ISC Class 11 Biology Syllabus

What is venation? Differentiate reticulate and parallel venation.

Venation is the arrangement of veins and veinlets in a leaf lamina. Reticulate venation (network-like) is typical of dicots; parallel venation (veins run parallel) is typical of monocots.

What are the four main types of animal tissues?

Epithelial tissue (covering/lining), Connective tissue (binding/support, e.g., bone, blood, cartilage), Muscular tissue (contraction/movement) and Nervous tissue (impulse conduction).

What are the main types of plant tissues?

Meristematic tissue (dividing cells: apical, intercalary, lateral) and permanent tissue. Permanent tissue is divided into simple (parenchyma, collenchyma, sclerenchyma) and complex (xylem, phloem) tissues.

Differentiate parenchyma, collenchyma and sclerenchyma.

Parenchyma: thin-walled living cells for storage/photosynthesis. Collenchyma: living cells with thickened corners providing flexible mechanical support. Sclerenchyma: dead, thick lignified-walled cells (fibres and sclereids) providing rigid mechanical support.

What are the components of xylem and phloem?

Xylem: tracheids, vessels, xylem parenchyma and xylem fibres (conducts water/minerals upward). Phloem: sieve tube elements, companion cells, phloem parenchyma and phloem fibres (conducts food/sugars).

What is the basic structural plan and function of epithelial tissue?

Epithelial tissue consists of tightly packed cells resting on a basement membrane with little intercellular space; it provides protection, absorption, secretion and forms linings. Types include squamous, cuboidal, columnar, ciliated and glandular epithelium.

State the three main postulates of the Cell Theory and who proposed/modified it.

Proposed by Schleiden (plants) and Schwann (animals); modified by Rudolf Virchow. Postulates: (1) all living organisms are made of cells, (2) the cell is the basic structural and functional unit of life, (3) all cells arise from pre-existing cells (Omnis cellula-e cellula).

What is the key difference between prokaryotic and eukaryotic cells?

Prokaryotic cells (bacteria, cyanobacteria) lack a true membrane-bound nucleus and membrane-bound organelles; their genetic material lies free in the cytoplasm (nucleoid). Eukaryotic cells have a true nucleus and membrane-bound organelles.

What is the function of mitochondria and why is it called the 'powerhouse of the cell'?

Mitochondria are the sites of aerobic respiration that produce energy in the form of ATP, hence called the powerhouse of the cell. They are double-membraned; the inner membrane folds into cristae, and the matrix contains its own DNA and ribosomes.

What is the function of the endoplasmic reticulum (RER vs SER)?

Rough ER (RER), studded with ribosomes, synthesizes and transports proteins. Smooth ER (SER), lacking ribosomes, synthesizes lipids and steroids and helps in detoxification.

What is the function of the Golgi apparatus?

The Golgi apparatus (dictyosome) packages, modifies, processes and secretes materials (proteins and lipids). It is the site of formation of glycoproteins, glycolipids and lysosomes.

What are ribosomes and what are their two subunit sizes in pro- and eukaryotes?

Ribosomes are the sites of protein synthesis, made of rRNA and proteins, with no membrane. Prokaryotic ribosomes are 70S (50S + 30S) and eukaryotic ribosomes are 80S (60S + 40S).

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

Lysosomes are single-membrane organelles filled with hydrolytic (digestive) enzymes that digest carbohydrates, proteins, lipids and nucleic acids. They are called 'suicidal bags' because they can digest the cell's own components (autolysis).

What is the role of the nucleolus and chromatin in the nucleus?

The nucleolus is the site of ribosomal RNA (rRNA) synthesis and ribosome assembly. Chromatin is the network of DNA and histone proteins that condenses into chromosomes during cell division, carrying the genetic information.

Differentiate plant cells from animal cells (three points).

Plant cells have a cellulose cell wall, large central vacuole and chloroplasts (plastids); animal cells lack a cell wall and chloroplasts, have small/no vacuoles, and possess centrioles (which most higher plant cells lack).

What are the phases of the cell cycle?

Interphase (G1, S, G2) and the M phase (mitosis). G1 = growth; S = DNA synthesis/replication; G2 = preparation for division; M = nuclear and cell division. Most of the cycle is spent in interphase.

List the stages of mitosis (karyokinesis) in order.

