Preliminary Biology Comprehensive Study Guide

Cell Structure and Function

• Cell Theory Fundamentals:

  • All living organisms are composed of one or more cells.

  • Cells are the basic unit of structure and organisation in living organisms.

  • All cells arise from pre-existing cells.

• Prokaryotic versus Eukaryotic Cells:

  • Prokaryotic Cells:

  • Definition: Cells that lack a membrane-bound nucleus and membrane-bound organelles ($\text{PRO} = \text{NO NUCLEUS}$).

  • Size: Simplest and smallest organisms on Earth, typically measuring $0.1\,\mu\text{m} - 0.5\,\mu\text{m}$.

  • Genetic Material: DNA exists as single circular chromosomes or small external circular rings called plasmids.

  • Cellular Structures: Possess ribosomes, cytosol, plasma membrane, cell wall, pili (external hair-like structures), and flagella (used by motile bacteria for movement towards or away from external stimuli).

  • Method of Cell Replication: Binary fission.

  • Biological Domains: Includes organisms within the domains Bacteria and Archaea.

  • Eukaryotic Cells:

  • Definition: Cells containing a true membrane-bound nucleus ($\text{EU} = \text{TRUE NUCLEUS}$) housing linear DNA, as well as distinct membrane-bound internal organelles.

  • Size: Larger and more complex cells, typically ranging from $10\,\mu\text{m} - 100\,\mu\text{m}$.

  • Cellular Structures: Contain a complex network of membrane-bound organelles (mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, chloroplasts in plants/algae) working together to carry out cell functions.

  • Complexity: Can exist as unicellular organisms (e.g., Amoeba, Paramecium) or multicellular organisms (includes animals, plants, fungi, and algae).

  • Method of Cell Replication: Mitosis and Meiosis.

• Binary Fission Process:

  • Definition: The process of asexual reproduction where a single parent cell or organism divides into two independent daughter cells.

  • Steps in Binary Fission:

  1. Parent cell contains genetic material.

  2. Cellular DNA duplicates/replicates.

  3. Cytoplasm divides as a septum forms down the centre of the cell.

  4. Two genetically identical daughter cells are produced.

• Plant versus Animal Cells:

  • Structures Unique to Plant Cells:

  • Chloroplasts: Membrane-bound organelles containing chlorophyll for photosynthesis.

  • Cell Wall: Rigid outer structural layer made of cellulose surrounding the plasma membrane.

  • Large Central Vacuole: Large permanent vacuole providing turgor pressure and storage.

  • Structures Unique to Animal Cells:

  • Lysosomes: Spherical vesicles containing hydrolytic enzymes that break down waste and organic materials.

  • Small Temporary Vacuoles: Small, transient storage vesicles.

  • Structures Common to Both:

  • Nucleus, cell membrane, mitochondria, cytoplasm, ribosomes, endoplasmic reticulum, and Golgi apparatus.

• Microscopy Technologies for Cell Observation:

  • Key Terms:

  • Magnification: How far an optical instrument zooms in on a specimen.

  • Resolution: The ability to distinguish two points or objects as separate entities.

  • Light Microscope:

  • Optical Path: Light passes from light source $\rightarrow$ condenser lens $\rightarrow$ specimen $\rightarrow$ objective lens $\rightarrow$ ocular lens (eyepiece).

  • Specifications: Magnifies up to $1500\times$, resolution of approximately $200\text{ nm}$.

  • Advantages: Cheap, portable, easy to use, and views living or dead specimens.

  • Disadvantages: Low resolution; cannot view fine internal ultrastructure or tiny organisms like bacteria without specialized oil immersion lenses.

  • Fluorescence Microscope:

  • Mechanism: Fluorescent dyes attach to specific cellular components; high-intensity light targets the dyes, causing them to glow.

  • Advantages: Selectively highlights specific organelles and target structures.

  • Disadvantages: Expensive, requires specialized operator training, provides limited overall visual field.

  • Electron Microscopes:

  • Mechanism: Utilises beams of electrons and electromagnetic lenses instead of light rays and glass lenses.

  • Sample Condition: Dead or non-living specimens only due to requirement of vacuum environment.

  • Transmission Electron Microscope (TEM): Electrons pass through ultra-thin specimen section $\rightarrow$ produces high-resolution 2D image of internal organelle ultrastructure. Sensitive to vibration and very expensive.

  • Scanning Electron Microscope (SEM): Electrons bounce off the specimen surface coated in thin metal $\rightarrow$ produces detailed 3D surface images. Requires heavy metal coating, expensive, cannot view live specimens.

  • Stereo Microscope (Dissecting Microscope):

  • Mechanism: Uses low magnification ($10\times - 40\times$) to view the 3D surface of larger intact specimens (e.g., whole insects, plant leaves).

  • Advantages: Provides true 3D visual, requires minimal specimen preparation.

  • Disadvantages: Low magnification; unable to observe microscopic internal cell structures.

• Organelle Structure and Function:

  • Cytoplasm: The entire gel-like region and fluid cytosol inside the cell membrane excluding the nucleus.

  • Nucleus: Spherical double-membraned organelle containing DNA; serves as the control centre for cellular metabolic activities.

  • Plastids: Double-membraned organelles in plants that produce and store chemical compounds (e.g., chloroplasts, amyloplasts).

  • Chloroplast: Specialized oval plastid containing chlorophyll pigments; carries out photosynthesis.

  • Vacuoles: Membrane-bound storage spaces; large and central in plants (maintains turgor pressure), small and temporary in animals.

  • Cell Membrane: Phospholipid bilayer surrounding the cell; regulates substance passage in and out of cytosol.

  • Mitochondria: Double-membraned organelle with folded inner membrane (cristae) creating a large surface area for cellular respiration to generate ATP ("powerhouse of the cell").

  • Golgi Bodies (Golgi Apparatus): Stacks of flattened membrane sacs that chemically modify, sort, and package proteins and lipids into vesicles for transport.

  • Lysosomes: Membrane-bound vesicles containing hydrolytic digestive enzymes that break down worn-out organelles, waste products, and foreign matter.

