Biology Compendium — Human Body Facts, Scientists & Firsts
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Why This Chapter Matters
This is the chapter you open the night before the exam. Static human-body facts, scientist-discovery pairs, and health-day dates show up almost every year in SSC CGL, CHSL, MTS, CPO, and RRB NTPC General Awareness sections, worth 1-2 direct marks on their own and another 1-2 indirectly when a question from an earlier chapter leans on a fact listed here. Banking exams lean on it too, usually as a single quick GK question tucked between current affairs.
You have already studied the systems chapter by chapter. What trips students on exam day is not lack of knowledge, it is mixing up two facts that sound similar: Fleming gets credited for Jenner's vaccine, Cushing's and Addison's get swapped, or a student picks "largest cell" when the question asked "longest cell." This chapter exists to kill exactly that confusion. Every table here is built to be read twice: once tonight to refresh, once tomorrow morning on the way to the center. Nothing new to learn, only facts arranged so they stick and stay separated in your head.
1. Human Body Records — The "Biggest, Smallest, Fastest" Table
SSC loves a one-line "which is the largest" question because it has a single correct answer and no room for debate. The trap is that "largest," "smallest," and "longest" are not the same organ every time, and examiners deliberately mix them up across attempts.
Exam trap: Skin is the largest organ overall, but the liver is the largest internal (or gland) organ. Read the question word by word before answering.
| Record | Answer | Extra fact worth knowing |
|---|---|---|
| Largest organ (overall) | Skin | Covers about 1.5-2 sq. m in an adult |
| Largest internal organ / largest gland | Liver | Also performs bile secretion and detoxification |
| Smallest bone | Stapes (in the middle ear) | Part of the three ear ossicles: malleus, incus, stapes |
| Longest bone | Femur (thigh bone) | Roughly a quarter of a person's height |
| Largest cell | Ovum (female egg cell) | Visible without a microscope, unlike most cells |
| Smallest cell | Sperm cell | Built almost entirely for movement, minimal cytoplasm |
| Longest cell | Nerve cell (neuron) | A single neuron's axon can run over a metre, foot to spine |
| Largest muscle | Gluteus maximus (buttock) | Powers standing up and climbing |
| Smallest muscle | Stapedius (in the ear) | Controls the stapes bone, protects against loud sound |
| Fastest-acting muscle | Muscles of the eye | Blink and eye movement are near-instant reflexes |
| Largest artery | Aorta | Carries oxygenated blood straight out of the left ventricle |
| Largest vein | Inferior vena cava | Returns blood from the lower body to the heart |
| Largest endocrine gland | Thyroid | Sits in the neck, controls metabolic rate |
| Largest lymphatic organ | Spleen | Filters blood, stores extra RBCs, fights infection |
| Largest part of the brain | Cerebrum | Handles thought, memory, voluntary action |
Think of the body as a household. The skin is the outer wall of the house, largest by far because it wraps everything. The liver is the biggest room inside the house. The femur is the main supporting pillar. Once you place each record physically in a "house," the numbers stop being abstract trivia and become a floor plan you already know.
Memory hook: For the three ear ossicles in order from outer to inner, remember "Mala Is Small" — Malleus, Incus, Stapes, and Stapes is the smallest bone in the whole body. That single sentence answers two different exam questions.
2. Vital Numbers Every Aspirant Must Know Cold
These are not "which is largest" facts, they are exact numbers examiners quote directly in the question stem, so a wrong number means a wrong answer with no way to reason your way out.
