The Human Body & Health

Your own body is the easiest exam topic to remember — you carry it everywhere. The paper repeatedly asks how many bones we have, how many chambers the heart has, who is the universal blood donor, and which mosquito spreads malaria. This chapter organises the human body into simple systems and then lists the diseases and deficiencies most asked in the exam, so a few minutes here can fetch several sure marks.

The Body's Organ Systems

The human body is made of many organ systems that work together. Each system does one main job. You should know the job of each in one line.

Major organ systems and their main jobs
SystemMain job
SkeletalSupports the body and protects organs (206 bones in adults)
MuscularEnables movement of the body
CirculatoryHeart pumps blood to carry oxygen and nutrients
RespiratoryLungs take in oxygen, remove carbon dioxide
DigestiveBreaks down food to absorb nutrients
NervousBrain and nerves control and coordinate the body
ExcretoryKidneys remove waste as urine
🎯 Why it matters
These systems appear as one-line factual questions. The three most tested facts are the skeletal (206 bones), the circulatory (4-chambered heart), and the respiratory (oxygen in, carbon dioxide out) systems — master these first.

Heart, Blood & Blood Groups

  • The heart has 4 chambers — 2 upper chambers (atria) and 2 lower chambers (ventricles).
  • Blood is pumped through arteries (away from the heart) and returns through veins (back to the heart).
  • Red blood cells carry oxygen using haemoglobin, which contains iron.
  • Blood groups (ABO system) are A, B, AB, O, each marked + or – by the Rh factor.
Blood group: donor and recipient
Special groupWhy it is special
O-negative (O–)Universal donor — can give blood to anyone
AB-positive (AB+)Universal recipient — can receive blood from anyone
🧠 Memory trick
Remember: O– gives to all, AB+ takes from all. "O" for "Offer to everyone" (donor); "AB+" for "Absorbs from everyone" (recipient).

Body Superlatives, Glands & Hormones

"Largest/smallest/longest" body facts are a favourite one-line question type, and so is matching a gland to the hormone it releases.

SuperlativeAnswer
Largest organ (overall)Skin
Largest internal organLiver
Longest boneFemur (thigh bone)
Smallest boneStapes (in the middle ear)
Normal body temperature~37°C (98.6°F)
Key endocrine glands and their hormones
GlandHormone(s) & role
Pituitary (in the brain)Called the "Master Gland" — controls other glands; releases growth hormone
PancreasReleases insulin (lowers blood sugar); insulin deficiency/resistance → diabetes
ThyroidReleases thyroxine; needs iodine to make it (deficiency → goitre)
Adrenal glandsRelease adrenaline — the "fight or flight" hormone
🧠 Memory trick
Pituitary = Master Gland (controls the others); Pancreas = insulin/diabetes; Thyroid = thyroxine/iodine/goitre; Adrenal = adrenaline/emergency response. One gland, one keyword.

Diseases by Cause

The exam loves to ask whether a disease is caused by bacteria, a virus, or spread by an insect (vector). Learn which basket each disease falls into.

Common diseases grouped by cause
CauseDiseases
BacterialTuberculosis (TB), Cholera, Typhoid
ViralCommon cold, Influenza, Dengue, Polio, COVID-19
Vector-borne (spread by insects)Malaria — Plasmodium parasite via female Anopheles mosquito; Dengue — Aedes mosquito
⚠️ Exam trap
Do not confuse the two mosquitoes: Malaria is spread by the female Anopheles mosquito and is caused by the Plasmodium parasite. Dengue is spread by the Aedes mosquito and is caused by a virus. Malaria = parasite; Dengue = virus.

Kala-azar: The Bihar-Specific Disease

Kala-azar (also called Visceral Leishmaniasis) is one of the most Bihar-relevant disease facts in the whole science syllabus — it is a protozoal disease caused by the parasite Leishmania donovani, spread by the bite of an infected female sandfly (Phlebotomus genus) — a different insect from any mosquito.

  • India is one of the countries most affected by Kala-azar, and within India, Bihar has historically reported the largest share of cases, concentrated in districts of the northern/eastern plains.
  • India runs a National Kala-azar Elimination Programme, targeting elimination (fewer than 1 case per 10,000 population at the block level) — a frequent current-affairs reference alongside Bihar's public health targets.
  • Other vector-borne diseases worth knowing alongside malaria and dengue: Chikungunya (also spread by the Aedes mosquito, a virus), Filariasis/elephantiasis (spread by the Culex mosquito, caused by thread-like parasitic worms), and Amoebiasis (a water-borne protozoal infection, not insect-spread, caused by Entamoeba histolytica).
🎯 Why it matters
Kala-azar is the single disease fact the paper is most likely to connect directly to Bihar's own public health story — remember the chain: sandfly (Phlebotomus) → Leishmania donovani → Kala-azar → historically concentrated in Bihar → National Elimination Programme.

Nutrition-Deficiency Diseases

Mineral deficiency and the resulting disease
Deficiency ofDisease
IronAnaemia (low haemoglobin, weakness)
IodineGoitre (swelling of the thyroid gland in the neck)
ℹ️ Note
These are mineral deficiencies, not vitamin ones. Iron → Anaemia, Iodine → Goitre. Vitamin-deficiency diseases (like night blindness, scurvy, rickets) are covered in the Everyday Science chapter.
🧠 Memory trick
Link them to the body: iron sits in the blood (haemoglobin) → too little iron = Anaemia. Iodine is used by the thyroid in the neck → too little iodine = Goitre (neck swelling).

