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Class 11 BiologyChapter Summaries

22 chapters · Quick revision in under 3 minutes per chapter · Updated 2025-26

Ch 1

The Living World

This chapter introduces the defining characteristics of living organisms — growth, reproduction, metabolism, cellular organisation, and consciousness. Students learn the need for classification and the concept of taxonomic hierarchy. Nomenclature rules (binomial nomenclature by Linnaeus) and the meaning of species, genera, families, orders, classes, phyla, and kingdoms are established. Key concepts like biodiversity and the difference between living and non-living are explored.

Topics covered

Characteristics of living organisms: growth, reproduction, metabolism, consciousnessTaxonomic hierarchy: species → genus → family → order → class → phylum → kingdomBinomial nomenclature: rules and examples (Homo sapiens, Mangifera indica)Need for classification and systematicsConcept of biodiversity and its significanceDifference between growth in living and non-living thingsTaxonomical aids: herbarium, botanical gardens, museum, zoological parks, taxonomic keys

Ch 2

Biological Classification

This chapter traces the history of classification systems from the two-kingdom system (Linnaeus) to the five-kingdom system proposed by R.H. Whittaker (1969). The five kingdoms — Monera, Protista, Fungi, Plantae, and Animalia — are described with their unique features. Viruses, viroids, prions, and lichens are discussed as special entities that do not fit neatly into the five kingdoms.

Topics covered

Two-kingdom, three-kingdom, and five-kingdom classification systems and their basisKingdom Monera: archaebacteria (extremophiles), eubacteria, mycoplasma, cyanobacteriaKingdom Protista: diatoms, dinoflagellates, slime moulds, protozoansKingdom Fungi: modes of nutrition, reproduction, examples (Mucor, Aspergillus, Agaricus, Puccinia)Kingdom Plantae and Kingdom Animalia — distinguishing featuresViruses: structure, DNA vs RNA viruses, bacteriophage structureViroids and prionsLichens: symbiotic association of algae and fungi — indicator species

Ch 3

Plant Kingdom

This chapter classifies plants into Algae, Bryophytes, Pteridophytes, Gymnosperms, and Angiosperms. The concept of alternation of generations — the interplay between gametophyte and sporophyte — is central to understanding the plant life cycle. Students study the general characters of each group, their reproduction, and representative examples. Classification of Angiosperms into monocots and dicots is also covered.

Topics covered

Algae: general characters, classes (Chlorophyceae, Phaeophyceae, Rhodophyceae), pigments, storage productsBryophytes: amphibians of plant kingdom, structure (liverworts, mosses), gametophyte-dominant life cyclePteridophytes: first vascular plants, sporophyte dominant generation, homosporous vs heterosporousGymnosperms: naked seeds, microsporophylls, megasporophylls, examples (Cycas, Pinus, Gnetum)Angiosperms: enclosed seeds, monocots vs dicots — distinguishing featuresAlternation of generations: gametophyte and sporophyte dominance in different groupsEconomic importance of algae (agar-agar, iodine) and gymnosperms (resin, turpentine)

⚠️ Removed from 2025-26 syllabus

Detailed life cycles of Fucus, Polysiphonia — only general characters retained in 2025-26

Ch 4

Animal Kingdom

This chapter classifies animals into non-chordates and chordates based on key characters such as symmetry, coelom, segmentation, notochord, and the presence of a vertebral column. The phyla from Porifera to Chordata are described with distinguishing features and representative examples. Special features like canal systems in sponges, polymorphism in coelenterates, and metamerism in annelids are highlighted.