| Parameter | Normal value | Where it gets tested |
|---|---|---|
| Bones in an adult human | 206 | Infants are born with about 270-300, some fuse as they grow |
| Chromosomes in a human cell | 46 (23 pairs) | Sex cells (sperm, ovum) carry only 23 |
| Normal body temperature | 37°C / 98.6°F | Basis for fever-related questions |
| Blood pH | 7.35–7.45 (slightly alkaline) | A common "blood is acidic or alkaline" trap |
| Average resting heart rate | 72 beats/min | Athletes often run lower, not higher |
| Total blood volume | 5-6 litres in an average adult | Roughly 7-8% of body weight |
| Normal blood pressure | 120/80 mmHg | 120 is systolic, 80 is diastolic, don't swap them |
| Number of skeletal muscles | About 640 | Muscles make up nearly 40% of body weight |
| Gestation period (pregnancy) | About 280 days / 9 months | Counted from the last menstrual period |
| RBC lifespan | About 120 days | Old RBCs are broken down in the spleen and liver |
Exam trap: Students confuse "206 bones in an adult" with "300 bones in an infant" and pick the infant number for an adult-body question, or vice versa. The trick: babies have MORE bones that later FUSE into fewer, bigger ones as they grow. More bones young, fewer bones old, the opposite of what intuition suggests.
3. Scientists, Discoveries and the "Father Of" Table
This is the single most repeated table format in SSC General Science, appearing as "who discovered," "who is known as the father of," or "match the scientist to the discovery." Most wrong answers happen because two scientists worked in overlapping fields and get swapped.
| Scientist | Known for | Field / title |
|---|---|---|
| Edward Jenner | Developed the smallpox vaccine (1796), first vaccine in history | Father of Immunology / Vaccination |
| Louis Pasteur | Germ theory of disease, pasteurisation, rabies vaccine | Father of Microbiology |
| Robert Koch | Identified the bacteria causing tuberculosis and anthrax | Father of Bacteriology |
| Alexander Fleming | Discovered penicillin from Penicillium mould (1928) | First antibiotic |
| Karl Landsteiner | Discovered human blood groups (A, B, AB, O) | Father of Blood Group / Transfusion Medicine |
| William Harvey | Explained the circulation of blood, heart as a pump | Father of Physiology |
| Antonie van Leeuwenhoek | Built early powerful microscopes, first to observe bacteria | Father of Microbiology (alongside Pasteur) |
| Robert Hooke | First to observe and name the "cell" (in cork tissue, 1665) | Coined the term "cell" |
| Matthias Schleiden & Theodor Schwann | Proposed the Cell Theory (all living things made of cells) | Founders of Cell Theory |
| Gregor Mendel | Laws of inheritance, pea-plant experiments | Father of Genetics |
| Charles Darwin | Theory of evolution by natural selection | Father of Evolution |
| Carl Linnaeus | Binomial nomenclature (two-word naming of species) | Father of Taxonomy |
| James Watson & Francis Crick | Worked out the double-helix structure of DNA (1953) | With data from Rosalind Franklin's X-ray images |
| Ronald Ross | Proved that the female Anopheles mosquito transmits malaria (worked in India, won Nobel 1902) | Malaria transmission |
| Jonas Salk | Developed the injectable (killed-virus) polio vaccine | Polio vaccine, injectable form |
| Albert Sabin | Developed the oral polio vaccine (the drops given to Indian children) | Polio vaccine, oral form |
| Ian Wilmut | Led the team that cloned Dolly the sheep (1996) | First mammal cloned from an adult cell |
| Har Gobind Khorana | Helped decode the genetic code, Nobel Prize 1968 | Indian-origin geneticist |
Exam trap: Jenner vs Fleming is the most common swap in the paper. Jenner gave the world its first vaccine (smallpox, a virus). Fleming gave the world its first antibiotic (penicillin, works against bacteria). A vaccine trains your immune system in advance; an antibiotic kills an infection you already have. Different tools, different scientists, don't let the exam blur them.
Memory hook: For Salk and Sabin, remember "Salk = Shot" (injectable) and "Sabin = Sip" (oral drops). Both start with S, so anchor the delivery method instead of the name.
Picture Robert Hooke looking at a slice of cork under his microscope and seeing tiny box-like chambers, like a beehive cut in half. He called them "cells" because they reminded him of a monk's small room. That single image, honeycomb rooms, is why "cell" is the word we still use nearly 360 years later.
