General Biology - Unit 1 Lecture Flashcards

The Science of Biology

• Definition of Biology:

  • Etymology: Derived from the Greek words bio (meaning life) and logos (meaning study).

  • Biology refers to a branch of study that deals with living things and their processes.

  • Biologist: A person who asks questions concerning living things and answers these questions through scientific investigation.

• Importance of Biology:

  • Enables an understanding of how cells and organisms work.

  • Helps individuals understand how their own body works.

  • Facilitates understanding of how different living things use different mechanisms to perform the same functions, such as making energy, eating, and moving.

  • Teaches methods to overcome disease and infection.

  • Provides training on how to investigate, learn new facts, study, search for information, and think critically to learn about the natural environment and human physiology.

• Historical Timeline of Major Figures in Biology:

  • Aristotle (4th Century B.C.): Greek philosopher and scientist recognized as the "Father of Biology".

  • Andreas Vesalius ($1543$): Studied human anatomy.

  • William Harvey ($1628$): Studied the circulation of blood; marked a landmark in medical history and the beginning of modern physiology.

  • Robert Hooke ($1665$): Studied the cell and coined the term "CELL" to describe biological organisms.

  • Anton van Leeuwenhoek ($1674$): Considered the "Father of Microbiology" and the first microbiologist; advanced microscopy and improved the microscope.

  • Theodor Schwann ($1838$): Proposed the Cell Theory.

  • Matthias Jakob Schleiden ($1839$): Proposed the Cell Theory.

  • Rudolf Virchow ($1858$): Proposed the Cell Theory.      

    

  • Charles Darwin ($1859$): English naturalist who published The Origin of Species, marking the end of the modern era of Biology, followed by discoveries in physiology and molecular biology.

  • Louis Pasteur ($1865$): Developed principles of vaccination, microbial fermentation, and pasteurization; disproved the spontaneous generation theory.

  • Gregor Johann Mendel ($1866$): Founder and "Father of Modern Genetics".

  • James D. Watson and Francis Crick ($1953$): Discovered the double-helix structure of DNA.      

    

• Subdivisions of Biology:

  • Natural Science: Deals with the study of nature; subdivided into Physical Science and Biological Science.

  • Physical Science: Study of non-living matter.

  • Physics: Study of matter and its behavior.

  • Chemistry: Study of matter, its composition, and the changes it undergoes.

  • Meteorology: Study of atmospheric conditions.

  • Volcanology: Study of volcanoes and their activity.

  • Mineralogy: Study of minerals, their nature, properties, and distribution.

  • Astronomy: Study of heavenly bodies.

  • Geology: Study of the Earth's surface, rocks, and minerals.

  • Biological Science: The science of life.

  • Botany: Study of plants.

  • Zoology: Study of animals.

  • Specialized subfields:

    • Morphology: Study of structures and forms of organisms.

    • Anatomy: Study of the parts and structures of organisms.

    • Physiology: Study of the normal functions of the parts of an organism.

    • Cytology: Study of the structure and function of cells.

    • Histology: Study of tissues.

    • Embryology: Study of the growth and development of new organisms.

    • Taxonomy: Study of the classification and naming of plants and animals.

    • Genetics: Study of heredity and how characteristics are transmitted from parent to offspring.

    • Evolution: Study of the origin and differentiation of different kinds of organisms.

    • Paleontology: Study of fossils of living things and their distribution in time.

    • Microbiology: Study of microorganisms (includes Bacteriology - study of bacteria; Virology - study of viruses; Protozoology - study of protozoans or one-celled organisms).

    • Biochemistry: Study of the chemistry of living things.

Scientific Method and Scope of Science

• The Scientific Method:

  • A systematic way of solving or investigating biological problems using a sequence or series of defined steps.

  • Main purpose: To discover or formulate conclusions through observation and experimentation.

  • Laymen: Term used to refer to individuals who are not scientists.

• Steps of the Scientific Method:

  1. Recognition of the Problem:

  • Initiated by observation using all five senses.

  • Identifies a specific problem from observations.

  1. Data Gathering:

  • Collection of relevant information via interviews, readings, surveys, and consultations with experts.

  • Qualitative Data: Pertains to quality (e.g., color, size, shape); used in social sciences; non-specific, imprecise, and varies between individuals.