Topics covered

Basis of classification: symmetry, coelom (acoelomate/pseudocoelomate/coelomate), segmentation, notochordPhyla: Porifera, Coelenterata/Cnidaria, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata — salient features and examplesPhylum Chordata: notochord, dorsal hollow nerve cord, pharyngeal gill slitsSub-phyla of Chordata: Urochordata, Cephalochordata, VertebrataClasses of Vertebrata: Cyclostomata, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, MammaliaCanal systems in Porifera: ascon, sycon, leucon typesPolymorphism and metagenesis in Cnidaria

⚠️ Removed from 2025-26 syllabus

Detailed classification of class Reptilia into orders — only general features retained in 2025-26

Detailed canal system diagrams of sponges — concept retained without labelled diagram

Ch 5

Morphology of Flowering Plants

This chapter describes the external structure and modifications of roots, stems, leaves, flowers, fruits, and seeds in angiosperms. Students learn the technical terms used to describe plant parts and how modifications serve adaptive functions such as storage, climbing, or protection. Floral formulas and floral diagrams are used to describe families. Families Fabaceae, Solanaceae, and Liliaceae are studied in detail.

Topics covered

Root: regions, types (tap root, fibrous, adventitious), modifications for storage, support, and nitrogen fixationStem: modifications (stolons, rhizomes, tubers, tendrils, thorns, bulbs, corms, phylloclades)Leaf: parts, venation (parallel vs reticulate), types (simple vs compound), phyllotaxy (alternate, opposite, whorled)Flower: parts (calyx, corolla, androecium, gynoecium), aestivation, placentation typesFruit types and seed structure (monocot vs dicot seed)Floral formula and floral diagram — symbols and conventionsFamilies: Fabaceae, Solanaceae, Liliaceae — floral formula, diagram, economic importance

Ch 6

Anatomy of Flowering Plants

This chapter explores the internal organisation of plants, covering tissue types (meristematic and permanent), tissue systems (epidermal, ground, and vascular), and the internal anatomy of roots, stems, and leaves in monocots and dicots. Secondary growth of dicot stems through vascular cambium and cork cambium is also described in detail.

Topics covered

Meristematic tissues: apical, lateral, intercalary — location and functionPermanent tissues: simple (parenchyma, collenchyma, sclerenchyma) and complex (xylem, phloem) — structure and functionTissue systems: epidermal, ground, vascularT.S. of dicot root vs monocot root — key differencesT.S. of dicot stem vs monocot stem — key differencesT.S. of dicot leaf vs monocot leaf — key differencesSecondary growth in dicot stem: vascular cambium (spring wood/autumn wood) and cork cambium (phellogen)

Ch 7

Structural Organisation in Animals

This chapter introduces the levels of organisation in animals — cell, tissue, organ, and organ system — and describes the four types of animal tissues with their subtypes and functions. The morphology and anatomy of the cockroach (Periplaneta americana) is studied in detail as a representative arthropod, including its digestive, circulatory, reproductive, and nervous systems.

Topics covered

Levels of organisation: cellular → tissue → organ → organ systemEpithelial tissue: simple (squamous, cuboidal, columnar, ciliated, glandular) and compound epitheliumConnective tissue: loose (areolar, adipose), dense (tendon, ligament), specialised (cartilage, bone, blood)Muscular tissue: striated (voluntary), smooth (unstriated/involuntary), cardiacNeural tissue: neuron structure, neurogliaCockroach external morphology: head, thorax, abdomen, appendagesCockroach internal systems: digestive system (labelled diagram), circulatory system, reproductive system

⚠️ Removed from 2025-26 syllabus

Detailed internal anatomy of earthworm — only cockroach retained in 2025-26 syllabus

Detailed internal anatomy of frog — removed from 2025-26 syllabus

Ch 8

Cell: The Unit of Life

This chapter establishes the cell as the structural and functional unit of life. The cell theory, prokaryotic and eukaryotic cell structures, and the ultrastructure of cell organelles are studied in detail using electron microscopy. Students learn the function of each organelle, distinguishing features of plant and animal cells, and the role of the nucleus as the control centre of cellular activity.

Topics covered

Cell theory and its significance; contributions of Schleiden, Schwann, and VirchowProkaryotic vs eukaryotic cells — key structural differencesCell membrane: fluid mosaic model (Singer and Nicolson, 1972)Cell wall: composition in plant cells (cellulose) and bacteria (peptidoglycan)Cell organelles: mitochondria, plastids (chloroplast, chromoplast, leucoplast), ER (RER/SER), Golgi apparatus, lysosomes, vacuoles, ribosomes (70S/80S), centrosomeNucleus: nuclear envelope (nuclear pores), nucleoplasm, chromatin, nucleolusDifferences between plant cell and animal cell

Ch 9

Biomolecules

This chapter covers the chemical composition of living cells — the structure and function of carbohydrates, proteins, lipids, nucleic acids, and enzymes. Students learn about primary and secondary metabolites, and how enzymes catalyse biochemical reactions. Enzyme kinetics, the lock-and-key model, induced-fit model, and competitive and non-competitive inhibition are studied.