Prophase, Metaphase, Anaphase, Telophase (followed by cytokinesis). Mnemonic: PMAT. In metaphase chromosomes align at the equator; in anaphase sister chromatids separate to opposite poles.

What is the significance of meiosis and how many divisions/cells does it produce?

Meiosis is reductional division producing four haploid daughter cells from one diploid cell through two successive divisions (meiosis I and II). It maintains chromosome number across generations and introduces genetic variation via crossing over and recombination.

What is crossing over and during which stage does it occur?

Crossing over is the exchange of segments between non-sister chromatids of homologous chromosomes, producing genetic recombination. It occurs during the pachytene stage of prophase I of meiosis.

What is the difference between mitosis and meiosis in terms of products?

Mitosis produces two genetically identical diploid daughter cells (equational division) for growth/repair; meiosis produces four genetically different haploid cells (reductional division) for gamete formation.

What are the three pathways of water/solute movement across roots toward the xylem?

Apoplast pathway (through cell walls and intercellular spaces), Symplast pathway (through cytoplasm via plasmodesmata), and Transmembrane pathway. The Casparian strip in the endodermis forces movement through the symplast.

Define osmosis, water potential, and the components of water potential.

Osmosis is the movement of water across a semipermeable membrane from higher to lower water potential. Water potential (Ψw) = Solute potential (Ψs, always negative) + Pressure potential (Ψp). Pure water has Ψw = 0 (highest).

What is transpiration and what is the transpiration pull (cohesion-tension) theory?

Transpiration is the loss of water vapour from aerial plant parts, mainly through stomata. The cohesion-tension/transpiration pull theory states that water is pulled up the xylem as a continuous column due to cohesion (water-water) and adhesion (water-wall) forces created by transpirational loss.

What are the criteria for an element to be classified as an essential mineral nutrient?

(1) The element must be absolutely necessary for normal growth and reproduction; (2) its requirement must be specific and not replaceable by another; (3) it must be directly involved in plant metabolism.

Differentiate macronutrients and micronutrients with examples.

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

What is biological nitrogen fixation and name the key enzyme?

Biological nitrogen fixation is the conversion of atmospheric N2 into ammonia by nitrogen-fixing organisms (e.g., Rhizobium in legume root nodules, Azotobacter). The enzyme is nitrogenase, which requires anaerobic conditions (protected by leghaemoglobin in nodules).

Write the overall balanced equation for photosynthesis.

6CO2 + 12H2O → (light, chlorophyll) → C6H12O6 + 6O2 + 6H2O. The water on the right shows that the O2 released comes from water (photolysis), not CO2.

What happens in the light reactions of photosynthesis and where do they occur?

Light reactions occur in the thylakoid membranes of chloroplasts. Light energy splits water (photolysis) releasing O2, and produces ATP (photophosphorylation) and NADPH via electron transport through Photosystems II and I.

What is the Calvin cycle (dark/light-independent reaction) and where does it occur?

The Calvin cycle (C3 cycle) occurs in the stroma of chloroplasts. It fixes CO2 using the enzyme RuBisCO onto RuBP, then uses ATP and NADPH to reduce it to glucose (G3P). Three turns fix one CO2; six turns make one glucose.

Differentiate C3 and C4 plants and their CO2 acceptors.

C3 plants fix CO2 directly via RuBisCO onto RuBP (5C), first product 3-PGA (3C). C4 plants (Kranz anatomy) first fix CO2 via PEP carboxylase onto PEP (3C) forming OAA (4C), concentrating CO2 in bundle sheath cells; they are more efficient and lack photorespiration.

Write the equation for aerobic respiration and the net ATP yield from one glucose molecule.

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy. Complete aerobic oxidation of one glucose yields a net of 36–38 ATP molecules (commonly stated as 38).

What are the four stages of aerobic respiration and where does each occur?

(1) Glycolysis — cytoplasm; (2) Pyruvate oxidation (link reaction) — mitochondrial matrix; (3) Krebs/citric acid cycle — mitochondrial matrix; (4) Oxidative phosphorylation/electron transport chain — inner mitochondrial membrane.

What is the respiratory quotient (RQ)? Give the RQ for carbohydrates, fats and proteins.

RQ = volume of CO2 released / volume of O2 consumed during respiration. RQ = 1 for carbohydrates, less than 1 (~0.7) for fats, and ~0.9 for proteins. For organic acids RQ is greater than 1.

