Biology — Static GK for Competitive Exams
Free study material · concepts, shortcuts & solved questions
Why Biology GK Matters for SSC GD and RPF Constable
Biology static GK is one of the most predictable scoring areas in SSC GD, RPF Constable and RRB general science sections. Questions rarely go beyond school-level facts — the largest organ of the human body, the number of bones in an adult, the vitamin whose deficiency causes night blindness, or the classification of animals without a backbone. Because the questions are direct and factual, a candidate who has memorised the core lists in this chapter — human body systems, diseases and their causes, vitamins and deficiency disorders, and the basics of plant and animal classification — can convert nearly every biology question attempted into a correct answer.
Cell — The Basic Unit of Life
The cell is the structural and functional unit of all living organisms. Robert Hooke first observed and named cells in 1665 while examining cork under a microscope. Cell theory, credited to Matthias Schleiden and Theodor Schwann, states that all living organisms are made of cells and that the cell is the basic unit of life.
- Prokaryotic cells — lack a well-defined nucleus and membrane-bound organelles; found in bacteria and blue-green algae.
- Eukaryotic cells — have a well-defined nucleus enclosed by a nuclear membrane and membrane-bound organelles; found in plants, animals, fungi and protists.
- Mitochondria — the "powerhouse of the cell," site of energy (ATP) production.
- Nucleus — contains chromosomes and controls cell activities; discovered by Robert Brown.
- Chloroplast — found in plant cells; site of photosynthesis, contains chlorophyll.
- Ribosomes — site of protein synthesis.
- Cell wall — rigid outer layer found in plant cells (made of cellulose), fungi and bacteria; animal cells lack a cell wall and instead have only a flexible cell membrane.
Human Body Systems
Skeletal System
An adult human body has 206 bones. A newborn infant has about 300 bones, many of which fuse together during growth. The skeletal system provides shape, support, protection to internal organs and enables movement in conjunction with muscles.
- The femur (thigh bone) is the longest and strongest bone in the human body.
- The stapes, located in the middle ear, is the smallest bone in the human body.
- The human skull consists of 22 bones (8 cranial and 14 facial).
- The vertebral column (backbone/spine) has 33 vertebrae, grouped into cervical (7), thoracic (12), lumbar (5), sacral (5, fused) and coccygeal (4, fused) regions.
- The rib cage has 12 pairs (24) of ribs.
Circulatory (Cardiovascular) System
The human heart has four chambers: two upper atria and two lower ventricles. It pumps blood through a double circulation — pulmonary circulation (heart to lungs and back) and systemic circulation (heart to the rest of the body and back). Karl Landsteiner discovered the ABO blood group system in 1901, for which he later received the Nobel Prize.
| Component | Function |
|---|---|
| Red blood cells (RBCs/erythrocytes) | Carry oxygen using haemoglobin; produced in bone marrow; have no nucleus in mammals |
| White blood cells (WBCs/leukocytes) | Fight infection; part of the immune system |
| Platelets (thrombocytes) | Help in blood clotting |
| Plasma | Liquid part of blood; carries nutrients, hormones and waste products |
Blood groups under the ABO system are A, B, AB and O, each further divided by Rh factor (positive or negative). O-negative is often called the universal donor and AB-positive the universal recipient.
Respiratory System
Humans breathe using a pair of lungs. Air enters through the nostrils, passes through the pharynx, larynx, trachea, bronchi and bronchioles, finally reaching tiny air sacs called alveoli, where gas exchange (oxygen in, carbon dioxide out) takes place. The normal breathing rate for a resting adult is roughly 12-16 breaths per minute.
Digestive System
Digestion begins in the mouth, where saliva (containing the enzyme salivary amylase) starts breaking down starch. Food then passes through the oesophagus (food pipe) to the stomach, where hydrochloric acid and the enzyme pepsin digest proteins. The small intestine (about 6-7 metres long) is the main site of digestion and nutrient absorption, aided by bile from the liver (stored in the gall bladder) and enzymes from the pancreas. The large intestine absorbs water and forms faeces, which is expelled through the rectum and anus.
- The liver is the largest gland/internal organ in the human body; it produces bile, detoxifies blood and stores glycogen.
- The pancreas is both an exocrine gland (secreting digestive enzymes) and an endocrine gland (secreting insulin and glucagon that regulate blood sugar).
- The skin is the largest organ of the human body by surface area and weight.
Nervous System
The nervous system is divided into the central nervous system (brain and spinal cord) and the peripheral nervous system (nerves connecting the CNS to the rest of the body). The human brain has three main parts:
- Cerebrum — largest part; controls voluntary actions, thought, memory and intelligence.
- Cerebellum — controls balance, posture and coordination of movement.