  • Quantitative Data: Pertains to quantity (amount of substance); precise, consistent across individuals, and involves numerical values and standard unit measurements.

  1. Formulation of Hypothesis:

  • A set of assumptions, possible explanations, or scientific guesses based on gathered data.

  • Serves as a preliminary conclusion.

  1. Experimentation:

  • A controlled procedure to prove or disprove the hypothesis, involving data recording and observation.

  • Experimental Group: Receives the specific treatment containing the variable being tested.

  • Control Group: Does not receive the experimental treatment, providing a baseline comparison.

  1. Analysis and Interpretation of Data:

  • Collected data is analyzed into a meaningful account, structured via tables or graphs, and evaluated using statistics.

  1. Generalization / Drawing of Conclusion:

  • Valid when drawn directly from interpretations supported by experimental evidence.

  • May lead to the formulation of a Theory (a generalized statement or conclusion proven through experiments, which may be further developed into principles).

• Scope and Limitations of Science:

  • Scope: Involves continuous testing of rules and principles through the collection of new empirical facts. Concepts that cannot be tested do not belong to science.

  • Limitations:

  • Cannot prove the existence of God (not scientifically testable).

  • Cannot make value judgments (e.g., cannot objectively measure or appreciate beauty).

  • Cannot make moral judgments (e.g., cannot scientifically determine if war is immoral).

Characteristics and Chemical Basis of Life

• Characteristics of Living Things:

  1. Organization:

  • Hierarchical structural arrangement:        $\text{Subatomic particles } (e^-, p^+, n) \rightarrow \text{Atoms} \rightarrow \text{Element} \rightarrow \text{Molecules} \rightarrow \text{Organelle} \rightarrow \text{Cell (basic unit)} \rightarrow \text{Tissue} \rightarrow \text{Organs} \rightarrow \text{Organ System} \rightarrow \text{Organism} \rightarrow \text{Population} \rightarrow \text{Community} \rightarrow \text{Ecosystem} \rightarrow \text{Biosphere}$

  1. Metabolism:

  • The totality of physical and chemical changes occurring in an organism.

  • Anabolism: "Building up" process; synthesis of complex substances from simpler ones.

  • Catabolism: "Breaking down" process; decomposition of complex substances into simpler ones.

  1. Growth:

  • Increase in size and structural figure.

  • Pathway: $\text{Food taken in} \rightarrow \text{Metabolized} \rightarrow \text{Assimilated (absorbed via circulatory system for nourishment)}$.

  1. Reproduction:

  • Formation of new individuals.

  • Sexual: Involves gametes and fertilization.

  • Asexual: No gametes involved; occurs without fertilization.

  1. Responsiveness and Irritability:

  • Ability to react to environmental factors (stimuli) resulting in movement.

  • Stimulus: Any environmental factor capable of producing cellular or behavioral activity.

  1. Adaptation:

  • Process where organisms adjust rapidly or slowly to be better suited to their environment for survival.

  • Involves change in traits (structural, physiological, or behavioral).

  1. Homeostasis:

  • Maintenance of a nearly constant internal state or condition within an organism.

  1. Definite Form, Size, and Genetic Composition:

  • Living organisms produce offspring similar to themselves, guided by species-specific genetic code.

  1. Evolution:

  • Gradual change in the characteristics of a species across successive generations (species-level change).

  • Purpose: Enables organisms to survive and function more efficiently than ancestors.

• Chemical Basis of Life:

  • Matter: Anything that occupies space, has mass, and exists in solid, liquid, or gas states.

  • Element: A substance that cannot be broken down chemically into simpler substances.

  • Major elements in living cells: Carbon ($C$), Hydrogen ($H$), Oxygen ($O$), Nitrogen ($N$).

  • Additional significant elements: Sulfur ($S$), Potassium ($K$), Calcium ($Ca$), Phosphorus ($P$), Iron ($Fe$), Sodium ($Na$), Chlorine ($Cl$), Manganese ($Mn$), Magnesium ($Mg$).

  • Trace elements: Required by organisms in minute amounts.

  • Compounds:

  • Inorganic Compounds: Smaller, less complex, lacking carbon-hydrogen backbones.