What are the five major plant growth regulators (phytohormones) and one function of each?

Auxins (cell elongation, apical dominance), Gibberellins (stem elongation, seed germination, bolting), Cytokinins (cell division, delay senescence), Ethylene (fruit ripening, abscission — a gaseous hormone), and Abscisic acid (stress/stomatal closure, dormancy — the 'stress hormone').

Define plant growth and name the phases of growth.

Growth is an irreversible permanent increase in size of an organ or its parts or even of an individual cell. The three phases are the meristematic (cell division) phase, the elongation phase, and the maturation/differentiation phase.

What is photoperiodism and vernalisation?

Photoperiodism is the response of plants to the relative length of day and night (light periods) for flowering (short-day, long-day, day-neutral plants). Vernalisation is the promotion of flowering by exposure to low temperature (cold treatment).

What is the role of HCl and pepsin in the human stomach?

HCl creates an acidic medium (pH ~1.8), kills bacteria, and activates the inactive enzyme pepsinogen into pepsin. Pepsin then digests proteins into proteoses and peptones (smaller peptides).

Name the three pancreatic enzymes and the substrates they digest.

Trypsin/chymotrypsin (proteins → peptides), Pancreatic amylase (starch/polysaccharides → maltose), and Lipase (fats/triglycerides → fatty acids and glycerol). The pancreas also secretes nucleases for nucleic acids.

What is the function of villi and bile in digestion and absorption?

Villi are finger-like projections of the small intestine that increase surface area for absorption of digested nutrients. Bile (from the liver, stored in gall bladder) emulsifies fats into small droplets and activates lipase; it contains no digestive enzymes.

What is the difference between breathing and respiration?

Breathing (ventilation) is the physical/mechanical process of inhalation and exhalation of air. Respiration (cellular respiration) is the biochemical process of oxidizing food to release energy (ATP) within cells.

How is oxygen and carbon dioxide transported in human blood?

O2 is mainly transported as oxyhaemoglobin (~97% bound to haemoglobin), small amount dissolved in plasma. CO2 is transported mainly as bicarbonate ions (~70%), about 20–25% as carbamino-haemoglobin, and ~7% dissolved in plasma.

Describe the mechanism of inspiration in humans.

During inspiration the diaphragm contracts and flattens, and external intercostal muscles contract raising the ribs and sternum, increasing thoracic volume. This decreases intrapulmonary pressure below atmospheric pressure, so air flows into the lungs.

Define tidal volume, vital capacity and residual volume.

Tidal volume (TV): air inhaled/exhaled in normal breathing (~500 mL). Vital capacity (VC): maximum air a person can breathe out after maximum inspiration (ERV+TV+IRV). Residual volume (RV): air remaining in lungs after forceful expiration (~1100–1200 mL).

What is the composition of human blood?

Blood is a fluid connective tissue made of plasma (~55%, fluid matrix) and formed elements (~45%): erythrocytes (RBCs), leucocytes (WBCs) and thrombocytes (platelets). Plasma is ~90–92% water with proteins, ions and nutrients.

Trace the path of blood through the human heart (double circulation).

Deoxygenated blood: body → vena cava → right atrium → right ventricle → pulmonary artery → lungs. Oxygenated blood: lungs → pulmonary veins → left atrium → left ventricle → aorta → body. This is double circulation (pulmonary + systemic).

What is the cardiac cycle and normal heart rate?

The cardiac cycle is one complete heartbeat consisting of atrial systole, ventricular systole, and joint diastole, lasting about 0.8 seconds. The normal resting heart rate is about 72 beats per minute, pumping ~70 mL per beat (cardiac output ~5 L/min).

What is the role of the SA node in the heart?

The sino-atrial (SA) node, located in the right atrium, is the pacemaker of the heart; it generates the action potential that initiates and regulates the heartbeat. The impulse then passes to the AV node, bundle of His and Purkinje fibres.

Name the main nitrogenous excretory products and classify organisms by them.

Ammonia (ammonotelic — most toxic, e.g., bony fishes, aquatic animals), Urea (ureotelic — e.g., mammals, terrestrial amphibians), and Uric acid (uricotelic — least toxic/least water, e.g., birds, reptiles, insects).

What is the structural and functional unit of the kidney, and its main parts?

