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ICSE Class 11 Biology★ ISC Class 11 Biology · Internal assessment + foundation for ISC Class 12 · Board: ISC

Biology — Diversity, Cell Biology, Plant & Animal Physiology

ISC Class 11 Biology: The LIVING WORLD and biological classification. PLANT and ANIMAL KINGDOMS. CELL structure and cell division. PLANT PHYSIOLOGY — photosynthesis, respiration, transport. And HUMAN PHYSIOLOGY — digestion, respiration, circulation, excretion, nervous system. ISC Class 11 Biology.

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By the end of this chapter you'll be able to…

1Apply Whittaker's Five Kingdom classification to categorise organisms; distinguish plant kingdom divisions from Thallophyta to Angiosperms with key features
2Compare prokaryotic and eukaryotic cell structure; describe the function of each major organelle (mitochondria, chloroplast, ER, Golgi, lysosomes, ribosomes)
3Explain the stages and significance of mitosis and meiosis; distinguish their products, locations, and genetic outcomes
4Trace the complete biochemical pathway of photosynthesis (light reaction + Calvin cycle) and cellular respiration (glycolysis + Krebs cycle + ETC); compare C3 and C4 plants
5Describe the physiology of human digestion, respiration (lung volumes, gas transport), circulation (cardiac cycle, SA node), excretion (nephron), and nervous and endocrine systems

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Why this chapter matters

ISC Class 11 Biology builds the entire conceptual scaffold for Class 12. Biological classification (Five Kingdoms, plant divisions, animal phyla) anchors taxonomy questions. Cell biology — prokaryotic vs eukaryotic, organelle functions, mitosis vs meiosis — appears in both Class 11 tests and as prerequisite knowledge for Class 12 genetics. Plant physiology (photosynthesis light/dark reactions, C3 vs C4, plant hormones, photoperiodism) and human physiology (digestion, circulation, excretion, nervous system, endocrine glands) are the two largest content blocks and form the backbone of NEET biology.

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Class 10 Science: cell structure basics, digestive system, life processes

Biology — Diversity, Cell & Physiology

1. The Living World

Characteristics of Living Things

Growth. Reproduction. METABOLISM. Cellular organisation. Consciousness (response to stimuli). 'Metabolism is the DEFINING FEATURE — all living organisms exhibit it.'

Binomial Nomenclature (Carolus Linnaeus)

Genus + Species (Italics or underlined). Homo sapiens. Panthera tigris.

Taxonomic Hierarchy

Kingdom → Phylum/Division → Class → Order → Family → Genus → Species.

2. Biological Classification

Five Kingdoms (Whittaker, 1969)

Kingdom	Cell Type	Nutrition	Examples
Monera	Prokaryotic	Auto/Hetero	Bacteria, Cyanobacteria
Protista	Eukaryotic. Unicellular.	Auto/Hetero	Amoeba, Paramecium, Algae
Fungi	Eukaryotic. Chitin wall.	Saprophytic	Mushroom, Yeast, Mould
Plantae	Eukaryotic. Cellulose wall.	Autotrophic	From algae to flowering plants
Animalia	Eukaryotic. No wall.	Heterotrophic	All animals

Kingdom Plantae — Divisions

Thallophyta (algae). Bryophyta (mosses — amphibians of plant kingdom). Pteridophyta (ferns — first vascular plants). Gymnosperms (naked seeds — pine). Angiosperms (flowering plants — seeds in fruits. Monocots/Dicots).

Kingdom Animalia — Major Phyla

Ten phyla from PORIFERA (sponges) to CHORDATA (vertebrates). Chordates: Fish → Amphibians → Reptiles → Birds → Mammals.

3. Plant Kingdom — Detailed

Algae (Thallophyta)

Chlorophyll-bearing. Autotrophic. Aquatic. Body = THALLUS (no roots, stem, leaves). Economic importance: food (Spirulina), agar, algin (ice cream, toothpaste).

Bryophytes (Mosses, Liverworts)

'AMPHIBIANS of the Plant Kingdom' — need water for reproduction. First land plants. No true roots (rhizoids). No vascular tissue.

Pteridophytes (Ferns)

FIRST VASCULAR PLANTS (xylem and phloem). True roots, stem, leaves. Spores on underside of leaves.

Gymnosperms

'Naked seeds' — not enclosed in fruit. Cones. Needle-like leaves adapted to cold/dry. Pine, Cycas.