    • Water ($H_2O$): Universal solvent and essential medium for chemical reactions.

    • Gases: Carbon dioxide ($CO_2$, raw material for photosynthesis) and Oxygen ($O_2$, byproduct of photosynthesis).

    • Salts: Chemical compounds formed by reacting acids with bases.

  • Organic Compounds: Primary structural and functional biological materials containing carbon (typically combined with hydrogen and oxygen).

    • Carbohydrates: Most abundant biomolecules; function in energy storage and transport. Building blocks are glucose molecules.

    1. Monosaccharides: Single sugar subunits for energy storage (Glucose, Galactose, Fructose).

    2. Disaccharides: Two sugar subunits for transport (Maltose, Sucrose, Lactose).

    3. Polysaccharides: Insoluble chains of multiple sugar subunits (Cellulose, Glycogen, Starch).

    • Lipids: Insoluble in water; building blocks are fatty acids. Provide long-term energy storage.

    1. Saturated Fats: Solid at room temperature (e.g., animal oils); double-stranded structure.

    2. Unsaturated Fats: Liquid at room temperature (e.g., plant oils); single-stranded structure.

    • Proteins: Diverse chains of amino acids (building blocks); abundant in animal protoplasm. Functions: Enzymatic catalysts, structural components, regulatory hormones, and immune defense.

    • Nucleic Acids: Control cell activities, direct functions, and manage reproduction. Building blocks are nucleotides.

Theories on the Origin of Life

• Divine Creation Theory:

  • Asserts life was created by a supernatural being (e.g., God, Buddha, Allah) as expressed in sacred texts (Bible, Koran).

  • Axiom accepted primarily by faith.

• Cosmozoic or Interplanetary Theory:

  • Proposes life originated from outer space as resistant protoplasmic spores propelled to Earth by radiation pressure via meteorites and comets, carrying organic molecules formed by abiotic space reactions.

• Spontaneous Generation Theory (Abiogenesis):

  • Proposed by Aristotle and ancient Greek scholars.

  • Asserts living organisms arise directly from non-living matter under the influence of warmth, moisture, sunlight, and starlight (e.g., frogs from damp soil, insects from dew, maggots from decaying meat).

• Biogenesis Theory:

  • Demonstrated by Francisco Redi; states that living organisms can only arise from pre-existing living organisms.

• Natural / Marine Theory:

  • Proposes Earth's primeval oceans contained dissolved inorganic and organic substances that formed complex biomolecules via chemical reactions in a metabolic atmosphere containing $O_2$ and $CO_2$.

• Philosophical Theory of Eternity:

  • Claims life has no singular point of origin or ultimate end, having always existed throughout time (Alpha and Omega).

• Physico-Chemical / Coacervate Droplet Theory:

  • Proposed by Russian biologist Alexander Oparin; considered the most scientific and widely accepted theory.

  • Earth and solar bodies formed $4.6 \text{ billion years ago}$ (BYA) from the explosion of a hot, rotating ball of gas. The first life forms emerged between $3.5 \text{ and } 4.0 \text{ BYA}$.

• Stanley Miller's Experiment:

  • Biochemical experiment testing abiotic synthesis under simulated primeval Earth conditions.

  • Apparatus Setup: Enclosed system circulating Water ($H_2O$), Methane ($CH_4$), Ammonia ($NH_3$), and Hydrogen ($H_2$), completely free of oxygen ($O_2$). Water was continuously boiled and condensed.

  • Energy Source: Electrical discharge (spark) between two electrodes in a gas chamber.

  • Results: After one week, paper chromatography confirmed the presence of several amino acids and organic compounds.

  • Subsequent Findings: Extended variants synthesized 17 out of the 20 natural amino acids and all purines and pyrimidines required for nucleic acid synthesis.

  • Synthesis of pyrimidine ribonucleotides under early Earth conditions was reported on May 14, 2009, in Nature.

  • Theoretical Challenge: Recent atmospheric models suggest early Earth's atmosphere was not actually rich in methane and ammonia.

Diversity of Life and Taxonomy

• Systems of Classification:

  1. Artificial System: Groups organisms based on superficial physical resemblances without reflecting evolutionary relationships (e.g., grouping all shelled animals together).