  • Endoplasmic Reticulum (ER): Network of intracellular membranous tubules:

  • Smooth ER: Lacks ribosomes; synthesises lipids, phospholipids, and steroid hormones.

  • Rough ER: Studded with ribosomes; processes and folds proteins synthesized by ribosomes.

  • Ribosomes: Small non-membrane-bound structures composed of RNA and proteins; primary site of protein synthesis.

Scale Diagrams and Cell Measurement

• Microscopic Units and Scale Conversions:

  • Centimetre ($\text{cm}$): $1\text{ cm} = 1.0 \times 10^{-2}\text{ m}$ ($100\text{ cm in } 1\text{ m}$).

  • Millimetre ($\text{mm}$): $1\text{ mm} = 1.0 \times 10^{-3}\text{ m}$ ($1000\text{ mm in } 1\text{ m}$).

  • Micrometre ($\mu\text{m}$): $1\,\mu\text{m} = 1.0 \times 10^{-6}\text{ m}$ ($1,000,000\,\mu\text{m in } 1\text{ m}$).

  • Nanometre ($\text{nm}$): $1\text{ nm} = 1.0 \times 10^{-9}\text{ m}$ ($1,000,000,000\text{ nm in } 1\text{ m}$).

  • Unit conversion relationships:

  • $1\text{ mm} = 1000\,\mu\text{m}$

  • $1\,\mu\text{m} = 1000\text{ nm}$

• Calculating Actual Size and Scale Bars:

  • Formula for Scale Determination:     $\text{Scale} = \frac{\text{Actual size}}{\text{Drawing size}}$

  • Formula for Actual Length:     $\text{Actual length} = \frac{\text{Length of drawing}}{\text{Magnification}}$

  • Worked Calculation Example (Cheek Cell):

  • Given: Actual diameter of cheek cell = $60\,\mu\text{m}$; desired drawing diameter = $5\text{ cm}$.

  • Scale Calculation:       $\text{Scale} = \frac{60\,\mu\text{m}}{5\text{ cm}} = \frac{12\,\mu\text{m}}{1\text{ cm}}$

  • A scale bar measuring $1\text{ cm}$ on the drawing represents an actual distance of $12\,\mu\text{m}$.

  • Finding nucleus representation: If the actual nucleus size is $6\,\mu\text{m}$, its drawn length must be:       $\text{Drawn Nucleus Size} = \frac{6\,\mu\text{m}}{12\,\mu\text{m/cm}} = 0.5\text{ cm}$

Cell Membrane Structure and Transport

• The Fluid Mosaic Model:

  • Model describing the cell membrane structure as a fluid dynamic phospholipid bilayer containing a mosaic pattern of embedded proteins, carbohydrates, and lipids.

  • Phospholipid Structure: Composed of a hydrophilic (water-attracting) phosphate head containing charged groups, and two hydrophobic (water-repelling) fatty acid tails containing non-polar hydrocarbons.

  • Lipid Bilayer Formation: Hydrophilic heads face outward towards extracellular fluid and internal cytoplasm; hydrophobic tails line up face-to-face internally to isolate the cell core from aqueous solutions.

• Membrane Components and Functions:

  • Integral Proteins: Transmembrane proteins embedded completely across the phospholipid bilayer; act as transport channels or carrier proteins for polar/charged substances.

  • Peripheral Proteins: Proteins bound temporarily to the outer or inner surface of the bilayer; function in cellular recognition, structural anchorages, and enzymatic activity.

  • Glycoproteins: Proteins with carbohydrate chains attached facing extracellularly; critical for cell recognition, cell signaling, and immune system identification.

  • Glycolipids: Phospholipids with carbohydrate chains attached; stabilize cell membrane structure and assist in cell-to-cell recognition.

  • Cholesterol: Lipid interspersed between phospholipid tails; regulates membrane fluidity across varying temperature fluctuations.

• Types of Transport Across Cell Membranes:

  • Selective Permeability: The cell membrane restricts entry based on molecular size, charge, and lipid solubility.

• Passive Transport Mechanisms:

  • Runs with (down) the concentration gradient (from high concentration to low concentration); requires no metabolic cellular energy (ATP).

  • Diffusion: Net movement of solute particles from high to low concentration until equilibrium is reached.

  • Simple Diffusion: Direct, unassisted passage of small, non-polar molecules (e.g., $O_2$, $CO_2$) straight through the lipid bilayer. Permeable materials diffuse freely; impermeable materials cannot cross regardless of gradient strength.

  • Facilitated Diffusion: Passive movement of large, polar, or charged molecules across membrane via specific transmembrane proteins:

  • Channel Proteins: Water-filled pores that open/close to allow specific ions (e.g., $Na^+$, $K^+$) to pass.

  • Carrier Proteins: Bind specific molecules (e.g., glucose, amino acids), undergo a conformational shape change, and release the molecule on the opposite side.

  • Diffusion Rate Factors: A steep concentration gradient results in rapid movement; a shallow concentration gradient results in slower movement.

  • Osmosis: Net movement of solvent (water) molecules from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) across a selectively permeable membrane.

• Tonicity and Cellular Responses:

  • Solute: The chemical substance dissolved in a fluid.

  • Solvent: The liquid medium doing the dissolving (water in biological systems).

  • Isotonic Solution: Fluid with an equal solute concentration compared to cell cytoplasm. Net water movement is zero; cell maintains constant shape.

  • Hypotonic Solution: Fluid with a lower solute concentration (higher water potential) than cell cytoplasm. Water rushes into the cell:

  • Animal Cells: Influx of water causes cells to swell and burst (lysis / lysed).

  • Plant Cells: Influx of water creates internal pressure against rigid cell wall; cell becomes firm and turgid without bursting.

  • Hypertonic Solution: Fluid with a higher solute concentration (lower water potential) than cell cytoplasm. Water moves out of the cell:

  • Animal Cells: Loss of water causes cells to shrivel (crenation).

  • Plant Cells: Loss of water causes cell contents to shrink away from cell wall; cell becomes flaccid or plasmolysed.

• Active Transport Mechanisms:

  • Runs against the concentration gradient (from low concentration to high concentration); requires metabolic energy input in the form of Adenosine Triphosphate (ATP).