Topics covered

Primary metabolites (amino acids, sugars) vs secondary metabolites (alkaloids, rubber, antibiotics)Carbohydrates: monosaccharides, disaccharides, polysaccharides — structures and functionsProteins: amino acids, peptide bonds, primary/secondary/tertiary/quaternary structureNucleic acids: DNA (Watson-Crick double helix) and RNA — structural differencesEnzymes: properties, IUB classification (6 classes), active site conceptMechanism of enzyme action: lock-and-key model vs induced-fit modelEnzyme inhibition: competitive and non-competitive; co-factors, coenzymes, prosthetic groups

Ch 10

Cell Cycle and Cell Division

This chapter describes the events of the cell cycle — interphase (G1, S, G2 phases) and the mitotic phase (M phase) — and explains the mechanisms of mitosis and meiosis. The significance of each type of division is emphasised: mitosis for growth and repair, meiosis for gamete formation and genetic variation. Diagrams of the stages of mitosis and sub-stages of prophase I are frequently asked.

Topics covered

Phases of cell cycle: G0 (quiescent), G1, S phase (DNA replication), G2, M phaseMitosis: prophase, metaphase, anaphase, telophase — key events at each stageCytokinesis: cleavage furrow (animal cells) vs cell plate formation (plant cells)Significance of mitosis: growth, repair, asexual reproductionMeiosis I: leptotene, zygotene, pachytene, diplotene, diakinesis — synapsis, crossing over, chiasmata formationMeiosis II — events and significance for genetic variationComparison of mitosis vs meiosis — key differences

Ch 11

Transport in Plants

This chapter explains how water, minerals, and food are transported across short and long distances in plants. Concepts like osmosis, plasmolysis, water potential, and transpiration pull are essential to understanding water movement. The pressure-flow hypothesis (Münch hypothesis) explains phloem translocation, while the cohesion-tension theory explains ascent of sap through xylem.

Topics covered

Diffusion, osmosis, water potential (ψ = ψs + ψp) — concepts and applicationPlasmolysis, turgidity, and flaccidityWater absorption by roots: apoplast and symplast pathways; Casparian stripsAscent of sap: root pressure theory and cohesion-tension theory (Dixon and Joly)Transpiration: types (stomatal, lenticular, cuticular), stomatal mechanism, significanceMineral ion transport: passive absorption vs active absorptionPhloem translocation: pressure-flow (mass flow) hypothesis — source and sink concept

Ch 12

Mineral Nutrition

This chapter covers the essential mineral nutrients required by plants, their functions, and deficiency symptoms. Students study macro- and micronutrients, the criteria for essentiality of an element (Arnon and Stout), and the role of nitrogen in plant nutrition. Biological nitrogen fixation by Rhizobium in root nodules and the nitrogen cycle are important topics.

Topics covered

Essential macronutrients: N, P, K, Ca, Mg, S — functions and deficiency symptomsEssential micronutrients: Fe, Mn, Cu, Mo, B, Zn, Cl, Ni — functionsCriteria for essentiality of a mineral element (Arnon and Stout's three criteria)Toxicity of micronutrients — manganese toxicity symptomsNitrogen cycle: fixation, ammonification, nitrification, denitrificationBiological nitrogen fixation: Rhizobium, root nodule formation, nitrogenase enzyme, leghaemoglobinHydroponics: definition, advantages, significance

Ch 13

Photosynthesis in Higher Plants

This chapter covers the mechanism of photosynthesis — the light reactions occurring in the thylakoid membrane and the dark reactions (Calvin cycle) occurring in the stroma of the chloroplast. C3, C4, and CAM pathways are distinguished with reference to the plants that use them. The Z-scheme of electron flow, photophosphorylation, and photorespiration are key topics.

