ALL of Edexcel IGCSE Biology 9-1 (Double Award) | 2026 ONWARDS! | SwH Learning

This video provides a comprehensive overview of Edexcel IGCSE Biology, focusing on key concepts, exam techniques, and past paper questions. **Characteristics of Living Organisms (MRS H GREN)** All living organisms share eight characteristics: * **M**ovement: Ability to change position. * **R**espiration: Chemical process releasing energy from food. The word equation is Oxygen + Glucose → Carbon Dioxide + Water + Energy (released). The balanced symbol equation is 6O2 + C6H12O6 → 6CO2 + 6H2O. * **S**ensitivity: Ability to respond to surroundings. * **H**omeostasis: Maintenance of a steady internal environment (e.g., body temperature, blood glucose, blood water levels). * **G**rowth: Increase in size and mass. * **R**eproduction: Increasing the number of organisms. * **E**xcretion: Removal of metabolic waste (e.g., sweat, carbon dioxide, urea). * **N**utrition: Obtaining and using food. **Classification of Organisms** Organisms are broadly divided into prokaryotes and eukaryotes. * **Eukaryotes**: Contain membrane-bound organelles (e.g., nucleus, chloroplasts, mitochondria). Examples include plant, animal, and fungi cells. * **Prokaryotes**: Do not contain membrane-bound organelles. Bacterial cells are a prime example, possessing a circular chromosome (nucleoid) and plasmids instead of a distinct nucleus. **Cell Structures and Functions** * **Animal Cell**: * **Nucleus**: Controls cell activities. * **Mitochondria**: Site of aerobic respiration (energy release). * **Cell membrane**: Controls substance entry and exit. * **Cytoplasm**: Where chemical reactions occur. * **Ribosomes**: Site of protein synthesis. * **Plant Cell**: Contains all animal cell organelles plus: * **Chloroplasts**: Site of photosynthesis (CO2 + Water + Light Energy → Glucose + Oxygen). * **Vacuole**: Filled with cell sap. * **Cellulose cell wall**: Protects and maintains cell shape. * **Bacterial Cell (Prokaryotic)**: * No distinct nucleus; contains a nucleoid and plasmids. * Cytoplasm, cell membrane, cell wall. * May have a flagellum for movement. * **Fungi Cell**: * Cell wall made of chitin. * Cell membrane, nucleus, cytoplasm, mitochondria, ribosomes. * Can be unicellular (yeast) or multicellular (mucor), with multicellular fungi forming hyphae and mycelium. * Saprotrophic nutrition: Secrete enzymes extracellularly to digest dead matter. * **Protoctists**: "Dustbin kingdom" – can be animal-like (amoeba) or plant-like (chlorella), unicellular or multicellular. Plasmodium causes malaria. * **Viruses**: Non-living because they don't exhibit all MRS H GREN characteristics (e.g., no homeostasis, respiration, excretion). * Structure: Protein coat surrounding DNA or RNA. * Always pathogenic (disease-causing). Examples: HIV, Tobacco Mosaic Virus (TMV). **Levels of Organization** * **Cell**: Group of similar organelles working together for a specific function. * **Tissue**: Group of similar cells working together for a specific function. * **Organ**: Group of similar tissues working together for the same function. * **Organ System**: Group of similar organs working together for the same function (e.g., digestive system, reproductive system). **Biological Molecules** * **Lipids (Fats)**: * Elements: Carbon, Hydrogen, Oxygen. * Structure: Three fatty acids and a glycerol. * Test: Add ethanol and water; milky white emulsion indicates presence. * **Proteins**: * Elements: Carbon, Hydrogen, Oxygen, Nitrogen (sometimes Sulfur). * Structure: Long chains of amino acids. * Test: Biuret reagent; blue (no protein) to purple (protein present). * Examples: Collagen, keratin, enzymes, hemoglobin. * **Carbohydrates**: * Elements: Carbon, Hydrogen, Oxygen. * Example: Glucose. * Glucose Test: Benedict's reagent + heat; blue (no glucose) to brick red (lots of glucose). * Storage: Starch (plants), Glycogen (animals, fungi). * Starch Test: Iodine; brown (no starch) to blue-black (starch present). **Enzymes** * **Metabolism**: Rate of chemical reactions in the body. * **Enzymes**: Biological catalysts that speed up reactions without being used up. Made of protein. * **Key Terms**: * **Substrate**: Substance acted upon by the enzyme. * **Active Site**: Specific site on enzyme where substrate binds. * **Enzyme-Substrate Complex**: Formed when substrate binds to active site. * **Optimum**: Condition for highest enzyme activity (temperature, pH). * **Denature**: Active site changes shape due to extreme temperature or pH, preventing substrate binding. * **Specificity**: Each enzyme fits only one specific substrate (lock and key model). * **Temperature Effect**: Increasing temperature initially increases kinetic energy and collision frequency, leading to higher reaction rate until optimum temperature. Beyond optimum, the enzyme denatures. * **pH Effect**: Enzymes have optimal pH ranges. Deviations from this range can cause denaturation. **Movement of Substances** * **Diffusion**: Net movement of a substance from high to low concentration (passive, no energy). * Factors increasing rate: Steep concentration gradient, large surface area, higher temperature, short