The nephron is the structural and functional unit of the kidney. Its parts: Bowman's capsule (with glomerulus = Malpighian/renal corpuscle), proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct.

What are the three main processes of urine formation?

(1) Glomerular filtration (ultrafiltration of blood in the glomerulus), (2) Tubular reabsorption (selective reabsorption of useful substances like glucose, water, ions), and (3) Tubular secretion (active secretion of wastes like H+, K+, ammonia into the filtrate).

What is the role of ADH in kidney function?

Antidiuretic hormone (ADH/vasopressin), from the posterior pituitary, increases water reabsorption in the distal tubule and collecting duct, producing concentrated urine and preventing diuresis. Its absence causes diabetes insipidus.

What are the three types of muscle tissue and their characteristics?

Skeletal (striated, voluntary, multinucleate — attached to bones), Cardiac (striated, involuntary, branched with intercalated discs — heart), and Smooth/visceral (non-striated, involuntary, spindle-shaped — walls of internal organs).

State the sliding filament theory of muscle contraction.

During contraction, the thin actin filaments slide over the thick myosin filaments toward the centre of the sarcomere. Cross-bridges of myosin heads attach to actin and pull it; the H-zone and I-band shorten while the A-band length stays constant. It requires Ca2+ and ATP.

How many bones are in the human skeleton, and what are the two divisions?

The adult human skeleton has 206 bones, divided into the axial skeleton (80 bones: skull, vertebral column, ribs, sternum) and the appendicular skeleton (126 bones: limbs and girdles).

Name the three types of joints with an example of each.

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

What is a neuron and its three main structural parts?

A neuron is the structural and functional unit of the nervous system. Its parts are the cell body (cyton/soma with nucleus), dendrites (receive impulses), and the axon (conducts impulses away from the cell body to the synapse).

Explain how a nerve impulse is transmitted across a synapse.

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

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

Resting potential is the polarized state (~ -70 mV, negative inside) maintained by the Na+/K+ pump when the neuron is not conducting. An action potential is the rapid depolarization (Na+ influx) and repolarization (K+ efflux) wave that travels along the axon as a nerve impulse.

What are the divisions of the human nervous system?

Central Nervous System (CNS: brain and spinal cord) and Peripheral Nervous System (PNS: cranial and spinal nerves). The PNS is further divided into somatic (voluntary) and autonomic (involuntary) systems; autonomic = sympathetic + parasympathetic.

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

Forebrain (cerebrum — intelligence, memory, voluntary actions), Midbrain (relay of visual/auditory reflexes), and Hindbrain (cerebellum — balance/coordination; medulla oblongata — controls heartbeat, breathing, blood pressure; pons).

What is the difference between endocrine and exocrine glands?

Endocrine (ductless) glands secrete hormones directly into the blood (e.g., pituitary, thyroid, adrenal). Exocrine glands secrete their products through ducts onto a surface or cavity (e.g., salivary, sweat, sebaceous glands).

What is the role of insulin and glucagon in blood sugar regulation?

Both are secreted by the islets of Langerhans of the pancreas. Insulin (beta cells) lowers blood glucose by promoting its uptake and conversion to glycogen. Glucagon (alpha cells) raises blood glucose by breaking down glycogen (glycogenolysis). Insulin deficiency causes diabetes mellitus.

Why is the pituitary gland called the 'master gland'?

The pituitary gland (hypophysis) is called the master gland because it secretes hormones (like TSH, ACTH, FSH, LH) that control and regulate the secretions of many other endocrine glands. It is itself controlled by the hypothalamus.

What hormones does the thyroid gland secrete and what is their function? Name a deficiency disorder.

The thyroid secretes thyroxine (T4) and triiodothyronine (T3), which regulate basal metabolic rate, growth and development; it also secretes calcitonin (lowers blood calcium). Iodine deficiency causes goitre; deficiency in children causes cretinism.

What are the hormones of the adrenal medulla and their effect?

The adrenal medulla secretes adrenaline (epinephrine) and noradrenaline — the 'emergency'/'fight-or-flight' hormones. They increase heart rate, blood pressure, blood glucose, alertness and breathing rate during stress.

Differentiate hormones from enzymes.

Hormones are chemical messengers secreted by endocrine glands, transported by blood, that regulate body functions and are not reused. Enzymes are biological catalysts (mostly proteins) that speed up biochemical reactions, act at the site of production, and are reusable/unchanged.