Topics covered

Chloroplast structure: grana, stroma, thylakoid — labelled diagramPhotosynthetic pigments: chlorophyll a, b, carotenoids — absorption and action spectraLight reactions: photolysis of water (Hill reaction), electron transport chain, Z-scheme, cyclic vs non-cyclic photophosphorylationCalvin cycle (C3 pathway): CO₂ fixation by RuBisCO, carboxylation → reduction → regeneration of RuBPC4 pathway (Hatch-Slack cycle): Kranz anatomy, role of PEP carboxylase, bundle sheath cellsCAM pathway in succulent plantsPhotorespiration: causes, significance, why C4 plants are unaffected

Ch 14

Respiration in Plants

This chapter covers the stepwise breakdown of glucose during aerobic and anaerobic respiration — glycolysis, the Krebs cycle, and the electron transport chain with oxidative phosphorylation. Students learn the energy balance (ATP yield), the amphibolic nature of respiration, and fermentation as the anaerobic pathway. The respiratory quotient (RQ) for different substrates is also studied.

Topics covered

Glycolysis: location (cytoplasm), substrate-level phosphorylation, net gain of 2 ATP and 2 NADH per glucoseFermentation: alcoholic (yeast) and lactic acid fermentation — products and conditionsPyruvate oxidation: formation of acetyl-CoA (mitochondrial matrix)Krebs cycle (TCA cycle): location (mitochondrial matrix), CO₂ release, NADH and FADH₂ productionElectron transport chain (ETC) and oxidative phosphorylation: chemiosmotic hypothesis (Peter Mitchell)Total ATP yield from complete oxidation of one glucose moleculeRespiratory quotient (RQ): carbohydrates (RQ=1), fats (RQ<1), proteins (RQ varies); amphibolic nature of respiration

Ch 15

Plant Growth and Development

This chapter covers the phases of plant growth, arithmetic and geometric growth curves, and the physiological roles of plant growth regulators — auxins, gibberellins, cytokinins, abscisic acid, and ethylene. The phenomena of photoperiodism and vernalisation are also explained with examples of short-day, long-day, and day-neutral plants.

Topics covered

Phases of growth: meristematic, elongation, maturation; arithmetic vs geometric growthAuxins: discovery (Went's Avena coleoptile experiment), role in phototropism, apical dominance, fruit settingGibberellins: role in stem elongation, seed germination, bolting, fruit developmentCytokinins: cell division, lateral shoot growth, delay of senescence (Richmond-Lang effect)Abscisic acid (ABA): stomatal closure, seed dormancy, stress responseEthylene: fruit ripening, abscission, senescence, breaking dormancyPhotoperiodism: short-day, long-day, day-neutral plants; role of phytochrome and critical night lengthVernalisation: definition, significance, examples

Ch 16

Digestion and Absorption

This chapter covers the human digestive system — the alimentary canal and associated digestive glands — and the process of digestion, absorption, and assimilation of food. Students learn about digestion in the buccal cavity, stomach, and small intestine, the role of digestive enzymes and bile, absorption through villi and microvilli, and common digestive disorders.

Topics covered

Human alimentary canal: buccal cavity, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, rectumDigestive glands: salivary glands (salivary amylase), gastric glands (HCl, pepsin, renin), liver (bile), pancreas (amylase, lipase, trypsin)Digestion of carbohydrates: salivary amylase → pancreatic amylase → maltase/sucrase/lactaseDigestion of proteins: pepsin (stomach) → trypsin, chymotrypsin (small intestine) → peptidasesDigestion of fats: bile salts (emulsification) → pancreatic lipaseAbsorption: jejunum/ileum (villi and microvilli); simple diffusion, facilitated diffusion, active transportDigestive disorders: constipation, diarrhoea, jaundice, vomiting, indigestion, PEM

Ch 17

Breathing and Exchange of Gases

This chapter covers the human respiratory system — the anatomy of the respiratory organs, the mechanism of breathing, lung volumes and capacities, and the transport of oxygen and CO₂ in blood. Regulation of respiration by the medullary respiratory centre and respiratory disorders such as asthma, emphysema, and occupational lung diseases are also discussed.