  • Individual Transporters: Transmembrane pump proteins (e.g., sodium-potassium pumps) utilize ATP to transport specific ions against gradients.

  • Bulk Transport: Transport of large particles, fluids, or macromolecular masses via vesicles:

  • Endocytosis: Plasma membrane invaginates around extracellular matter to form a vesicle, pulling material into cytoplasm. Includes phagocytosis (cellular eating) and pinocytosis (cellular drinking).

  • Exocytosis: Intracellular secretory vesicles fuse with plasma membrane to release cellular wastes or synthesized products (e.g., hormones, enzymes) out of the cell.

Surface Area to Volume Ratio and Cell Requirements

• Surface Area to Volume Ratio (SA:V):

  • Definitions:

  • Surface Area (SA): Total surface space on the exterior of an object ($\text{cm}^2$). For rectangular prisms: $\text{SA} = \text{Length} \times \text{Width} \times \text{number of sides}$.

  • Volume (V): Amount of three-dimensional space occupied by an object ($\text{cm}^3$). $\text{V} = \text{Length} \times \text{Width} \times \text{Height}$.

  • $\text{SA:V Ratio} = \frac{\text{Surface Area}}{\text{Volume}}$.

  • Efficiency Rules:

  • Cells require a HIGH SA:V ratio to efficiently exchange nutrients and metabolic wastes across the plasma membrane.

  • Smaller cells possess a substantially higher SA:V ratio than larger cells of the same shape.

  • Long, flattened, or thin cells possess a higher SA:V ratio than spherical cells of equivalent volume.

  • As a cell grows in size, its volume increases much faster than its surface area, causing SA:V to decrease; this limits maximum efficient cell size and forces cell division.

• Rate of Exchange Dynamics:

  • Concentration Gradient: Steeper concentration gradients produce faster movement toward low concentration areas in passive transport, but require more metabolic effort in active transport.

  • Temperature Effects: Higher thermal kinetic energy increases particle movement speed, increasing rates of passive diffusion and osmosis.

• Nutrient and Chemical Requirements of Cells:

  • Organic Compounds: Complex carbon- and hydrogen-containing molecules synthesized by living organisms. Function as energy sources and structural components.

  • Inorganic Compounds: Simple chemical substances derived from the non-living environment lacking long carbon-hydrogen chains.

  • Light versus Chemical Energy Sources:

  • Light Energy: Trapped by chlorophyll in photosynthetic organisms (plants, algae, cyanobacteria) to manufacture organic matter. Organisms utilizing light energy are autotrophs.

  • Chemical Energy: Stored in high-energy chemical bonds within organic molecules (carbohydrates, lipids, proteins). Organisms consuming organic matter to extract chemical energy via breakdown are heterotrophs.

• Summary of Cell Requirements:

Waste Management and Biomolecules

• Cellular Waste Product Removal:

  • Metabolic wastes are unwanted chemical by-products generated by intracellular biochemical pathways that must be removed to avoid cell toxicity.

• Major Biological Macromolecules (Biomolecules):

  • Carbohydrates: Composed of carbon, hydrogen, and oxygen ($\text{C}, \text{H}, \text{O}$). Used as primary short-term energy source, energy storage (starch, glycogen), and cell wall structural support (cellulose).

  • Lipids: Non-polar molecules composed of carbon, hydrogen, and oxygen ($\text{C}, \text{H}, \text{O}$). Used for long-term energy storage, cell membrane structural component (phospholipids), and signaling molecules (steroid hormones).

  • Proteins: Polymers composed of amino acid chains linked by peptide bonds containing carbon, hydrogen, oxygen, nitrogen ($\text{C}, \text{H}, \text{O}, \text{N}$). Serve structural roles in cytoskeleton/tissues and functional catalytic roles as biological enzymes.

  • Nucleic Acids: Complex polymers composed of nucleotide monomers (sugar, phosphate, nitrogenous base) containing $\text{C}, \text{H}, \text{O}, \text{N}, \text{P}$:

  • Deoxyribonucleic Acid (DNA): Contains hereditary genetic instructions controlling cell activities and protein expression.

  • Ribonucleic Acid (RNA): Translates DNA code to assist directly in protein synthesis.

Biochemical Processes: Photosynthesis and Respiration

• Adenosine Triphosphate (ATP) Energy Cycle:

  • ATP serves as the primary mobile chemical energy source inside cells.

  • Structure: Composed of adenosine bound to three phosphate groups via high-energy chemical bonds.

  • Energy Release Mechanism: When cell activity requires energy, the terminal high-energy phosphate bond is hydrolysed, releasing chemical energy, a free inorganic phosphate group ($\text{P}_i$), and converting ATP into Adenosine Diphosphate (ADP).     $\text{ATP} \xrightarrow{\text{energy release}} \text{ADP} + \text{P}_i + \text{Free Energy}$

• Photosynthesis:

  • Definition: An endergonic biochemical pathway where autotrophic organisms trap solar light energy using chlorophyll pigments and convert it into chemical energy stored within glucose molecules.

  • Word Equation:     $\text{carbon dioxide} + \text{water} \xrightarrow{\text{light energy, chlorophyll}} \text{glucose} + \text{oxygen}$

  • Balanced Chemical Equation:     $6\text{CO}_2 + 6\text{H}_2\text{O} \xrightarrow{\text{light energy, chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

• Two Stages of Photosynthesis:

  1. Light-Dependent Stage (Photolysis): Occurs within the thylakoid grana of chloroplasts. Absorbed solar light energy is used to split water molecules ($\text{H}_2\text{O}$) into oxygen gas ($\text{O}_2$) and hydrogen ions ($\text{H}^+$), generating ATP.

  2. Light-Independent Stage (Carbon Fixation / Calvin Cycle): Occurs within the fluid stroma of chloroplasts. Hydrogen ions and ATP produced in stage 1 combine with carbon dioxide ($\text{CO}_2$) through enzymatic reactions to synthesize glucose ($\text{C}_6\text{H}_{12}\text{O}_6$).

  • Cellular Respiration:

• Definition: The catabolic pathway converting chemical energy stored in nutrient molecules (glucose) into usable ATP energy for cell work.