Key takeaways

  • An adult human body has 206 bones; the skeletal system supports the body and protects organs.
  • The heart has 4 chambers — 2 atria and 2 ventricles. Arteries carry blood away; veins bring it back.
  • Red blood cells carry oxygen using haemoglobin, which contains iron. Lungs take in oxygen, give out carbon dioxide.
  • O-negative is the universal donor; AB-positive is the universal recipient.
  • Bacterial: TB, Cholera, Typhoid. Viral: cold, influenza, Dengue, Polio, COVID-19.
  • Malaria = Plasmodium parasite via female Anopheles mosquito; Dengue = virus via Aedes mosquito.
  • Mineral deficiency: iron → Anaemia, iodine → Goitre.
  • Body superlatives: largest organ = skin, largest internal organ = liver, longest bone = femur, smallest bone = stapes. Glands: Pituitary = Master Gland; Pancreas → insulin/diabetes; Thyroid → thyroxine/goitre; Adrenal → adrenaline.
  • Kala-azar (Visceral Leishmaniasis) = Leishmania donovani parasite, spread by the female sandfly (Phlebotomus); historically concentrated in Bihar. India runs a National Kala-azar Elimination Programme. Also know: Chikungunya (Aedes), Filariasis (Culex), Amoebiasis (water-borne protozoan).

Practice questions (11)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

  1. How many bones are there in the body of an adult human?

    1. 186
    2. 206
    3. 216
    4. 306
    Show answer

    Answer: B — 206

    An adult human has 206 bones. (A newborn baby has more, which fuse together with age.)

  2. How many chambers does the human heart have?

    1. 2
    2. 3
    3. 4
    4. 5
    Show answer

    Answer: C — 4

    The human heart has 4 chambers — 2 atria (upper) and 2 ventricles (lower).

  3. Which blood group is called the universal donor?

    1. AB-positive
    2. A-positive
    3. O-negative
    4. B-negative
    Show answer

    Answer: C — O-negative

    O-negative (O–) is the universal donor and can give blood to anyone. AB-positive is the universal recipient.

  4. Malaria is caused by which parasite?

    1. Aedes
    2. Plasmodium
    3. Anopheles
    4. Culex
    Show answer

    Answer: B — Plasmodium

    Malaria is caused by the Plasmodium parasite, which is spread by the bite of the female Anopheles mosquito. Anopheles is the mosquito, not the parasite.

  5. The mineral present in haemoglobin, which helps carry oxygen, is:

    1. Calcium
    2. Iodine
    3. Iron
    4. Sodium
    Show answer

    Answer: C — Iron

    Haemoglobin in red blood cells contains iron, which binds and carries oxygen. Iron deficiency causes anaemia.

  6. Deficiency of iodine in the body causes which disease?

    1. Anaemia
    2. Goitre
    3. Scurvy
    4. Rickets
    Show answer

    Answer: B — Goitre

    Iodine deficiency causes goitre — a swelling of the thyroid gland in the neck. Iron deficiency causes anaemia.

  7. Which one of the following diseases is caused by a bacterium?

    1. Dengue
    2. Polio
    3. Tuberculosis
    4. Influenza
    Show answer

    Answer: C — Tuberculosis

    Tuberculosis (TB) is a bacterial disease. Dengue, polio and influenza are all viral diseases.

  8. Consider the following statements:
    1. Dengue is spread by the Aedes mosquito.
    2. AB-positive is the universal blood recipient.
    Which is/are correct?

    1. Only 1
    2. Only 2
    3. Both 1 and 2
    4. Neither 1 nor 2
    Show answer

    Answer: C — Both 1 and 2

    Both are correct. Dengue is spread by the Aedes mosquito, and AB-positive can receive blood from any group, making it the universal recipient.

  9. Which gland is known as the "Master Gland" because it controls the activity of other endocrine glands?

    1. Thyroid
    2. Pancreas
    3. Pituitary
    4. Adrenal
    Show answer

    Answer: C — Pituitary

    The pituitary gland, located in the brain, is called the "Master Gland" because it controls the activity of most other endocrine glands.

  10. Kala-azar (Visceral Leishmaniasis), a disease historically concentrated in Bihar, is spread by the bite of which insect?

    1. Female Anopheles mosquito
    2. Aedes mosquito
    3. Female sandfly (Phlebotomus)
    4. Culex mosquito
    Show answer

    Answer: C — Female sandfly (Phlebotomus)

    Kala-azar is caused by the Leishmania donovani parasite, spread by the bite of the female sandfly (Phlebotomus genus) — not any mosquito. India runs a National Kala-azar Elimination Programme, and Bihar has historically reported the largest share of cases.

  11. Deficiency or malfunction of insulin, released by the pancreas, leads to which disease?

    1. Goitre
    2. Diabetes
    3. Anaemia
    4. Rickets
    Show answer

    Answer: B — Diabetes

    Insulin, released by the pancreas, lowers blood sugar; its deficiency or the body's resistance to it leads to diabetes.