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