CBSE Class 11 Biology Revision Notes for All Chapters

CBSE Class 11 Biology Revision Notes explain the important terms, classifications, structures and biological processes included in the current syllabus. The notes cover all 19 chapters across five units of the NCERT Class 11 Biology textbook for the 2026–27 academic year.

Class 11 Biology studies the diversity, structure and functioning of living organisms. It begins with the classification of plants and animals before moving to tissues, cells, biomolecules, plant physiology and human physiology.

Use these CBSE Class 11 Biology Revision Notes to review important concepts, diagrams, cycles and biological terms. The current NCERT textbook contains 19 chapters arranged under five thematic units.

Key Takeaways

• 19 chapters: The current textbook begins with The Living World and ends with Chemical Coordination and Integration.
• Five units: The syllabus covers diversity, structural organisation, cells, plant physiology and human physiology.
• 70 theory marks: Human Physiology carries 18 marks, the highest unit-wise allocation.
• 30 practical marks: Practical work includes experiments, slide preparation, spotting and project or record-based assessment.

Access CBSE Class 11 Biology Revision Notes in 30 Minutes

Revise the subject in three parts:

• First 10 minutes: Biological classification, plant groups, animal phyla, morphology and anatomy
• Next 10 minutes: Cell organelles, biomolecules, cell division, photosynthesis and respiration
• Final 10 minutes: Breathing, circulation, excretion, movement, neural control and hormones

Need help revising complex biological processes and labelled diagrams?

Access chapter-wise notes, interactive practice and doubt-solving support on the Extramarks Learning App. Sign Up Free

Chapter-Wise CBSE Class 11 Biology Notes

The Chapter-wise Class 11 Biology Notes follow the current sequence of the NCERT textbook.

The older Extramarks page lists 22 chapters. Transport in Plants, Mineral Nutrition and Digestion and Absorption are not separate chapters in the current 2026–27 textbook.

Unit I: Diversity in the Living World

This unit introduces biodiversity and the systems used to identify and classify organisms.

The Living World Notes

Living organisms show growth, reproduction, metabolism, cellular organisation and the ability to respond to their environment.

Biodiversity refers to the variety of living organisms found on Earth. Since millions of organisms exist, biologists use standard systems to identify, name and classify them.

Taxonomy and Systematics

Taxonomy deals with the identification, nomenclature and classification of organisms.

Systematics studies organism diversity along with evolutionary relationships.

The main taxonomic categories are:

Species → Genus → Family → Order → Class → Phylum or Division → Kingdom

A species is the basic unit of classification.

Binomial Nomenclature

Each organism receives a two-word scientific name:

• The first word represents the genus.
• The second word represents the specific epithet.
• The genus begins with a capital letter.
• The specific epithet begins with a small letter.
• Printed scientific names appear in italics.

For example, the scientific name of mango is Mangifera indica.

Taxonomical Aids

Important aids include:

• Herbarium
• Botanical gardens
• Museums
• Zoological parks
• Keys
• Flora and manuals

A taxonomic key helps identify organisms through contrasting characteristics.

Biological Classification Notes

R.H. Whittaker proposed the five-kingdom classification based on cell structure, body organisation, nutrition, reproduction and evolutionary relationships.

Monera

Monerans include bacteria, cyanobacteria, mycoplasma and archaebacteria.

Bacteria may be autotrophic or heterotrophic. They reproduce mainly through binary fission.

Protista

Protists are primarily aquatic, unicellular eukaryotes.

Major groups include:

• Chrysophytes
• Dinoflagellates
• Euglenoids
• Slime moulds
• Protozoans

Fungi

Fungi obtain nutrients through absorption. Their body generally consists of thread-like structures called hyphae, which together form a mycelium.

Major fungal groups include phycomycetes, ascomycetes, basidiomycetes and deuteromycetes.

Viruses are acellular and reproduce only within living host cells. Lichens represent a symbiotic association between algae and fungi.