Angiosperms — Flowering Plants

Seeds ENCLOSED IN FRUIT. DOMINANT land plants. Monocot (1 cotyledon, parallel venation, fibrous roots — grass, rice). Dicot (2 cotyledons, reticulate venation, tap root — mango, bean).

4. Cell — The Unit of Life

Cell Theory (Schleiden, Schwann, Virchow)

All organisms made of cells. Cell = BASIC UNIT. Cells arise from PRE-EXISTING cells ('Omnis cellula e cellula').

Prokaryotic vs Eukaryotic

Feature	Prokaryote	Eukaryote
Nucleus	No true nucleus (nucleoid)	True nucleus with membrane
Organelles	No membrane-bound organelles	ER, Golgi, mitochondria, etc.
Ribosomes	70S	80S
Size	1-10 μm	10-100 μm

Eukaryotic Cell Organelles

Organelle	Function
Mitochondria	POWERHOUSE. Aerobic respiration. ATP. Double membrane. Own DNA.
Chloroplast	Photosynthesis. Double membrane. Own DNA.
ER (Endoplasmic Reticulum)	Rough (with ribosomes — protein synthesis). Smooth (lipid synthesis).
Golgi Apparatus	Packaging. Secretion.
Lysosomes	'Suicide bags.' Digest waste and foreign material.
Ribosomes	Protein synthesis.

Cell Division

Mitosis (Somatic cells)

IPMAT: Interphase → Prophase → Metaphase → Anaphase → Telophase → Cytokinesis. Result: 2 DIPLOID (2n) DAUGHTER CELLS — genetically IDENTICAL.

Meiosis (Germ cells — gametes)

Two divisions. Meiosis I (Reductional — homologues separate → 2n → n). Meiosis II (Equational — chromatids separate). Result: 4 HAPLOID (n) CELLS — genetically DIFFERENT (crossing over in Prophase I). Significance: GENETIC VARIATION. Maintains chromosome number across generations.

5. Plant Physiology

Photosynthesis

6CO₂ + 12H₂O →(Light, Chlorophyll)→ C₆H₁₂O₆ + 6O₂ + 6H₂O Two phases: Light Reaction (thylakoid membranes — light → ATP + NADPH + O₂). Dark Reaction / Calvin Cycle (stroma — CO₂ fixed using ATP and NADPH → glucose).

C3 vs C4 Plants

C3: First product = 3-carbon compound (PGA). Rice, wheat. C4: First product = 4-carbon (OAA). Maize, sugarcane. C4 plants are MORE EFFICIENT in hot/dry conditions — less photorespiration.

Respiration in Plants

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Glycolysis (cytoplasm — glucose → 2 pyruvate. Net 2 ATP).
Krebs Cycle (mitochondrial matrix — acetyl CoA → CO₂. NADH, FADH₂ produced).
Electron Transport Chain (inner mitochondrial membrane — NADH, FADH₂ → ATP. O₂ is final electron acceptor). ~34-36 ATP per glucose molecule.

Plant Growth and Development

Plant Growth Regulators: Auxins (cell elongation — phototropism). Gibberellins (stem elongation). Cytokinins (cell division). ABA (abscisic acid — stress, dormancy). Ethylene (fruit ripening).
Photoperiodism: Response to day length. SDP (short-day — flower when nights LONG). LDP (long-day — flower when nights SHORT).
Vernalisation: Cold treatment to induce flowering.

6. Human Physiology

Digestion and Absorption

Alimentary Canal: Mouth (saliva — amylase: starch → maltose) → Oesophagus → Stomach (HCl. Pepsinogen → Pepsin: proteins → peptides) → Small Intestine (BILE from liver/gall bladder — emulsifies fat. Pancreatic juice — trypsin, lipase, amylase. Intestinal juice — disaccharidases, peptidases. COMPLETE digestion → Absorption through VILLI) → Large Intestine (water, mineral absorption. E.coli produces vitamins) → Rectum → Anus.

Breathing and Respiration

Mechanism: Inspiration (diaphragm CONTRACTS → flattens. Rib cage EXPANDS. Lungs expand. Air enters). Expiration (diaphragm RELAXES. Rib cage contracts. Air expelled).
Lung Volumes: Tidal Volume (~500 mL). Vital Capacity (~3.5-4.5 L).
Gas Transport: O₂ carried by HAEMOGLOBIN (oxyhaemoglobin). CO₂ carried as: bicarbonate (~70%). Carbaminohaemoglobin. Dissolved in plasma.

