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ICSE Class 9 Science★ ICSE Class 9 Biology · Full Year Coverage · Board: ICSE

Biology — Cell, Tissues, Diversity, Nutrition & Human Body Systems

The CELL — the fundamental unit of life. TISSUES — plant and animal. The MIND-BLOWING diversity of life. How plants and animals NUTRIFY themselves. The DIGESTIVE, SKELETAL, and RESPIRATORY systems. ICSE Class 9 Science.

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1State the 3 postulates of Cell Theory; distinguish prokaryotic from eukaryotic cells
2State the function of each major organelle: nucleus, mitochondria, ribosomes, ER, Golgi, lysosomes
3Distinguish plant from animal cells: cell wall, chloroplasts, vacuole size
4Name plant tissues: meristematic and permanent (simple: parenchyma/collenchyma/sclerenchyma; complex: xylem/phloem)
5Name 9 phyla of Animalia with key characteristics and examples
6Trace the 5 steps of human nutrition: Ingestion→Digestion→Absorption→Assimilation→Egestion
7Describe the digestive system: enzyme actions in mouth, stomach, and small intestine
8State the functions of the skeletal system; distinguish axial (80) from appendicular (126) skeleton
9Describe the mechanism of breathing: diaphragm and rib cage changes during inhalation and exhalation
10Distinguish biodegradable from non-biodegradable waste; state the 3 Rs

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Why this chapter matters

This ICSE Class 9 Biology chapter covers all major topics tested in the annual exam. The Cell Theory (3 postulates, Rudolf Virchow) and the prokaryotic vs eukaryotic comparison table are MCQ staples. Cell organelles with functions (mitochondria='powerhouse', lysosomes='suicide bags') appear in 3-4 mark questions every year. The Animalia phyla table (Porifera→Chordata) is a reliable 6-8 mark matching question. The nutrition steps (Ingestion→Digestion→Absorption→Assimilation→Egestion) and the digestive system organ-by-organ sequence are 4-5 mark questions. The respiratory mechanism (diaphragm contracts=inhale, relaxes=exhale) and the axial/appendicular skeleton (80/126 bones) are tested annually.

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Biology — Cell, Tissues, Diversity, Nutrition & Body Systems

1. The Cell — The Unit of Life

Cell Theory

All living organisms are made of CELLS.
The cell is the BASIC UNIT of structure and function.
All cells arise from PRE-EXISTING cells (Rudolf Virchow: 'Omnis cellula e cellula').

Prokaryotic vs. Eukaryotic

Feature	Prokaryotic	Eukaryotic
Nucleus	NO true nucleus (nucleoid)	TRUE nucleus with membrane
Organelles	No membrane-bound organelles	Has mitochondria, ER, Golgi, etc.
Size	Smaller (1-10 µm)	Larger (10-100 µm)
Example	Bacteria	Plant and animal cells

Plant vs. Animal Cell

Feature	Plant	Animal
Cell Wall	Present (cellulose)	Absent
Chloroplasts	Present	Absent
Vacuole	LARGE central vacuole	Small, temporary

Cell Organelles

Organelle	Function
Nucleus	Control centre. Contains DNA.
Mitochondria	POWERHOUSE. Site of respiration. Produces ATP.
Ribosomes	PROTEIN synthesis
Endoplasmic Reticulum (ER)	Transport network. Rough ER (with ribosomes). Smooth ER.
Golgi Apparatus	Packaging and secretion
Lysosomes	'Suicide bags.' Digest waste.

2. Tissues — Plant and Animal

Plant Tissues

Tissue	Location	Function
Meristematic	Root/shoot tips	CELL DIVISION. Growth.
Simple Permanent — Parenchyma	Soft parts	Storage, photosynthesis
— Collenchyma	Below epidermis	Flexible SUPPORT
— Sclerenchyma	Hard parts	STRENGTH. Dead cells.
Complex — Xylem	Vascular bundles	Transport WATER (up). Dead cells.
— Phloem	Vascular bundles	Transport FOOD (both ways). Living cells.