diffusion distance. * **Active Transport**: Net movement of molecules from low to high concentration (against gradient, requires ATP/energy). Example: Glucose uptake in small intestine. * **Osmosis**: Net movement of water molecules from high water potential to low water potential across a partially permeable membrane. * **Partially permeable membrane**: Allows certain molecules (e.g., water) to pass, traps larger ones. * **High water potential**: Dilute solution, many water molecules. * **Low water potential**: Concentrated solution, few water molecules. * **Animal cells in pure water**: Water enters, cell swells and bursts (hemolysis for red blood cells) due to lack of cell wall. * **Animal cells in concentrated solution**: Water leaves, cell shrivels. * **Plant cells in pure water**: Water enters, cell becomes turgid (swollen) but does not burst due to cell wall. * **Plant cells in salt solution**: Water leaves, cell becomes flaccid and plasmolysed (cell membrane pulls away from cell wall). * **Investigation**: Potato cylinders in different salt concentrations. Measure percentage change in mass. Point where mass change is zero indicates isotonic solution (water potential of potato = solution). **Plant Nutrition (Photosynthesis)** * **Photosynthesis**: Carbon Dioxide + Water + Light Energy → Glucose + Oxygen. * Symbol equation: 6CO2 + 6H2O → C6H12O6 + 6O2. * Occurs in chloroplasts, mainly in palisade mesophyll of leaves. * **Limiting Factors**: Factors in shortest supply that limit the rate of photosynthesis (temperature, light intensity, CO2 concentration). * **Leaf Adaptations**: * Flat, large surface area for light absorption. * Thin for short diffusion distance. * Waxy cuticle prevents water loss. * Transparent upper epidermis allows light penetration. * Palisade mesophyll: Many chloroplasts for photosynthesis. * Spongy mesophyll: Air spaces for gas diffusion (CO2). * Stomata (on lower surface): Allow CO2 entry and water exit (transpiration). * Guard cells: Control stomata opening/closing to regulate water loss and CO2 intake. * Xylem: Transports water to leaves. * **Investigating Photosynthesis Rate**: Measure oxygen bubble production from pondweed at different light intensities. * **Starch Test in Leaves**: 1. Destarch plant (place in dark for 12+ hours). 2. Boil leaf (kill cells). 3. Boil in ethanol (remove chlorophyll, flammable, use water bath). 4. Wash in cold water. 5. Add iodine (brown → blue-black if starch present). * **Mineral Ions**: * Nitrate ions: Build plant protein. * Magnesium ions: Produce chlorophyll. **Balanced Diet and Digestion** * **Balanced Diet**: Provides all nutrients in correct amounts for life processes and health. * **Nutrients**: * **Carbohydrates**: Energy source (bread, pasta). * **Fats**: Concentrated energy, insulation (butter, cream). * **Proteins**: Growth and repair (meat, lentils). Deficiency: Kwashiorkor, marasmus. * **Water**: Solvent, supports chemical reactions. * **Fiber**: Roughage, aids peristalsis, prevents constipation (fruits, vegetables). * **Calcium**: Strong teeth and bones (dairy). Deficiency: Weak teeth/bones. * **Iron**: Hemoglobin component, oxygen transport (red meat, spinach). Deficiency: Anemia. * **Vitamin A**: Vision (fish liver oils). Deficiency: Night blindness. * **Vitamin D**: Strong teeth and bones (fish liver oils, sunlight). Deficiency: Rickets. * **Vitamin C**: Healthy gums (citrus fruits). Deficiency: Scurvy. * **Dietary Needs**: Vary with activity, lifestyle (e.g., sedentary vs. physical jobs, pregnancy, menstruation). * **Digestion**: Breakdown of large insoluble food molecules into small soluble ones for absorption. * **Mechanical Digestion**: Physical breakdown (chewing by teeth, stomach churning). * **Chemical Digestion**: Chemical alteration by enzymes (e.g., amylase in mouth digests starch). * **Digestive Pathway**: * **Mouth**: Mechanical (teeth), chemical (amylase). * **Esophagus**: Peristalsis moves food. * **Stomach**: Mechanical (muscle contraction), chemical (protease, HCl kills bacteria). * **Small Intestine**: Main site of chemical digestion and absorption. * Bile (from liver, stored in gallbladder): Emulsifies fats, neutralizes stomach acid. * Enzymes (from pancreas): Amylase, protease, maltase (maltose → glucose), lipase (lipids → fatty acids + glycerol). * Adaptations for absorption: Villi and microvilli (increase surface area), lacteal (fat absorption), rich blood supply, thin walls. * **Large Intestine**: Reabsorbs water. * **Rectum**: Stores feces. * **Anus**: Egestion (removal of feces). * **Key Definitions**: * **Ingestion**: Intake of food. * **Egestion**: Removal of feces. * **Excretion**: Removal of metabolic waste. * **Assimilation**: Buildup of large molecules from small ones. * **Absorption**: Movement of soluble food molecules into blood. **Respiration** * **Aerobic Respiration**: With oxygen. * Word equation: Oxygen + Glucose → Carbon Dioxide + Water + Energy (released). * Symbol equation: 6O2 + C6H12O6 → 6CO2 + 6H2O. * Energy (ATP) used for: Muscle contraction, active transport, assimilation, cell division, organelle manufacture. * **Gas Exchange in Lungs**: O