also Lamarck’s idea (e.g., giraffes stretching necks).
Correct Answer: B. Natural selection.

Explanation: C
Since most offspring resemble parental types but some recombinants appear, the genes are partially linked

Explanation: A
1. Biceps muscle action:
• The biceps brachii is a flexor muscle of the upper arm.
• When it contracts, it pulls the radius bone upwards at the elbow joint.
• This causes the forearm to bend toward the upper arm (flexion at the elbow).
2. Check options:
A. Arm bends → Correct, contraction of biceps = flexion.
B. Arm straightens → Straightening (extension) is caused by the triceps muscle, not biceps.
C. Arm rotates → Rotation involves shoulder joint muscles (like deltoid, rotator cuff).
D. Nothing happens → Wrong, contraction of biceps definitely produces movement.
Correct Answer: A. Arm bends.

Explanation: B
Recombinant DNA technology produces vaccines containing harmless antigenic proteins rather than entire microbes.

Explanation: C
The blood has a slightly basic pH, maintained by buffer systems like bicarbonate buffer.

Explanation: A
1. Impulse conduction in neurons:
• Myelinated neurons: Have myelin sheath → impulse “jumps” from node to node = saltatory conduction (fast).
• Non-myelinated neurons: Lack myelin sheath → impulse moves step by step along the entire membrane = continuous conduction (slower).
2. Check options:
• A. Continuous (Correct) → conduction is continuous along the axon.
• B. Stationary → impulse never stays still; it propagates.
• C. Electrical → impulse is electrochemical, not purely electrical.
• D. All of them → since only A is correct.
Correct Answer: A. Continuous
In non-myelinated neurons, the action potential spreads continuously along the membrane because there are no myelin gaps (nodes of Ranvier) to speed up conduction.

Explanation: A
1. Syphilis → a sexually transmitted disease (STD) caused by a spirochete bacterium.
• The bacterium is Treponema pallidum.
2. Check options:
A. Treponema pallidum Correct.
B. Mycoplasma pneumoniae Causes atypical pneumonia.
C. Plasmodium Protozoan causing malaria.
D. Vibrio cholerae Bacterium causing cholera.
Correct Answer: A. Treponema pallidum
Syphilis is caused by the spirochete bacterium Treponema pallidum, transmitted mainly through sexual contact, from mother to fetus (congenital syphilis), or less commonly through blood transfusion.

Explanation: A
The acrosome originates from the Golgi complex and contains hyaluronidase and acrosin enzymes to penetrate the ovum

Explanation: B
Lamarck proposed that environmental needs cause changes in organ use; these acquired traits are passed on.

Explanation: B
Each muscle fiber contains numerous myofibrils, and each myofibril has a diameter of about 1–2 micrometers (µm)

Explanation: B
Vaccines stimulate adaptive immunity, causing memory cells to form for long-term protection

Explanation: B
1. Main function of the respiratory system:
• Exchange of gases → oxygen in, carbon dioxide out.
• This process is fundamentally breathing (ventilation + gas exchange).
2. Check options:
• A. Smell → Olfactory function of the nose, not the basic ability of the respiratory system.
• B. Breathe → This is the most direct, fundamental ability provided by the respiratory system.
• C. Give out CO₂ → Correct but secondary; it is part of breathing.
• D. Giving out CO₂ → Same as C, but less precise wording.
Correct Answer: B. Breathe
The respiratory system’s basic ability is to breathe, which includes both oxygen intake and carbon dioxide removal. Smelling is an associated function, and CO₂ exhalation is part of the process, but the primary ability is breathing.

Explanation: B
1. Background:
• Before genetic engineering, diabetic patients were treated with animal insulin (from pigs or cattle).
• This caused some allergic reactions and was expensive.
2. Modern method:
• Scientists introduced the human insulin gene into plasmids (circular DNA) of E. coli bacteria using recombinant DNA technology.
• The bacteria multiply rapidly, producing large amounts of human insulin.
• The insulin is then extracted and purified for medical use.
3. Check options:
A. Viruses → Not used in commercial insulin production.
B. Bacteria (E. coli) Correct → main organism used in recombinant DNA technology for insulin.
C. Fungi → Some fungi are used for producing antibiotics (e.g., Penicillium), but not insulin.
D. Animals → Earlier source, but not modern genetic engineering method.
Correct Answer: B. Bacteria (E. coli)
In genetic engineering, the human insulin gene is inserted into a bacterial plasmid, and this recombinant plasmid is introduced into E. coli. As the bacteria multiply, they produce human insulin, which is harvested, purified, and sold under names like Humulin. This method provides a safe, cheap, and allergy-free source of insulin for diabetic patients.