Topics covered

Human respiratory organs: nasal passage, pharynx, larynx, trachea, bronchi, bronchioles, alveoli — labelled diagramMechanism of breathing: inspiration (diaphragm + external intercostals contract) and expirationRespiratory volumes: tidal volume (500 mL), IRV (2500 mL), ERV (1100 mL), RV (1100 mL); vital capacity and TLCGas exchange across alveolar membrane — partial pressures of O₂ and CO₂Transport of O₂: oxyhaemoglobin; oxyhaemoglobin dissociation curve; Bohr effectTransport of CO₂: carbamino-haemoglobin (20-25%), bicarbonate ions (70%), dissolved in plasma (7%)Regulation of respiration: medullary respiratory centre; role of CO₂/H+ levelsRespiratory disorders: asthma, emphysema, pneumonia, occupational diseases (silicosis, asbestosis)

Ch 18

Body Fluids and Circulation

This chapter covers the composition of blood and lymph, the structure and functioning of the human heart, the cardiac cycle, cardiac output, the conduction system, and ECG. Blood pressure, blood groups (ABO and Rh), double circulation, and common circulatory disorders are also studied.

Topics covered

Blood composition: plasma, RBCs, WBCs (neutrophil, eosinophil, basophil, monocyte, lymphocyte), platelets — functionsBlood groups: ABO system (antigens on RBCs, antibodies in plasma), Rh factor, importance in transfusionStructure of the human heart: four chambers, valves (tricuspid, bicuspid/mitral, semilunar), coronary vessels — labelled diagramCardiac cycle: atrial systole, ventricular systole, diastole; heart sounds (lubb-dupp); cardiac output = HR x SVConduction system: SA node (pacemaker at 72 bpm), AV node, Bundle of His, Purkinje fibresElectrocardiogram (ECG): P wave, QRS complex, T waveDouble circulation: pulmonary and systemic circuitsCirculatory disorders: hypertension, coronary artery disease, angina, heart failure

Ch 19

Excretory Products and their Elimination

This chapter covers the modes of excretion (ammonotelism, ureotelism, uricotelism), the structure of the human excretory system, the nephron's role in urine formation, the counter-current mechanism for concentration of urine, and hormonal regulation of urine output. The roles of other organs (lungs, liver, skin) in excretion and renal disorders are also discussed.

Topics covered

Types of excretion: ammonotelism (aquatic animals), ureotelism (mammals), uricotelism (birds, reptiles)Human excretory system: kidneys, ureters, urinary bladder, urethra; cortex and medulla of kidneyNephron structure (labelled diagram): Bowman's capsule + glomerulus, PCT, loop of Henle, DCT, collecting ductUrine formation: glomerular filtration (GFR approx 125 mL/min), tubular reabsorption, tubular secretionCounter-current mechanism in loop of Henle and vasa recta for urine concentrationHormonal regulation: ADH (water reabsorption), RAAS (renin-angiotensin-aldosterone), ANFRenal disorders: acute/chronic renal failure, uremia, haemodialysis, kidney transplant

Ch 20

Locomotion and Movement

This chapter covers the different types of movement in living organisms and the mechanism of skeletal muscle contraction at the molecular level using the sliding filament theory. The structure of the human skeletal system — axial and appendicular — and the types of joints are described. Disorders of the muscular and skeletal systems are also included.

Topics covered

Types of movement: amoeboid (pseudopodia), ciliary (paramecium), flagellar (sperm), muscularStructure of skeletal muscle: myofibril, sarcomere — A-band, I-band, H-zone, Z-line, M-lineSliding filament theory: role of Ca2+, troponin, tropomyosin, cross-bridges; ATP requirementNeuromuscular junction (motor end plate); role of acetylcholineHuman skeleton: axial (80 bones) and appendicular (126 bones)Types of joints: fibrous (immovable), cartilaginous (slightly movable), synovial (ball-and-socket, hinge, pivot, gliding, saddle, condyloid)Disorders: myasthenia gravis, muscular dystrophy, tetany, arthritis, osteoporosis, gout

Ch 21

Neural Control and Coordination

This chapter explains how the nervous system detects stimuli and coordinates responses. The structure of the neuron, generation and conduction of nerve impulses (action potential), synaptic transmission, and the organisation of the human nervous system are covered. Reflex actions, the structure of the human brain and spinal cord, and the sense organs (eye and ear) are key topics.

