Comprehensive Study Notes: Cells, Organisation, Diversity, Ecosystem Dynamics, and Atomic Trends

Module 1: Cells as the Basis of Life

  • Types of Cells

    • Prokaryotic cells: No nucleus; small; simple (e.g., bacteria).
    • Eukaryotic cells: Nucleus present; more complex (e.g., plant and animal cells).

  • Viewing Cells (Microscopes)

    • Light microscopes: Use light to view specimens; limited resolution.
    • Electron microscopes: Use electron beams; higher magnification and resolution.

  • Enzymes

    • Factors affecting activity: Temperature, pH, substrate concentration.
    • Models of enzyme-substrate interaction:
    • Lock and Key model: enzyme is specific to its substrate.
    • Induced Fit model: enzyme changes shape slightly to accommodate substrate.

  • Transport Across Membranes

    • Passive transport: No energy; includes diffusion and osmosis.
    • Active transport: Requires energy (ATP) to move substances against a gradient.

  • Diffusion vs Osmosis

    • Diffusion: Movement of particles from high to low concentration.
    • Osmosis: Diffusion of water across a semi-permeable membrane.

  • Organelles & Their Functions

    • Nucleus: Controls cell activities.
    • Mitochondria: Site of cellular respiration (energy production).
    • Chemical equation for cellular respiration (overall):
      C<em>6H</em>12O<em>6+6O</em>2→6CO<em>2+6H</em>2O+ATP\text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + 6\text{O}</em>2 \rightarrow 6\text{CO}<em>2 + 6\text{H}</em>2\text{O} + \text{ATP}
    • Ribosomes: Protein synthesis.
    • Chloroplasts (plants): Photosynthesis.
    • Overall photosynthesis equation:
      6CO<em>2+6H</em>2O→C<em>6H</em>12O<em>6+6O</em>26\text{CO}<em>2 + 6\text{H}</em>2\text{O} \rightarrow \text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + 6\text{O}</em>2
    • Golgi apparatus: Modifies and packages proteins.
    • Endoplasmic Reticulum (ER): Transport within cells – smooth (lipids) and rough (proteins).
    • Lysosomes: Digestive enzymes.

  • Surface Area to Volume Ratio (SA:V)

    • High SA:V ratio = more efficient exchange of materials.
    • Note: For a sphere, SA=4πr2,V=43πr3,SA:V=SAV=3rSA = 4\pi r^2, \quad V = \frac{4}{3}\pi r^3, \quad SA:V = \frac{SA}{V} = \frac{3}{r}

  • Plasma Membrane: Fluid Mosaic Model

    • Structure: Phospholipid bilayer with embedded proteins; glycoproteins and cholesterol.
    • Function: Controls entry and exit of substances.

  • Module 2 starts here with Connections to Module 1 about Organisation of Cells, but the content continues as part of an integrated overview.

Module 2: Organisation of Cells

  • Vascular Systems (Animal and Plant Contexts)

    • Autotrophs: Make their own food (e.g., plants).
    • Heterotrophs: Consume other organisms.

  • Photosynthesis vs Respiration

    • Photosynthesis: CO<em>2+H</em>2O→C<em>6H</em>12O<em>6+O</em>2\text{CO}<em>2 + \text{H}</em>2\text{O} \rightarrow \text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + \text{O}</em>2 (in chloroplasts).
    • Respiration: C<em>6H</em>12O<em>6+6O</em>2→6CO<em>2+6H</em>2O+ATP\text{C}<em>6\text{H}</em>{12}\text{O}<em>6 + 6\text{O}</em>2 \rightarrow 6\text{CO}<em>2 + 6\text{H}</em>2\text{O} + \text{ATP} (in mitochondria).

  • Gas Exchange

    • Plants: Stomata.
    • Mammals: Alveoli in lungs.
    • Amphibians: Skin and lungs.
    • Insects: Tracheal system.

  • Cohesion-Tension Theory

    • Explains water movement in plants through xylem due to transpiration and cohesion of water molecules.

  • Classification & Structural Hierarchy

    • Unicellular: One cell (e.g., bacteria).
    • Multicellular: Many specialised cells (e.g., humans).
    • Colonial: Groups of identical cells (e.g., Volvox).
    • Structural Hierarchy: Cell → Tissue → Organ → System → Organism.

  • Gas & Nutrient Needs

    • Autotrophs: Need light, CO₂, water, minerals.
    • Heterotrophs: Need oxygen, water, and organic compounds.

  • Cell Specialisation

    • Cells develop specific structures/functions (e.g., nerve cells, muscle cells).

  • Circulatory Systems

    • Open: Blood not entirely in vessels (e.g., insects).
    • Closed: Blood always in vessels (e.g., humans).

  • Digestion in Mammals

    • Pathway: Mouth → Stomach → Small Intestine → Large Intestine.
    • Involves mechanical and chemical digestion.