Circulation

Heart: 4 chambers. Double circulation. Heartbeat ~72/min.
SA Node (pacemaker) → AV Node → Bundle of His → Purkinje fibres.
Cardiac Cycle: Systole (contraction ~0.3s). Diastole (relaxation ~0.5s).
Blood: RBCs (erythrocytes — O₂ transport). WBCs (leukocytes — immunity). Platelets (thrombocytes — clotting).

Excretion

Kidneys: Filters. Functional unit = NEPHRON.
Urine formation: Glomerular FILTRATION → Tubular REABSORPTION → Tubular SECRETION.
Osmoregulation: ADH (antidiuretic hormone) controls water reabsorption.

Nervous System

Neuron: Structural and functional unit. Dendrites (receive). Axon (transmits). Synapse (gap — neurotransmitter).
Central NS: Brain + Spinal Cord. Peripheral NS: Cranial + Spinal nerves.
Brain: Forebrain (Cerebrum — thinking, memory. Hypothalamus — homeostasis). Midbrain. Hindbrain (Cerebellum — balance. Medulla — heartbeat, breathing).

Endocrine System

Gland	Hormone	Function
Pituitary	GH, TSH, ACTH, ADH	'Master gland.'
Thyroid	T3, T4 (Thyroxine)	Metabolism. IODINE needed.
Adrenal	Adrenaline	Fight or flight. Cortisol (stress).
Pancreas	Insulin (↓glucose). Glucagon (↑glucose).	Blood sugar regulation.

Locomotion and Movement

Types of movement: Amoeboid (pseudopodia). Ciliary (trachea, oviduct). Muscular.
Muscle Types: Skeletal (striated, voluntary). Smooth (non-striated, involuntary — gut, blood vessels). Cardiac (striated, involuntary — heart).
Sliding Filament Theory: Actin (thin) and Myosin (thick) filaments SLIDE past each other. Ca²⁺ and ATP needed.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Biological Classification — Five Kingdoms (Whittaker, 1969)

MONERA: Prokaryotic, auto/heterotrophic (bacteria, cyanobacteria). PROTISTA: Eukaryotic, unicellular, auto/heterotrophic (Amoeba, Paramecium, algae). FUNGI: Eukaryotic, chitin wall, saprophytic (mushroom, yeast). PLANTAE: Eukaryotic, cellulose wall, autotrophic. ANIMALIA: Eukaryotic, no wall, heterotrophic. Plant divisions: Thallophyta (algae) → Bryophyta (mosses, no vascular tissue) → Pteridophyta (first vascular plants, ferns) → Gymnosperms (naked seeds, cones) → Angiosperms (seeds in fruit, monocots vs dicots).

Bryophytes = 'amphibians of the plant kingdom' — need water for reproduction. Pteridophytes = first true vascular plants (xylem + phloem). Angiosperms: Monocots (1 cotyledon, parallel venation, fibrous root — rice, wheat). Dicots (2 cotyledons, reticulate venation, tap root — mango, bean).

Cell Division — Mitosis vs Meiosis

MITOSIS (IPMAT): Interphase → Prophase → Metaphase → Anaphase → Telophase → Cytokinesis. Result: 2 diploid (2n) daughter cells, genetically IDENTICAL. Location: somatic (body) cells. Purpose: GROWTH and REPAIR. MEIOSIS: 2 divisions (Meiosis I = reductional; Meiosis II = equational). Result: 4 haploid (n) cells, genetically DIFFERENT (crossing over in Prophase I). Location: germ cells (gonads). Purpose: gamete formation; maintains chromosome number across generations.

Crossing over in Prophase I of meiosis = genetic recombination = source of genetic variation. Key distinction: Mitosis produces CLONES; meiosis produces VARIETY.

Photosynthesis and Respiration — Core Equations

PHOTOSYNTHESIS: 6CO₂ + 12H₂O → (Light, Chlorophyll) → C₆H₁₂O₆ + 6O₂ + 6H₂O. Light Reaction (thylakoid): Light → ATP + NADPH + O₂. Dark Reaction/Calvin Cycle (stroma): CO₂ + ATP + NADPH → glucose. C3 plants: first product = 3-carbon PGA (rice, wheat). C4 plants: first product = 4-carbon OAA (maize, sugarcane) — more efficient in hot/dry. RESPIRATION: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Glycolysis (cytoplasm): glucose → 2 pyruvate, net 2 ATP. Krebs Cycle (mitochondrial matrix): acetyl CoA → CO₂ + NADH + FADH₂. ETC (inner mitochondrial membrane): NADH/FADH₂ → ~34-36 ATP. O₂ = final electron acceptor.