  2. Natural System: Formulated by Carolus Linnaeus; groups organisms based on true evolutionary and structural relationships (e.g., classifying animals by embryonic development patterns).

• Nomenclature and Scientific Naming:

  • Nomenclature: The system of naming organisms.

  • Binomial Nomenclature: System introduced by Linnaeus where every organism is assigned a unique two-part universal scientific name consisting of the Genus and species names.

  • Rules of Binomial Nomenclature:

  1. Names are written in Latin, comprising a genus name followed by a species name.

  2. The first letter of the genus name is capitalized; all other letters and the species name are lowercase.

  3. The full scientific name must be italicized or underlined (e.g., Canis familiaris or Canis familiaris for the domestic dog; Felis domestica for domestic cat; Homo sapiens for human).

  4. The earliest published scientific name takes precedence as valid; subsequent names become synonyms.

  5. Scientific names published prior to the 10th volume of Linnaeus's Systema Naturae are invalid.

• Hierarchical Taxonomic Levels (Taxa):

  • Ranked from broadest (highest) to most specific (lowest):     $\text{Kingdom} \rightarrow \text{Phylum / Division} \rightarrow \text{Class} \rightarrow \text{Order} \rightarrow \text{Family} \rightarrow \text{Genus} \rightarrow \text{Species}$

  • Definitions:

  • Species: The fundamental, smallest unit of classification; a group of organisms that is reproductively isolated from other groups.

  • Genus: A group of closely related species.

  • Family: A group of related genera.

  • Order: A group of related families.

  • Class: A group of related orders.

  • Phylum / Division: A group of related classes. (The term Phylum is applied to Kingdoms Animalia and Protista; Division is applied to Kingdoms Plantae, Fungi, and Monera).

  • Kingdom: The highest classification rank, comprising related phyla/divisions.

• Criteria for Homology in Classification:

  1. Homology in Structure/Appearance: e.g., grouping organisms with jointed legs.

  2. Homology in Chromosome Number: Members of the same species share identical chromosome counts.

  3. Homology in Function: e.g., presence of insulin-secreting cells across vertebrates.

  4. Homology in Chemical Composition: e.g., turkey and pigeon proteins differ by 4 amino acids, whereas turkey and turtle proteins differ by 8 amino acids.

• The Five-Kingdom Scheme (Introduced by Robert H. Whittaker):

  • Criteria for Classification:

  1. Cell Type: Prokaryotic (lacking nuclear membrane) vs. Eukaryotic (bound nuclear membrane).

  2. Cellular Organization: Unicellular vs. Multicellular.

  3. Mode of Nutrition: Photosynthetic (autotrophic synthesis), Absorptive (uptake of assimilated nutrients), or Ingestive (ingestion of whole food particles).

• Overview of the Five Kingdoms:

  1. Kingdom Monera:

  • Unicellular prokaryotic organisms (some form colonies or filaments).

  • Nutrition: Absorptive or photosynthetic.

  • Examples: Bacteria, blue-green algae.

  1. Kingdom Protista:

  • Unicellular eukaryotic organisms (some colonial forms).

  • Nutrition: Absorptive, ingestive, or photosynthetic.

  • Examples: Amoeba, Paramecium, Euglena.

  1. Kingdom Fungi:

  • Multicellular eukaryotic organisms.

  • Nutrition: Strictly absorptive (lacks chlorophyll).

  • Non-motile; reproduce via microscopic spores.

  • Examples: Mushrooms, yeasts, molds.

  1. Kingdom Plantae:

  • Multicellular, photosynthetic, non-motile eukaryotic organisms.

  • Division Thallophyta: Plant body lacks true roots, stems, and leaves (thallus body).

    • Class Chlorophyta: Green algae.

    • Class Phaeophyta: Brown algae.

    • Class Rhodophyta: Red algae.

  • Division Embryophyta: Higher plants featuring true roots, stems, and leaves.

    • Subdivision Bryophyta: Non-vascular forms (liverworts, hornworts, mosses).

    • Subdivision Tracheophyta: Vascular plants.

      • Class Filicinae: Ferns.

      • Class Angiospermae: Flowering seed plants.

      • Class Gymnospermae: Cone-bearing seed plants.