Explanation: C
CO₂ binds with the globin part of haemoglobin to form carbamino haemoglobin (HbCO₂), which carries around 23% of CO₂.

Explanation: C
FSH acts on Sertoli cells to support spermatogenesis. Without their activation, developing sperm lose nourishment despite normal testosterone levels from Leydig cells.

Explanation: A
Acquired traits affect somatic cells only; germline DNA remains unchanged, so they’re not heritable.

Explanation: C
Bone matrix is mineralized with hydroxyapatite; cartilage matrix is firm/elastic but non-mineralized. Cartilage is largely avascular; bone is vascular.

Explanation: B
DNA probes are labeled sequences that hybridize with complementary nucleic acids for pathogen identification.

Explanation: D
1. Pathway of air in humans:
Trachea → Primary bronchi → Secondary bronchi → Tertiary bronchi → Bronchioles → Alveolar ducts → Alveolar sacs → Alveoli.
2. Alveoli are the tiny air sacs where gas exchange occurs.
3. Alveolar sacs are clusters (bunches) of alveoli at the ends of bronchioles.
4. So, bronchioles don’t end directly in a single alveolus but in alveolar sacs made up of many alveoli.
Correct Answer: D. Both B and C
Bronchioles terminate in alveolar sacs, which consist of clusters of alveoli. These alveoli are the true sites of gaseous exchange in the lungs.

Explanation: B
1. Thermoregulation in humans:
• Hypothalamus → the control center for temperature (“body’s thermostat”).
• Blood vessels (in skin) → vasodilation releases heat, vasoconstriction conserves heat.
• Sweat glands → sweating removes heat through evaporation.
• Skeletal muscles → shivering generates heat when body is cold.
2. Check options:
• A. Blood vessels + cerebellum + sweat glands Cerebellum controls coordination of movement, not temperature.
• B. Blood vessels + hypothalamus + skeletal muscles Correct → all three play a direct role in thermoregulation.
• C. Kidneys + cerebellum + sweat glands Kidneys regulate excretion and water balance, not body temperature.
• D. Kidneys + hypothalamus + skeletal muscles Kidneys not involved in temperature control.
Correct Answer: B. Blood vessels + hypothalamus + skeletal muscles
The hypothalamus detects temperature changes, blood vessels and sweat glands regulate heat loss, and skeletal muscles produce heat through shivering. This integrated system maintains homeostasis of body temperature.

Explanation: C
1. Set symbols: Let B = allele for black coat, b = allele for light brown coat.
We are told all 20 offspring are black.
2. Dominance from the result:
If black appears in every lamb, black must be dominant over light brown. (If black were recessive, mating a black male with light-brown females would produce many light-brown lambs, not all black.)
3. Genotypes of the parents:
• Light brown females must be bb (recessive phenotype).
• For every lamb to be black, the black male must contribute a B to each offspring → the male must be BB (homozygous dominant).
4. Punnett square (BB × bb):

All offspring are Bb (black phenotype).
5. Why not heterozygous male (Bb)?
Bb (male) × bb (female) would give 50% Bb (black) and 50% bb (light brown)—not all black. (Getting 20/20 black from this cross would be extremely unlikely.)
Conclusion: The observation (“all offspring black”) is explained only if black is dominant and the male is homozygous (BB) → Option C.

Explanation: B
Seminal vesicles contribute ~60% of semen, adding fructose (for sperm energy) and prostaglandins. Removal reduces volume and energy supply but sperm production continues.

Explanation: B
Excess offspring create struggle for existence; only better-adapted individuals survive.

Explanation: B
Actin–myosin filaments underlie contraction in skeletal, cardiac, and smooth muscles. Multinucleation and voluntary control are not universal; intercalated discs are cardiac only.

Explanation: B
Hybridoma technology fuses antibody-producing B cells with immortal myeloma cells to create monoclonal antibodies.

