NCERT Solutions
Class 11 Biology
22 chapters · 110 important questions · Updated 2025-26
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.
Key Topics
Important Questions
What is binomial nomenclature? State the rules to be followed while writing scientific names. Give two examples.
Define taxonomy. What are the different taxonomic categories? Arrange them in hierarchical order from species to kingdom.
Distinguish between growth in living organisms and growth in non-living things. Give one example of each.
What is a herbarium? How is it useful in taxonomical studies?
Which of the following is NOT a characteristic feature of living organisms? (a) Metabolism (b) Growth (c) Crystallisation (d) Reproduction
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.
Key Topics
Important Questions
Give an account of R.H. Whittaker's five-kingdom classification. What are the criteria used for this classification?
What are viruses? Describe the structure of a bacteriophage with a well-labelled diagram.
Distinguish between archaebacteria and eubacteria. Give two examples of each.
What are lichens? Why are they considered good indicators of air pollution?
Name the kingdom to which Mycoplasma belongs. State two characteristics of Mycoplasma.
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.
Key Topics
⚠️ Deleted from Syllabus 2025-26
- — Detailed life cycles of Fucus, Polysiphonia — only general characters retained in 2025-26
Important Questions
Describe the general characteristics of bryophytes. Why are they called amphibians of the plant kingdom?
Distinguish between gymnosperms and angiosperms with four points. Give two examples of each.
What is alternation of generations? Explain with reference to the life cycle of a bryophyte.
Name the three classes of algae and state one characteristic pigment and one storage food product for each.
The plant body in mosses represents the _____ generation. (a) Sporophytic (b) Gametophytic (c) Diploid (d) Mixed
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.
Key Topics
⚠️ Deleted from Syllabus 2025-26
- — 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
Important Questions
Give the salient features and two examples each of Porifera, Coelenterata, and Platyhelminthes.
What are the distinguishing characters of phylum Chordata? Name the three sub-phyla.
Distinguish between Chondrichthyes and Osteichthyes with four distinguishing points.
What is metamerism? In which phylum is it observed? Name one example.
Which of the following is an acoelomate organism? (a) Earthworm (b) Tapeworm (c) Starfish (d) Cockroach
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.
Key Topics
Important Questions
What are the different types of root modifications? Give one example and state one function of each type.
Describe the structure of a typical dicotyledonous seed with a well-labelled diagram.
What is phyllotaxy? Name the three types and give one example of each.
Write the floral formula for the family Fabaceae. Draw and label its floral diagram.
Distinguish between simple and compound leaves. Give one example of each type.
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.
Key Topics
Important Questions
Draw and label a transverse section of a dicot stem. How does it differ from a monocot stem? List three differences.
Describe the different types of simple permanent tissues in plants with their functions.
What is secondary growth? Describe the role of vascular cambium in secondary growth of a dicot stem.
Distinguish between xylem and phloem with four points.
Which tissue is responsible for the increase in girth of a plant stem? (a) Apical meristem (b) Lateral meristem (c) Intercalary meristem (d) Epidermis
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.
Key Topics
⚠️ Deleted from Syllabus 2025-26
- — Detailed internal anatomy of earthworm — only cockroach retained in 2025-26 syllabus
- — Detailed internal anatomy of frog — removed from 2025-26 syllabus
Important Questions
Describe the different types of epithelial tissues with their location and one function each.
Draw a well-labelled diagram of the digestive system of a cockroach.
Distinguish between striated, unstriated, and cardiac muscle with their location and function.
What is areolar tissue? Where is it found in the body? State two functions.
Name the type of tissue that forms the inner lining of kidney tubules. Name one other location of this tissue.
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.
Key Topics
Important Questions
Draw a well-labelled diagram of a plant cell as seen under an electron microscope.
Describe the structure and functions of mitochondria with a labelled diagram. Why is it called the 'powerhouse of the cell'?
What is the fluid mosaic model of the cell membrane? Who proposed it? Describe the arrangement of lipids and proteins.
