Human Body - General Facts PYQs – Biology, SSC & Railway

Correct Answer:
Correct Answer: Option 4 – Nephrons
Explanation:
Nephronsare the microscopic filtering units of thekidney(excretory system), not part of the musculoskeletal system. Muscles, bones, and tendons are all structural/functional components of the musculoskeletal system.
Important Facts:
• The musculoskeletal system includes bones, muscles, tendons, ligaments, and joints.
• Nephrons belong to the urinary/excretory system.

Topic: Types of Joints in Human Body
Ball and Socket Jointallows the widest range of movement.
Movement types: Flexion, extension, abduction, adduction,
medial rotation, and lateral rotation (360° movement).
Examples: Shoulder joint (glenohumeral) and Hip joint.
Other joints have limited movement:
• Pivot: Only rotation (neck)
• Hinge: Only flexion/extension (elbow, knee)
• Gliding: Sliding movement only (wrist, ankle)
Answer: Option 2 → Ball and Socket Joint

The correct answer is option 2.
If tooth decay (dental caries) is left untreated, bacteria and microorganisms gradually erode the enamel and dentine, eventually reaching the dental pulp. The pulp contains nerves and blood vessels, and its infection causes pulpitis (inflammation). This can lead to severe toothache, abscess formation, and in serious cases, spread of infection to surrounding bone and tissues.
Option 1 is incorrect: Tooth decay causes darkening and discolouration of teeth, not whitening.
Option 3 is incorrect: Extensive research clearly documents the serious consequences of untreated tooth decay.
Option 4 is incorrect: Plaque does not dissolve on its own; it hardens into tartar if not removed and continues to promote decay.

Dental plaque is composed of both bacterial cells (I) and food particles (II), along with saliva proteins and other substances. It forms a sticky film on the teeth. Only I and Only II are incomplete; Neither is factually wrong.

The correct answer is (b) Skin.
The skin (integumentary system) is the largest organ in the human body by surface area (approximately 1.5-2 square meters) and weight (about 3.5-4 kg in an average adult). It serves multiple functions: protection against pathogens, physical damage, and UV radiation; thermoregulation through sweat glands and blood vessels; prevention of water loss; and sensory perception.
(a) Liver: The largest internal (solid) organ of the body; plays roles in metabolism, detoxification, and bile production; but the skin is larger overall.
(c) Brain: The control center of the nervous system; weighs about 1.3-1.4 kg; much smaller than the skin by weight and area.
(d) Heart: A fist-sized muscular organ pumping blood; much smaller than the skin.

The sarcomere is the fundamental structural and functional (contractile) unit of a muscle fibre . It extends from one Z-disc (Z-line) to the next and contains interdigitating thick (myosin) and thin (actin) filaments that slide past each other during muscle contraction.
(b) Incorrect: Myosin is the thick filament protein involved in contraction but is not the contractile unit itself.
(c) Incorrect: Tropomyosin is a regulatory protein that covers the actin-binding sites; it is not the contractile unit.
(d) Incorrect: Actin forms thin filaments in muscle but is a protein component, not the contractile unit.

Correct Answer: Age
The ossification test (also known as bone ossification or skeletal maturity test) is a forensic and medical test used to estimate the age of a person by examining the degree of bone development and fusion (ossification) of bone epiphyses (growth plates). As a person ages, bones gradually harden and growth plates fuse. This test is widely used in medico-legal cases to determine the age of individuals when birth records are unavailable.
Why other options are wrong:
- Height: Height is measured directly; ossification test does not determine height.
- Weight: Weight is measured directly; unrelated to bone ossification.
- Blood group: Determined by blood typing (ABO test), not bone examination.

Correct Answer: Option 3 — Nerve cell
The nerve cell (neuron) is the longest cell in the human body. A single neuron consists of a cell body (cyton) with dendrites, and one very long fibre called the axon. The axon of a nerve running from the spinal cord to the toe can be nearly one metre long — in tall people even more.
This great length is exactly what a neuron needs: it must carry an electrical impulse from a receptor to the brain or spinal cord, and back to a muscle, in one unbroken stretch without relaying it from cell to cell. Neurons are also amitotic — once formed, they usually do not divide, which is why nerve injuries heal so poorly.
❌ Why the other options are incorrect
✗ Ovum — the human egg is the largest cell by diameter (about 0.1 mm) and can just be seen with the naked eye, but it is round, not long.
✗ Fat cell — an adipocyte of adipose tissue; it is a large, rounded cell swollen with a fat droplet, but it is nowhere near the length of a neuron.
✗ Blood cell — the RBC is a tiny biconcave disc about 7 micrometres wide with no nucleus in mammals; it is one of the smallest cells.
📌 SSC & Railway Exam Facts
• Smallest cell — Mycoplasma (PPLO); smallest human cell — the sperm; largest human cell — the ovum.
• Largest cell in nature — the ostrich egg.
• Parts of a neuron — dendrite → cell body (cyton) → axon → nerve endings; the gap between two neurons is the synapse.
• Myelin sheath insulates the axon and speeds up impulse conduction.
• Longest bone — femur; smallest bone — stapes (in the ear); largest gland — liver; largest organ — skin.