Biology

Chapter 1 of the Class 11 Biology NCERT textbook, "The Living World", introduces the diversity of life forms on Earth — estimated at 1.7–1.8 million known species — and the foundational processes of taxonomy: identification, nomenclature, classification and systematics used to study and organise organisms.

• 1The living world contains 1.7–1.8 million known species across diverse habitats; new organisms are continuously being identified
• 2Identification is the process of recognizing and describing organisms; nomenclature is standardizing their names using Latin-based scientific names
• 3Binomial nomenclature assigns each organism a two-word scientific name: the Genus (capitalized) and specific epithet (lowercase), e.g., Mangifera indica for mango
• 4Taxonomic categories form a hierarchy from species through genus, family, order, class, phylum, and kingdom, with higher categories containing organisms with fewer shared characteristics
• 5Taxonomy is the branch of biology dealing with identification, nomenclature, classification, and systematics of organisms based on morphological, structural, developmental, and ecological features

Chapter 2 of the Class 11 Biology NCERT textbook, "Biological Classification", explains this topic. Biological classification is the scientific system of organizing living organisms into kingdoms, phyla, and other groups based on cell structure, body organization, mode of nutrition, and evolutionary relationships. The five-kingdom system by R.H. Whittaker divides all life into Monera, Protista, Fungi, Plantae, and Animalia.

• 1Whittaker's five-kingdom system classifies organisms by cell type, body organization, mode of nutrition, and evolutionary relationships
• 2Kingdom Monera contains bacteria (prokaryotic organisms) including archaebacteria in extreme habitats and eubacteria with diverse metabolic capabilities
• 3Kingdom Protista includes single-celled eukaryotes like diatoms, dinoflagellates, euglenoids, slime moulds, and protozoans that primarily inhabit aquatic environments
• 4Kingdom Fungi comprises heterotrophic organisms with chitinous cell walls, classified into Phycomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes based on spore formation and fruiting bodies
• 5Kingdom Plantae contains eukaryotic chlorophyll-containing organisms including algae, bryophytes, pteridophytes, gymnosperms, and angiosperms with alternating gametophytic and sporophytic generations

Chapter 3 of the Class 11 Biology NCERT textbook, "Plant Kingdom", covers this topic. It classifies plants into five major groups—Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms—based on the Whittaker classification system.

• 1Plant Kingdom classification follows Whittaker's Five Kingdom system, now excluding Fungi and members of Monera and Protista that possess cell walls
• 2Algae reproduce via three methods: vegetative (fragmentation), asexual (zoospores), and sexual (isogamous, anisogamous, or oogamous)
• 3Bryophytes are called plant kingdom amphibians because they live in soil but require water for sexual reproduction and play crucial roles in plant succession on bare rock/soil
• 4Pteridophytes are the first terrestrial plants with true vascular tissues (xylem and phloem) and true roots, stems, and leaves; they require water for gamete transfer
• 5Gymnosperms have naked ovules exposed before and after fertilization, producing true seeds without fruit coverings

Chapter 4 of the Class 11 Biology NCERT textbook, "Animal Kingdom", explains this topic. Animal Kingdom classification organizes over one million animal species based on fundamental features like body organization level, symmetry, coelom presence, and segmentation, with 11 major phyla ranging from simple sponges to complex chordates with notochords.

• 1Porifera (sponges) are multicellular with cellular-level organization and water canal systems for food gathering and waste removal.
• 2Coelenterata (cnidarians) exhibit tissue-level organization, are diploblastic with radial symmetry, and possess cnidoblasts (stinging capsules) for prey capture.
• 3Platyhelminthes (flatworms) are bilaterally symmetrical, triploblastic, acoelomate animals with incomplete digestive systems.
• 4Annelida (segmented worms) and Arthropoda (insects and relatives) show metameric segmentation and are coelomate animals with complete digestive systems.
• 5Chordata possess notochord, dorsal hollow nerve cord, and pharyngeal gill slits; vertebrates replace the notochord with a vertebral column in adults.