- Medulla oblongata — part of the brainstem; controls involuntary functions like heartbeat, breathing and blood pressure.
The basic functional unit of the nervous system is the neuron (nerve cell).
Excretory System
The kidneys are the main excretory organs, filtering waste (mainly urea) from the blood to form urine. The functional unit of the kidney is the nephron. Humans have a pair of kidneys, and urine passes through the ureters to the urinary bladder before being expelled via the urethra.
Vitamins, Minerals and Deficiency Diseases
This is one of the single most frequently tested biology tables in SSC and RRB exams.
| Vitamin | Chemical Name | Deficiency Disease | Source |
|---|---|---|---|
| Vitamin A | Retinol | Night blindness | Carrot, milk, liver, papaya |
| Vitamin B1 | Thiamine | Beriberi | Whole grains, pulses, nuts |
| Vitamin B2 | Riboflavin | Cracked lips/skin (ariboflavinosis) | Milk, eggs, green vegetables |
| Vitamin B3 | Niacin | Pellagra | Meat, fish, groundnut |
| Vitamin B6 | Pyridoxine | Anaemia, skin disorders | Meat, bananas, whole grains |
| Vitamin B12 | Cobalamin | Pernicious anaemia | Meat, eggs, dairy (not found in plant sources) |
| Vitamin C | Ascorbic acid | Scurvy (bleeding gums) | Citrus fruits, amla, guava |
| Vitamin D | Calciferol | Rickets (children), osteomalacia (adults) | Sunlight, fish oil, egg yolk |
| Vitamin E | Tocopherol | Infertility, muscle weakness | Vegetable oils, nuts, seeds |
| Vitamin K | Phylloquinone | Delayed blood clotting | Green leafy vegetables |
Important minerals: calcium (bones and teeth; deficiency causes weak bones), iron (haemoglobin formation; deficiency causes anaemia), iodine (thyroid hormone; deficiency causes goitre), and sodium/potassium (nerve and muscle function).
Common Human Diseases
| Disease | Causative Agent | Type |
|---|---|---|
| Malaria | Plasmodium (spread by female Anopheles mosquito) | Protozoan |
| Dengue | Dengue virus (spread by Aedes aegypti mosquito) | Viral |
| Chikungunya | Chikungunya virus (spread by Aedes mosquito) | Viral |
| Tuberculosis (TB) | Mycobacterium tuberculosis | Bacterial |
| Typhoid | Salmonella typhi | Bacterial |
| Cholera | Vibrio cholerae | Bacterial |
| Tetanus | Clostridium tetani | Bacterial |
| Leprosy | Mycobacterium leprae | Bacterial |
| Pneumonia | Streptococcus pneumoniae (often bacterial) | Bacterial/viral |
| Chickenpox | Varicella-zoster virus | Viral |
| Measles | Measles virus | Viral |
| Polio | Poliovirus | Viral |
| Rabies | Rabies virus (transmitted by animal bites) | Viral |
| Hepatitis | Hepatitis A/B/C/D/E viruses | Viral |
| AIDS | Human Immunodeficiency Virus (HIV) | Viral |
| Influenza (flu) | Influenza virus | Viral |
| Ringworm | Fungal infection | Fungal |
| Athlete's foot | Fungal infection | Fungal |
| Amoebiasis | Entamoeba histolytica | Protozoan |
| Kala-azar | Leishmania (spread by sandfly) | Protozoan |
Edward Jenner developed the first vaccine, for smallpox, in 1796. Louis Pasteur developed the rabies vaccine and pioneered the germ theory of disease along with the process of pasteurisation. Alexander Fleming discovered penicillin, the first antibiotic, in 1928.
Plant Kingdom Basics
Plants are broadly classified based on the presence of vascular tissue and seed formation:
- Thallophyta (algae) and Bryophyta (mosses, liverworts) — simple plants lacking true roots, stems and leaves; bryophytes are called "amphibians of the plant kingdom" because they need water to reproduce.
- Pteridophyta (ferns) — have true roots, stems and leaves but reproduce through spores, not seeds.
- Gymnosperms — seed-bearing plants with "naked" seeds not enclosed in a fruit, e.g. pine, cycas, deodar.
- Angiosperms — flowering plants with seeds enclosed inside a fruit; further divided into monocotyledons (one seed leaf, e.g. wheat, rice, maize, with parallel leaf venation) and dicotyledons (two seed leaves, e.g. gram, pea, mango, with net-like leaf venation).
Photosynthesis is the process by which green plants use sunlight, carbon dioxide and water to make glucose and release oxygen, using the pigment chlorophyll present in chloroplasts. Respiration in plants, as in animals, uses oxygen to break down glucose and release energy, producing carbon dioxide and water as by-products.
