CBSE Class 11 Biology Syllabus

Differentiate prokaryotic and eukaryotic cells.

Prokaryotic cells (bacteria, cyanobacteria, mycoplasma, PPLO) lack a true membrane-bound nucleus and membrane-bound organelles; their genetic material is a single naked circular DNA (nucleoid) and ribosomes are 70S. Eukaryotic cells have a true membrane-bound nucleus, membrane-bound organelles, linear DNA with histones, and 80S ribosomes (70S in their organelles).

Describe the structure and chemical composition of the bacterial cell wall.

The bacterial cell wall is made of peptidoglycan (murein). Based on cell wall composition, bacteria are classified by Gram staining into Gram-positive (thick peptidoglycan, retain crystal violet) and Gram-negative (thin peptidoglycan with an outer lipopolysaccharide membrane). The cell wall gives shape, structural support, and prevents bursting/lysis.

What is the chemical composition of the plant cell wall and its layers?

The plant cell wall is mainly composed of cellulose, hemicellulose, pectin and proteins (and lignin in secondary walls). It consists of the middle lamella (pectin, cements adjacent cells), the primary wall (formed first, capable of growth), and the secondary wall (formed inside, towards the membrane, in mature cells). Plasmodesmata connect adjacent cells.

State the fluid mosaic model of the plasma membrane and who proposed it.

The fluid mosaic model, proposed by Singer and Nicolson (1972), describes the plasma membrane as a phospholipid bilayer with proteins (integral and peripheral) embedded in or attached to it, with the lipids able to move laterally (quasi-fluid nature), giving the membrane fluidity that allows growth, endocytosis, etc.

Differentiate mitochondria and chloroplasts in function and key features.

Mitochondria are the 'powerhouses of the cell' performing aerobic respiration to produce ATP; they have a smooth outer and folded inner membrane (cristae) with a matrix. Chloroplasts perform photosynthesis; they contain chlorophyll in stacked thylakoids (grana) suspended in the stroma. Both are double-membraned, semi-autonomous organelles with their own 70S ribosomes and circular DNA.

What is the endoplasmic reticulum and how do rough and smooth ER differ?

The ER is a network of membranous tubules in the cytoplasm. Rough ER (RER) bears ribosomes on its surface and is the site of protein synthesis and secretion. Smooth ER (SER) lacks ribosomes and is the site of lipid (steroid) synthesis and detoxification.

State the structure and functions of the Golgi apparatus.

The Golgi apparatus consists of flat, stacked membranous sacs called cisternae with a convex cis (forming) face and a concave trans (maturing) face. It packages, modifies (e.g. glycosylation), and dispatches materials synthesised near the ER; it is the site of formation of glycoproteins and glycolipids.

What are lysosomes and why are they called 'suicidal bags'?

Lysosomes are single-membrane-bound vesicles formed by the Golgi apparatus, rich in hydrolytic (digestive) enzymes (lipases, proteases, carbohydrases) active at acidic pH. They digest carbohydrates, proteins, lipids and nucleic acids. They are called 'suicidal bags' because their enzymes can digest the cell's own worn-out organelles and dead cells (autolysis).

What is the structure of a eukaryotic ribosome and what is its function?

The eukaryotic ribosome is an 80S particle (S = Svedberg sedimentation unit) made of two subunits: a 60S large subunit and a 40S small subunit, composed of rRNA and proteins. Ribosomes are not membrane-bound and are the site of protein synthesis (translation). Prokaryotic and organellar ribosomes are 70S (50S + 30S).

Name the phases of the cell cycle and the two main divisions of M phase.

The cell cycle has interphase (G1 phase, S phase — DNA replication, G2 phase) and the M phase (mitotic phase). The M phase consists of karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).

List the stages of mitosis (karyokinesis) in order with one key event each.