Chapter 5 of the Class 11 Biology NCERT textbook, "Morphology of Flowering Plants", covers this topic. It describes the morphology of flowering plants, including roots, stems, leaves, flowers, fruits, and seeds, with their structural variations and adaptations.

• 1Root systems vary by plant type: dicots have tap roots (primary + lateral branches), monocots have fibrous roots (many roots from stem base), and some plants have adventitious roots from non-radicle parts
• 2Stems are distinguished by nodes (where leaves attach) and internodes (portions between nodes); they bear buds and conduct water, minerals, and photosynthates
• 3Leaves consist of leaf base, petiole, and lamina; venation patterns are reticulate (network) in dicots or parallel in monocots; leaves can be simple or compound (pinnate or palmate)
• 4Flowers are modified shoots with four whorls: calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels); flower symmetry can be actinomorphic, zygomorphic, or asymmetric
• 5Fruits develop from ripened ovaries after fertilization and contain seeds; the pericarp may be dry or fleshy (differentiated into epicarp, mesocarp, endocarp)

Chapter 6 of the Class 11 Biology NCERT textbook, "Anatomy of Flowering Plants", explains this topic. Anatomy of flowering plants studies the internal tissue organization of plants through their epidermal, ground, and vascular tissue systems, which differ markedly between dicotyledonous and monocotyledonous species.

• 1Three tissue systems organize plant anatomy: epidermal (protective outer layer), ground (supporting and storage bulk tissue), and vascular (water and mineral conducting system)
• 2Stomata regulate transpiration and gas exchange; each comprises two guard cells enclosing a pore, with subsidiary cells forming the stomatal apparatus
• 3Dicots have open vascular bundles with cambium between xylem and phloem enabling secondary growth; monocots have closed bundles without cambium preventing secondary growth
• 4Dicot roots have 2-4 xylem bundles and small pith; monocot roots have more than six polyarch xylem bundles with large, well-developed pith
• 5Dorsiventral dicot leaves contain distinct palisade parenchyma (adaxial) and spongy parenchyma (abaxial); isobilateral monocot leaves lack mesophyll differentiation with bulliform cells

Chapter 7 of the Class 11 Biology NCERT textbook, "Structural Organisation in Animals", covers this topic. It explains the structural organisation of animals through tissues, organs, and organ systems, with detailed anatomy and morphology of the frog as a representative vertebrate example.

• 1Animals are organised hierarchically: cells form tissues, tissues form organs, organs form organ systems that work together for survival
• 2All complex animals contain four basic tissue types: epithelial, connective, muscular, and neural tissue
• 3Frogs are cold-blooded (poikilothermic) amphibians with moist skin enabling both cutaneous and pulmonary respiration
• 4Frog digestive system is short because they are carnivores; food is captured by a bilobed tongue and processed through the mouth, oesophagus, stomach, intestine, and cloaca
• 5Frog circulatory system has a three-chambered heart (two atria, one ventricle) with portal systems connecting liver-intestine and kidney-body

Chapter 8 of the Class 11 Biology NCERT textbook, "Cell: The Unit of Life", explains this topic. The cell is the basic structural and functional unit of all living organisms; all organisms are composed of cells that vary in shape, size, and function, and cell theory states that all cells arise from pre-existing cells.

• 1Cell is the fundamental structural and functional unit of all living organisms composed of cytoplasm, nucleus (in eukaryotes), and cell membrane.
• 2Prokaryotic cells lack a membrane-bound nucleus and organelles; eukaryotic cells possess a nucleus and compartmentalized organelles like mitochondria, ER, and Golgi apparatus.
• 3The cell membrane is selectively permeable with lipid bilayer and proteins, facilitating transport of molecules via passive transport (diffusion, osmosis) and active transport (ATP-dependent).
• 4Double membrane-bound organelles include mitochondria (ATP production via aerobic respiration) and chloroplasts (photosynthesis in plant cells).
• 5The endomembrane system includes endoplasmic reticulum (protein and lipid synthesis), Golgi apparatus (packaging and secretion), lysosomes (digestion), and vacuoles (storage and osmoregulation).