• Aerobic Respiration: Occurs in the presence of oxygen within cell mitochondria. Breaks down glucose completely, yielding a high net energy output ($36 - 38\text{ ATP}$).     $\text{glucose} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water} + 36\text{-}38\text{ ATP}$     $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{-}38\text{ ATP}$

• Anaerobic Respiration (Fermentation): Occurs in the absence of oxygen within the cell cytoplasm. Incompletely breaks down glucose, yielding a small net output ($2\text{ ATP}$):

  • Alcohol Fermentation (Yeasts/Plants): $\text{Glucose} \rightarrow \text{Ethanol} + \text{Carbon Dioxide} + 2\text{ ATP}$.

  • Lactic Acid Fermentation (Animals): $\text{Glucose} \rightarrow \text{Lactic Acid} + 2\text{ ATP}$.

• Interdependence: Photosynthesis products ($\text{C}_6\text{H}_{12}\text{O}_6$ and $\text{O}_2$) serve as cellular respiration reactants; cellular respiration products ($\text{CO}_2$ and $\text{H}_2\text{O}$) serve as photosynthesis reactants.

  • Secretion versus Excretion:

• Excreted Materials: Metabolic toxic waste products leaving the cell entirely (e.g., $\text{CO}_2$, urea).

• Secreted Materials: Useful metabolic substances synthesized by cells and released to function externally elsewhere (e.g., hormones, digestive enzymes, neurotransmitters).

• Synaptic Secretion Mechanism: Neurotransmitters contained in membrane-bound secretory vesicles migrate to presynaptic cell membrane, dock, fuse, and rupture to discharge chemical contents into the extracellular synaptic gap via exocytosis.

Enzymes and Enzyme Kinetics

• Enzyme Properties and Function:

  • Enzymes are specialized globular protein molecules acting as organic biological catalysts.

  • Catalyst Definition: A chemical substance that speeds up the rate of a chemical reaction without undergoing permanent chemical alteration or being consumed in the reaction.

  • Mode of Action: Enzymes lower the reaction's required activation energy (the initial energy required to break bonds and start a reaction).

  • Specificity: Every enzyme possesses a uniquely folded 3D active site that binds exclusively to specific target molecule(s) called substrates.

• Enzymatic Process Steps:

  1. Substrates collide with and enter the active site of a specific enzyme.

  2. Binding forms an unstable temporary enzyme-substrate complex.

  3. Chemical bonds in the substrate are strained, weakened, broken, or synthesized.

  4. New chemical products are released; the unaltered enzyme active site becomes free to repeat the process.

• Specific Enzyme Examples:

  • Lipase: Catalyses breakdown of lipids/fats into glycerol and fatty acid tails.

  • Pepsin (Protease): Catalyses breakdown of proteins into polypeptide chains and amino acids.

  • Amylase (Carbohydrase): Catalyses breakdown of complex starch carbohydrates into simple glucose sugars.

• Models of Enzyme Action:

  • Lock-and-Key Model: Older historic model proposing that the enzyme active site possesses a rigid, non-flexible shape that fits the substrate key precisely.

  • Induced-Fit Model: Currently accepted model proposing that the active site is flexible; upon binding, the active site undergoes minor conformational changes to mold snugly around the substrate.

• Factors Affecting Enzyme Activity:

  • Temperature:

  • Low Temperatures: Kinetic energy of enzyme and substrate molecules is low, resulting in fewer effective collisions and slow reaction rates. Enzymes are inactive, not denatured.

  • Optimum Temperature: Temperature at which collision rate and catalytic speed reach maximum velocity.

  • High Temperatures: Thermal energy disrupts hydrogen bonds holding the enzyme's 3D tertiary protein shape, permanently altering active site structure. The enzyme becomes denatured, substrate can no longer fit, and activity permanently drops to zero.

  • pH (Acidity/Alkalinity):

  • Every enzyme exhibits maximum catalytic efficiency at a specific optimum pH (e.g., pepsin at pH 2, amylase at pH 7).

  • Deviations above or below optimum pH alter ionic charges on amino acid side chains, disrupting hydrogen bonding and denaturing the 3D active site shape.

  • Substrate Concentration:

  • Increasing substrate concentration increases reaction rate due to increased collision frequency between substrate and active site.

  • Rate increases up to the saturation point, where all available enzyme active sites are continuously occupied catalysing reactions.

  • Beyond saturation point, further substrate additions do not increase reaction rate. The only way to increase rate further is to add more enzyme.

Organisation of Living Things

• Levels of Cellular Organisation:

  • Unicellular Organisms:

  • Single-celled organisms responsible for executing all life functions independently within one cell.

  • Can be prokaryotic (e.g., bacteria) or eukaryotic (e.g., Paramecium, Amoeba).

  • Metabolic reactions in prokaryotes are limited by lack of membrane-bound organelles; eukaryotic unicells achieve high metabolic efficiency via organelle compartmentalization.

  • Feeding mechanisms: Engulf food via pseudopodia (Amoeba) or sweep food into oral grooves/gullets.

  • Waste expulsion: Contractile vacuoles pump out excess water and metabolic waste.

  • Locomotion: Movement achieved via beating cilia, flagella, or cytoplasmic streaming in pseudopodia.

  • Colonial Organisms:

  • Collections of individual single-celled organisms living joined together in inter-dependent groups or colonies.

  • Individual cells can survive independently if separated, but display rudimentary cell specialization and coordination within the colony.

  • Examples: Volvox algae colonies, coral polyps, and Physalia (Portuguese man-o'-war / bluebottle jellyfish containing feeding gastrozooids).

  • Multicellular Organisms:

  • Complex organisms consisting of millions to trillions of highly specialized, differentiated cells organized into tissues, organs, and body systems.

  • Individual specialized cells lose ability to survive independently.

• Hierarchical Structural Organisation:

  • Organelles: Subcellular structures performing specialized tasks (e.g., mitochondria generating ATP).

  • Cells: Specialized structural units displaying unique shapes and biochemical features optimized for specific roles (e.g., biconcave red blood cells lacking nuclei packed with hemoglobin for optimal oxygen transport).