Prophase (chromosomes condense, spindle begins, nuclear envelope disappears), Metaphase (chromosomes align at the metaphase plate/equator), Anaphase (sister chromatids separate and move to opposite poles), Telophase (chromosomes decondense, nuclear envelope reforms). Followed by cytokinesis.

How does meiosis differ from mitosis in outcome and number of divisions?

Mitosis is a single division producing two genetically identical diploid (2n) daughter cells (for growth/repair). Meiosis involves two successive divisions (meiosis I and II) producing four genetically variable haploid (n) cells (gametes/spores), and includes crossing over (recombination) in prophase I.

What is crossing over and in which stage of meiosis does it occur?

Crossing over is the exchange of genetic material (segments) between non-sister chromatids of homologous chromosomes, producing genetic recombination/variation. It occurs during the pachytene stage of prophase I of meiosis at points called chiasmata.

Define water potential, solute potential, and pressure potential, with their relationship.

Water potential (Ψw) is the potential energy of water determining the direction of its movement. Pure water has Ψw = 0 (the highest). The relationship is Ψw = Ψs (solute potential, always negative) + Ψp (pressure potential, usually positive due to turgor). Water moves from higher to lower water potential.

Differentiate osmosis, diffusion, and active transport in plant water/solute movement.

Diffusion is passive net movement of molecules from high to low concentration, no energy, no membrane needed. Osmosis is passive movement of water across a semipermeable membrane from higher to lower water potential. Active transport uses carrier proteins and ATP energy to move solutes against the concentration gradient.

What is the transpiration pull (cohesion-tension) theory of water ascent in plants?

Water is pulled up the xylem as a continuous column. Transpiration from leaves creates a tension (negative pressure) that pulls water upward; water molecules stick together (cohesion) and to xylem walls (adhesion), maintaining an unbroken column. This is the most widely accepted theory for the ascent of sap.

Differentiate macronutrients and micronutrients in plants with examples.

Macronutrients (macroelements) are required in large amounts (>10 mmol/kg dry matter), e.g. C, H, O, N, P, K, Ca, Mg, S. Micronutrients (microelements/trace elements) are required in small amounts (<10 mmol/kg), e.g. Fe, Mn, Cu, Zn, B, Mo, Cl, Ni.

What is biological nitrogen fixation, and name a symbiotic and a free-living nitrogen fixer.

Biological nitrogen fixation is the reduction of atmospheric N2 to ammonia (NH3) by living organisms using the enzyme nitrogenase. Symbiotic example: Rhizobium (in legume root nodules). Free-living examples: Azotobacter (aerobic) and Clostridium (anaerobic); cyanobacteria like Anabaena and Nostoc also fix nitrogen.

Write the overall balanced equation of photosynthesis.

6CO2 + 12H2O → (in presence of light and chlorophyll) → C6H12O6 + 6O2 + 6H2O. The O2 released comes from water, not CO2 (proven by Ruben using isotopes).

Differentiate the light reaction and the dark reaction (Calvin cycle) of photosynthesis.

The light reaction (photochemical phase) occurs in the thylakoid membranes; it splits water (photolysis), releases O2, and produces ATP and NADPH using light energy. The dark reaction (biosynthetic phase / Calvin cycle) occurs in the stroma; it is light-independent and uses ATP and NADPH to fix CO2 into sugars (does not require light directly).

Differentiate C3 and C4 plants based on the primary CO2 acceptor and first product.

In C3 plants the primary CO2 acceptor is RuBP (a 5-carbon molecule) and the first stable product is 3-phosphoglyceric acid (3-PGA, a 3-carbon compound), via the enzyme RuBisCO. In C4 plants the primary acceptor is PEP (phosphoenolpyruvate, 3C) and the first product is oxaloacetic acid (OAA, a 4-carbon compound), via PEP carboxylase; they have Kranz anatomy and lack photorespiration.

What is photorespiration and why is it considered wasteful?