Chapter 9 of the Class 11 Biology NCERT textbook, "Biomolecules", covers this topic. Biomolecules are organic compounds found in living organisms—including proteins, lipids, carbohydrates, and nucleic acids—which together form the chemical foundation of all living systems.

• 1Living organisms contain water (70-90%), proteins (10-15%), carbohydrates (3%), and lipids (2%) with nucleic acids making up 5-7% of cellular mass
• 2Biomolecules are classified into micromolecules (<1000 Da) found in acid-soluble fractions and macromolecules (>10,000 Da) including proteins, nucleic acids, and polysaccharides
• 3Amino acids are the building blocks of proteins with 20 types occurring in nature, each containing amino, carboxyl, and variable R groups
• 4Proteins exhibit four levels of structure: primary (amino acid sequence), secondary (helix and pleated sheet), tertiary (3D folding), and quaternary (multiple subunit assembly)
• 5Enzymes are protein catalysts that lower activation energy and accelerate biochemical reactions by forming substrate-enzyme complexes at their active sites

Chapter 10 of the Class 11 Biology NCERT textbook, "Cell Cycle and Cell Division", explains this topic. It covers how cells divide through mitosis and meiosis: mitosis produces identical diploid daughter cells for growth and repair, while meiosis creates four haploid gametes for sexual reproduction.

• 1Cell cycle consists of interphase (95% of duration) and M phase, with DNA replication occurring only during the S phase
• 2Mitosis is equational division conserving chromosome number; includes prophase, metaphase, anaphase, telophase, and cytokinesis
• 3Significance of mitosis: growth of multicellular organisms, cell repair, and continuous plant growth via meristematic tissues
• 4Meiosis is reduction division halving chromosome number through two sequential divisions with crossing over and genetic recombination
• 5Meiosis I features synapsis of homologous chromosomes, bivalent formation, and crossing over between non-sister chromatids

Chapter 11 of the Class 11 Biology NCERT textbook, "Photosynthesis in Higher Plants", covers this topic. Photosynthesis is a physico-chemical process where green plants use light energy to synthesize organic compounds from carbon dioxide and water, producing oxygen; it occurs in chloroplasts and consists of light-dependent and light-independent (dark) reactions.

• 1Photosynthesis is the process by which green plants synthesize food using light energy; the overall equation is 6CO2 + 12H2O → C6H12O6 + 6H2O + 6O2 with light as the driving force
• 2Light reactions occur in thylakoid membranes and involve water splitting, electron transport through Photosystem II and I, producing ATP, NADPH, and O2; dark reactions (Calvin cycle) occur in stroma using ATP and NADPH to fix CO2 into glucose
• 3The Z scheme describes electron flow from PSII through an electron transport chain to PSI, with both non-cyclic (producing ATP and NADPH) and cyclic (producing only ATP) photophosphorylation pathways possible
• 4Chemiosmosis explains ATP synthesis: water splitting creates protons in the thylakoid lumen, establishing a proton gradient that drives ATP synthase to phosphorylate ADP into ATP
• 5The Calvin cycle has three stages—carboxylation (CO2 fixation by RuBP carboxylase-oxygenase), reduction (using ATP and NADPH), and regeneration (restoring the CO2 acceptor RuBP); each CO2 requires 3 ATP and 2 NADPH

Chapter 12 of the Class 11 Biology NCERT textbook, "Respiration in Plants", explains this topic. Respiration in plants is the cellular process of breaking down organic molecules through oxidation to release energy, which is captured in ATP for use in life processes; all living organisms require it to obtain energy for growth, reproduction, and other functions.

• 1Respiration is the oxidative breakdown of organic molecules to release energy, occurring in cytoplasm and mitochondria; glucose is the primary respiratory substrate
• 2Glycolysis occurs in the cytoplasm and breaks one glucose molecule into two pyruvic acid molecules with net gain of 2 ATP
• 3Aerobic respiration (Krebs' cycle and electron transport system) completely oxidizes pyruvate to CO₂ and H₂O, yielding approximately 38 ATP per glucose molecule
• 4Fermentation occurs under anaerobic conditions and produces either lactic acid or ethanol with less than 7% energy release compared to aerobic respiration
• 5The electron transport system (ETS) on the inner mitochondrial membrane uses oxygen as the final electron acceptor, driving ATP synthesis through oxidative phosphorylation

Chapter 13 of the Class 11 Biology NCERT textbook, "Plant Growth and Development", covers this topic. Plant growth and development is the irreversible increase in size and formation of organs through division and differentiation of meristematic cells, controlled by plant growth regulators like auxins, gibberellins, cytokinins, ethylene, and abscisic acid.

