Paper IPaper I · General Science
Human Body and Its Systems
Digestive, respiratory, circulatory, nervous, excretory, endocrine, skeletal and reproductive systems with key organs, functions, glands and hormones, blood groups, sense organs, and headline numerical facts at CAPF recognition depth
CAPF wiki•10 min read•23 sections
At a glance
PaperPaper ISubjectGeneral ScienceSyllabusGeneral Science: general awareness, scientific temper, comprehension and appreciation of scientific phenomena of everyday observation, including new areas such as Information Technology, Biotechnology, and Environmental ScienceImportanceHigh
BiologyHuman BodyPhysiologyOrgansSystemsHormonesGlandsBlood Groups
This note maps the major organ systems of the human body to their key organs, functions and headline facts. CAPF tests the organ-to-function match (which organ makes insulin, which is the body's largest gland), the number of bones, the chambers of the heart, the gland-to-hormone match, the universal donor and recipient, and the enzyme-to-site match. The depth target is NCERT Class X "Life Processes" and "Control and Coordination", with a few Class VII and VIII basics. Almost every question here is a single clean fact, so the reference tables below are the highest-yield revision in the biology block.
- Digestion begins in the mouth, where saliva and the enzyme amylase (ptyalin) start breaking down starch.
- Food passes down the food pipe (oesophagus) to the stomach, which secretes hydrochloric acid (kills germs, activates enzymes) and the enzyme pepsin (acts on protein).
- Most digestion and absorption happen in the small intestine, helped by bile from the liver (emulsifies fat) and enzymes from the pancreas (trypsin for protein, lipase for fat, amylase for starch). The inner finger-like villi increase the absorbing surface.
- The large intestine absorbs water; undigested waste is expelled.
- The liver is the largest gland and the largest internal organ; it makes bile, stores glycogen and detoxifies the blood. The pancreas is both a digestive gland and an endocrine gland.
- Air enters through the nose, the windpipe (trachea), the bronchi and bronchioles into the two lungs.
- Gas exchange happens in tiny air sacs called alveoli: oxygen diffuses into the blood and carbon dioxide diffuses out.
- The diaphragm, a dome-shaped muscle below the lungs, drives breathing. The right lung has three lobes, the left two.
- Cellular respiration releases energy from glucose; with oxygen (aerobic) it gives carbon dioxide, water and much energy; without oxygen (anaerobic) muscles make lactic acid (causing cramp).
- The heart is a four-chambered muscular pump: two atria (upper, thin-walled) and two ventricles (lower, thick-walled). The double circulation keeps oxygenated and deoxygenated blood separate.
- The right side handles deoxygenated blood (sent to the lungs); the left side handles oxygenated blood (sent to the body). The left ventricle has the thickest wall.
- Arteries carry blood away from the heart (oxygenated, except the pulmonary artery); veins return blood to the heart (deoxygenated, except the pulmonary vein); capillaries are the thin vessels of exchange.
- Blood has red cells (carry oxygen via haemoglobin, made in bone marrow, no nucleus), white cells (defence and immunity), platelets (clotting) and plasma (the liquid part).
- Normal blood pressure is about 120/80 mmHg (systolic over diastolic). The normal heart rate is about 70 to 72 beats per minute. Blood pressure is measured by a sphygmomanometer.
- The four ABO blood groups are A, B, AB and O, plus the Rh factor (positive or negative).
- O negative is the universal donor; AB positive is the universal recipient. ABO grouping was discovered by Karl Landsteiner.
- The brain and spinal cord form the central nervous system; the nerves form the peripheral nervous system. The neuron is the basic structural and functional unit.
- The brain has three main parts: the cerebrum (thought, memory, intelligence, voluntary action, the largest part), the cerebellum (balance, posture and coordination) and the medulla oblongata (involuntary actions such as heartbeat, breathing, blood pressure).
- A reflex action is a quick, automatic, involuntary response routed through the spinal cord (the reflex arc), such as pulling a hand off a hot object.
- The two bean-shaped kidneys filter the blood and remove the nitrogenous waste urea as urine; the functional unit is the nephron (about a million per kidney).