Photorespiration is the light-dependent uptake of O2 and release of CO2 occurring in C3 plants when RuBisCO binds O2 instead of CO2 (forming phosphoglycolate). It is wasteful because there is no synthesis of sugars, ATP, or NADPH — it consumes energy without producing useful products. C4 plants avoid it.

Differentiate glycolysis, the Krebs cycle, and oxidative phosphorylation by location and net ATP yield.

Glycolysis occurs in the cytoplasm, breaking glucose into 2 pyruvate (net 2 ATP, 2 NADH). The Krebs (TCA/citric acid) cycle occurs in the mitochondrial matrix, producing NADH, FADH2, and 2 ATP (as GTP). Oxidative phosphorylation occurs at the inner mitochondrial membrane (ETС), where NADH/FADH2 generate most ATP. Total ~36–38 ATP per glucose in aerobic respiration.

What is the respiratory quotient (RQ) and what does its value indicate?

RQ = volume of CO2 evolved / volume of O2 consumed during respiration. RQ = 1 for carbohydrates, RQ < 1 for fats (~0.7), RQ > 1 (or infinity) for organic acids / anaerobic respiration. It indicates the type of respiratory substrate being used.

Name the five major plant growth regulators (phytohormones) and one key function of each.

Auxin (promotes cell elongation, apical dominance), Gibberellin (stem elongation, breaks seed dormancy, bolting), Cytokinin (promotes cell division, delays senescence), Ethylene (gaseous; promotes fruit ripening, abscission), and Abscisic acid (ABA; stress hormone, induces dormancy and stomatal closure).

What is photoperiodism and what are short-day and long-day plants?

Photoperiodism is the response of plants to the relative lengths of day and night (photoperiod) for flowering. Short-day plants flower when the day length is below a critical period; long-day plants flower when the day length is above a critical period; day-neutral plants flower regardless of photoperiod.

Name the four steps of food processing in the human digestive system.

The processes are: (1) Ingestion (taking in food), (2) Digestion (mechanical and chemical breakdown into absorbable forms), (3) Absorption (uptake of digested nutrients into blood/lymph), and (4) Assimilation/Egestion (utilisation of nutrients and elimination of undigested waste as faeces).

Match these digestive enzymes to their substrates: salivary amylase, pepsin, trypsin, lipase.

Salivary amylase (ptyalin) digests starch into maltose in the mouth. Pepsin (from gastric juice, active in acidic pH) digests proteins into peptones/proteoses in the stomach. Trypsin (pancreatic) digests proteins/peptides into smaller peptides. Lipase (pancreatic/intestinal) digests emulsified fats (triglycerides) into fatty acids and glycerol.

What is the difference between inspiration and expiration in terms of pressure and muscles?

Inspiration is active: the diaphragm contracts (flattens) and external intercostals contract, increasing thoracic volume and lowering intra-pulmonary pressure below atmospheric, so air flows in. Expiration is usually passive: the diaphragm and intercostals relax, decreasing thoracic volume and raising intra-pulmonary pressure above atmospheric, so air flows out.

Define tidal volume, vital capacity, and residual volume.

Tidal volume (TV): volume of air inspired or expired in a normal breath (~500 mL). Vital capacity (VC): maximum air a person can breathe out after a maximum inspiration (ERV + TV + IRV). Residual volume (RV): volume of air remaining in the lungs after a maximal expiration (~1100–1200 mL).

How is oxygen and carbon dioxide transported in human blood?

Oxygen is transported mainly (~97%) as oxyhaemoglobin (bound to haemoglobin) and ~3% dissolved in plasma. CO2 is transported ~70% as bicarbonate ions (HCO3-) in plasma, ~20–25% as carbamino-haemoglobin (bound to Hb), and ~7% dissolved in plasma.

Name the components and functions of human blood.

Blood is a fluid connective tissue with plasma (~55%, mostly water with proteins like albumin, globulin, fibrinogen) and formed elements (~45%): RBCs/erythrocytes (carry O2 via haemoglobin), WBCs/leukocytes (immunity/defence), and platelets/thrombocytes (blood clotting).