4. Disease, Vitamin and Hormone Confusion Pairs — Side by Side
This is where marks are lost the most. Two conditions sound related, come from opposite causes (deficiency vs excess, or two different glands entirely), and the exam banks on you not reading closely.
4.1 Vitamin deficiency diseases that get mixed up
| Vitamin | Chemical name | Deficiency disease | Common confusion with |
|---|---|---|---|
| Vitamin A | Retinol | Night blindness, xerophthalmia | Confused with Vitamin D deficiency (both affect eyes/bones in some memory shortcuts, but A is strictly vision) |
| Vitamin B1 | Thiamine | Beriberi (nerve and heart weakness) | Confused with B3 deficiency |
| Vitamin B3 | Niacin | Pellagra (skin, digestion, nerve issues) | Confused with B1's Beriberi |
| Vitamin B12 | Cobalamin | Pernicious anaemia | Confused with iron-deficiency anaemia (different cause entirely) |
| Vitamin C | Ascorbic acid | Scurvy (bleeding gums, weak connective tissue) | Confused with Vitamin K, which is about blood clotting, not gum bleeding |
| Vitamin D | Calciferol | Rickets (children), Osteomalacia (adults) | Confused with calcium deficiency alone; Vitamin D helps the body absorb calcium in the first place |
| Vitamin K | Phylloquinone | Delayed blood clotting | Confused with Vitamin C's bleeding-gum symptom |
Exam trap: Both Vitamin C deficiency (scurvy) and Vitamin K deficiency involve bleeding, but for different reasons. Scurvy weakens the blood vessel walls and gums directly. Vitamin K deficiency stops the blood from clotting properly even if the vessels are healthy. If the question mentions "gums," think C. If it mentions "clotting" or "wound doesn't stop bleeding," think K.
4.2 Hormone deficiency vs excess — same gland, opposite disease
| Gland | Hormone | Deficiency (too little) | Excess (too much) |
|---|---|---|---|
| Pituitary (in childhood) | Growth Hormone | Dwarfism | Gigantism |
| Pituitary (in adults) | Growth Hormone | — | Acromegaly (enlarged hands, feet, jaw) |
| Thyroid | Thyroxine | Goitre, Myxoedema (adults), Cretinism (children) | Hyperthyroidism / Grave's disease |
| Adrenal cortex | Cortisol | Addison's disease | Cushing's syndrome |
| Pancreas | Insulin | Diabetes mellitus | (excess insulin causes hypoglycaemia, low blood sugar) |
| Parathyroid | Parathormone | Low calcium, muscle cramps (tetany) | Weak, brittle bones |
Exam trap: Addison's disease and Cushing's syndrome both involve the same hormone, cortisol, from the same gland, the adrenal cortex, but they are opposites. Addison's is too little cortisol, patients feel weak and lose weight. Cushing's is too much cortisol, patients gain weight and develop a round "moon face." One easy anchor: "Addison's" and "absence" both start with A, so Addison's means the hormone is absent (deficient).
Memory hook: For thyroxine problems by age, remember the chain: cretin child, myxoedema man. Cretinism is the childhood form of thyroxine deficiency (affects growth and mental development), myxoedema is the adult form (affects metabolism and energy). Same missing hormone, different life stage, different name.
Think of a gland like a tap. Too little flow (deficiency) and the tank downstream runs dry, causing one set of symptoms. Tap stuck fully open (excess) and the tank overflows, causing a completely different set of symptoms. Same tap, same water, opposite problem. That is the entire logic behind every deficiency/excess pair in this table.