Plant tissues that transport substances: xylem carries water and minerals upward from roots to leaves; phloem carries food (prepared by photosynthesis) from leaves to other parts of the plant.
Animal Kingdom Basics
Animals are broadly divided into two major groups based on the presence of a backbone:
- Invertebrates (without a backbone) — include Porifera (sponges), Coelenterata (jellyfish, corals), Platyhelminthes (flatworms, e.g. tapeworm), Nematoda (roundworms), Annelida (segmented worms, e.g. earthworm), Arthropoda (the largest animal phylum, includes insects, spiders, crustaceans), Mollusca (snails, octopus) and Echinodermata (starfish, sea urchin).
- Vertebrates (with a backbone) — divided into five classes: Pisces (fish, cold-blooded, gills), Amphibia (frogs, live both on land and water), Reptilia (snakes, lizards, cold-blooded, dry scaly skin), Aves (birds, warm-blooded, feathers, lay eggs) and Mammalia (warm-blooded, hair/fur, mostly give birth to live young and produce milk for offspring).
Notable exceptions worth remembering: the platypus and echidna are mammals that lay eggs (monotremes); the whale and dolphin are mammals that live in water; the bat is the only mammal capable of true, sustained flight.
Genetics Basics
Gregor Mendel, an Austrian monk, is known as the "Father of Genetics" for his experiments on pea plants that established the basic laws of inheritance. James Watson and Francis Crick discovered the double-helix structure of DNA (Deoxyribonucleic Acid) in 1953, work that built on X-ray diffraction images produced by Rosalind Franklin. A normal human somatic cell has 46 chromosomes (23 pairs); the reproductive (sex) cells — sperm and egg — each carry 23 chromosomes. Sex in humans is determined by the X and Y chromosomes: XX produces a female, XY produces a male, and the sex chromosome contributed by the father determines the sex of the child.
Endocrine System — Glands and Hormones
The endocrine system consists of glands that secrete hormones directly into the bloodstream. Unlike exocrine glands (such as sweat and salivary glands, which release secretions through ducts), endocrine glands are ductless.
| Gland | Location | Key Hormone(s) and Function |
|---|---|---|
| Pituitary gland | Base of the brain | Called the "master gland"; secretes growth hormone and regulates other glands |
| Thyroid gland | Neck, near the larynx | Secretes thyroxine, which regulates metabolism; requires iodine |
| Parathyroid glands | Behind the thyroid | Regulate calcium and phosphorus levels in blood |
| Adrenal glands | On top of each kidney | Secrete adrenaline (epinephrine), the "fight or flight" hormone |
| Pancreas | Abdomen, near the stomach | Secretes insulin (lowers blood sugar) and glucagon (raises blood sugar) |
| Testes (male) | Scrotum | Secrete testosterone |
| Ovaries (female) | Pelvic cavity | Secrete oestrogen and progesterone |
Insufficient insulin production or poor insulin response leads to diabetes mellitus, marked by high blood glucose levels. Insufficient thyroxine causes an enlarged thyroid gland, known as goitre, commonly linked to iodine deficiency; this is why iodised salt is promoted for public health.
Nutrition — Carbohydrates, Proteins and Fats
Food provides the body with energy and materials for growth and repair. The three major nutrient classes are:
- Carbohydrates — the body's primary energy source; made of carbon, hydrogen and oxygen; found in rice, wheat, potato and sugar. Excess carbohydrate is stored in the liver and muscles as glycogen.
- Proteins — needed for growth and repair of body tissue; made of amino acids; found in pulses, milk, eggs, meat and fish. Proteins are broken down by the enzyme pepsin (in the stomach) and trypsin (in the small intestine).
- Fats — the most concentrated source of energy; found in oils, ghee, butter and nuts; also help absorb fat-soluble vitamins A, D, E and K.
A balanced diet also requires roughage (dietary fibre) for proper digestion, along with adequate water, vitamins and minerals. Deficiency of protein and calories in children causes disorders such as kwashiorkor and marasmus.
Human Reproductive System — Basic Facts
Human reproduction is sexual, involving the fusion of a male gamete (sperm, produced in the testes) and a female gamete (egg/ovum, produced in the ovaries) to form a zygote. Fertilisation normally occurs in the fallopian tube, and the fertilised egg implants and develops in the uterus over a gestation period of about 280 days (approximately nine months) in humans. Puberty is the stage at which reproductive organs become functional, generally between ages 10 and 19.