Total ATP per glucose = ~36-38. Glycolysis occurs even without O₂ (anaerobic). Krebs Cycle and ETC require O₂ (aerobic only). C4 plants have LESS photorespiration — that is why they are more productive in hot climates.

Human Physiology — Key Systems

DIGESTION: Mouth (amylase: starch→maltose) → Stomach (HCl + pepsin: protein→peptides) → Small intestine (bile emulsifies fat; pancreatic juice — trypsin, lipase, amylase; complete digestion; villi absorb nutrients). GAS TRANSPORT: O₂ as oxyhaemoglobin. CO₂: 70% as bicarbonate, remainder as carbaminohaemoglobin. HEART: SA node (pacemaker) → AV node → Bundle of His → Purkinje fibres. Cardiac cycle: Systole ~0.3s, Diastole ~0.5s. KIDNEY (NEPHRON): Filtration → Reabsorption → Secretion. ADH controls water reabsorption. ENDOCRINE: Pituitary (GH, TSH, ADH — master gland), Thyroid (T3/T4 — metabolism, needs iodine), Adrenal (adrenaline — fight-or-flight), Pancreas (insulin ↓glucose, glucagon ↑glucose).

Muscle contraction: Sliding Filament Theory — actin (thin) and myosin (thick) filaments slide past each other, requiring Ca²⁺ and ATP. Three muscle types: Skeletal (striated, voluntary), Smooth (non-striated, involuntary), Cardiac (striated, involuntary).

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Saying mitosis and meiosis both produce 2 cells

✓ Mitosis produces 2 diploid daughter cells. Meiosis produces 4 haploid cells (via two sequential divisions). Also: mitosis = genetically identical cells; meiosis = genetically variable cells due to crossing over. Only meiosis occurs in reproductive organs to make gametes.

WATCH OUT

✗ Confusing the location of the light reaction vs Calvin cycle in chloroplasts

✓ The LIGHT REACTION occurs in the THYLAKOID MEMBRANES (grana) — produces ATP, NADPH, and O₂. The DARK REACTION (Calvin cycle) occurs in the STROMA (the fluid surrounding thylakoids) — uses ATP and NADPH to fix CO₂ into glucose. Remember: Light → thylakoid. Dark → stroma.

WATCH OUT

✗ Saying CO₂ is transported entirely by haemoglobin

✓ CO₂ is transported in three forms: (1) ~70% as BICARBONATE IONS (HCO₃⁻) in plasma — the dominant form. (2) ~23% as carbaminohaemoglobin (bound to haemoglobin but NOT to the iron — binds to protein part). (3) ~7% dissolved directly in plasma. Only O₂ binds to the iron of haemoglobin (forming oxyhaemoglobin).

Practice problems

Work through this chapter's problems as a readiness check — reveal each solution, mark yourself honestly, and get your gap report at the end.

Readiness check

Are you exam-ready for Biology — Diversity, Cell Biology, Plant & Animal Physiology?

3 problems from this chapter. Try each one, reveal the worked solution, mark yourself honestly — get your gap report at the end.

3 questions~2 min

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Five Kingdoms: Monera (prokaryotic), Protista (unicellular eukaryotic), Fungi (chitin, saprophytic), Plantae (cellulose, autotrophic), Animalia (no wall, heterotrophic).
•Bryophytes = amphibians of plant kingdom (need water for reproduction). Pteridophytes = first vascular plants.
•Mitosis: 2 diploid identical cells. Meiosis: 4 haploid varied cells. Crossing over in Prophase I = genetic variation.
•Cell Theory (Schleiden, Schwann, Virchow): cells from pre-existing cells — 'Omnis cellula e cellula.'
•Prokaryotes: 70S ribosomes, no membrane organelles. Eukaryotes: 80S ribosomes, membrane-bound organelles.
•Photosynthesis light reaction = thylakoid (O₂ + ATP + NADPH). Dark reaction = stroma (Calvin cycle → glucose).
•Respiration: Glycolysis (2 ATP, cytoplasm) → Krebs (NADH/FADH₂, matrix) → ETC (~34 ATP, inner membrane).
•C4 plants (maize, sugarcane) fix CO₂ via OAA first — more efficient in hot/dry, less photorespiration.
•SA node = pacemaker. Cardiac cycle: Systole 0.3s + Diastole 0.5s = 0.8s (72 beats/min).
•Nephron: Filtration (Bowman's capsule) → Reabsorption (tubules, ADH-regulated) → Secretion → Urine.