Topics covered

Neuron structure: dendrites, cyton, axon, myelin sheath, nodes of Ranvier, Schwann cells — labelled diagramResting membrane potential (-70 mV) and action potential — ionic basis (Na+/K+ flux)Conduction: saltatory conduction in myelinated vs continuous conduction in unmyelinated fibresSynaptic transmission: chemical synapse, role of neurotransmitters (acetylcholine), EPSP/IPSPOrganisation: CNS (brain + spinal cord), PNS (somatic + autonomic — sympathetic/parasympathetic)Human brain: cerebrum (lobes), cerebellum (coordination), medulla oblongata (vital reflexes), hypothalamus, limbic systemReflex arc: receptor to afferent neuron to nerve centre to efferent neuron to effector — labelled diagramEye structure and mechanism of vision (rods and cones); Ear structure and mechanism of hearing (Organ of Corti)

Ch 22

Chemical Coordination and Integration

This chapter covers the endocrine system — hormones secreted by various glands, their chemical nature (peptide, steroid, amino acid derivatives), and their mechanisms of action. The hypothalamus-pituitary axis, and hormones of the thyroid, parathyroid, adrenal, pancreas, and gonads are studied along with their disorders. Feedback regulation of hormone secretion is a central concept.

Topics covered

Endocrine glands: hypothalamus, pituitary anterior (GH, TSH, ACTH, FSH, LH, prolactin) and posterior (ADH, oxytocin), thyroid, parathyroid, adrenal, pancreas, gonads, thymus, pinealChemical nature of hormones: peptide/protein (insulin, GH), steroids (cortisol, sex hormones), amino acid derivatives (adrenaline, thyroxine)Hypothalamus-pituitary axis: releasing hormones, tropic hormones, feedback regulationThyroid hormones (T3, T4): regulation of BMR and growth; calcitonin (Ca2+ regulation); disorders: goitre, cretinism, myxoedema, Graves diseaseAdrenal cortex: glucocorticoids (cortisol) and mineralocorticoids (aldosterone); adrenal medulla: adrenaline and noradrenaline (fight-or-flight)Pancreatic hormones: insulin (lowers blood glucose) and glucagon (raises blood glucose); diabetes mellitus Types I and IIMechanism of hormone action: peptide hormones (cAMP as second messenger) vs steroid hormones (nuclear receptor, gene expression)Other hormones: PTH (parathyroid), melatonin (pineal), thymosin (thymus), ANF (heart), erythropoietin (kidney)

Frequently Asked Questions

Can I revise Class 11 Biology in one day using summaries?

Yes. Each chapter summary here takes under 3 minutes to read. With 22 chapters, you can cover all of Class 11 Biology in a focused 2–3 hour session. Use these summaries to identify gaps — then revisit only those chapters in detail.

Are chapter summaries enough for CBSE Class 11 Biology board exam?

Summaries are for revision, not first learning. Use them after you've already studied the chapter — they quickly confirm what you remember and flag what you don't. For first-time study, read the NCERT textbook and work through important questions chapter-by-chapter.

What is covered in Class 11 Biology chapter summaries?

Each summary here covers the main concepts of the chapter, key topics that CBSE tests, and important points for the board exam. Deleted topics (removed from the 2025-26 CBSE syllabus) are clearly marked so you don't waste time on content that won't be tested.

What is the fastest way to revise Class 11 Biology for CBSE boards?

Read the chapter summary, then immediately close it and try to recall the key topics listed — without looking. Anything you miss, mark for one more read. This active recall method is proven to be 3× more effective than re-reading the textbook, and takes a fraction of the time.

Complete Study Pack — Class 11 Biology

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