  1. Kingdom Animalia:

  • Multicellular eukaryotic organisms lacking cell walls and photosynthetic pigments.

  • Nutrition: Ingestive; primarily motile.

  • Major Animal Phyla:

    • Porifera: Sponges.

    • Coelenterata: Corals, jellyfish, sea anemones.

    • Platyhelminthes: Flatworms (flukes, tapeworms).

    • Nematoda: Roundworms (Ascaris).

    • Annelida: Segmented worms (earthworms, leeches, marine worms).

    • Mollusca: Soft-bodied invertebrates (clams, snails, squids, octopuses, nautiluses).

    • Arthropoda: Invertebrates with jointed legs (crabs, shrimps, lobsters, insects, spiders, scorpions, centipedes, millipedes).

    • Echinodermata: Spiny-skinned marine animals (sea stars, sea urchins, sea cucumbers, brittle stars).

    • Chordata: Vertebrates possessing a backbone (fishes, amphibians, reptiles, birds/aves, mammals).

Cell Theory and Cell Structure

• Formulation of the Cell Theory:

  • Primary credit given to Theodor Schwann ($1838$), Matthias Schleiden ($1839$), and Rudolf Virchow ($1858$).

  • Classical Cell Theory Postulates:

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

  2. Organisms may be unicellular or multicellular.

  3. The cell is the fundamental basic unit of life.

  4. Cells arise exclusively from pre-existing cells.

  • Modern Version Tenets:

  1. All known living things are composed of one or more cells.

  2. All living cells arise from pre-existing cells by cell division.

  3. The cell is the fundamental unit of structure and function in all living organisms.

  4. An organism's overall activity depends on the total activity of independent cells.

  5. Energy flow (metabolism and biochemistry) occurs within cells.

  6. Hereditary information (DNA) is passed from cell to cell during cell division.

  7. All cells are basically identical in chemical composition in organisms of similar species.

• General Cellular Characteristics:

  • Etymology: From Latin cella, meaning "small room".

  • Average size: Most cells measure approximately $\frac{1}{1{,}000} \text{ inch}$ ($0.0025 \text{ cm}$) in diameter.

  • Morphological diversity: Shapes include snowflakes, spheres, cubes, saucers, rectangles, boxes, coils, or irregular blobs.

  • General universal features: Microscopic size, membrane-enclosed boundary, filled with cytosol, contains genetic material, and capable of independent self-replication.

  • Universal structural components across all cellular life:

  1. Genetic material (contained within a nucleoid or membrane-bound nucleus).

  2. Cytoplasm (a semifluid structural matrix).

  3. Plasma membrane (a phospholipid bilayer boundary).

• Prokaryotic vs. Eukaryotic Comparison:

  • Prokaryotes: Primitive cells that evolved approximately $4 \text{ billion years ago}$; lack membrane-bound nuclei and internal organelles. Ranging from $0.5 \text{ to } 2.0 \,\mu\text{m}$ in diameter.

  • Eukaryotes: Complex cells featuring membrane-bound nuclei and organelles; approximately $10 \text{ times}$ the linear size and $1{,}000 \text{ times}$ the volume of prokaryotic cells.

• Anatomy of the Prokaryotic Cell:

  1. Capsule: Outer cellular layer protecting against phagocytosis, retaining moisture, and adhering to surfaces.

  2. Cell Wall: Rigid exterior structure providing cellular shape and structural protection.

  3. Cytoplasm: Gel-like aqueous interior containing metabolic enzymes, salts, and organic molecules.

  4. Cell Membrane: Phospholipid boundary regulating selective molecular transport.

  5. Pili / Fimbriae: Proteinaceous hair-like surface protrusions for attachment to host tissues or other bacteria.

  6. Flagella: Long, whip-like structural appendages enabling active locomotion.

  7. Ribosomes: Unbound RNA-protein complexes responsible for translation and protein synthesis ($70\text{S}$ size).

  8. Plasmids: Small, extra-chromosomal circular DNA molecules carrying accessory genes.

  9. Nucleoid Region: Unenclosed cytoplasmic region housing the single circular bacterial chromosome.

• Anatomy of Eukaryotic Cells:

• Animal Cell Structure:

  1. Cell Membrane: Semi-permeable outer boundary composed of a lipid bilayer.

  2. Cytoplasm: Fluid matrix suspending intracellular structures.

  3. Nucleus: Double-membrane organelle housing cellular DNA.

  4. Nucleolus: Dense intra-nuclear site for ribosome biogenesis.

  5. Nucleopore: Perforations in the nuclear envelope permitting nuclear-cytoplasmic transport.

  6. Centrioles: Microtubule-organizing structures crucial for mitotic spindle formation.

  7. Endoplasmic Reticulum (ER): Network of membranes divided into Rough ER (protein translation) and Smooth ER (lipid synthesis).