- Urine passes through the ureters to the urinary bladder and out through the urethra.
- Dialysis artificially filters the blood when the kidneys fail, until a transplant.
- Ductless endocrine glands secrete hormones directly into the blood. The pituitary gland (at the base of the brain) is the master gland; it controls the other glands and secretes growth hormone.
- Thyroid: secretes thyroxine (needs iodine; deficiency causes goitre, excess causes hyperthyroidism).
- Pancreas (islets of Langerhans): secretes insulin (lowers blood sugar; deficiency causes diabetes mellitus) and glucagon (raises blood sugar).
- Adrenal glands: secrete adrenaline, the fight-or-flight hormone.
- Reproductive glands: testes secrete testosterone; ovaries secrete oestrogen and progesterone.
- An adult human has 206 bones; a newborn has about 300, many of which later fuse.
- The skeleton supports the body, protects organs (the skull protects the brain, the rib cage protects the heart and lungs) and works with muscles for movement.
- The femur (thigh bone) is the longest bone; the stapes in the middle ear is the smallest. The skull is fused; the only movable skull bone is the lower jaw.
- Joints allow movement: ball-and-socket (shoulder, hip), hinge (elbow, knee), pivot (neck) and fixed (skull).
- The eye uses a convex lens; the retina has light-sensitive rods (dim light) and cones (colour). The iris controls the size of the pupil.
- The ear hears (the cochlea) and maintains balance (the semicircular canals). The skin is the largest sense organ and the largest organ overall.
| Item |
Fact |
| Largest gland and internal organ |
liver |
| Largest organ overall |
skin |
| Master gland |
pituitary |
| Insulin produced by |
pancreas (islets of Langerhans) |
| Thyroxine produced by |
thyroid (needs iodine) |
| Fight-or-flight hormone |
adrenaline (adrenal gland) |
| Growth hormone |
pituitary gland |
| Functional unit of kidney |
nephron |
| Functional unit of nervous system |
neuron |
| Gas exchange site in lungs |
alveoli |
| Breathing muscle |
diaphragm |
| Item |
Fact |
| Heart chambers |
four (two atria, two ventricles) |
| Normal blood pressure |
about 120/80 mmHg |
| Normal heart rate |
about 70 to 72 beats per minute |
| Number of bones (adult) |
206 |
| Longest bone |
femur (thigh) |
| Smallest bone |
stapes (ear) |
| Universal donor blood group |
O negative |
| Universal recipient blood group |
AB positive |
| Oxygen carrier in blood |
haemoglobin (red blood cells) |
| Blood groups discovered by |
Karl Landsteiner |
| Enzyme |
Site |
Acts on |
| Amylase (ptyalin) |
mouth (saliva) |
starch |
| Pepsin |
stomach |
protein |
| Trypsin |
small intestine (pancreas) |
protein |
| Lipase |
small intestine (pancreas) |
fat |
| Bile (not an enzyme) |
liver to small intestine |
emulsifies fat |
- Iodised salt prevents goitre by supplying iodine for thyroxine; this is a public-health measure relevant to troops posted in iodine-deficient hill regions.
- Insulin therapy manages diabetes when the pancreas does not make enough; modern insulin is made by biotechnology, see biotechnology and genetics.
- Dialysis sustains patients with kidney failure until transplant.
- Knowing blood groups is essential for safe transfusion in field medical care, see nutrition diseases and health.
- Physical fitness and physiology underpin the CAPF Physical Efficiency Test; understanding muscles, the heart and respiration helps with endurance and altitude acclimatisation for forces such as the ITBP and SSB.
- Adrenaline and the fight-or-flight response explain heightened alertness under combat or crowd-control stress.
Q1Insulin is secreted by the
- Aliver
- Bthyroid
- Cpancreas
- Dadrenal gland. Answer:
- C. The islets of Langerhans in the pancreas secrete insulin, which lowers blood sugar.
Q2The largest gland in the human body is the
- Apancreas
- Bliver
- Cthyroid
- Dsalivary gland. Answer:
- B. The liver is both the largest gland and the largest internal organ.
Q3The universal donor blood group is
- AAB positive
- BA positive
- CO negative
- DB negative. Answer:
- C. O negative can be given to any recipient.