Plant Kingdom Notes

Plants are classified by body organisation, vascular tissues, seed formation and the presence of flowers or fruits.

Major Plant Groups

Bryophytes are called the amphibians of the plant kingdom because they live on land but require water for sexual reproduction.

Pteridophytes are the first terrestrial plants to possess vascular tissues.

Angiosperms are divided into monocotyledons and dicotyledons based on the number of cotyledons in the seed.

Alternation of Generations

Plants alternate between:

• A haploid gametophyte that produces gametes
• A diploid sporophyte that produces spores

The dominant phase differs among plant groups.

Animal Kingdom Notes

Animals are classified using features such as:

• Level of organisation
• Body symmetry
• Germ layers
• Body cavity
• Segmentation
• Notochord

Main Classification Terms

Radial symmetry: Body can be divided into similar halves through several planes.

Bilateral symmetry: Body can be divided into two equal halves through one plane.

Diploblastic animals: Body develops from two germ layers.

Triploblastic animals: Body develops from three germ layers.

Coelom: Body cavity lined by mesoderm.

Major Animal Groups

Non-chordates include Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata and Hemichordata.

Chordates possess a notochord, dorsal hollow nerve cord, pharyngeal gill slits and post-anal tail at some stage.

Vertebrates include fishes, amphibians, reptiles, birds and mammals.

Unit II: Structural Organisation in Plants and Animals

This unit studies the external and internal structures that allow plants and animals to perform specialised functions.

Morphology of Flowering Plants Notes

Morphology is the study of the external form and structure of organisms.

Root

The root anchors the plant, absorbs water and minerals, and may store food.

Root systems include:

• Tap root system
• Fibrous root system
• Adventitious roots

Roots may be modified for storage, support or respiration.

Stem

The stem bears branches, leaves, flowers and fruits. It transports water, minerals and food.

Stem modifications may help in:

• Storage
• Vegetative propagation
• Protection
• Climbing

Leaf

A typical leaf includes the leaf base, petiole and lamina.

Venation may be reticulate or parallel. Phyllotaxy describes the arrangement of leaves on a stem.

Flower, Fruit and Seed

A flower generally contains four whorls:

• Calyx
• Corolla
• Androecium
• Gynoecium

After fertilisation, the ovary generally develops into the fruit and ovules develop into seeds.

Important families covered through floral characters include Fabaceae, Solanaceae and Liliaceae.

Anatomy of Flowering Plants Notes

Anatomy studies the internal structure of plants.

Plant Tissues

Meristematic tissues contain actively dividing cells.

They include:

• Apical meristem
• Intercalary meristem
• Lateral meristem

Permanent tissues consist of differentiated cells.

Simple permanent tissues include parenchyma, collenchyma and sclerenchyma.

Complex tissues include xylem and phloem.

Tissue Systems

Plants possess three tissue systems:

• Epidermal tissue system
• Ground tissue system
• Vascular tissue system

Xylem transports water and minerals. Phloem transports organic food.

The internal structures of dicot and monocot roots, stems and leaves differ in the arrangement of vascular bundles and ground tissues.

Structural Organisation in Animals Notes

Animal tissues are organised into four main types.

Epithelial tissue covers surfaces and lines cavities. Connective tissues include blood, cartilage, bone, tendons, ligaments and adipose tissue.

Muscular tissue may be skeletal, smooth or cardiac. Neural tissue contains neurons and supporting cells.

Unit III: Cell: Structure and Functions

This unit explains the cellular and molecular organisation common to living organisms.

Cell: The Unit of Life Notes

The cell is the structural and functional unit of life.

Schleiden and Schwann proposed the cell theory. Virchow later stated that all cells arise from pre-existing cells.