  8. Golgi Complex: Stacked membrane sacs functioning in modification, sorting, and packaging of proteins.

  9. Lysosomes: Hydrolytic enzyme-filled vesicles for intracellular digestion and waste management.

  10. Microtubules: Hollow structural filaments providing mechanical support and intracellular transport pathways.

  11. Mitochondria: Double-membrane organelles responsible for aerobic ATP production via cellular respiration.

• Plant Cell Structure:

  1. Cell Wall: Rigid outer boundary providing structural rigidity and defense against infection; composed of cellulose, pectins, glycoproteins, hemicellulose, and lignin across three distinct layers (primary wall, secondary wall, middle lamella).

  2. Cell Membrane: Inner semi-permeable boundary regulating cytosol content.

  3. Chromoplasts: Pigment-synthesizing plastids responsible for non-photosynthetic coloration in flowers and fruits.

  4. Golgi Complex: Processes and packages cellular macromolecules.

  5. Ribosomes: RNA-protein synthesis units ($80\text{S}$ cytosolic).

  6. Endoplasmic Reticulum: Interconnected tubular system involved in protein/lipid biosynthesis and calcium storage.

  7. Lysosomes: Degradative enzyme sacs (rare in plant cells).

  8. Microbodies: Single-membrane organelle housing specific oxidative/degradative enzymes.

  9. Cytoskeleton: Microtubule and microfilament framework maintaining shape.

  10. Microtubules: Structural hollow cylinder networks.

  11. Microfilaments: Solid actin-based structural rods.

  12. Plasmodesmata: Microscopic trans-wall cytoplasmic channels facilitating inter-cellular movement.

  13. Vacuole: Large membrane-bound central organelle occupying up to $90\%$ of cell volume; functions in storage, excretion, and turgor maintenance.

  14. Tonoplast: The selective membrane enclosing the central vacuole.

  15. Plastids: Metabolic storage organelles synthesizing fats and terpenes.

  16. Leucoplasts: Non-pigmented plastids dedicated to starch and nutrient storage.

  17. Mitochondria: Power plants converting glucose energy to ATP; contain independent circular DNA.

  18. Cytoplasm: Supporting aqueous matrix.

  19. Nucleus: Control center bound by a porous nuclear envelope.

Cellular Transport and Metabolism

• Plasma Membrane Architecture:

  • Composed of a fluid Phospholipid Bilayer featuring:

  • Polar, hydrophilic (water-loving) phosphate heads pointing outward.

  • Non-polar, hydrophobic (water-fearing) fatty acid tails pointing inward.

  • Embedded transmembrane and peripheral proteins.

  • Functions: Maintains homeostasis by regulating material passage; provides structural support.

• Cellular Transport Mechanisms:

  • Passive Transport: No cellular energy ($ATP$) expenditure; relies on natural thermal motion down a concentration gradient (High Concentration $\rightarrow$ Low Concentration).

  1. Diffusion: Random movement of solute particles until equilibrium is achieved.

  2. Facilitated Diffusion: Passive movement of specific large or charged molecules across the bilayer via selective protein channels/transporters.

  3. Osmosis: Diffusion of free water molecules across a selectively permeable membrane.

  • Active Transport: Requires metabolic energy expenditure ($ATP$) to move solutes against a concentration gradient (Low Concentration $\rightarrow$ High Concentration).

  1. Protein Pumps: Transmembrane carriers (e.g., Sodium-Potassium Pump [$Na^+/K^+$ pump] essential for nerve impulse conduction).

  2. Endocytosis: Active uptake of bulky bulk materials via membrane invagination ("cell eating"), forming an intracellular food vacuole.

