IGCSE Biology Notes

Ch. 1: Characteristics & Classification of Living Organisms

  • Living organisms share characteristics: Movement, Reproduction, Sensitivity, Growth, Respiration, Excretion, Nutrition (MRS GREN).
  • Respiration: Chemical reactions that break down nutrient molecules to release energy.
  • Metabolism: All chemical reactions inside cells, including respiration.
  • Excretion: Removal of metabolic waste, toxins, and excess substances.
  • Species: Organisms sharing appearance/behavior, interbreeding to produce fertile offspring.
  • Classification reflects evolutionary relationships using morphology, anatomy, and DNA sequencing.
  • Binomial Naming System: Genus (capitalized) and species (lowercase), underlined or italicized (e.g., Homo sapiens).
  • Five Kingdoms: Animals, Plants, Fungi, Protoctists, Prokaryotes (Bacteria).
  • Viruses: Non-living, reproduce inside host cells, made of DNA or RNA with a protein coat.

Ch. 2: Organisation of the Organism

  • All organisms are made of cells.
  • Cells → Tissues → Organs → Organ Systems → Organism.
  • Animal cells lack cell walls, chloroplasts, and large vacuoles; plant cells have these.
  • Cell Wall: Fully permeable.
  • Cell Membrane: Partially permeable, controls substance movement.
  • Chloroplasts: Photosynthesis.
  • Mitochondria: Aerobic respiration (Powerhouse of the cell).
  • Specialized Cells: Ciliated, root hair, xylem vessels, nerve, red blood, sperm, egg.
  • Magnification = Image size / Actual size (ensure same units).

Ch. 3: Movement Into and Out of Cells

  • Diffusion: Movement from high to low concentration, down the concentration gradient, passive process.
  • Factors affecting Diffusion: Temperature, surface area, concentration gradient, distance.
  • Active Transport: Movement from low to high concentration, against the concentration gradient, requires energy.
  • Osmosis: Net movement of water molecules from high to low water potential through a partially permeable membrane.

Ch. 4: Biological Molecules

  • Carbohydrates: C, H, O (H:O ratio is 2:1). Monosaccharides (e.g., glucose), disaccharides (e.g., sucrose), polysaccharides (e.g., starch, glycogen, cellulose).
  • Proteins: C, H, O, N (S in some). Made of amino acids. Important for growth, repair, enzymes, and antibodies.
  • Fats: C, H, O. Made of glycerol and fatty acids. Used for energy storage, insulation, and cell membranes.
  • Food Tests: Starch (iodine), reducing sugars (Benedict’s), proteins (Biuret), fats (ethanol emulsion).
  • Water: Solvent, transport.
  • DNA: Genetic material; double helix with bases A, T, G, C.

Ch. 5: Enzymes

  • Enzymes: Biological catalysts (proteins) that speed up reactions.
  • Lock and Key Hypothesis: Substrate fits into the enzyme's active site.
  • Factors Affecting Enzyme Action: Temperature, pH, surface area of the substrate.
  • Denaturation: Change in active site shape, usually irreversible.

Ch. 6: Photosynthesis

  • Photosynthesis: CO<em>2+H</em>2O→C<em>6H</em>12O<em>6+O</em>2CO<em>2 + H</em>2O _\rightarrow C<em>6H</em>{12}O<em>6 + O</em>2 (uses light energy).
  • Chlorophyll: Absorbs light energy.
  • Leaf Adaptations: Transparent cuticle, many stomata, palisade cells near surface with many chloroplasts.
  • Limiting Factors: Light intensity, carbon dioxide concentration, temperature.
  • Testing for Starch: Evidence of photosynthesis.

Ch. 7: Human Nutrition

  • Balanced Diet: Intake of nutrients in correct proportions.
  • Vitamins and Minerals: Needed for various body functions; deficiencies cause diseases.
  • Dietary Fiber: Stimulates peristalsis.
  • Alimentary Canal: Ingestion, digestion (physical & chemical), absorption, assimilation, egestion.
  • Teeth: Incisors, canines, molars, premolars.
  • Enzymes: Amylase, protease, lipase.
  • Liver:* Bile juice, Neutralizing acidity, Emulsification of fats into smaller globules.
  • Small intestine: Absorbs digested food, increased surface area, blood capillaries + lacteals.

Ch. 8: Transport in Plants

  • Xylem: Transports water and minerals (upwards).
  • Phloem: Transports sucrose and amino acids (bidirectional).
  • Transpiration: Water loss from leaves via evaporation and diffusion.
  • Factors affecting transpiration: Temperature, light intensity, humidity, wind speed.
  • Translocation: Movement of sucrose and amino acids from source to sink in phloem.