Prokaryotic and Eukaryotic Cells

Major Cell Organelles

• Nucleus: Stores genetic material and controls cellular activities
• Mitochondria: Produce ATP through aerobic respiration
• Chloroplasts: Carry out photosynthesis
• Endoplasmic reticulum: Synthesises and transports proteins or lipids
• Golgi apparatus: Modifies, packages and secretes substances
• Lysosomes: Contain hydrolytic enzymes
• Ribosomes: Synthesise proteins
• Vacuoles: Store materials and maintain cell pressure
• Centrosome: Supports spindle formation in animal cells

The plasma membrane is selectively permeable and controls movement between the cell and its surroundings.

Biomolecules Notes

Living cells contain inorganic and organic compounds.

Important biomolecules include:

• Carbohydrates
• Proteins
• Lipids
• Nucleic acids

Carbohydrates

Carbohydrates serve as energy sources and structural materials.

They include monosaccharides, disaccharides and polysaccharides.

Proteins

Proteins are polymers of amino acids joined by peptide bonds. They function as enzymes, hormones, structural components, transport molecules and antibodies.

Nucleic Acids

DNA stores genetic information. RNA supports protein synthesis and performs other cellular roles.

Nucleotides contain:

• A nitrogenous base
• A pentose sugar
• A phosphate group

Enzymes

Enzymes are biological catalysts. They increase reaction rates without being permanently consumed.

Enzyme activity depends on:

• Temperature
• pH
• Substrate concentration
• Enzyme concentration
• Inhibitors

Cell Cycle and Cell Division Notes

The cell cycle includes interphase and the division phase.

Interphase

Interphase includes:

• G₁ phase: Cell growth
• S phase: DNA replication
• G₂ phase: Preparation for division

Mitosis

Mitosis produces two genetically similar daughter cells.

Its stages are:

Prophase → Metaphase → Anaphase → Telophase

Mitosis supports growth, repair and asexual reproduction.

Meiosis

Meiosis involves two divisions and produces four haploid cells.

It reduces the chromosome number and creates variation through crossing over and independent assortment.

Meiosis is essential for sexual reproduction.

Unit IV: Plant Physiology

Plant physiology explains how plants capture energy, release energy and regulate growth.

Photosynthesis in Higher Plants Notes

Photosynthesis converts light energy into chemical energy.

The simplified equation is:

Carbon dioxide + Water → Glucose + Oxygen

The process occurs mainly in chloroplasts.

Photosynthetic Pigments

Chlorophyll a is the primary pigment. Chlorophyll b, carotenoids and xanthophylls act as accessory pigments.

Light Reaction

The light reaction occurs in the thylakoid membranes.

It produces:

• ATP
• NADPH
• Oxygen

Photosystems I and II participate in electron transport and photophosphorylation.

Carbon Fixation

The Calvin cycle occurs in the chloroplast stroma.

It includes:

• Carboxylation
• Reduction
• Regeneration

RuBisCO catalyses carbon dioxide fixation.

C₄ plants reduce photorespiration by separating initial carbon fixation and the Calvin cycle between different cell types.

Respiration in Plants Notes

Cellular respiration releases energy from organic compounds.

Main Stages

1. Glycolysis: Glucose breaks into pyruvate in the cytoplasm.
2. Krebs cycle: Acetyl CoA is oxidised in the mitochondrial matrix.
3. Electron transport system: Electrons support ATP formation on the inner mitochondrial membrane.

Aerobic respiration uses oxygen and releases more energy.

Anaerobic respiration occurs without oxygen. Fermentation can produce ethanol and carbon dioxide or lactic acid.

The respiratory quotient is:

RQ = Volume of carbon dioxide evolved ÷ Volume of oxygen consumed

Its value varies with the respiratory substrate.

Plant Growth and Development Notes

Growth is a permanent increase in size, mass or cell number.

Plant growth occurs mainly in meristematic regions.

Phases of Growth

• Meristematic phase
• Elongation phase
• Maturation phase

Growth may be arithmetic or geometric.