Describe the double circulation of blood in humans.

Double circulation means blood passes through the heart twice per complete cycle. Pulmonary circulation: deoxygenated blood goes from the right ventricle to the lungs and oxygenated blood returns to the left atrium. Systemic circulation: oxygenated blood goes from the left ventricle to body tissues and deoxygenated blood returns to the right atrium.

What are nitrogenous excretory products, and classify animals as ammonotelic, ureotelic, and uricotelic.

Ammonotelic animals excrete ammonia (most toxic, needs much water; e.g. bony fishes, aquatic amphibians). Ureotelic animals excrete urea (less toxic; e.g. mammals, many adult amphibians, marine fishes). Uricotelic animals excrete uric acid (least toxic, least water; e.g. reptiles, birds, insects, land snails).

Name the structural and functional unit of the kidney and its main parts.

The nephron is the structural and functional unit of the kidney (~1 million per kidney). Its parts are the Malpighian/renal corpuscle (glomerulus enclosed by Bowman's capsule) and the renal tubule (proximal convoluted tubule, loop of Henle, distal convoluted tubule, leading to the collecting duct).

List the three main steps of urine formation in the nephron.

(1) Glomerular filtration (ultrafiltration of blood in the glomerulus/Bowman's capsule forming filtrate), (2) Reabsorption (selective reabsorption of useful substances like glucose, amino acids, water, ions in the tubules), and (3) Secretion (tubular secretion of H+, K+, NH3 into the filtrate to maintain ionic and acid-base balance).

Differentiate the three types of muscle tissue (skeletal, smooth, cardiac).

Skeletal (striated) muscle: striated, multinucleate, voluntary, attached to bones. Smooth (visceral) muscle: non-striated, spindle-shaped, uninucleate, involuntary, in walls of internal organs. Cardiac muscle: striated, branched, uninucleate, involuntary, found only in the heart, with intercalated discs.

Name the proteins involved in muscle contraction and outline the sliding filament theory.

The main proteins are actin (thin filament), myosin (thick filament), and the regulatory proteins troponin and tropomyosin. By the sliding filament theory, muscle contraction occurs when actin (thin) filaments slide over myosin (thick) filaments; cross-bridges form, the sarcomere shortens, the H-zone and I-band shrink, but the A-band length stays constant. It requires Ca2+ and ATP.

Name the three types of skeletal joints (functional) with examples.

Fibrous (immovable) joints, e.g. the sutures of the skull; Cartilaginous (slightly movable) joints, e.g. between adjacent vertebrae; and Synovial (freely movable) joints, e.g. ball-and-socket (shoulder, hip) and hinge (knee, elbow) joints.

Describe the structure of a neuron and name its three parts.

A neuron is the structural and functional unit of the nervous system. Its three parts are: the cell body/cyton (contains nucleus and cytoplasm with Nissl's granules), dendrites (short branched processes that receive impulses), and the axon (a single long process that transmits impulses away from the cell body, often myelinated).

What is a resting membrane potential and an action potential in a neuron?

The resting potential is the polarised state of a non-conducting axon membrane (~ -70 mV, with more Na+/positive outside and K+/negative inside, maintained by the Na+/K+ pump). An action potential (nerve impulse) is a transient reversal (depolarisation) of this potential when Na+ rushes in, followed by repolarisation as K+ moves out.

How is a nerve impulse transmitted across a chemical synapse?

At a chemical synapse, the arriving impulse triggers Ca2+ influx into the pre-synaptic axon terminal, causing synaptic vesicles to release neurotransmitters (e.g. acetylcholine) into the synaptic cleft. These bind to receptors on the post-synaptic membrane, opening ion channels and generating a new impulse in the post-synaptic neuron.

Differentiate the central nervous system (CNS) and the peripheral nervous system (PNS).