5. National and International Health Days
SSC and RRB occasionally ask "which day is observed as ___" as a standalone one-mark question. You don't need every UN observance, only the ones with a strong biology or health link that actually show up in papers.
| Date | Observance | Focus area |
|---|---|---|
| February 4 | World Cancer Day | Cancer awareness and prevention |
| March 8 | International Women's Day | Broader theme, occasionally linked to women's health |
| March 24 | World Tuberculosis Day | Marks the day Robert Koch announced discovery of the TB bacillus (1882) |
| 2nd Thursday of March | World Kidney Day | Kidney disease awareness |
| April 7 | World Health Day | Marks the founding date of the WHO (1948) |
| April 25 | World Malaria Day | Malaria prevention and control |
| May 31 | World No Tobacco Day | Tobacco-related disease prevention |
| June 14 | World Blood Donor Day | Chosen to mark Karl Landsteiner's birthday |
| July 1 | National Doctors' Day (India) | Honours Dr. Bidhan Chandra Roy |
| July 11 | World Population Day | Population growth awareness |
| July 28 | World Hepatitis Day | Chosen to mark the birthday of Baruch Blumberg, who discovered the Hepatitis B virus |
| August 20 | World Mosquito Day | Marks Ronald Ross's discovery of malaria transmission by mosquitoes (1897) |
| September 1-7 | National Nutrition Week (India) | Nutrition and diet awareness |
| September 29 | World Heart Day | Cardiovascular disease prevention |
| October 10 | World Mental Health Day | Mental health awareness |
| November 14 | World Diabetes Day | Marks the birthday of Frederick Banting, co-discoverer of insulin |
| December 1 | World AIDS Day | HIV/AIDS awareness |
Exam trap: World Blood Donor Day (June 14) is fixed to Karl Landsteiner's birthday, and World Mosquito Day (August 20) is fixed to Ronald Ross's discovery date. Students often guess randomly on "why this date" sub-questions. If you remember which scientist a day is named after, the date locks into memory far better than the date alone.
Memory hook: Chain the three "discovery-linked" days as a story: Ross found the mosquito culprit in August, Landsteiner sorted blood into groups so we could donate it safely in June, and the world thanked doctors on July 1. Mosquito, blood, doctor, in that seasonal order, a short chain instead of three unrelated flashcards.
6. How These Facts Actually Show Up in the Paper
Examiners rarely ask "what is the largest organ" in isolation forever, they rotate the phrasing every year while testing the same fact. You should recognise the fact under any of its disguises, not just the version you first memorised.
A single fact like "liver is the largest gland" can appear as a direct one-liner, as an odd-one-out question ("which of these is NOT a gland"), as a statement to mark true/false, or buried inside a passage about digestion where you're expected to spot it without being told which chapter it belongs to. The scientist table works the same way: instead of asking "who discovered penicillin," a paper might ask "which of these pairs is correctly matched" and give you four scientist-discovery combinations, three of them swapped on purpose. That is exactly why this chapter groups facts in pairs and tables rather than as a flat list, so you train yourself to spot the swap, not just recall a single fact in isolation.
Treat the health-days list the same way. A question won't always name the day directly, it might describe the event ("this day marks the founding of the WHO") and ask you to identify it. If you know the story behind a date, both directions of the question become easy. If you only memorised the date without the story, a rephrased question can catch you off guard even though you technically "knew" the fact.
One more pattern worth flagging: several papers have asked students to match a disease to its cause, then in the very next question, asked the opposite condition from the same gland or vitamin. If you answered "Addison's disease" correctly for a cortisol-deficiency question, expect the same paper to test whether you also know Cushing's syndrome is the excess version. Preparing pairs, not single facts, is what actually protects your score.
You don't need to reread the whole book the night before. Read this chapter twice, once slowly with the tables open, once fast just scanning the bold terms, and you will walk into the exam with the highest-yield static facts of the entire Biology syllabus fresh in your head.
Quick Revision — One-Line Facts
- Skin is the largest organ of the human body; the liver is the largest internal organ.
- The femur (thigh bone) is the longest bone; the stapes (ear) is the smallest bone.
- The ovum is the largest human cell; the sperm is the smallest.
- A nerve cell (neuron) is the longest cell in the body.
- Gluteus maximus is the largest muscle; stapedius is the smallest.