Explanation: A
1. Respiration’s role:
• Cellular respiration provides ATP, the energy source for processes that need energy.
• Processes that require ATP → depend on respiration.
• Processes that do not need ATP (passive) → do not depend on respiration.
2. Option A: Diffusion of glucose
• Diffusion is a passive process (down a concentration gradient).
• No ATP is required.
• Does not depend on respiration.
3. Option B: Active uptake of ions
• “Active” = energy required (ATP from respiration).
• Depends on respiration.
4. Option C: Conduction of nerve impulses
• Nerve impulses rely on active transport (Na⁺/K⁺ pump) to restore ionic gradients.
• Requires ATP → depends on respiration.
5. Option D: Muscle contraction
• Contraction requires ATP for actin-myosin interaction and calcium ion pumps.
• Depends on respiration.
Correct Answer: A. Diffusion of glucose.

Explanation: A
1. Role of the nervous system:
• The nervous system directly controls rapid responses such as muscle movement, reflexes, gland secretion, and functions of smooth/cardiac muscle.
2. Option A: Blood glucose concentration
• This is mainly regulated by hormones (insulin and glucagon from the pancreas).
• Not under direct nervous system control.
3. Option B: Dilation of blood vessels
• Controlled by the autonomic nervous system (sympathetic/parasympathetic) acting on smooth muscle in vessel walls.
4. Option C: Heart rate
• Directly controlled by the autonomic nervous system via the sinoatrial (SA) node.
5. Option D: Pupil diameter in the eye
• Controlled by the autonomic nervous system (sympathetic → dilation, parasympathetic → constriction).
Correct Answer: A. Blood glucose concentration.

Explanation: C
1. Definition of natural selection:
• Natural selection is the process by which individuals with advantageous traits (that improve survival or reproduction) are more likely to survive and pass on those traits to the next generation.
• It is not directed by humans; it happens due to environmental pressures.
2. Look at the options:
• A. Dogs that are friendly to humans → This is due to artificial selection (selective breeding) by humans, not natural selection.
• B. Grapes that contain no seeds → Also a result of artificial selection or genetic modification, not natural selection.
• C. Mosquitoes resistant to insecticides → This is natural selection:
• Some mosquitoes randomly have mutations that make them resistant.
• When insecticides are sprayed, most mosquitoes die, but resistant ones survive.
• Survivors reproduce, passing resistance genes to the next generation.
• Over time, the population becomes resistant.
• D. Onion crops with pleasant taste → Again, this is due to human-controlled breeding, not natural selection.
Correct Answer: C. Mosquitoes that are resistant to insecticides

Explanation: A
The middle piece supplies energy (ATP) to power flagellar movement for motility; the acrosome releases enzymes for ovum penetration.

Explanation: B
Genetic similarity reflects common ancestry; closer DNA sequences imply evolutionary relationships.

Explanation: C
Osteoclasts (multinucleate) dissolve mineral and matrix; osteoblasts form bone; osteocytes maintain matrix.

Explanation: B
They are uniform antibodies binding to a single specific antigenic site

Explanation: C
1. When body temperature drops:
• The hypothalamus activates mechanisms to generate and conserve heat.
2. Responses:
• Shivering: Rapid, involuntary muscle contractions that produce heat through respiration.
• Vasoconstriction (of skin blood vessels): Narrowing of blood vessels near the skin surface reduces blood flow → less heat lost to the environment.
3. Why not the other options?
A. Shivering + vasodilation → Vasodilation increases heat loss, which would worsen cooling.
B. Sweating + vasoconstriction → Sweating reduces body temperature, not correct in cold conditions.
D. Sweating + vasodilation → Both are mechanisms for cooling, not warming.
Correct Answer: C. Shivering and vasoconstriction in blood vessels near the skin surface.

Explanation: D
1. Option A:
• “A dominant characteristic is seen in phenotype of a heterozygote” → Correct.
• Example: In pea plants, Tt (tall) shows the dominant trait “tall”.
2. Option B:
• “A homozygous genotype may be either dominant or recessive” → Correct.
• Example: TT (homozygous dominant) or tt (homozygous recessive).
3. Option C:
• “Recessive phenotypes always have two recessive alleles” → Correct.
• Example: Short pea plants = tt only.
4. Option D:
• “The phenotype of a homozygote is always dominant” → Incorrect.
• Because a homozygote can be dominant (TT → tall) or recessive (tt → short).
• So the phenotype of a homozygote is not always dominant.
Correct Answer: D. The phenotype of a homozygote is always dominant.

Explanation: B
The oviduct conveys the ovum from the ovary and provides the ampulla site for fertilization before zygote moves to the uterus.

Explanation: C
CSF fills the subarachnoid space (between pia and arachnoid mater), ventricles of the brain, and central canal of spinal cord.