  3. Exocytosis: Fusion of internal membrane-bound vesicles with the plasma membrane to secrete wastes or cellular products (e.g., hormones) outside the cell.

• Tonicity and Osmotic Solutions:

  • Hypertonic Solution: Solute concentration outside the cell is greater than inside (Low water concentration outside).

  • Effect: Water exits the cell via osmosis, causing cellular shrinkage (Plasmolysis).

  • Hypotonic Solution: Solute concentration outside the cell is lower than inside (High water concentration outside).

  • Effect: Water rushes into the cell, causing swelling and osmotic lysis (Cytolysis).

  • Isotonic Solution: Solute concentration inside and outside the cell is equal.

  • Effect: Equal rates of water influx and efflux (Dynamic Equilibrium); cells remain flaccid/stable.

  • Osmotic Adaptations:

  • Plants and bacteria utilize rigid cell walls to resist bursting, generating Turgor Pressure.

  • Freshwater protists (e.g., Paramecium) utilize active contractile vacuoles to pump out excess water.

  • Marine fish actively pump excess salts across specialized gill structures.

  • Mammals maintain isotonic blood plasma via renal regulation in kidneys.

• Cellular Bioenergetics and Enzymes:

  • Energy: The capacity to do work or induce change. Cannot be created or destroyed, only transformed.

  • Potential Energy: Stored energy.

  • Kinetic Energy: The energy of active movement.

  • Adenosine Triphosphate (ATP): The primary energy currency of cellular processes.

  • Enzymes: Biological protein catalysts that accelerate chemical reactions by lowering activation energy without being consumed or permanently altered.

• Energy Extraction Pathways from Glucose:

  • Redox Reactions: Chemical reactions involving electron transfer.

  • Reduction: Gain of one or more electrons.

  • Oxidation: Loss of one or more electrons.

  • Oxidation and reduction reactions always occur simultaneously.

  • Glycolysis:

  • Anaerobic conversion of one 6-carbon glucose molecule into two 3-carbon pyruvate molecules in the cytoplasm, yielding a net gain of usable energy.

  • Cellular Respiration (Aerobic Pathway):

  • Complete enzymatic oxidation of pyruvate in the presence of oxygen ($O_2$).

  • Net energy yield: $32 \text{ ATP}$ per glucose molecule.

  • Waste products: Carbon dioxide ($CO_2$) and water ($H_2O$).

  • Four stages: Glycolysis $\rightarrow$ Formation of Acetyl Coenzyme A $\rightarrow$ Citric Acid (Krebs) Cycle $\rightarrow$ Electron Transport Chain & Chemiosmosis.

  • Equation: $C_6H_{12}O_6 + 6\,O_2 + 6\,H_2O \rightarrow 6\,CO_2 + 12\,H_2O + \text{Energy}$

  • Fermentation (Anaerobic Pathway):

  • Incomplete oxidation occurring in the absence of oxygen ($O_2$).

  • Net energy yield: $2 \text{ ATP}$ per glucose molecule.

  • Products: Lactic acid or ethanol ($\text{ethyl alcohol}$) plus $CO_2$.

• Photosynthetic Metabolism:

  • Anabolic process occurring within plant chloroplasts, converting light energy into chemical energy.

  • Overall Equation:     $6\,CO_2 + 12\,H_2O \rightarrow C_6H_{12}O_6 + 6\,H_2O + 6\,O_2$      

    

  • Raw Materials: Light energy, Carbon dioxide ($CO_2$), Water ($H_2O$), and Photosynthetic Pigments (Chlorophyll a, Chlorophyll b, Carotenoids).

  • Two Main Stages:

  1. Light Reactions: Converts solar light energy into chemical energy stored in $ATP$ and $NADPH$.

  2. Light-Independent Reactions (Calvin Cycle / Carbon-Fixation): Uses generated $ATP$, $NADPH$, and atmospheric $CO_2$ to synthesize carbohydrates. Involves three phases: $CO_2$ uptake, Carbon reduction, and RuBP regeneration.

Cellular Reproduction and Genetics

• Prokaryotic Cell Division:

  • Prokaryotes reproduce asexually via Binary Fission, directly segregating replicated circular chromosomes equally into two identical daughter cells.      