- Adults have 206 bones; infants are born with about 270-300, which fuse over time.
- Humans carry 46 chromosomes (23 pairs) in a normal body cell.
- Normal body temperature is 37°C (98.6°F).
- Blood pH stays between 7.35 and 7.45, slightly alkaline.
- Average resting heart rate is about 72 beats per minute.
- Normal blood pressure reads 120/80 mmHg (systolic/diastolic).
- An RBC lives for roughly 120 days before being broken down in the spleen and liver.
- Edward Jenner developed the first vaccine, against smallpox, in 1796.
- Alexander Fleming discovered penicillin, the first antibiotic, in 1928.
- Karl Landsteiner discovered the ABO blood group system.
- Robert Hooke first observed and named the "cell" while studying cork.
- Gregor Mendel is called the Father of Genetics for his pea-plant inheritance experiments.
- Ronald Ross proved the female Anopheles mosquito spreads malaria, and did this work in India.
- Watson and Crick described the double-helix structure of DNA in 1953.
- Salk's polio vaccine is injectable; Sabin's polio vaccine is given orally as drops.
- Ian Wilmut's team produced Dolly, the first cloned mammal, in 1996.
- Vitamin A deficiency causes night blindness; Vitamin D deficiency causes rickets in children.
- Vitamin B1 deficiency causes Beriberi; Vitamin B3 deficiency causes Pellagra.
- Vitamin C deficiency causes scurvy; Vitamin K deficiency delays blood clotting.
- Growth hormone deficiency in childhood causes dwarfism; excess causes gigantism.
- Thyroxine deficiency causes cretinism in children and myxoedema in adults.
- Cortisol deficiency causes Addison's disease; cortisol excess causes Cushing's syndrome.
- Insulin deficiency from the pancreas causes diabetes mellitus.
- World Health Day falls on April 7, marking the founding of the WHO.
- World Blood Donor Day (June 14) marks Karl Landsteiner's birthday.
Memory Tables
Table A: "Largest vs Smallest" Quick-Match Grid
| Category | Largest | Smallest |
|---|---|---|
| Organ (overall) | Skin | — |
| Internal organ / gland | Liver | Pituitary is smallest endocrine gland |
| Bone | Femur | Stapes |
| Cell | Ovum | Sperm |
| Muscle | Gluteus maximus | Stapedius |
| Artery | Aorta | Arteriole |
Table B: Deficiency-Excess Pairs at a Glance
| Hormone/Vitamin | Too little | Too much |
|---|---|---|
| Growth hormone (childhood) | Dwarfism | Gigantism |
| Growth hormone (adult) | — | Acromegaly |
| Thyroxine | Goitre / Myxoedema / Cretinism | Hyperthyroidism (Grave's disease) |
| Cortisol | Addison's disease | Cushing's syndrome |
| Insulin | Diabetes mellitus | Hypoglycaemia |
| Vitamin A | Night blindness | Toxicity (rare, high-dose supplements) |
| Vitamin D | Rickets/Osteomalacia | Toxicity (rare, high-dose supplements) |
Practice MCQs
Q1. Which is the largest organ of the human body? (a) Liver (b) Skin (c) Brain (d) Lungs
Q2. Who is known for discovering penicillin? (a) Edward Jenner (b) Alexander Fleming (c) Louis Pasteur (d) Robert Koch
Q3. How many bones are present in the skeleton of a normal human adult? (a) 200 (b) 206 (c) 212 (d) 300
Q4. Which vitamin's deficiency causes scurvy? (a) Vitamin A (b) Vitamin B1 (c) Vitamin C (d) Vitamin K
Q5. Which scientist is credited with discovering human blood groups? (a) William Harvey (b) Karl Landsteiner (c) Robert Hooke (d) Charles Darwin
Q6. World Health Day is observed every year on which date? (a) March 24 (b) April 7 (c) June 14 (d) December 1