Animal Tissues (Review)

Type	Function	Examples
Epithelial	Covering/lining	Skin, gut lining
Connective	Support, connect	Bone, cartilage, blood, adipose
Muscular	Movement	Striated, smooth, cardiac
Nervous	Signal transmission	Neurons, brain, spinal cord

3. Diversity in Living Organisms

The Five Kingdoms (Whittaker)

Monera (bacteria). Protista (amoeba, algae). Fungi (mushroom, yeast). Plantae (plants). Animalia (animals).

Kingdom Plantae — Divisions

Thallophyta (algae). Bryophyta (mosses — amphibians of the plant kingdom). Pteridophyta (ferns — first vascular plants). Gymnosperms (naked seeds — pine, cycas). Angiosperms (flowering plants — seeds in fruits. Monocot and Dicot).

Kingdom Animalia — Phyla

Phylum	Characteristics	Examples
Porifera	Pore-bearing. No tissues.	Sponges
Cnidaria (Coelenterata)	Stinging cells. Radial symmetry.	Jellyfish, Hydra
Platyhelminthes	Flatworms. Bilateral symmetry.	Tapeworm, Planaria
Nematoda	Roundworms.	Ascaris (roundworm)
Annelida	Segmented body.	Earthworm, Leech
Arthropoda	Jointed legs. Exoskeleton. LARGEST phylum.	Insects, spiders, crabs
Mollusca	Soft body. Often shell.	Snail, Octopus
Echinodermata	Spiny skin. Radial symmetry (adults).	Starfish
Chordata	Notochord. Dorsal nerve cord.	Fish, Amphibians, Reptiles, Birds, Mammals

4. Nutrition

Modes of Nutrition

Autotrophic: Make own food. Plants (photosynthesis).
Heterotrophic: Depend on others. Animals (holozoic). Fungi (saprophytic). Parasites.

Nutrition in Humans — The Five Steps

Ingestion → Digestion → Absorption → Assimilation → Egestion.

The Digestive System

Mouth (saliva — amylase: starch → sugar). Stomach (HCl + pepsin: proteins → peptides). Small intestine (BILE from liver emulsifies fats. Pancreatic juices. Intestinal juices. COMPLETE digestion. Absorption through VILLI into blood). Large intestine (water absorption. Waste formation).

5. The Skeletal System

Functions

Support. Protection (skull protects brain. Rib cage protects heart/lungs). Movement (with muscles). Blood cell production (bone marrow).

The Human Skeleton

Axial (80 bones): Skull, vertebral column (backbone), ribs, sternum.
Appendicular (126 bones): Limbs and girdles.

Joints

Joint	Movement	Example
Ball and Socket	All directions	Shoulder, Hip
Hinge	One plane (like a door)	Elbow, Knee
Pivot	Rotation	Head-neck (atlas-axis)
Gliding	Sliding	Wrist, ankle

6. The Respiratory System

Why We Breathe

Every cell needs OXYGEN for cellular respiration: glucose + O₂ → energy (ATP) + CO₂ + H₂O. 'Breathing is the PHYSICAL process of taking in air. Respiration is the CHEMICAL process of releasing energy in cells.'

The Respiratory Organs

Nose → Pharynx → Larynx (voice box) → Trachea (windpipe) → Bronchi → Lungs (bronchioles → ALVEOLI — tiny air sacs. Gas exchange: O₂ into blood, CO₂ out).

Mechanism of Breathing

Inhalation: Diaphragm CONTRACTS (flattens). Rib cage EXPANDS. Lungs expand. Air rushes IN.
Exhalation: Diaphragm RELAXES. Rib cage contracts. Lungs compress. Air pushed OUT.

7. Waste Generation and Management

Types of Waste

Biodegradable: Decomposed by microorganisms. Vegetable peels, paper, wood.
Non-biodegradable: NOT decomposed. Plastic, glass, metals, e-waste.

The 3 R's: REDUCE. REUSE. RECYCLE.

