CBSE Class 9 Biology Cheatsheet

Cheatsheet Content

The Fundamental Unit of Life - Cell Cell: Basic structural & functional unit of all living organisms. Discovery: Robert Hooke (1665) discovered cells in cork. Cell Theory: Schleiden & Schwann (1838-39). All organisms are made of cells. Cell is the basic unit of life. Rudolf Virchow (1855) added: All cells arise from pre-existing cells ($Omnis\ cellula\ e\ cellula$). Types of Cells: Prokaryotic Cells: No true nucleus, no membrane-bound organelles (e.g., Bacteria, Blue-green algae). Genetic material (nucleoid) is naked. Eukaryotic Cells: True nucleus with nuclear membrane, membrane-bound organelles (e.g., Plants, Animals, Fungi, Protists). Cell Organelles & Functions Cell Membrane (Plasma Membrane): Selectively permeable, controls passage of substances. Made of lipids and proteins. Cell Wall (Plants, Fungi, Bacteria): Rigid outer layer, provides structural support & protection. Made of cellulose in plants. Cytoplasm: Jelly-like substance, site of most cellular activities. Nucleus: "Control centre" of the cell. Contains chromosomes (DNA), nuclear membrane, nucleolus. Endoplasmic Reticulum (ER): Network of membranes. Rough ER (RER): Has ribosomes, involved in protein synthesis & transport. Smooth ER (SER): Lacks ribosomes, involved in lipid synthesis, detoxification, and storage of Ca2+. Ribosomes: Protein synthesis ("protein factories"). Present in both prokaryotes and eukaryotes. Golgi Apparatus (Golgi complex/body): Modifies, sorts, and packages proteins and lipids. Forms lysosomes. Lysosomes: "Suicidal bags" of the cell. Contain digestive enzymes to break down waste & cellular debris. Mitochondria: "Powerhouse of the cell." Site of cellular respiration, produces ATP (energy currency). Double-membraned. Plastids (Plants only): Chloroplasts: Contain chlorophyll, site of photosynthesis. Double-membraned. Leucoplasts: Store starch, oils, proteins. Chromoplasts: Give colour to fruits and flowers. Vacuoles: Storage sacs for water, nutrients, waste. Large central vacuole in plant cells provides turgidity. Osmosis & Diffusion Diffusion: Movement of particles from higher to lower concentration. (e.g., gases). Osmosis: Movement of water molecules through a selectively permeable membrane from higher water concentration to lower water concentration. Isotonic solution: No net movement of water. Cell size remains same. Hypotonic solution: Water enters cell, cell swells/bursts (animal), becomes turgid (plant). Hypertonic solution: Water leaves cell, cell shrinks (animal), plasmolysis (plant). Tissues Tissue: A group of cells similar in structure and function. Plant Tissues: Meristematic Tissue: Actively dividing cells, responsible for growth. Apical: At tips of roots & stems, increases length. Lateral (Cambium): Increases girth (width) of stem & root. Intercalary: At base of leaves/internodes, increases length (e.g., grasses). Permanent Tissue: Derived from meristematic tissue, lost ability to divide. Simple Permanent Tissue: Parenchyma: Living, thin-walled, loosely packed. Storage, photosynthesis (chlorenchyma), buoyancy (aerenchyma). Collenchyma: Living, thick at corners, provides flexibility & mechanical support. Sclerenchyma: Dead, thick-walled (lignified), provides strength & rigidity (e.g., husk of coconut). Fibres & Sclereids. Complex Permanent Tissue: More than one type of cell working together. Xylem: Conducts water & minerals from roots to leaves. Composed of tracheids, vessels, xylem parenchyma, xylem fibres. Phloem: Transports food (sugars) from leaves to other parts. Composed of sieve tubes, companion cells, phloem parenchyma, phloem fibres. Animal Tissues Epithelial Tissue: Covering or protective tissue. Forms lining of body cavities, organs. Squamous: Flat, delicate lining (e.g., oesophagus, mouth). Cuboidal: Cube-shaped, secretion & absorption (e.g., kidney tubules, salivary glands). Columnar: Pillar-like, secretion & absorption (e.g., intestine). Ciliated in respiratory tract. Glandular: Modified columnar/cuboidal cells, specialized for secretion. Connective Tissue: Connects various body parts. Cells are loosely spaced in an intercellular matrix. Areolar: Fills space inside organs, supports internal organs, repairs tissues. Adipose: Stores fat, acts as insulator. Bone: Hard, strong matrix of calcium & phosphorus compounds. Forms skeleton. Cartilage: Smooth, flexible matrix of proteins & sugars (e.g., nose tip, ear, trachea). Ligament: Connects bone to bone. Elastic. Tendon: Connects muscle to bone. Strong, inelastic. Blood: Fluid matrix (plasma) with RBCs, WBCs, Platelets. Transports gases, food, hormones, waste. Muscular Tissue: Responsible for movement. Contains contractile proteins (actin & myosin). Striated/Skeletal: Voluntary, attached to bones, striped appearance. Smooth/Unstriated: Involuntary, in internal organs (e.g., digestive tract, blood vessels), no stripes. Cardiac: Involuntary, only in heart, branched, rhythmic contraction & relaxation. Nervous Tissue: Transmits messages. Neuron: Basic unit. Composed of cell body (cyton), dendrites, axon. Neuroglia: Supporting cells. Improvement in Food Resources Sustainable Agriculture: Practices to meet food needs without harming environment or future generations. Green Revolution: Increased food grain production (wheat, rice) using HYV (High Yielding Varieties) seeds, fertilizers, irrigation. White Revolution: Increased milk production in India. Crop Production Management Nutrient Management: Manure: Organic matter (animal excreta, plant waste). Adds humus, improves soil structure. Fertilizers: Commercial plant nutrients (N, P, K). High nutrient content, but can cause water pollution. Irrigation: Supplying water to crops. Wells, canals, river lift systems, tanks, rainwater harvesting. Cropping Patterns: Mixed Cropping: Growing two or more crops together on same field. Inter-cropping: Growing two or more crops in definite row patterns. Crop Rotation: Growing different crops in succession on same field. Crop Protection Management: Weed Control: Manual removal, herbicides. Pest Control: Pesticides, biological control. Disease Control: Fungicides, resistant varieties. Storage: Proper drying, fumigation, temperature control, pest control. Animal Husbandry Scientific management of livestock. Cattle Farming: For milk (milch animals - cows, buffaloes) and draught labour. Indigenous breeds: Red Sindhi, Sahiwal. Exotic breeds: Jersey, Brown Swiss. Poultry Farming: For eggs (layers) and meat (broilers). Breeds: Leghorn (layers), Plymouth Rock (broilers). Fish Production: Capture fishing: From natural resources (oceans, rivers). Culture fishing (Aquaculture): Rearing fish in ponds. Mariculture: Culture of marine fish. Inland fisheries: From fresh water. Composite fish culture: Growing 5-6 species in one pond. Apiculture (Beekeeping): For honey and wax. Indian bee: Apis cerana indica. Italian bee: Apis mellifera (high honey yielding).