• 1Growth is irreversible size increase measured by fresh/dry weight, length, area, volume, or cell number, driven by meristematic cell division.
• 2Three growth phases—meristematic (active cell division), elongation (cell enlargement and vacuolation), and maturation (cell wall thickening and specialization).
• 3Arithmetic growth shows linear increase; geometric growth shows exponential increase followed by plateau (sigmoid curve).
• 4Plant growth regulators—auxins (rooting, flowering, apical dominance), gibberellins (elongation, ripening), cytokinins (cell division, leaf growth), ethylene (ripening, senescence), and abscisic acid (stress tolerance, dormancy)—control all developmental phases.
• 5Differentiation specializes cells for function; dedifferentiation restores division capacity; redifferentiation specializes anew—enabling plant flexibility and tissue regeneration.

Chapter 14 of the Class 11 Biology NCERT textbook, "Breathing and Exchange of Gases", explains this topic. It is the process by which oxygen from the atmosphere is continuously supplied to cells and carbon dioxide produced during metabolism is released, involving respiratory organs, gas diffusion across alveolar membranes, transport of gases by blood, and cellular utilization of oxygen.

• 1Respiration involves breathing, gas diffusion across alveolar membranes, gas transport by blood, tissue diffusion, and cellular utilization of oxygen
• 2Inspiration increases thoracic volume via diaphragm contraction and external intercostal muscle action, decreasing intra-pulmonary pressure below atmospheric pressure
• 3Expiration occurs when diaphragm and intercostal muscles relax, increasing intra-pulmonary pressure to release air from lungs
• 4Oxygen (97%) is transported primarily as oxyhaemoglobin; carbon dioxide (70%) is transported as bicarbonate with carbonic anhydrase enzyme
• 5Gas exchange occurs by simple diffusion across the thin alveolar-capillary diffusion membrane (~0.1 mm) following partial pressure gradients

Chapter 15 of the Class 11 Biology NCERT textbook, "Body Fluids and Circulation", covers this topic. Blood is a connective tissue of plasma and formed elements (red cells, white cells, platelets), lymph is a fluid derived from tissue fluid that transports nutrients and fats, and the circulatory system continuously delivers oxygen and nutrients to cells while removing waste.

• 1Blood comprises plasma (55%) and formed elements—RBCs (gas transport), WBCs (immunity), platelets (clotting)—with ABO and Rh antigen grouping for transfusions
• 2The sino-atrial node (SAN) acts as the heart's pacemaker, generating 70-75 action potentials per minute and maintaining normal heart rate of 72 beats/minute
• 3Cardiac cycle consists of atrial and ventricular systole (contraction) and diastole (relaxation), with heart valves preventing backward blood flow
• 4Double circulation involves two pathways: pulmonary circulation (right ventricle → lungs → left atrium) and systemic circulation (left ventricle → body tissues → right atrium)
• 5Lymph is a colorless tissue fluid containing lymphocytes for immunity, serving as transport medium for nutrients and fats absorbed in the intestines

Chapter 16 of the Class 11 Biology NCERT textbook, "Excretory Products and Their Elimination", covers this topic. It explains the human excretory system, urine formation through glomerular filtration and reabsorption, and hormonal regulation of kidney function, including nephron structure, osmotic mechanisms, and disorders like uremia treated via hemodialysis.