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Cell, Tissues, Diversity, Nutrition, and Human Body Systems

CELL THEORY (3 POSTULATES): (1) All living organisms are made of CELLS. (2) The cell is the BASIC UNIT of structure and function. (3) All cells arise from PRE-EXISTING CELLS (Rudolf Virchow: 'Omnis cellula e cellula'). PROKARYOTIC vs EUKARYOTIC: Prokaryotic = NO TRUE NUCLEUS (nucleoid only), no membrane-bound organelles, smaller (1-10 μm), example: bacteria. Eukaryotic = TRUE nucleus with membrane, has organelles, larger (10-100 μm), examples: plants and animals. PLANT vs ANIMAL CELL: Plant = cell wall (cellulose) PRESENT + chloroplasts PRESENT + LARGE central vacuole. Animal = no cell wall, no chloroplasts, small/temporary vacuoles. ORGANELLES: Nucleus = control centre, contains DNA. Mitochondria = POWERHOUSE, site of respiration, produces ATP. Ribosomes = PROTEIN synthesis. Endoplasmic Reticulum = transport network (rough ER has ribosomes; smooth ER does not). Golgi Apparatus = packaging and secretion. Lysosomes = 'SUICIDE BAGS,' digest waste. PLANT TISSUES: Meristematic (root/shoot tips, cell division, growth). Simple Permanent: Parenchyma (storage, photosynthesis, living). Collenchyma (flexible support, living). Sclerenchyma (strength, DEAD cells, e.g., nutshells). Complex: Xylem (water transport UP, DEAD cells). Phloem (food transport both ways, living sieve tubes). FIVE KINGDOMS: Monera (bacteria, prokaryotic). Protista (amoeba, algae, unicellular eukaryotic). Fungi (chitin cell wall, saprophytic). Plantae (cellulose cell wall, autotrophic). Animalia (no cell wall, heterotrophic). ANIMALIA PHYLA: Porifera (pore-bearing, no tissues, sponges). Cnidaria (stinging cells, radial symmetry, jellyfish/hydra). Platyhelminthes (flatworms, bilateral symmetry, tapeworm). Nematoda (roundworms, ascaris). Annelida (segmented, earthworm/leech). Arthropoda (jointed legs, exoskeleton, LARGEST phylum, insects/spiders/crabs). Mollusca (soft body, often shell, snail/octopus). Echinodermata (spiny skin, radial symmetry in adults, starfish). Chordata (notochord, dorsal nerve cord, fish/amphibians/reptiles/birds/mammals). FIVE STEPS OF NUTRITION: INGESTION → DIGESTION → ABSORPTION → ASSIMILATION → EGESTION. DIGESTIVE SYSTEM: Mouth (saliva+amylase: starch→sugar). Stomach (HCl+pepsin: proteins→peptides). Small intestine (bile from liver emulsifies fats; pancreatic+intestinal juices complete digestion; VILLI absorb into blood). Large intestine (water absorption, waste). SKELETAL SYSTEM: 4 FUNCTIONS: Support, Protection, Movement (with muscles), Blood cell production (bone marrow). AXIAL skeleton: 80 bones (skull, vertebral column, ribs, sternum). APPENDICULAR skeleton: 126 bones (limbs and girdles). JOINTS: Ball-and-socket (shoulder, hip — all directions). Hinge (elbow, knee — one plane). Pivot (head-neck atlas-axis — rotation). Gliding (wrist, ankle). RESPIRATORY MECHANISM: INHALATION: diaphragm CONTRACTS (flattens) + rib cage EXPANDS → lungs expand → air rushes IN. EXHALATION: diaphragm RELAXES + rib cage contracts → lungs compress → air pushed OUT. CELLULAR RESPIRATION: glucose + O₂ → energy (ATP) + CO₂ + H₂O. WASTE: Biodegradable (decomposed by microorganisms: vegetable peels, paper). Non-biodegradable (NOT decomposed: plastic, glass, metals, e-waste). 3 Rs: REDUCE. REUSE. RECYCLE.