Distinguish between rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER) with two points.
What are the functions of lysosomes? Why are they called 'suicidal bags'?
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.
Key Topics
Important Questions
Describe the structure of DNA. Draw a diagram showing the double helix model. How does it differ from RNA?
What are enzymes? Describe the induced-fit model of enzyme action. How does it differ from the lock-and-key model?
Distinguish between competitive and non-competitive inhibition of enzymes with suitable examples.
What are co-factors? Distinguish between coenzymes and prosthetic groups with one example each.
Name the monomer of proteins. What is a peptide bond? How is it formed?
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.
Key Topics
Important Questions
Describe the various stages of mitosis with labelled diagrams. What is the significance of mitosis?
Draw labelled diagrams of (a) Metaphase I of meiosis and (b) Metaphase of mitosis. State two differences.
Distinguish between mitosis and meiosis. Explain with any four points.
Define synapsis and crossing over. During which stages of meiosis do they occur?
What major event occurs during the S phase of the cell cycle? What is its significance?
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.
Key Topics
Important Questions
What is water potential? How does it influence the direction of water movement in plants? What are its components?
Describe the cohesion-tension theory of ascent of sap. Who proposed it? What evidence supports it?
Explain the pressure-flow hypothesis of phloem translocation. Name the scientist who proposed it.
What is plasmolysis? Under what conditions does it occur? Draw a labelled diagram showing a plasmolysed cell.
Differentiate between apoplast and symplast pathways of water movement in plants.
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.
Key Topics
Important Questions
What are macro- and micronutrients? Give two examples of each and state their role in plant metabolism.
Describe biological nitrogen fixation. What is the role of leghaemoglobin in root nodules?
What are the criteria for essentiality of a mineral element? State all three criteria.
What is hydroponics? Give one advantage of this technique.
Name the element that plays an important role in biological nitrogen fixation. State its function.
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.
Key Topics
Important Questions
Draw a well-labelled diagram of a chloroplast. Where do the light reactions and dark reactions occur?
Explain the Calvin cycle (C3 pathway) with a diagram. Name the key enzyme and the CO₂ acceptor molecule.
Distinguish between C3 and C4 plants with respect to (i) primary CO₂ acceptor (ii) primary fixation product (iii) cells involved (iv) photorespiration.
What is the Z-scheme of electron flow? Describe the roles of Photosystem I and Photosystem II.
What is photorespiration? Under what conditions does it occur? Why is it absent in C4 plants?
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.
Key Topics
Important Questions
Describe glycolysis. Where does it occur? What is the net gain of ATP and NADH in this process?
Explain the Krebs cycle with a labelled diagram. Where does it occur? What are the net products per cycle?
What is the respiratory quotient (RQ)? Calculate the RQ for glucose and for a fat. What does RQ less than 1 indicate?
What is fermentation? Give the end products of (a) alcoholic fermentation and (b) lactic acid fermentation.
What is oxidative phosphorylation? Explain the chemiosmotic hypothesis for ATP synthesis in mitochondria.
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.
Key Topics
Important Questions
What are plant growth regulators? Describe the physiological roles of auxins with examples.
What is photoperiodism? Distinguish between short-day plants and long-day plants with examples. What is the critical photoperiod?
What is vernalisation? What is its significance for plants? Give one example.
What role does abscisic acid play in plants under drought stress conditions?
Which plant hormone promotes fruit ripening and is released as a gas? (a) Auxin (b) Cytokinin (c) Ethylene (d) Gibberellin
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.
Key Topics
Important Questions
Draw a well-labelled diagram of the human digestive system.
Describe the process of digestion of proteins in the human digestive tract. Name the enzymes involved at each stage.
What is the role of the liver in digestion? What is bile and what does it contain?
What is emulsification? Which substance is responsible for it and where does it occur?
Name the enzyme present in saliva, the substrate it acts upon, and the products of its action.