Q4The functional unit of the kidney is the
- Aneuron
- Bnephron
- Calveolus
- Dvillus. Answer:
- B. The nephron filters blood and forms urine.
Q5An adult human body has how many bones?
- A196
- B206
- C216
- D300. Answer:
- B. An adult has 206 bones; a newborn has about 300, many of which fuse.
- Arteries versus veins: arteries carry blood away from the heart (mostly oxygenated); veins return blood to the heart (mostly deoxygenated). The pulmonary artery and vein are the exceptions.
- Atria versus ventricles: atria are the upper receiving chambers; ventricles are the lower thick-walled pumping chambers.
- Insulin versus thyroxine: insulin (pancreas) controls blood sugar; thyroxine (thyroid, needs iodine) controls metabolism.
- Largest gland versus master gland: the liver is the largest gland; the pituitary is the master gland.
- Cerebrum versus cerebellum: the cerebrum does thinking and voluntary action; the cerebellum does balance and coordination.
- Universal donor versus recipient: O negative donates to all; AB positive receives from all.
- Heart chambers: "2 up, 2 down", atria above and ventricles below; left side serves the body so its wall is thickest.
- "O gives to all (dOnor), AB takes from all (grAB all)" for blood groups.
- Bones: "2-0-6" for the adult count; femur is the furthest and fat one (longest), stapes is the smallest.
- "Iodine for the thyroid, insulin from the pancreas" keeps the two endocrine facts apart.
- The liver is the largest gland and internal organ; the skin is the largest organ overall.
- The heart has four chambers; arteries carry blood away, veins return it.
- Haemoglobin in red blood cells carries oxygen; normal blood pressure is about 120/80 mmHg.
- O negative is the universal donor; AB positive the universal recipient.
- The kidney's unit is the nephron; the nervous system's unit is the neuron.
- Pituitary is the master gland; thyroxine needs iodine; insulin comes from the pancreas; adrenaline is fight-or-flight; an adult has 206 bones (femur longest, stapes smallest).
- Digestion of starch begins in the mouth with amylase; the stomach uses hydrochloric acid and pepsin.
- The liver is the largest gland and largest internal organ and makes bile.
- Gas exchange in the lungs happens in the alveoli; the diaphragm drives breathing.
- The heart has four chambers; arteries carry blood away, veins return it.
- Haemoglobin in red blood cells carries oxygen; normal blood pressure is about 120/80 mmHg.
- O negative is the universal donor; AB positive the universal recipient; Landsteiner discovered blood groups.
- The kidney's functional unit is the nephron; dialysis substitutes for failed kidneys.
- The pituitary is the master gland; thyroxine needs iodine; insulin comes from the pancreas.
- Adrenaline is the fight-or-flight hormone from the adrenal gland.
- The cerebrum handles thought; the cerebellum balance; the medulla the heartbeat and breathing.
- A reflex action is a fast involuntary response via the spinal cord.
- An adult has 206 bones; the femur is longest, the stapes smallest.
- The eye uses a convex lens with a light-sensitive retina; the skin is the largest sense organ.
- The neuron is the unit of the nervous system; the nephron is the unit of the kidney.
- Enzyme: a biological catalyst that speeds up a chemical reaction in the body.
- Alveolus: a tiny air sac in the lung where gases are exchanged.
- Haemoglobin: the iron-containing red pigment in red blood cells that carries oxygen.
- Atrium: an upper receiving chamber of the heart.
- Ventricle: a lower pumping chamber of the heart.
- Hormone: a chemical messenger secreted by an endocrine gland into the blood.
- Nephron: the microscopic filtering unit of the kidney.
- Neuron: the structural and functional unit of the nervous system.
- Reflex action: an automatic, involuntary response routed through the spinal cord.
- Insulin: the pancreatic hormone that lowers blood sugar.
- Thyroxine: the iodine-containing thyroid hormone that controls metabolism.
- Dialysis: the artificial filtering of blood when the kidneys fail.
- Systolic and diastolic pressure: the higher (contraction) and lower (relaxation) blood-pressure readings.