• 1Nitrogenous waste forms—ammonia (highly toxic, needs water), urea (moderate toxicity), uric acid (least toxic)—vary by organism habitat and adaptation
• 2Nephron structure: glomerulus + Bowman's capsule (Malpighian body), proximal convoluted tubule, Henle's loop, distal convoluted tubule, collecting duct; human kidneys contain ~1 million nephrons
• 3Glomerular filtration rate (GFR) ~125 ml/minute (180 L/day); 99% reabsorbed by tubules through active/passive transport, leaving ~1.5 L urine excreted daily
• 4Counter current mechanism: Henle's loop and vasa recta maintain osmotic gradient (300–1200 mOsmol/L) to concentrate filtrate up to 4× via NaCl and urea recycling
• 5Hormonal regulation: ADH promotes water reabsorption; renin-angiotensin-aldosterone system increases GFR and blood pressure; ANF counteracts by vasodilation

Chapter 17 of the Class 11 Biology NCERT textbook, "Locomotion and Movement", explains this topic. It covers locomotion and movement, explaining muscle contraction through the sliding filament theory, the skeletal system's structure (206 bones), and the joint types that enable body movement.

• 1Three types of cellular movements exist in humans: amoeboid (by pseudopodia), ciliary (in trachea and reproductive tract), and muscular (for limbs and locomotion)
• 2The sarcomere is the functional unit of muscle contraction, composed of thick myosin and thin actin filaments separated by Z lines
• 3Muscle contraction follows the sliding filament theory: calcium ions trigger actin-myosin cross-bridges, pulling thin filaments over thick filaments to shorten the sarcomere
• 4The human skeleton has 206 bones: 80 axial (skull, spine, ribs, sternum) and 126 appendicular (limbs and girdles)
• 5Synovial joints (ball-and-socket, hinge, pivot, gliding, saddle) permit considerable movement unlike fibrous (immobile) and cartilaginous (limited) joints

Chapter 18 of the Class 11 Biology NCERT textbook, "Neural Control and Coordination", covers this topic. It explains how the neural system coordinates body functions through neurons, nerve impulses, and synapses, and how the brain controls voluntary movements and vital organs through three divisions: forebrain, midbrain, and hindbrain.

• 1The neural system maintains homeostasis through coordination of organ systems via neurons that detect, receive, and transmit stimuli.
• 2Neurons have three parts: cell body (with Nissl's granules), dendrites (transmit impulses toward cell body), and axon (transmit impulses away from cell body).
• 3Nerve impulses are generated by ion channel permeability changes — Na⁺ influx depolarizes the membrane, while K⁺ efflux restores resting potential.
• 4Synapses are junctions between neurons; chemical synapses use neurotransmitters released from synaptic vesicles to transmit impulses across the synaptic cleft.
• 5The brain divides into forebrain (controls sensory/motor functions, temperature, eating, emotions), midbrain, and hindbrain (controls respiration, heart rate, balance).

Chapter 19 of the Class 11 Biology NCERT textbook, "Chemical Coordination and Integration", explains this topic. Chemical coordination is carried out by hormones—non-nutrient chemicals produced by endocrine glands and other tissues that act as intercellular messengers—working alongside the neural system to regulate metabolism, growth, development, and homeostasis.

• 1The endocrine system comprises organized glands (pituitary, thyroid, adrenal, pancreas, parathyroid, thymus, pineal, gonads) plus hormone-secreting cells in the heart, kidney, and gastrointestinal tract
• 2The hypothalamus regulates the pituitary through releasing and inhibiting hormones via a portal circulatory system, controlling anterior pituitary; the posterior pituitary is under direct neural regulation
• 3Thyroid hormones (T3, T4) regulate basal metabolic rate, carbohydrate/protein/fat metabolism, and require iodine; deficiency causes hypothyroidism (goitre, cretinism); excess causes hyperthyroidism (Graves' disease)
• 4Pancreatic insulin (β-cells) decreases blood glucose by promoting uptake and glycogenesis, while glucagon (α-cells) increases blood glucose via glycogenolysis and gluconeogenesis; imbalance causes diabetes mellitus
• 5Adrenal catecholamines (epinephrine, norepinephrine) trigger fight-or-flight responses increasing heart rate, respiration, and glucose availability; cortical glucocorticoids regulate metabolism and immunity, mineralocorticoids control electrolyte balance