  • Tissues: Groups of similar specialized cells performing a specific collective function (e.g., elongated muscle tissue capable of contraction and expansion to generate movement).

  • Organs: Structure composed of distinct tissue types working together to perform vital metabolic functions (e.g., heart composed of muscle, nerve, and connective tissue).

  • Systems: Groups of interdependent organs working collectively to carry out major body processes (e.g., circulatory system containing heart, blood, and blood vessels).

  • Organism: Integrated living individual composed of interconnected organ systems. All systems are interdependent; failure of one system causes systemic death.

Plant Structure, Function, and Transport Systems

• Autotrophic Plant Requirements and Organs:

  • Autotrophs synthesize organic molecules via photoautotrophy (light energy) or chemoautotrophy (chemical oxidation energy in lightless environments like hydrothermal vents).

  • Plant Structures:

  • Roots: Anchor plant into soil substrate; absorb water and dissolved inorganic mineral ions via specialized root hair cells that increase surface area.

  • Stems: Provide structural support; house vascular tissues for transport.

  • Leaves: Primary organ for light interception and photosynthesis.

• Microscopic and Macroscopic Leaf Anatomy:

  • Cuticle: Exterior waxy layer secreted by epidermis; waterproofs leaf surface to prevent evaporative water loss.

  • Epidermis: Outermost cellular layer protecting underlying leaf tissue layers.

  • Stomata: Microscopic pores located predominantly on lower leaf epidermis, bounded by pairs of specialized guard cells that swell or shrink to regulate pore opening/closing for gas exchange ($\text{CO}_2$ in, $\text{O}_2$ out) and transpiration control.

  • Palisade Mesophyll: Densely packed column-shaped cells located under upper epidermis packed with chloroplasts; main site of photosynthesis.

  • Spongy Mesophyll: Loosely organized cells with extensive intercellular air spaces to facilitate gaseous diffusion throughout leaf interior.

  • Vascular Bundles: Plant transport strands containing xylem, phloem, and cambium tissue.

  • Cambium: Meristematic tissue layer producing new xylem and phloem cells during secondary growth.

• Vascular Transport Tissues:

  • Xylem:

  • Structure: Non-living, hollow continuous tubes formed from dead vessel elements and tracheids reinforced with tough lignin rings.

  • Function: Transports water and dissolved mineral ions unidirectionally upward from roots to leaves.

  • Phloem:

  • Structure: Living vascular tissue consisting of elongated sieve tube cells (lacking nuclei and organelles, separated by perforated sieve plates) supported by adjacent companion cells containing nuclei and organelles to regulate metabolic transport.

  • Function: Transports organic sugars (glucose/sucrose) and amino acids bidirectionally from source tissues to consumer sinks.

• Transport Theories in Plants:

  • Cohesion-Tension Theory (Transpiration Stream):

  • Explains passive upward movement of water in xylem.

  • Transpiration: Evaporation of water vapour through open stomata creates negative pressure (tension) at leaf surface.

  • Cohesion: Strong hydrogen bonding causes water molecules to stick tightly to one another, forming an unbroken water column.

  • Adhesion: Water molecules stick to hydrophilic walls of xylem vessels.

  • Root Pressure: Osmotic entry of water into root tissues pushes water column upward from base.

  • Source-to-Sink Theory (Translocation):

  • Explains active movement of sugars through phloem.

  • Sugar Loading: Glucose produced in photosynthetic leaves (source) is actively pumped into sieve tube cells by companion cells.

  • Osmotic Influx: High sugar concentration inside phloem draws water passively from adjacent xylem by osmosis, creating high hydrostatic pressure.

  • Mass Flow: High pressure forces nutrient-rich phloem sap to flow toward low-pressure region (sink: growing roots, fruit, flowers).

  • Unloading: Sugar is actively removed at sink for storage/respiration; water exits phloem back to xylem by osmosis.

• Imaging Technologies for Plant Study:

  • Magnetic Resonance Imaging (MRI): Uses radio waves and magnetic fields to generate 3D spatial images tracking internal water dynamics and transport flow in live stems.

  • X-Ray Computed Microtomography (Micro-CT): Rotates specimen within X-ray beams to produce high-resolution non-destructive 3D digital reconstructions of internal cellular architecture.

Animal Systems and Gas Exchange

• Gas Exchange Structures in Animals:

  • Common Requirements: Respiratory surfaces must possess a large surface area, be extremely thin (short diffusion path), be moist (gases must dissolve to diffuse), and maintain a steep concentration gradient via close contact with transport networks.

  • Mammalian Respiratory System:

  • Path: Air enters nose/mouth $\rightarrow$ trachea (windpipe supported by flexible cartilaginous rings) $\rightarrow$ main bronchi $\rightarrow$ branching bronchioles $\rightarrow$ microscopic alveoli clusters.

  • Alveoli: Microscopic air sacs wrapped in capillary networks. Walls are one cell thick, providing a massive surface area for rapid passive gas exchange ($\text{O}_2$ diffuses into blood, $\text{CO}_2$ diffuses out).

  • Protective Structures: Ciliated epithelial cells and goblet cells secreting mucus line airways to trap and sweep away inhaled debris and pathogens.

• Fish Respiratory System:

  • Gills: External respiratory structures containing delicate gill filaments covered in primary and secondary lamellae.

  • Counter-Current Exchange: Water flows across gill filaments in the opposite direction to blood flow within lamellar capillaries. Maintains a steep concentration gradient along the entire contact length, maximizing oxygen extraction from water.

  • Mammalian Digestion System:

• Physical (Mechanical) Digestion:

  • Mouth: Teeth cut, tear, and grind large food chunks into smaller pieces to increase surface area for enzyme action.

  • Stomach: Smooth muscle contractions churn food with gastric juices into acidic liquid chyme via peristalsis.

• Chemical Digestion:

  • Enzymatic cleavage of complex polymers into absorbable monomers:

    • Carbohydrases (Salivary/Pancreatic Amylase): Complex carbohydrates $\rightarrow$ simple disaccharides and glucose sugars.

    • Proteases (Pepsin/Trypsin): Complex proteins $\rightarrow$ peptide chains and amino acids.

