Biology IGCSE Triple Award Study Notes

1. The Nature and Variety of Living Organisms

a. Characteristics of Living Organisms

  • Movement: All living organisms move voluntarily or involuntarily.
  • Respiration: Biological process to release energy from food.
  • Sensitivity: Ability to respond to environmental stimuli.
  • Control Internal Conditions: Homeostasis processes regulate internal conditions.
  • Nutrition: Intake of substances for energy and growth.
  • Excretion: Removal of waste products from metabolic processes.
  • Reproduce: Ability to produce offspring to ensure species continuation.
  • Grow: Increase in size and mass over time.

b. Variety of Living Organisms

Definitions
  • Eukaryotic: Cells with membrane-bound organelles (e.g., animal cells which contain mitochondria, ribosomes, and a nucleus).
  • Prokaryotic: Cells lacking membrane-bound organelles, e.g., bacteria and viruses.
Common Structures in Animal and Plant Cells
  • Nucleus: Controls cell activities.
  • Cell membrane: Regulates entry and exit of substances.
  • Cytoplasm: Site of chemical reactions.
  • Mitochondria: Location of aerobic respiration, releasing energy.
  • Ribosomes: Sites of protein synthesis.
Plant Cell Unique Features
  • Vacuole: Contains cell sap, maintaining cell turgidity.
  • Chloroplasts: Site of photosynthesis.
  • Cell Wall: Provides protection and structural support, made of cellulose.

c. The 5 Kingdoms of Life

  1. Plants
  2. Animals
  3. Fungi
  4. Protoctists
  5. Bacteria

d. Definitions

  • Multicellular: Organisms made up of many cells.
  • Carbohydrate Storage:
      - Animals: Stored as glycogen.
      - Plants: Stored as starch.
      - Fungi: Stored as glycogen.
  • Saprotrophic Nutrition: Process in fungi where digestive enzymes are used externally to break down dead organic matter.
  • Pathogen: A micro-organism causing disease (includes viruses, bacteria, protoctists, fungi).
Pathogen Characteristics
  • Viruses: Non-living organisms with a protein coat surrounding DNA or RNA.
      - Cannot reproduce without a host cell.
  • Bacteria: May have a cell wall but no true nucleus.
  • Protoctist: Can be unicellular or multicellular, e.g., algae, amoeba.
  • Fungi: Usually multicellular, e.g., mushrooms, with structures called hyphae that form mycelium.

2. Structure and Functions in Living Organisms

a. Level of Organisation

  • Cell: Basic unit of life composed of organelles.
  • Tissue: A group of cells with a common function.
  • Organ: A structure composed of different types of tissues working together.
  • Organ System: A group of organs performing a shared function.
Main Plant Organs
  • Leaves, Roots, Stems, Flowers
Human Organ Systems
  1. Reproductive system
  2. Circulatory system
  3. Digestive system
  4. Gas exchange system
  5. Nervous system
  6. Excretory system
  7. Endocrine system
Organs in the Digestive System
  • Oesophagus, Stomach, Small intestine, Large intestine.

b. Cell Structure

Key Concepts
  • Zygote: A fertilised egg, the first cell of an organism.
  • Differentiation: Process of cells becoming specialized.
  • Stem Cell: Undifferentiated cell with potential to divide and differentiate.
Types of Stem Cells
  • Embryonic Stem Cells: Can differentiate into any cell type, found in early embryos.
  • Adult Stem Cells: Found in specific tissues, limited in differentiation (e.g., bone marrow).

c. Biological Molecules

Elements
  • Carbohydrates: Comprised of carbon, hydrogen, and oxygen.
  • Proteins: Composed of carbon, hydrogen, oxygen, and nitrogen (sulfur sometimes included).
  • Lipids: Made of carbon, hydrogen, and oxygen.
Lipid Structure
  • Composed of three fatty acids attached to a glycerol molecule.
Protein Composition
  • Made of long chains of amino acids (20 different amino acids).
Tests for Biological Molecules
  • Starch: Add iodine (positive result: blue/black).
  • Glucose: Heat with water and Benedict’s solution (positive result: brick red).
  • Protein: Add Biuret reagent (positive result: purple).
  • Fat: Add ethanol followed by water (positive result: milky white emulsion).

d. Movement of Substances Into and Out of Cells

Key Definitions
  • Diffusion: Movement of particles from high concentration to low concentration along a gradient.
  • Active Transport: Movement from low to high concentration requiring ATP.
  • Osmosis: Movement of water across a semipermeable membrane from high water potential to low water potential.
Biological Implications
  • Plant Cell Responses: In salty solutions, cells shrink (plasmolysis); in pure water, cells swell (turgid).
  • Animal Cell Responses: Bursts in pure water due to lack of a cell wall to contain it.

e. Nutrition

Plant Nutrition
  • Photosynthesis
      - Word Equation: Water + Carbon Dioxide (+ Light Energy) → Glucose + Oxygen
      - Balanced Symbol Equation: 6CO2+6H2O<br/>ightarrow6O2+C6H12O66CO_2 + 6H_2O <br /> ightarrow 6O_2 + C_6H_{12}O_6
Limiting Factors of Photosynthesis
  • Carbon dioxide levels, light intensity, temperature affect the rate of reaction.

f. Respiration

Definitions
  • Respiration: Process of converting glucose to energy.
  • Aerobic Respiration: Uses oxygen.
      - Equation: Oxygen + Glucose → Carbon Dioxide + Water + Energy
      - Symbol Equation: C6H12O6+6O2<br/>ightarrow6H2O+6CO2C_6H_{12}O_6 + 6O_2 <br /> ightarrow 6H_2O + 6CO_2
  • Anaerobic Respiration: Occurs without oxygen leading to incomplete glucose breakdown (e.g., in yeast and muscle cells).