Q7. Deficiency of which hormone causes dwarfism in children? (a) Insulin (b) Thyroxine (c) Growth hormone (d) Cortisol
Q8. Which of these is the smallest bone in the human body? (a) Femur (b) Stapes (c) Humerus (d) Tibia
Q9. Who first used the term "cell" for the basic unit of life? (a) Charles Darwin (b) Robert Hooke (c) Gregor Mendel (d) Louis Pasteur
Q10. Excess secretion of cortisol from the adrenal cortex leads to which condition? (a) Addison's disease (b) Cushing's syndrome (c) Acromegaly (d) Myxoedema
Q11. Which scientist proved that the female Anopheles mosquito transmits malaria, working in India? (a) Robert Koch (b) Ronald Ross (c) Jonas Salk (d) Ian Wilmut
Q12. Which of the following pairs is correctly matched? (a) Vitamin B1 deficiency — Pellagra (b) Vitamin B3 deficiency — Beriberi (c) Vitamin B12 deficiency — Pernicious anaemia (d) Vitamin K deficiency — Scurvy
Q13. Salk's polio vaccine and Sabin's polio vaccine differ mainly in which respect? (a) Salk's is oral, Sabin's is injectable (b) Salk's is injectable, Sabin's is oral (c) Both are injectable, differ in dosage (d) Both are oral, differ in dosage
Q14. Cretinism and myxoedema are both caused by deficiency of which hormone, differing only by the age group affected? (a) Insulin (b) Thyroxine (c) Growth hormone (d) Parathormone
Q15. World Blood Donor Day, observed on June 14, marks the birthday of which scientist? (a) Alexander Fleming (b) Edward Jenner (c) Karl Landsteiner (d) Robert Koch
Answer Key
| Q | Answer | Reason |
|---|---|---|
| Q1 | (b) Skin | Skin is the largest organ overall; the liver is only the largest internal organ. |
| Q2 | (b) Alexander Fleming | Fleming discovered penicillin in 1928, the world's first antibiotic; Jenner is linked to vaccination, not antibiotics. |
| Q3 | (b) 206 | An adult has 206 bones; infants have more (270-300) that fuse together while growing. |
| Q4 | (c) Vitamin C | Scurvy causes bleeding gums and weak connective tissue; don't confuse with Vitamin K, linked to clotting, not scurvy. |
| Q5 | (b) Karl Landsteiner | Landsteiner discovered the ABO blood group system; Harvey explained blood circulation, a different discovery entirely. |
| Q6 | (b) April 7 | This date marks the founding of the World Health Organization in 1948. |
| Q7 | (c) Growth hormone | Growth hormone deficiency in childhood causes dwarfism; excess in childhood causes gigantism instead. |
| Q8 | (b) Stapes | The stapes, one of the three ear ossicles, is the smallest bone in the human body. |
| Q9 | (b) Robert Hooke | Hooke coined "cell" in 1665 while examining cork under a microscope; Cell Theory itself came later from Schleiden and Schwann. |
| Q10 | (b) Cushing's syndrome | Excess cortisol causes Cushing's syndrome; deficiency of the same hormone causes the opposite condition, Addison's disease. |
| Q11 | (b) Ronald Ross | Ross proved mosquito-borne transmission of malaria while working in India and won the Nobel Prize in 1902. |
| Q12 | (c) Vitamin B12 deficiency — Pernicious anaemia | B1 deficiency causes Beriberi, B3 deficiency causes Pellagra, and Vitamin K deficiency delays clotting, not scurvy. |
| Q13 | (b) Salk's is injectable, Sabin's is oral | Remember "Salk = Shot, Sabin = Sip" to keep the delivery methods straight. |
| Q14 | (b) Thyroxine | Thyroxine deficiency causes cretinism in children and myxoedema in adults; same missing hormone, different life stage. |
| Q15 | (c) Karl Landsteiner | June 14 was chosen as World Blood Donor Day specifically to honour Landsteiner's birthday. |