    • Lipases: Emulsified lipids $\rightarrow$ glycerol and fatty acid molecules.

• Absorption and Elimination:

  • Small Intestine: Primary site of chemical digestion and nutrient absorption. Inner walls folded into microscopic villi and microvilli to maximize SA:V ratio.

  • Large Intestine: Absorbs remaining water, salts, and vitamins; consolidates indigestible waste into feces.

  • Rectum and Anus: Stores and expels feces from body via egestion.

  • Mammalian Circulatory Systems:

• Closed Circulatory System: Blood remains strictly enclosed within continuous blood vessels pumped by a central heart. Ensures rapid, high-pressure transport of nutrients, gases, and wastes.

• Heart Anatomy and Double Circulation:

  • Composed of 4 chambers: 2 superior receiving atria and 2 inferior pumping ventricles.

  • Left Ventricle: Possesses thick, highly muscular walls because it must contract with immense force to pump oxygenated blood throughout systemic body circulation.

  • Deoxygenated Blood Path: Right Atrium $\rightarrow$ Right Ventricle $\rightarrow$ Pulmonary Artery $\rightarrow$ Lungs (oxygenated).

  • Oxygenated Blood Path: Pulmonary Vein $\rightarrow$ Left Atrium $\rightarrow$ Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Systemic Body Tissues.

  • Valves: Flap-like structures preventing backflow of blood between chambers and exiting vessels.

• Blood Vessels:

  • Arteries: Thick, muscular, elastic walls; carry blood away from heart under high hydraulic pressure.

  • Veins: Thin walls, wide lumen, contain internal one-way valves; carry blood towards heart under low pressure.

  • Capillaries: Microscopic walls exactly one cell thick; site of nutrient, gas, and fluid exchange with body cells.

• Blood Composition:

  • Plasma: Fluid matrix making up $55\%$ of total blood volume ($90\%$ water); carries dissolved nutrients, glucose, $\text{CO}_2$, urea, hormones, and proteins.

  • Red Blood Cells (Erythrocytes): Biconcave discs lacking nuclei; packed with iron-containing hemoglobin protein to bind and transport oxygen.

  • White Blood Cells (Leukocytes): Large nucleated cells involved in immune defence and fighting infections.

  • Platelets: Cell fragments responsible for blood clotting.

Biological Diversity and Selection Pressures

• Environmental Selection Pressures:

  • Selection Pressures: External environmental factors that alter the survival and reproductive success of individuals within a population, driving natural selection.

  • Abiotic Pressures (Non-living): Temperature fluctuations, solar light availability, rainfall/water access, salinity levels, soil/water pH, water clarity, oxygen/gas concentrations.

  • Biotic Pressures (Living): Availability of food, competition for resources, mate availability, predator density, pathogen/disease prevalence.

  • Impact: Abiotic and biotic pressures govern the geographical distribution (where species live) and abundance (population size) of organisms.

• Aquatic versus Terrestrial Environmental Pressures:

• Case Studies of Selection Pressures in Australia:

  • Prickly Pear (Opuntia):

  • Introduced into Australia from Americas to establish a cochineal dye industry.

  • Prickly pear thrived due to favorable warm climate, abundant land, and total absence of natural biological predators, causing population explosion across millions of hectares.

  • Introduced Biological Control: Cactoblastis cactorum moth introduced in 1920s; moth larvae feed exclusively on prickly pear tissue, creating an intense biotic selection pressure that decimated invasive cactus populations. Resistant plants survived in low numbers.

  • Cane Toads (Rhinella marina):

  • Introduced to northern Queensland in 1935 to control greyback cane beetles in sugarcane plantations.

  • Evolutionary Selection Pressures on Toads:

    • Climate/Habitat: Spreading into temperate regions select for individuals with higher thermal tolerance and water conservation mechanisms.

    • Invasion Front Selection: Toads at the leading edge of invasion fronts face selection pressure for dispersal speed, evolving longer legs and increased physical activity.

    • Trade-off: Longer-legged fast-moving toads suffer higher rates of spinal osteoarthritis/injury.

  • Pressure on Native Predators: Cane toads produce lethal bufotoxins; native predators (quolls, snakes, monitor lizards) lacking resistance die upon consuming toads, causing severe predator population declines. Selecting for toad-smart behavior or physical toxin resistance in survivors.

Adaptations

• Types of Adaptations:

  • Definition: An inherited feature, structure, function, or behavior that enhances an organism's ability to survive and reproduce in its specific environment. Adaptations arise from random genetic mutations, not conscious intent.

  • Structural Adaptations: Inherited physical or anatomical features of an organism's structure:

  • Long necks in giraffes to reach high tree foliage.

  • Thick blubber layer in penguins for thermal insulation in freezing waters.

  • Leaf spines in cacti to reduce surface area and minimize evaporative water loss.

  • Physiological Adaptations: Inherited functional processes occurring internally at the cellular, tissue, or organ system level:

  • Specialized multi-chambered stomachs in cows housing symbiotic microbes to digest cellulose.

  • Sweating and vasodilation in humans to dissipate heat via evaporative cooling.

  • Production of capsaicin chemical compounds in chili plants to deter herbivore consumption.

  • Behavioural Adaptations: Inherited or learned actions performed by an organism in response to external environmental stimuli:

  • Birds constructing nests in high canopy trees to protect eggs from ground predators.

  • Ectothermic lizards basking on sun-warmed rocks to raise internal body temperature.

  • Ants laying chemical pheromone trails to guide nestmates to discovered food sources.

Theory of Evolution and Evidence

• Evolutionary Theory Development:

  • Evolution: The gradual change in the genetic composition of populations over successive generations, giving rise to new species and biological diversity.

  • Natural Selection: Mechanism proposed independently by Charles Darwin and Alfred Russel Wallace.

  • Principle: Within any population, natural genetic variation exists. Environmental selection pressures select for individuals possessing advantageous variations best suited to the environment. These individuals survive ("survival of the fittest"), reproduce, and pass advantageous traits to offspring. Over time, these traits become more common in the population.