Explanation: B
Cardiac muscle is striated, involuntary, has intercalated discs, and is myogenic

Explanation: B
Recombinant Factor VIII restores clotting ability in hemophilia A patient.

Explanation: D
1. What is negative feedback?
• A control mechanism where a change in a condition triggers a response that reverses (negates) that change, keeping conditions stable (homeostasis).
2. In this case (osmoregulation):
• If water in blood falls → hypothalamus detects high solute concentration → pituitary releases more ADH.
• ADH makes kidneys reabsorb more water → urine becomes more concentrated (less water lost).
• This restores blood water concentration back to normal.
3. Why is it negative feedback?
• Because the body reverses the initial change (low blood water → response increases blood water again).
4. Check options:
A. It decreases the amount of water in blood → Wrong, it restores it.
B. It increases any change → That describes positive feedback, not negative.
C. It increases the amount of water in the blood → Incomplete; it doesn’t always “increase,” it restores balance.
D. It reverses any change in the amount of water in the blood → Correct.
Correct Answer: D. It reverses any change in the amount of water in the blood.

Explanation: C
1. Genetic basis of haemophilia:
• Haemophilia is caused by a recessive allele on the X chromosome.
• Symbol:
Xᴴ = normal allele
Xʰ = haemophilia allele
2. Parents’ genotypes:
Female carrier = XᴴXʰ
Normal male = XᴴY
3. Cross (Punnett square):

Result:
• Daughters: 50% normal, 50% carriers (but not diseased).
• Sons: 50% normal, 50% haemophiliac.
5. Answer to question:
• The probability that a son will be haemophiliac = 50% 
Correct Answer: C. 50%.

Explanation: B
The LH surge is essential for ovulation. If estrogen fails to trigger positive feedback at mid-cycle, no LH peak occurs, preventing follicle rupture.

Explanation: B
Neisseria gonorrhoeae is a Gram-negative diplococcus that infects mucous membranes of the urethra, cervix, and eyes.

Explanation: C
Thin filaments slide toward center; H-zone (thick-only region) narrows/disappears; A-band length remains constant.

Explanation: D
1. Sequence of events:
• The loud noise is detected by receptors in the ear.
• A sensory neuron carries this information as an impulse to the central nervous system (CNS).
• Inside the CNS, the impulse passes to a relay (interneuron), which processes and connects sensory input to the appropriate response pathway.
• The relay neuron transmits the signal to a motor neuron, which carries impulses to muscles (e.g., vocal cords, diaphragm) to make the child shout for help.
2. Check options
A. Motor → relay → sensory wrong order (backwards).
B. Motor → sensory → relay wrong, action doesn’t come before detection.
C. Sensory → motor → relay wrong, relay comes before motor in the CNS.
D. Sensory → relay → motor correct order.
Correct Answer: D. Sensory neuron → relay neuron → motor neuron

Explanation: C
1. Nature of haemophilia:
• It is an X-linked recessive disorder.
• The faulty gene is carried on the X chromosome.
2. Males (XY):
• If the single X has the defective allele (XʰY), there is no second X to mask it.
→ Males express haemophilia more often.
3. Females (XX):
• For a female to express haemophilia, both X chromosomes must carry the defective allele (XʰXʰ).
• If only one X carries it (XᴴXʰ), the normal allele on the other X masks the effect → female becomes a carrier but not diseased.
4. Check options:
A. The gene is present on autosomes → Wrong, it is on the X chromosome, not autosomes.
B. They have a stronger immune system → Not relevant to genetic inheritance.
C. They require two defective X-chromosomes to express the trait → Correct explanation.
D. Hormonal protection suppresses the gene → Hormones are not involved here.
Correct Answer: C. They require two defective X-chromosomes to express the trait.

Explanation: B
CSF is formed by diffusion, pinocytosis, and active transport from the blood vessels of brain and spinal cord.

Explanation: C
James Hutton first proposed the principle of uniformitarianism, suggesting that geological processes operating today also shaped the Earth in the past.

Explanation: B
Ca²⁺–troponin C shifts tropomyosin, exposing actin sites; myosin-ATP cycle then proceeds.

Explanation: A
1. Reflex arc pathway:
• Receptor detects stimulus (e.g., pain).
• Sensory neuron carries impulse → CNS (spinal cord/brain).
• Relay neuron processes signal inside CNS.
• Motor neuron carries impulse from CNS to an effector (muscle or gland).
• Effector produces response (e.g., muscle contracts).
2. Check the options:
A. Carrying nerve impulses from the central nervous system to an effector → This is the exact function of motor neurons.
B. Connecting a receptor to the central nervous system → That’s the job of sensory neurons.
C. Forming a synapse with a sensory neuron → Relay neurons connect sensory and motor neurons.
D. Transferring energy from the stimulus to a nerve impulse → That’s the role of receptors, not motor neurons.
Correct Answer: A. Carrying nerve impulses from the central nervous system to an effector.