The CNS consists of the brain and spinal cord and is the site of information processing and control. The PNS consists of all the nerves (cranial and spinal) connecting the CNS to body parts; it has an afferent (sensory) division carrying impulses to the CNS and an efferent (motor) division carrying impulses from the CNS to effectors.

Differentiate the sympathetic and parasympathetic nervous systems.

Both are divisions of the autonomic nervous system. The sympathetic system prepares the body for emergency 'fight or flight' responses (increases heart rate, dilates pupils, inhibits digestion). The parasympathetic system promotes 'rest and digest' activities (slows heart rate, constricts pupils, stimulates digestion) — they are antagonistic.

Name the major endocrine glands and one key hormone secreted by each.

Hypothalamus (releasing hormones), Pituitary (GH, TSH, ACTH, etc.), Thyroid (thyroxine/T4, T3), Parathyroid (PTH), Adrenal (adrenaline, cortisol), Pancreas (insulin, glucagon), Pineal (melatonin), Thymus (thymosin), and Gonads — testes (testosterone) and ovaries (estrogen, progesterone).

What is the difference between endocrine and exocrine glands?

Endocrine (ductless) glands secrete hormones directly into the blood, which act on distant target organs (e.g. thyroid, pituitary). Exocrine glands have ducts that carry their secretions (enzymes, sweat, saliva) to a specific site or surface (e.g. salivary glands, sweat glands). The pancreas is a mixed (heterocrine) gland.

Compare the actions of insulin and glucagon in blood glucose regulation.

Both are secreted by the islets of Langerhans of the pancreas. Insulin (from beta cells) lowers blood glucose by promoting cellular glucose uptake and glycogenesis (glucose → glycogen). Glucagon (from alpha cells) raises blood glucose by stimulating glycogenolysis (glycogen → glucose) and gluconeogenesis in the liver. They are antagonistic.

Which hormones regulate calcium balance in the body and how?

Parathyroid hormone (PTH) from the parathyroid glands raises blood calcium by stimulating bone resorption, increasing intestinal absorption (via vitamin D activation) and renal reabsorption. Calcitonin (from the thyroid) lowers blood calcium by suppressing bone resorption. They act antagonistically to maintain calcium homeostasis.

What hormones does the thyroid gland produce and what is their main function?

The thyroid gland produces thyroxine (T4) and triiodothyronine (T3), which contain iodine and regulate the basal metabolic rate (BMR), growth, and development. It also secretes thyrocalcitonin (TCT/calcitonin) which lowers blood calcium. Iodine deficiency causes goitre and hypothyroidism.

What is a reflex action and a reflex arc?

A reflex action is a rapid, automatic, involuntary response to a stimulus, not requiring conscious thought (e.g. knee-jerk). The reflex arc is the neural pathway involved: receptor → afferent (sensory) neuron → CNS (spinal cord, with an interneuron) → efferent (motor) neuron → effector (muscle/gland).

Name the three main parts of the human brain and a key function of each.

Forebrain (cerebrum — thinking, memory, intelligence, voluntary actions; plus thalamus and hypothalamus for homeostasis), Midbrain (controls visual and auditory reflexes), and Hindbrain (cerebellum — balance and coordination; pons; medulla oblongata — controls heartbeat, breathing, blood pressure).

What are the five kingdoms in Whittaker's system of classification?

R.H. Whittaker (1969) proposed five kingdoms: Monera (prokaryotes — bacteria), Protista (single-celled eukaryotes), Fungi (heterotrophic, cell wall of chitin), Plantae (multicellular autotrophs — plants), and Animalia (multicellular heterotrophs — animals). The criteria included cell structure, body organisation, mode of nutrition, and phylogeny.

What are guttation and transpiration, and how do they differ?

Transpiration is the loss of water as vapour from the aerial parts (mainly stomata) of a plant. Guttation is the loss of water in liquid (droplet) form from the margins/tips of leaves through special pores called hydathodes, occurring due to root pressure when transpiration is low (e.g. early morning).