ICSE marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

C4 photosynthesis efficiency is the basis for engineering…

C4 photosynthesis efficiency is the basis for engineering 'super crops' — converting C3 rice to C4 to increase yield and drought tolerance

Understanding insulin-glucagon balance (endocrine system)…

Understanding insulin-glucagon balance (endocrine system) is the entire basis of diabetes management

Sliding filament theory (muscle physiology) guides physio…

Sliding filament theory (muscle physiology) guides physiotherapy and sports science training protocols

Nephron physiology underpins dialysis machine design for …

Nephron physiology underpins dialysis machine design for patients with kidney failure

Meiosis and crossing over are the genetic basis of all se…

Meiosis and crossing over are the genetic basis of all selective breeding, from crop improvement to animal husbandry

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

ISC Biology exams reward students who include LABELLED DIAGRAMS. For any 4+ mark question on a body system, draw and label first, then explain. For classification questions, use a table format (Kingdom / Cell type / Nutrition / Example). For physiology, use the sequence: Structure → Process → Product/Result. Distinguish mitosis and meiosis using a side-by-side comparison table — examiners consistently award full marks for this format. Memorise 2-3 key facts per organelle (function + disease/consequence if it fails).

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

STRETCH

Research the Endosymbiotic Theory (Lynn Margulis, 1960s) — mitochondria and chloroplasts were originally free-living prokaryotes engulfed by ancestral eukaryotic cells. Evidence: their own circular DNA, 70S ribosomes (like bacteria), double membranes, binary fission. This theory was rejected for decades before becoming accepted — a remarkable scientific revolution.

STRETCH

Investigate the Three Domain System (Carl Woese, 1990) — based on rRNA sequencing, life is divided into Bacteria, Archaea, and Eukarya. Archaea (extremophiles in hot springs, deep ocean vents) are as different from bacteria as they are from us. This replaces Whittaker's 5 Kingdoms in modern biology and has implications for the origin of life.

STRETCH

Explore C3, C4, and CAM photosynthesis pathways — adaptations to different climates. C3 plants (rice, wheat) lose efficiency in hot/dry conditions due to photorespiration. C4 plants (maize, sugarcane) concentrate CO₂ in bundle sheath cells, eliminating photorespiration. CAM plants (cacti, pineapple) open stomata only at night, conserving water. Investigate how this affects crop yields globally.

STRETCH

Research the Microbiome — trillions of bacteria living in and on us, outnumbering our own cells. The gut microbiome influences digestion, immunity, mental health (gut-brain axis), and even behaviour. Modern medicine is rediscovering microbes as essential to human health. How does this change our view of the 'human' as an organism?

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

ISC Class 11 Biology School Exam

ISC Class 12 Biology Board

NEET-UG Biology (50% of paper, directly aligned with ISC Bio)

KVPY SX Biology

AIIMS MBBS entrance

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LIGHT REACTION (Photo-chemical phase): Occurs in the THYLAKOID MEMBRANES. Requires LIGHT. Products: ATP, NADPH, and O₂ (from photolysis of water). The light energy is converted to chemical energy. DARK REACTION (Calvin Cycle / Biosynthetic phase): Occurs in the STROMA. Does NOT directly require light — but depends on ATP and NADPH from the light reaction. CO₂ is fixed (attached to a 5-carbon compound, RuBP) and reduced step-by-step to glucose. The enzyme RuBisCO catalyses CO₂ fixation. In C3 plants, the first stable product is a 3-carbon compound (PGA); in C4 plants, it is a 4-carbon compound (OAA).

Plant Growth Regulators (PGRs) are chemical messengers that regulate plant growth. Five major PGRs: (1) AUXINS: Produced at shoot tips. Cause CELL ELONGATION — responsible for phototropism (bending towards light) and gravitropism. (2) GIBBERELLINS: Cause STEM ELONGATION, break seed dormancy, trigger germination. (3) CYTOKININS: Promote CELL DIVISION. Delay leaf senescence (ageing). (4) ABSCISIC ACID (ABA): The 'stress hormone.' Causes STOMATAL CLOSURE during drought, induces SEED DORMANCY. Inhibits growth. (5) ETHYLENE: A GAS. Promotes FRUIT RIPENING, causes leaf and fruit ABSCISSION (falling). Used commercially to ripen bananas.

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