Explanation: B
During meiosis, homologous chromosomes separate, ensuring each gamete carries one allele per gene.

Explanation: B
FSH stimulates growth of new follicles at the beginning of each cycle, marking its restart.

Explanation: C
The philosopher Herbert Spencer coined the term “Survival of the Fittest” after reading Darwin’s Origin of Species (1859). Darwin later accepted and used the phrase in later editions to describe natural selection.

Explanation: B
Without ATP, myosin heads cannot detach from actin, producing rigidity.

Explanation: B
Transduction converts stimulus energy into receptor potentials/action potentials.

Explanation: B
According to Mendel’s monohybrid cross, phenotypic ratio = 3 tall : 1 dwarf.

Explanation: B
Each fallopian tube (also called oviduct) is about 10 cm long, extending from the ovary to the uterus.

Explanation: B
Dominant alleles express their effect in the heterozygous condition, masking the recessive allele

Explanation: C
Synovial cavity contains synovial fluid, not “periosteal lymph.”

Explanation: D
Nociceptors respond to damaging stimuli; taste receptors handle sweetness

Explanation: B
The 9:3:3:1 ratio demonstrates independent assortment of two gene pairs during gamete formation.

Explanation: B
After infection by Treponema pallidum, the first symptom (chancre) appears after an incubation period of 2–4 weeks.

Explanation: B
Arthritis = joint inflammation, often with pain, stiffness, swelling, reduced motion.

Explanation: C
Myelin insulates (↑Rm, ↓Cm), enabling saltatory conduction between nodes.

Explanation: B
Linked genes are transmitted together because they are physically close and rarely separated by crossing over.

Explanation: B
Nissl substance synthesizes proteins (RER + ribosomes).

Explanation: B
Crossing over occurs during prophase I of meiosis, exchanging segments between homologous chromosomes

Explanation: B
High K⁺ permeability and Na⁺/K⁺ ATPase establish negativity inside.

Explanation: B
The closer two genes are, the less likely crossing over occurs between them, resulting in stronger linkage.

Explanation: B
This is the canonical arc.

Explanation: C
Morgan’s experiments with fruit flies revealed gene linkage and mapped chromosome inheritance patterns.

Explanation: C
Cerebral cortex integrates higher-order processing and voluntary control.

Explanation: B
Daughters receive one X from father (carrying hemophilia gene) and one normal X from mother → carriers.

Explanation: B
Cerebellum refines motor output; damage → ataxia.

Explanation: B
Hemophilia is an X-linked recessive condition due to absence of clotting factor VIII.

Explanation: B
LH (Interstitial Cell Stimulating Hormone) acts on Leydig cells located between seminiferous tubules to secrete testosterone.

Explanation: B
Daughters receive a defective X from mother and a normal X from father → carriers.

Explanation: D
Mechanistic aid: Alcohol reacts with SOCl₂ forming an alkyl chlorosulfite intermediate.
Pyridine as a base/HCl scavenger: The reaction generates HCl; pyridine (a base) neutralizes HCl to pyridinium chloride, preventing acid‑catalyzed side reactions and driving the reaction forward. (⇒ B and C true.)
Solvent & facilitator: Pyridine commonly serves as the solvent and can form a reactive complex with SOCl₂ that accelerates the SN² pathway, often giving inversion of configuration at a chiral center. (⇒ A true.)
Bottom line: It acts as solvent, traps HCl, and serves as base → All.

Explanation: D
Hint: Metallicity ↔ low IE;
Non‑metallicity ↔ high EN/EA.
Metallic character = ease of losing electrons (forming M⁺).
Lower ionization energy (IE) ⇒ electrons are removed more easily ⇒ more metallic.
Electronegativity and electron affinity are indices of non‑metallic character. Conductivity is a property of metals but varies with structure/impurities and is not the accepted periodic “index.”
Therefore: Ionization energy is the best index; lower IE ⇒ higher metallic character.

Explanation: C
Alkane to alcohol is oxidation.
Oxidation of C: count O’s ↑ / H’s ↓ / OS goes up (e.g., CH₄ → CH₃OH).