Plant Growth Regulators

Photoperiodism is the response to day length. Vernalisation is the promotion of flowering through low-temperature treatment.

Unit V: Human Physiology

Human Physiology studies the coordinated functioning of respiratory, circulatory, excretory, muscular, nervous and endocrine systems.

Breathing and Exchange of Gases Notes

Breathing includes inspiration and expiration.

During inspiration, the diaphragm contracts and thoracic volume increases. During expiration, the diaphragm relaxes and thoracic volume decreases.

Gas exchange occurs by diffusion across the alveolar membrane.

Oxygen is transported mainly through haemoglobin. Carbon dioxide is transported mainly as bicarbonate ions.

Respiratory disorders include:

• Asthma
• Emphysema
• Occupational respiratory disorders

Body Fluids and Circulation Notes

Blood consists of plasma and formed elements.

The formed elements include:

• Red blood cells
• White blood cells
• Platelets

Red blood cells transport oxygen. White blood cells support defence. Platelets assist blood clotting.

Human Heart

The human heart contains four chambers:

• Right atrium
• Right ventricle
• Left atrium
• Left ventricle

Humans show double circulation because blood passes through the heart twice during one complete circuit.

The cardiac cycle includes atrial systole, ventricular systole and joint diastole.

The electrocardiogram records the electrical activity of the heart.

Excretory Products and Their Elimination Notes

Excretion removes metabolic wastes from the body.

Humans are ureotelic because urea is the main nitrogenous waste.

Nephron

The nephron is the structural and functional unit of the kidney.

Urine formation involves:

1. Glomerular filtration
2. Selective reabsorption
3. Tubular secretion

The loop of Henle and vasa recta help produce concentrated urine through the counter-current mechanism.

Antidiuretic hormone regulates water reabsorption. The renin-angiotensin mechanism supports blood-pressure and fluid regulation.

Locomotion and Movement Notes

Movement may involve cilia, flagella or muscles.

Skeletal muscles contain fibres made of myofibrils. Actin and myosin filaments interact during contraction.

According to the sliding-filament theory, thin filaments slide over thick filaments and shorten the sarcomere.

The skeletal system provides:

• Support
• Protection
• Movement
• Mineral storage
• Sites for blood-cell formation

Common disorders include arthritis, osteoporosis, gout, muscular dystrophy and myasthenia gravis.

Neural Control and Coordination Notes

The nervous system receives stimuli, processes information and produces responses.

Neuron

A neuron contains:

• Cell body
• Dendrites
• Axon

A nerve impulse travels through changes in membrane potential.

At a chemical synapse, neurotransmitters carry the signal from one neuron to another.

Human Nervous System

The nervous system includes:

• Central nervous system
• Peripheral nervous system
• Autonomic nervous system

The brain consists of the forebrain, midbrain and hindbrain.

A reflex action is a rapid, automatic response carried through a reflex arc.

The chapter also covers the structures and functions of the human eye and ear.

Chemical Coordination and Integration Notes

The endocrine system coordinates body functions through hormones.

Hormones act on specific target tissues and commonly operate through feedback mechanisms.

Hormonal imbalances may cause conditions such as diabetes mellitus, goitre, dwarfism, gigantism and Addison’s disease.

CBSE Class 11 Biology Unit-Wise Marks 2026–27

The practical examination carries an additional 30 marks.

Important Diagrams for Class 11 Biology Revision

Practise diagrams that explain structures or processes, including:

• Taxonomic hierarchy
• Floral parts and floral diagrams
• Dicot and monocot root, stem and leaf
• Prokaryotic and eukaryotic cells
• Mitochondrion and chloroplast
• Mitosis and meiosis
• Light reaction and Calvin cycle
• Human respiratory system
• Human heart
• Nephron
• Sarcomere
• Neuron
• Human brain
• Endocrine glands

Use clean lines and write labels horizontally wherever possible. A diagram should support the written answer rather than replace the explanation.