• Historic Observations Supporting Natural Selection:

  • Darwin's Galápagos Finches: Darwin observed distinct finch species across different Galápagos islands, each possessing uniquely shaped beaks adapted to specific food sources (thick heavy beaks for crushing hard seeds, slender pointed beaks for probing insects). Concluded all finches evolved from a common ancestral species via adaptive divergence.

  • Wallace Line and Biogeography: Wallace noted distinctfaunal boundaries in the Malay Archipelago separating Asian species from Australian-derived marsupials across narrow marine straits, proving geographical isolation drives divergent evolution.

  • Australian Flora and Fauna: Unique Australian fauna (platypus, marsupials) occupying ecological niches filled by placental mammals elsewhere challenged static species concepts.

• Lines of Evidence Supporting Evolution:

  • Biochemical Evidence:

  • Universal Genetic Code: DNA and RNA use identical nucleotide bases across all living domains.

  • DNA-DNA Hybridisation: Measures genetic similarity by heating double-stranded DNA from two species to separate strands, mixing them, and cooling to form hybrid double strands. Higher melting temperatures required to separate hybrid DNA indicate higher sequence similarity and closer evolutionary relationship.

• Comparative Anatomy (Homologous Structures):

  • Homologous Structures: Anatomical features found in different species that share a common underlying structural plan due to shared ancestry, despite performing different functions.

  • Example: The pentadactyl limb structure present across mammals, birds, reptiles, and amphibians (human arm, horse leg, cat paw, bat wing, bird wing, whale flipper) demonstrates divergence from a common ancestral limb.

• Comparative Embryology:

  • Comparing early embryonic development stages across different vertebrate species.

  • All vertebrate embryos (fish, salamander, tortoise, chick, human) display striking structural similarities during early development, such as pharyngeal gill slits and post-anal tails, indicating shared evolutionary origins.

• Biogeography:

  • Study of geographical distribution of living and fossil organisms across geological space and time.

  • Gondwana Fossil Distribution: Identical fossils of the extinct freshwater reptile Mesosaurus, land reptile Cynognathus, Lystrosaurus, and fern Glossopteris found across matching coastlines of South America, Africa, India, Antarctica, and Australia prove these continents were united prior to continental drift.

Evolutionary Dynamics and Patterns

• Observed Examples of Microevolutionary Change:

  • Industrial Melanism in Peppered Moths (Biston betularia):

  • Prior to Industrial Revolution in England, pale speckled moths were camouflaged against light lichen-covered tree bark; dark (melanic) moths were rare due to bird predation.

  • Industrial soot blackened tree trunks and killed lichens (selection pressure). Dark moths became camouflaged while light moths were preyed upon. Dark moths survived, reproduced, and became the dominant phenotype within decades.

• Antibiotic Resistance in Bacteria:

  1. Natural genetic variation exists within bacterial populations due to random DNA mutations; a few individual bacteria possess pre-existing resistance genes.

  2. Antibiotic exposure acts as an intense selective pressure, killing susceptible normal bacteria.

  3. Resistant bacteria survive, reproduce rapidly, and pass resistance genes horizontally (via plasmids) and vertically to offspring.

  4. Over short timescales, resistant bacterial strains (e.g., MRSA) become dominant.

• Levels of Biological Diversity:

  • Genetic Diversity: Total number of genetic characteristics and allele variations present in the genetic makeup of a species.

  • Species Diversity: Measure of the variety of different species and their relative abundance within an ecological community.

  • Ecosystem Diversity: The array of different ecosystems, habitats, and ecological processes operating within a given geographical region.

• Microevolution versus Macroevolution:

  • Microevolution: Small-scale phenotypic and genetic changes occurring within a single population over short periods (e.g., change in moth wing colour, antibiotic resistance).

  • Macroevolution: Large-scale evolutionary changes occurring over geological time scales resulting in the origination of new taxonomic groups, adaptive radiation, and speciation (e.g., evolution of horses, evolution of platypus).

• Specific Macroevolution Case Studies:

  • Evolution of the Horse:

  • Extensive continuous fossil record spanning 50 million years tracking transition from small dog-sized forest browser (Hyracotherium) to modern grassland runner (Equus).

  • Evolutionary changes driven by environmental shift from warm humid forests to open dry grasslands:

    • Body Size: Increased significantly over time.

    • Tooth Structure: High-crowned teeth with complex enamel ridges evolved to grind tough silica-rich grasses.

    • Foot Structure: Reduction of multi-toed feet (4 toes on front, 3 on back) to a single strong toe encased in a hooved toe structure for fast running on hard terrain.

  • Evolution of the Platypus:

  • Macroevolutionary example of monotreme evolution.

  • Fossil lineage (Teinolophos, Steropodon, Obdurodon) shows ancient relatives possessed functional teeth, whereas modern adult platypuses (Ornithorhynchus anatinus) lose teeth and possess horny keratinized beak plates.

• Patterns of Evolution:

  • Divergent Evolution: Related species sharing a recent common ancestor evolve distinct phenotypic adaptations due to isolation in differing environments with different selection pressures (e.g., Darwin's finches; adaptive radiation of foxes and domestic dogs from ancestral wolf).

  • Convergent Evolution: Unrelated organisms lacking a recent common ancestor independently evolve strikingly similar body forms and functional traits due to living in similar environments with identical selection pressures (e.g., streamlined body shapes in sharks [fish], penguins [birds], and dolphins [mammals]).

• Pacing of Evolution:

  • Gradualism (Darwinian Model): Proposes that evolutionary change occurs slowly, continuously, and incrementally over vast geological time frames, with cumulative small changes producing major transitions.

  • Punctuated Equilibrium (Eldredge and Gould Model): Proposes that species experience long periods of evolutionary stability (stasis), punctuated by brief, rapid bursts of evolutionary change and speciation triggered by sudden environmental collapse or catastrophic changes.

• Fossils and Geologic Dating Methods:

  • Fossil: Any preserved remnant, impression, or trace of past organism life preserved in rock strata.

  • Transitional Fossils: Fossils possessing structural features intermediate between major ancestral and descendant taxonomic groups (e.g., Archaeopteryx linking feathered birds to carnivorous theropod dinosaurs with teeth and long bony tail).