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.
Key Topics
Important Questions
Draw a well-labelled diagram of the human respiratory system.
Describe the transport of oxygen in blood. What is the Bohr effect? Draw the oxyhaemoglobin dissociation curve.
Define vital capacity. Name the lung volumes that make up vital capacity.
How is CO₂ transported in blood? Explain any two mechanisms with their approximate percentages.
What is emphysema? What causes it and what is its effect on breathing?
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.
Key Topics
Important Questions
Draw a well-labelled diagram of the human heart and describe its structure and function.
Describe the cardiac cycle. What is cardiac output? How is it calculated?
What is an ECG? What do the P wave, QRS complex, and T wave represent?
Distinguish between blood and lymph with four points.
Why is the SA node called the pacemaker of the heart? What happens if it fails?
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.
Key Topics
Important Questions
Draw a well-labelled diagram of a nephron and describe the process of urine formation.
Explain the counter-current mechanism in the loop of Henle and vasa recta. How does it help in concentration of urine?
What is glomerular filtration rate (GFR)? What is its normal value? What factors affect it?
Distinguish between ammonotelism, ureotelism, and uricotelism. Give one example of each.
What is the role of ADH (vasopressin) in kidney function? What happens when ADH secretion is deficient?
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.
Key Topics
Important Questions
Describe the sliding filament theory of muscle contraction. What is the role of calcium ions?
Draw a well-labelled diagram of a sarcomere. Identify the A-band, I-band, H-zone, and Z-line.
What are the different types of synovial joints? Give one example of each type.
Distinguish between red muscle fibres and white muscle fibres with three points.
What is osteoporosis? Name the age group most commonly affected and one causative factor.
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.
Key Topics
Important Questions
Draw a well-labelled diagram of the human brain and describe the functions of its major parts.
Describe the mechanism of conduction of a nerve impulse. Explain action potential with reference to Na+/K+ ion movements.
Draw a well-labelled diagram of a reflex arc and explain the mechanism of reflex action.
Draw a labelled diagram of the human eye and describe the mechanism of vision. How are rods and cones involved?
What is synaptic transmission? Describe the events that occur at a chemical synapse.
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.
Key Topics
Important Questions
Name the hormones secreted by the anterior pituitary gland and state the function of each hormone.
Describe the role of the adrenal gland in the body. Name the hormones secreted by the adrenal cortex and adrenal medulla and state one function of each.
Explain the mechanism of action of steroid hormones. How does it differ from the mechanism of action of peptide hormones?
What is diabetes mellitus? Distinguish between Type I (insulin-dependent) and Type II (non-insulin-dependent) diabetes.
What is the role of insulin in blood glucose regulation? What hormonal imbalance leads to diabetes mellitus?
Frequently Asked Questions
Is NCERT enough for CBSE Class 11 Biology board exam?
Yes. CBSE board exams are designed entirely around NCERT. 80–90% of questions in the Class 11 Biology paper are directly based on NCERT concepts — sometimes reworded, never from outside NCERT. Completing all 110 important questions listed here is the minimum you need.
How to study NCERT Class 11 Biology for board exams?
Go chapter-by-chapter. Read the chapter first, then attempt the important questions without looking at answers. Check your answer structure — CBSE gives marks per point, so structure matters as much as content. For 5-mark answers: brief intro + 4–5 numbered points with keywords + conclusion.
Which chapters are most important in Class 11 Biology for CBSE boards?
Chapters with the most long-answer (5-mark) important questions carry the most marks in the board paper. Look at which chapters here have the highest question count — those are the ones CBSE has historically focused on. Don't skip any chapter, but spend extra time on these.
How many questions come from NCERT in CBSE Class 11 Biology exam?
Nearly all 110 questions in the Class 11 Biology board paper are rooted in NCERT. The exact question may be reworded, but the concept, definition, or formula always comes from the NCERT textbook. Practicing these 110 important questions covers the vast majority of what can be asked.