IGCSE Biology summarized

IGCSE Biology Revision Notes

Introduction

  • Overview of key biological concepts.

  • Emphasizes the importance of a comprehensive understanding for achieving high grades.

  • Reminder about the availability of revision guides for in-depth study.

Characteristics of Living Organisms

  • Features Shared by All Living Organisms:

    • Movement

    • Respiration

    • Sensitivity (Response to stimuli)

    • Nutrition

    • Excretion

    • Reproduction

    • Growth (Becoming larger over time)

  • Non-living entities (e.g., viruses) do not exhibit these features—it can be specifically stated that they do not:

    • Move

    • Respire

    • Excrete

Cellular Biology

  • Main Concepts in Plant and Animal Cells:

    • Common Organelles:

    • Cell membrane

    • Cytoplasm

    • Nucleus

    • Ribosomes

    • Mitochondria

    • Specific to Plant Cells:

    • Cell wall (made of cellulose, provides protection and support)

    • Vacuole (filled with cell sap, maintaining cell structure)

    • Chloroplasts (contain chlorophyll for photosynthesis)

Function of Organelles

  • Nucleus: Controls cell activities.

  • Cytoplasm: Site of chemical reactions.

  • Cell Membrane: Regulates entry and exit of substances.

  • Ribosomes: Site of protein synthesis.

Distinction Between Cell Types

  • Eukaryotes are cells (e.g., animal and plant cells) that contain membrane-bound organelles.

  • Prokaryotes (e.g., bacteria and viruses) lack membrane-bound organelles, only have strands of DNA or RNA.

Bacterial Cells

  • Bacterial cells have:

    • Cell wall

    • Often a slime capsule

    • Flagella for movement

    • Nucleoid region (circular chromosome)

    • Plasmids (small rings of DNA)

  • Pathogenic vs. Non-Pathogenic Bacteria:

    • Pathogenic: Causes diseases (e.g., pneumococcus, tuberculosis).

    • Non-pathogenic: Beneficial (e.g., Lactobacillus bulgaricus in yogurt).

Viruses

  • Much smaller than bacteria, composed of a protein coat and either DNA or RNA.

  • Main Characteristics:

    • Non-living (cannot excrete, grow or respond)

    • Pathogenic (e.g., flu virus, HIV, tobacco mosaic virus).

Protists and Fungi

  • Protists:

    • Diverse group that may resemble either animal or plant cells (e.g., algae, amoeba).

    • Can be unicellular or multicellular (e.g., Plasmodium causing malaria).

  • Fungi:

    • Have a cell wall made of chitin, lack chloroplasts.

    • Nutrition: Saprotrophic (digestive enzymes secreted onto dead matter).

    • Example: Yeast (used in bread and beer) carries out anaerobic respiration to produce alcohol and CO2.

Levels of Organization in Organisms

  • Hierarchy:

    • Cell: Basic unit of life.

    • Tissue: Group of cells working together.

    • Organ: Group of tissues functioning together.

    • Organ System: Group of organs working together.

    • Organism: Full functional unit (all organ systems together).

Specific Organ Systems in Humans

  • Digestive System, Circulatory System, Respiratory System, etc.

Digestive Processes

  • Mechanical vs. Chemical Digestion:

    • Mechanics: Physical process (e.g., chewing).

    • Chemistry: Enzymatic breakdown of food.

  • Key Enzymes:

    • Amylase: Breaks starch into glucose (saliva, pancreas).

    • Protease: Breaks proteins into amino acids (stomach, pancreas).

    • Lipase: Breaks fats into fatty acids and glycerol.

Enzyme Activity

  • Factors Influencing Activity:

    • Temperature & pH: Enzymes have optimum temperatures and pH levels; extremes lead to denaturation.

  • Digestive Process Outline:

    1. Mouth (mechanical and amylase action).

    2. Esophagus (peristalsis).

    3. Stomach (hydrochloric acid and protease action).

    4. Small intestine (lipase, proteases, and amylase at a higher pH, absorption of nutrients).

Transport Mechanisms

  • Diffusion: Movement from high to low concentration (e.g., perfume scent in a room).

  • Osmosis: Movement of water from high water potential to low water potential across a selectively permeable membrane.

  • Active Transport: Movement against concentration gradient, requiring energy.

Photosynthesis

  • Process: Occurs in chloroplasts; uses light to convert CO2 and H2O into glucose and O2.

  • Word Equation: CO2 + H2O → Glucose + O2.

  • Balanced Equation: C6H{12}O6 + 6 O2
    ightarrow 6 CO2 + 6 H2O + ext{Energy}.

  • Limiting Factors: Light intensity, carbon dioxide levels, temperature.

Leaf Structure and Adaptation for Photosynthesis

  • Large surface area for light absorption;

  • Thin for easy gas diffusion;

  • Waxy cuticle to prevent water loss;

  • Stomata for gas exchange controlled by guard cells.

Plant Nutrition

  • Plants absorb water and minerals through roots, with specific requirements for magnesium and nitrates for chlorophyll and proteins respectively.

Respiration

  • Aerobic vs. Anaerobic: Aerobic requires O2 (efficient), anaerobic does not (less efficient, produces lactate in muscles or alcohol in yeast).

  • Equations for Respiration:

    1. Aerobic: C6H{12}O6 + 6 O2 → 6 CO2 + 6 H2O + ext{Energy}.

    2. Anaerobic in yeast: C6H{12}O6 → 2 C2H5OH + 2 CO2 + ext{Energy}.

Human Circulatory System

  • Heart Structure: 4 chambers—left/right atrium and left/right ventricle.

  • Blood Flow Pathway: Oxygenation cycle via pulmonary arteries and veins, systemic circulation through the aorta and vena cava.

  • Importance of Coronary Arteries: Supply oxygen to heart muscle; blockages lead to heart attacks.

Homeostasis

  • Mechanisms Used: Control of body temperature, hydration, and blood glucose levels.

Reproduction

  • Sexual vs. Asexual: Sexual involves genetic diversity through gametes, while asexual leads to genetically identical offspring.

  • Pollination Processes: Insects vs. wind pollination differentiated by flower structure and attraction mechanisms (e.g., color, scent).

Genetics and Evolution

  • Key Definitions: Gene, phenotype, genotype, homozygous, heterozygous, allele.

  • Mendelian Genetics: Understanding inheritance patterns through monohybrid and dihybrid crosses, Punnett squares, and pedigree diagrams.

Ecology

  • Ecosystem Components: Biotic (living things, including predators, prey, decomposers) and abiotic factors (temperature, pH, humidity).

  • Food Chains and Webs: Energy transfer depicted through pyramids of energy, biomass, and numbers.

Biodiversity and Conservation

  • Importance of Biodiversity: Ecosystem resilience and stability; human impact through pollution, habitat destruction, and conservation efforts highlighted.

Genetic Engineering and Biotechnology

  • Applications in agriculture and medicine, including insulin production, and characteristics of transgenic organisms.

Conclusion

  • Encouragement to engage with material through interactive study (revision guides) and clarification on intricate biological mechanisms covered herein.

  • Website for Revision Aids: www.cannainsider.com/itunes