ICSE CLASS 9 BIOLOGY KEY TRAPS: (1) CELL THEORY: 'All cells from pre-existing cells' = Rudolf VIRCHOW (not Schleiden or Schwann, who stated the first two postulates). (2) XYLEM = DEAD cells (no cell contents at maturity). PHLOEM sieve tubes = LIVING. Sclerenchyma = also DEAD. (3) ARTHROPODA = LARGEST phylum of the animal kingdom (more species than all other phyla combined — insects alone make up ~75% of all animal species). (4) DIGESTION: BILE is made by the LIVER and stored in the GALL BLADDER — it EMULSIFIES fats (breaks them into droplets) but does NOT digest them with enzymes. Pancreatic enzymes actually digest fats. (5) DIAPHRAGM: CONTRACTS during INHALATION (it flattens, creating more space). Many students say 'relaxes' during inhaling — this is wrong. (6) AXIAL = 80 (head and trunk). APPENDICULAR = 126 (arms and legs). Total = 206 bones.

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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 the diaphragm relaxes during inhalation, or that bile digests fats

✓ TWO CORRECTIONS: (1) DIAPHRAGM DURING BREATHING: INHALATION: Diaphragm CONTRACTS (flattens/moves downward). Rib muscles contract (ribs move up and out). Chest volume INCREASES. Lung pressure FALLS. Air rushes IN (high pressure outside → low pressure inside). EXHALATION: Diaphragm RELAXES (returns to dome shape). Rib muscles relax. Chest volume DECREASES. Lung pressure RISES. Air pushed OUT. Memory aid: 'Breathing IN = muscles contract to MAKE SPACE. Breathing OUT = muscles relax, space disappears.' (2) BILE: Bile does NOT contain enzymes and does NOT digest anything chemically. It EMULSIFIES fats — breaks large fat globules into many small droplets. This INCREASES the surface area for lipase (the fat-digesting enzyme from the pancreas) to act on. Think of bile as a DETERGENT (it contains bile salts) that breaks up the fat — like washing-up liquid breaking up grease. The actual DIGESTION of fat is done by lipase.

Practice problems

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Q1MEDIUM· cell-organelles-digestion

Match the organelle to its nickname: (a) Mitochondria (b) Lysosomes (c) Ribosomes. Then describe what happens to a piece of bread (starch) from the moment it enters the mouth until its nutrients reach the blood.

▶ Show solution

ORGANELLE NICKNAMES: (a) Mitochondria = 'POWERHOUSE of the cell.' They are the site of CELLULAR RESPIRATION where glucose and oxygen are converted to ATP (energy), CO₂, and water. ALL energy-requiring activities in the cell depend on ATP from mitochondria. (b) Lysosomes = 'SUICIDE BAGS.' They contain powerful digestive enzymes that break down worn-out organelles, bacteria, and cell debris. When a cell dies, lysosomes may burst and digest the entire cell — hence the name. (c) Ribosomes = 'PROTEIN FACTORIES.' They are the site of PROTEIN SYNTHESIS — they read instructions from mRNA and assemble amino acids into proteins. JOURNEY OF BREAD (STARCH): (1) MOUTH: Bread is chewed (mechanical digestion). Saliva is released. Salivary AMYLASE begins breaking starch → maltose (a sugar). Bolus (food ball) formed. (2) STOMACH: Bolus enters stomach. HYDROCHLORIC ACID (HCl) creates acidic environment. PEPSIN breaks proteins → peptides. Starch digestion by amylase STOPS (amylase is inactivated by acid). (3) SMALL INTESTINE: BILE (from liver, stored in gall bladder) emulsifies any fats. PANCREATIC AMYLASE resumes starch → maltose. MALTASE in intestinal lining breaks maltose → GLUCOSE. Complete digestion of starch to glucose. VILLI (finger-like projections) absorb glucose into the blood through capillaries. Glucose enters the bloodstream and travels to all cells.

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