Ch. 9: Transport in Animals

  • Circulatory System: Heart, blood vessels, blood.
  • Heart: Muscular pump with four chambers (atria & ventricles).
  • Coronary Arteries: Supply heart muscle with blood.
  • Double Circulation: Blood passes through the heart twice per circuit.
  • Arteries: Thick, elastic walls. transport away from the heart
  • Veins: Thin walls, valves, return blood to the heart
  • Capillaries: One-cell-thick walls, exchange.
  • Blood: Red blood cells, white blood cells, platelets, plasma.

Ch. 10: Diseases and Immunity

  • Pathogen: Disease-causing microorganism.
  • Transmissible Disease: Spread from host to host.
  • Body Defenses: Mechanical and chemical barriers.
  • Immune Response: Antibodies secreted by lymphocytes to destroy pathogens.
  • Vaccination: Provides active immunity, stimulates production of Memory cells.
  • Active Immunity: Long term immunity & Involves immune response
  • Passive Immunity: Short term immunity & no immune response.
  • Transplant Rejection: Immune response against transplanted organ.
  • Cholera: Causes diarrhea; treated with oral rehydration therapy.

Ch. 11: Gas Exchange and Respiration

  • Trachea, bronchi, bronchioles, alveoli.
  • Alveoli: One-cell-thick walls & large surface area for efficient gas exchange.
  • Inhalation & Exhalation: Diaphragm and intercostal muscles.
  • Aerobic Respiration: Glucose + Oxygen → Carbon Dioxide + Water + Energy.
  • Anaerobic Respiration: (Muscles) Glucose → Lactic Acid + Energy; (Yeast) Glucose → Ethanol + Carbon Dioxide + Energy.
  • Breathing rate and heart rate remain high after exercise for -Supply more oxygen to pay off Oxygen debt & To provide the liver with extra oxygen for aerobic respiration of lactic acid

Ch. 12: Excretion

  • Excretion: Removal of metabolic waste.
  • Excretory Products: Urea (from deamination in liver) and carbon dioxide.
  • Urine Formation: Filtration, reabsorption, osmoregulation.

Ch. 13: Coordination and Response

  • Nervous System: Neurons transmit electrical impulses, synapses transmit chemicals.
  • Synapse : A junction between two neurones.
  • Eyes: Light receptors (rods & cones) in retina.
  • Lenses changes for accommodation & ciliary muscle contracts causing for near Accommodation and for long distance Ciliary muscle relaxes
  • Hormones: Chemical messengers secreted from endocrine glands, transported in blood.
  • Adrenaline increases heart rate and blood glucose concentration.
  • Homeostasis: Constant internal environment; maintained by negative feedback.
  • Blood glucose maintenance relies upon the pancreas that releases either Insulin or Glucagon which reach the liver( the Effectors)
  • Tropic Responses: Auxins cause phototropism (growth towards light) and gravitropism (growth with/against gravity).

Ch. 14: Drugs

  • Antibiotics: Treat bacterial infections (not viruses).
  • Must take treatment is completed to kill all bacteria & Avoid reuse in order to avoid higher chance for mutations.

Ch. 15: Reproduction

  • Asexual Reproduction: Genetically identical offspring from one parent.
  • Sexual Reproduction: Fusion of gametes to form a zygote with genetically variable offspring.
  • Pollination: Transfer of pollen from anther to stigma.
  • Fertilization: Fusion of gametes to form seed & Then seed is germinated for the new plants with the necessary conditions of water, oxygen & adequate temprature.
    *Sexually Transmitted Infections - Diseases transmitted from one person to another as a result of direct contact through body fluids (such as AIDS , sexually transmitted during sexual intercourse).

Ch. 16: Inheritance, Variation & Selection

  • Chromosomes: DNA-containing structures. & it is the genetic makup located inside the nucleus.
  • Gene: Sequence of DNA that codes for a specific characteristic.
  • Allele: Variant of a gene.
  • Two homozygous Dominant will lead to 100% results & To find for an unknown testcross with a recessif
  • Mitosis: Cell division that produces genetically identical cells (growth, repair).
  • Meiosis: Cell division that produces genetically distinct gametes with a smaller number of chromosomes
  • Variation: Differences among individuals of a species.
  • Mutation: Change in DNA sequence that alters the genes by ionizing radiation, tar & pesticides causing randoms effecf either can be positive or negitive.
  • Natural Selection: Organisms with advantageous traits survive and reproduce better than organisms without that trait. & For example, some bacteria are antibiotic resistant
    *Organisms (crops) with useful effects are selected for and genetically over multigenerational times by humans during artificial breeding ( artificial breeding also involved, artificial insemination & Invitro Fertiliation in order to maintain the breed & genetic traits)