  • Relative Dating:

  • Law of Superposition: Older rock strata lie at the bottom; upper layers are progressively younger.

  • Index Fossils: Fossils of widespread, short-lived organisms used to correlate relative ages of rock layers across different geographic sites.

  • Absolute Dating (Radiometric Dating):

  • Measures precise age of rocks/fossils in actual years using radioactive isotope decay rates (half-lives, e.g., Carbon-14, Potassium-Argon dating).

Ecosystem Dynamics

• Ecosystem Terminology:

  • Ecosystem: A biological system formed by a community of living organisms interacting with one another and with the non-living physical factors of their environment.

  • Community: All populations of different species coexisting and interacting within a shared habitat.

  • Habitat: The specific physical region where an organism lives.

  • Environment: The sum total of all biotic and abiotic factors influencing an organism throughout its life.

  • Distribution: Where individuals of a species are spatially located across an ecosystem.

  • Abundance: The total count or density of individuals of a species present in an ecosystem.

• Biotic Relationships in Communities:

• Predator-Prey Population Dynamics:

  • Predator and prey populations are closely linked in cyclical fluctuations:

  1. As prey population increases, abundant food availability causes predator population to increase.

  2. Increased predator numbers consume prey rapidly, causing prey population to collapse.

  3. Declining prey population starves predators, causing predator population to crash.

  4. Reduced predation pressure allows prey population to recover, repeating the cycle.

  • Note: Predator population peaks always lag behind prey population peaks.

• Food Chains, Food Webs, and Energy Pyramids:

  • Trophic Roles:

  • Producers (Autotrophs): Manufacture organic food molecules from solar light energy (e.g., plants, phytoplankton).

  • Consumers (Heterotrophs): Consume other living organisms to obtain energy (Primary consumers eat producers; Secondary/Tertiary consumers eat other consumers).

  • Decomposers: Fungi and heterotrophic bacteria that chemically break down complex organic matter in dead organisms and wastes, recycling inorganic nutrients to the soil/environment.

  • Food Chain: Linear diagram depicting energy transfer path from producer through consumers.

• Food Web: Complex interconnected network of food chains representing all trophic feeding relationships operating within an ecosystem.

• Ecological Biomass / Energy Pyramids:

  • Depicts total living organic mass (biomass) or usable energy present at each sequential trophic level.

  • $10\%\text{ Rule}$: Only approximately $10\%$ of available energy stored as biomass is successfully transferred up to the next trophic level. Approximately $90\%$ of energy is lost at each level as metabolic heat, respiration energy, movement, and undigested waste.

  • Quantitative Trophic Levels Example:

    • Primary Producers: $20,000\text{ kcal/m}^2\text{/yr}$

    • Primary Consumers: $2,000\text{ kcal/m}^2\text{/yr}$

    • Secondary Consumers: $200\text{ kcal/m}^2\text{/yr}$

    • Tertiary Consumers: $20\text{ kcal/m}^2\text{/yr}$

    • Quaternary Consumers: $2\text{ kcal/m}^2\text{/yr}$

• Ecological Niches and Keystone Species:

  • Ecological Niche: The precise functional role and position of a species within its ecosystem, including its habitat, resource use, abiotic tolerances, and biotic interactions.

  • Competitive Exclusion Principle: Two distinct species cannot occupy identical ecological niches within the same habitat indefinitely; the superior competitor will inevitably outcompete and exclude the other.

  • Keystone Species: A crucial species whose presence exerts disproportionately immense control over community structure and biodiversity relative to its abundance (e.g., Yellowstone wolves controlling herbivore populations and stream hydrology).

Ecological Field Sampling and Human Impacts

• Population Sampling Techniques:

  • Random Quadrat Sampling:

  • Methodology: Standardized square frames (e.g., $1\text{ m}^2$) placed randomly across a designated study area. Counts of target sessile (non-moving) organisms inside quadrats are taken and averaged to extrapolate total population size.

  • Applicable Organisms: Plants, corals, barnacles, slow-moving snails.

  • Density Formula:       $\text{Estimated Population} = \frac{\text{Average count per quadrat} \times \text{Total study area}}{\text{Quadrat area}}$

• Capture-Mark-Recapture Sampling:

  • Methodology: A sample of mobile animals is captured ($M$), tagged/marked safely, and released back to blend into the population. After a period, a second sample is captured ($C$), and the number of marked individuals in this second group ($R$) is counted.

  • Applicable Organisms: Highly mobile animals (birds, fish, turtles, mammals).

  • Population Abundance Calculation:       $\text{Abundance (N)} = \frac{\text{Number marked in 1st sample (M)} \times \text{Total number caught in 2nd sample (C)}}{\text{Number of marked animals recaptured (R)}}$

  • Percentage Error Formula:       $\text{Percentage Error} = \frac{\text{|Estimated number - Actual number|}}{\text{Actual number}} \times 100$

• Transect Sampling:

  • Methodology: A calibrated tape measure or line stretched across an environmental gradient (e.g., elevation, moisture, distance from shore). Organisms touching or located within a set distance of the line are logged alongside abiotic parameters (pH, light, soil moisture) to assess distribution changes.

• Human Impacts and Ecosystem Dynamics:

  • Human-Induced Selection Pressures: Land clearing, deforestation, agricultural runoff, ocean acidification, habitat fragmentation, and introduced invasive species act as powerful artificial selection pressures, accelerating global extinction rates.

  • Land Clearing Impacts: Over $50\%$ of Australian eucalypt forests cleared or altered since 1788, causing loss of biodiversity, loss of hollow-bearing trees, soil erosion, and dryland salinity.

  • Anthropogenic Climate Change: Increased global greenhouse gas emissions ($\text{CO}_2$, $\text{CH}_4$) trap heat, elevating global average terrestrial and sea surface temperatures. Causes polar ice sheet degradation, coral bleaching, altered species migration patterns, and rapid habitat loss.

  • Mining Site Restoration: Australian mining operations are legally governed by the Mining Act 1992. Requirements include submitting mandatory Environmental Impact Statements (EIS), consulting Traditional Owners, and enacting detailed environmental rehabilitation plans to restore mined land topsoil, vegetation, and ecosystem stability post-operation.