  • Blood Composition

    • Varies with location in body:
    • Arteries: oxygen-rich.
    • Veins: CO₂-rich.
    • Capillaries: exchange of materials.

Module 3: Biological Diversity

  • Biotic & Abiotic Factors

    • Biotic: Living factors (predators, prey).
    • Abiotic: Non-living factors (temperature, sunlight).

  • Selection Pressures

    • Environmental factors that affect survival and reproduction (predators, disease, climate).

  • Types of Evolution

    • Convergent: Unrelated species evolve similar traits.
    • Divergent: Common ancestor evolves into different species.
    • Parallel: Related species evolve similarly.

  • Evolution Evidence

    • Fossils, DNA similarities, comparative anatomy, embryology.

  • Adaptations

    • Structural (e.g., fur for warmth).
    • Behavioural (e.g., migration).
    • Physiological (e.g., venom production).

  • Darwin & Wallace

    • Theory of natural selection: organisms with advantageous traits survive and reproduce.

  • Technology in Evolution

    • Carbon dating, DNA sequencing, comparative genomics.

Module 4: Ecosystem Dynamics

  • Sampling Techniques

    • Quadrats, transects, capture-recapture – for estimating population size and biodiversity.

  • Types of Adaptations

    • Structural, behavioural, physiological (see Module 3).

  • Ecosystem Relationships

    • Predator-prey: One eats the other.
    • Competition: Compete for resources.
    • Symbiosis:
    • Mutualism (both benefit)
    • Commensalism (one benefits, other unaffected)
    • Parasitism (one benefits, one harmed)

  • Working Scientifically Skills

    • Drawing a Graph: Title, labelled axes with units, appropriate scale, line of best fit.
    • Designing a Practical Investigation:
    • Reliability: Repeat trials.
    • Validity: Only one variable changed (fair test).
    • Accuracy: Use precise instruments and methods.
    • Scientific Models: Draw and annotate:
    • Fluid mosaic model, enzyme-substrate complex, cells, etc.
    • Fluid Mosaic Model of the cell membrane: clearly shows phospholipids, integral and peripheral proteins, glycoproteins, and cholesterol.

  • Ecosystem Food Web

    • Highlights trophic levels—producers, consumers, decomposers—and energy flow within ecosystems.

  • Darwin–Wallace Evolution Model

    • Visualizes natural selection, variation, and survival of the fittest.

  • Bonus Tips for Studying

    • Spaced repetition beats cramming.
    • Use a timer (Pomodoro) to stay focused.
    • Soft instrumental music or white noise can help study mood.
    • Study out loud or standing up to boost memory.

  • Additional notes on Cell Biology (repeated content for emphasis):

    • Prokaryotic vs Eukaryotic differences: nucleus presence, size, complexity.
    • Cell organisation: unicellular, colonial, multicellular.
    • Microscopy: light vs electron.
    • Organelles and their functions, including the plasma membrane and transport mechanisms.
    • Enzyme properties and models; SA:V importance; cell specialization; structural hierarchy.
    • Nutrient and gas needs for autotrophs and heterotrophs.

Fundamental Atomic Properties and Periodic Table Trends

  • Atomic Radius

    • Across a period (left to right): decreases. This is because the number of protons increases, pulling electrons closer to the nucleus.
    • Down a group (top to bottom): increases. Additional electron shells place outer electrons farther from the nucleus.
    • Elements in the bottom-left generally have the largest atomic radii.

  • Ionization Energy

    • Across a period: increases. More protons increase the attraction on electrons, making them harder to remove.
    • Down a group: decreases. Outer electrons are farther and more shielded from the nucleus.
    • Noble gases have very high ionization energies due to full outer shells; alkali metals have low ionization energies due to easily losing a single outer electron.

  • Electronegativity

    • Across a period: increases.
    • Down a group: decreases.
    • Rationale: more protons increase pull on bonding electrons; more shielding and distance reduce attraction.

  • Reactivity

    • Metals:
    • Increases down a group (more reactive as outer electron is farther from the nucleus and easier to lose).
    • Decreases across a period (more protons hold electrons more strongly).
    • Non-metals:
    • Increases across a period (stronger tendency to gain electrons to complete outer shells).
    • Decreases down a group (outer electrons are farther and less strongly attracted).
    • Examples:
    • Sodium (alkali metal) is highly reactive due to easy loss of its outer electron.
    • Halogens are highly reactive non-metals that readily gain one electron.
    • Fluorine vs Iodine: Fluorine is more reactive because it has fewer electron shells, allowing a stronger attraction to electrons.

  • Summary: The fundamental atomic properties—nuclear charge (protons), number of electron shells, and the resulting attraction/shielding—underlie periodic trends in atomic radius, ionization energy, electronegativity, and reactivity.

Notes on how to use these notes

  • Use the Q&A prompts at the end of each module to test recall.
  • Practice drawing the labeled diagrams of the plasma membrane, enzyme-substrate interactions, and the fluid mosaic model.
  • Revisit difficult topics with spaced repetition and active recall.