Immunity and Vaccination
Immunity is the body's ability to resist infection. Innate immunity is the natural, non-specific defence present from birth (skin, mucus, white blood cells). Acquired immunity develops after exposure to a specific pathogen or after vaccination. A vaccine contains a weakened, inactivated or partial form of a pathogen that trains the immune system to recognise and fight the real infection without causing the disease itself. Antibiotics work against bacterial infections but are ineffective against viruses, which is why viral diseases like the common cold cannot be cured with antibiotics.
Biology Superlatives and Notable Facts
- The blue whale is the largest animal on Earth, and also the largest animal known to have ever existed.
- The cheetah is the fastest land animal, capable of speeds over 100 km/h in short bursts.
- The giraffe is the tallest living land animal.
- The ostrich is the largest living bird and also lays the largest egg among living birds; it cannot fly.
- The hummingbird is the smallest bird and the only bird capable of flying backwards.
- The elephant is the largest living land animal.
- The peregrine falcon is the fastest bird, capable of diving at speeds exceeding 300 km/h.
- Among plants, the banyan tree is renowned for its wide-spreading canopy supported by aerial prop roots; it is India's national tree.
- The lotus is India's national flower; the mango is India's national fruit.
- The tiger is India's national animal; the peacock is India's national bird.
Pioneers of Biology and Medicine
| Scientist | Contribution |
|---|---|
| Charles Darwin | Proposed the theory of evolution by natural selection ("On the Origin of Species", 1859) |
| Gregor Mendel | Father of Genetics; discovered laws of inheritance using pea plants |
| Louis Pasteur | Germ theory of disease; pasteurisation; rabies vaccine |
| Robert Koch | Identified the bacteria causing tuberculosis and cholera |
| Alexander Fleming | Discovered penicillin, the first antibiotic, in 1928 |
| Edward Jenner | Developed the first vaccine, against smallpox |
| Karl Landsteiner | Discovered the ABO human blood group system |
| Watson and Crick | Discovered the double-helix structure of DNA (1953) |
| Har Gobind Khorana | Indian-origin scientist; Nobel laureate for work on the genetic code |
Key Facts at a Glance
- An adult human has 206 bones; the femur is the longest bone and the stapes is the smallest.
- The liver is the largest internal organ/gland; the skin is the largest organ overall.
- The heart has four chambers — two atria and two ventricles.
- Vitamin C deficiency causes scurvy; Vitamin D deficiency causes rickets; Vitamin A deficiency causes night blindness.
- Malaria is caused by Plasmodium, spread by the female Anopheles mosquito.
- Edward Jenner developed the smallpox vaccine; Alexander Fleming discovered penicillin.
- Gregor Mendel is called the Father of Genetics; Watson and Crick discovered the DNA double helix.
- Photosynthesis occurs in chloroplasts and requires sunlight, carbon dioxide, water and chlorophyll.
- Xylem transports water; phloem transports food in plants.
- Mammals are warm-blooded and typically give birth to live young, though the platypus is an egg-laying exception.
- A normal human cell has 46 chromosomes; sex cells carry 23.
- The functional unit of the kidney is the nephron; of the nervous system, the neuron.
Practice MCQs
- Who is known as the "Father of Genetics"?
- (a) Charles Darwin
- (b) Gregor Mendel
- (c) Louis Pasteur
- (d) James Watson
- Which is the largest organ of the human body?
- (a) Liver
- (b) Skin
- (c) Lungs
- (d) Heart
- Deficiency of Vitamin D leads to which disease in children?
- (a) Scurvy
- (b) Beriberi
- (c) Rickets
- (d) Night blindness
- Malaria is caused by which organism?
- (a) Bacteria
- (b) Virus
- (c) Fungus
- (d) Plasmodium (protozoan)
- How many bones are there in an adult human body?
- (a) 196
- (b) 206
- (c) 216
- (d) 226
- Which is the longest bone in the human body?
- (a) Humerus
- (b) Tibia
- (c) Femur
- (d) Radius
- The powerhouse of the cell is:
- (a) Nucleus
- (b) Ribosome
- (c) Mitochondria
- (d) Golgi body
- Who discovered the smallpox vaccine?
- (a) Louis Pasteur
- (b) Alexander Fleming
- (c) Edward Jenner
- (d) Robert Koch
- Which blood component is responsible for clotting?
- (a) Red blood cells
- (b) White blood cells
- (c) Platelets
- (d) Plasma
- Xylem tissue in plants is mainly responsible for:
- (a) Transport of food
- (b) Transport of water and minerals
- (c) Photosynthesis
- (d) Respiration
- Which mammal is known to lay eggs?
- (a) Whale
- (b) Platypus
- (c) Bat
- (d) Dolphin
- The functional unit of the kidney is called the:
- (a) Neuron
- (b) Alveolus
- (c) Nephron
- (d) Villus