    

• Eukaryotic Cell Cycle:

  • Interphase: Long preparatory phase divided into:

  • G1 Phase (First Gap): Cell increases in physical size, synthesizes RNA, and produces operational proteins.

  • S Phase (Synthesis): Complete replication of genomic DNA.

  • G2 Phase (Second Gap): Continued cell growth and synthesis of specialized proteins required for cell division.

• Mitosis (Vegetative Cell Division):

  • Process by which a eukaryotic parent cell duplicates its genetic material to produce two genetically identical diploid daughter cells ($2n \rightarrow 2n$).

  • Significance: Organismal growth, tissue repair, cellular replacement, regeneration, and asexual reproduction (e.g., yeast, Paramecium, Amoeba, Hydra budding).

  • Phases of Mitosis:

  1. Prophase: Preparatory phase; chromatin condenses into visible chromosomes (sister chromatids); nucleolus and nuclear membrane dissolve; centrioles migrate to opposite poles; mitotic spindle apparatus (aster microtubules) begins assembly.

  2. Prometaphase: Kinetochore protein complexes form on centromeres; spindle microtubules attach to kinetochores; chromosomes begin active movement.

  3. Metaphase: Mitotic apparatus fully formed; spindle fibers align chromosomes along the central equatorial plane (metaphase plate).

  4. Anaphase: Migration phase; centromeres divide; motor proteins move separated sister chromatids toward opposite spindle poles along shortening microtubules ($ATP$ dependent).

  5. Telophase & Cytokinesis: Reconstruction phase; daughter chromosomes reach opposite poles, uncoil, and lengthen; nuclear membranes and nucleoli re-form; spindle apparatus disperses; physical cleavage/division of cytoplasm (Cytokinesis) occurs.

• Meiosis (Reductive Division & Gametogenesis):

  • Specialized cell division occurring in germ cells, producing four genetically distinct haploid daughter cells ($2n \rightarrow 1n$) to form gametes.

  • Human chromosome reduction: $46 \rightarrow 23$ chromosomes. Fertilization restores diploidy ($1n + 1n \rightarrow 2n$).

  • Meiosis I (Reductional Division):

  • Prophase I: Longest stage; divided into sub-stages:

    • Leptonema: Chromosomes appear as thin, thread-like structures.

    • Zygonema: Homologous chromosomes undergo physical pairing (Synapsis), forming a Tetrad.

    • Pachynema: Homologous non-sister chromatids exchange genetic segments (Crossing-over).

    • Diplonema: Homologous pairs begin repelling each other but remain bound at chiasmata.

  • Metaphase I: Synapsed tetrads line up along the equatorial plate.

  • Anaphase I: Homologous chromosome pairs separate and move toward opposite poles (sister chromatids remain attached).

  • Telophase I: Chromosomes reach poles; nuclear membranes re-form, yielding two haploid ($1n$) intermediate cells.

  • Meiosis II (Equational Division):

  • Separates sister chromatids without intervening DNA replication.

  • Prophase II: Dyad chromosomes condense.

  • Metaphase II: Dyads line up along the equatorial plate.

  • Anaphase II: Centromeres divide; sister chromatids move to opposite poles.

  • Telophase II: Chromosomes uncoil, nuclear envelopes form, yielding four haploid gametes.

  • Sources of Genetic Variation: Crossing-over during Prophase I and random assortment of maternal/paternal chromosomes (yielding $2^{23} = 8{,}388{,}608$ unique chromosomal combinations in humans).

• Patterns of Inheritance and Mendelian Genetics:

  • Genetics: Derived from Greek gen (meaning to become or grow); term coined by William Bateson in $1906$.

  • Gregor Mendel: Augustinian monk recognized as the "Father of Genetics". Discovered basic laws of inheritance using the Garden Pea (Pisum sativum).

  • Advantages of Pisum sativum: Native to Mediterranean region, easy to cultivate, short life cycle, abundant commercial varieties, and simple to manipulate manually.

• Mendel's Principles of Inheritance:

  1. Gene Concept: Inherited traits are transmitted by discrete unit factors (genes) occurring in paired alternative forms (alleles).

  2. Principle of Dominance: When two different alleles are present in an individual, the dominant allele masks the expression of the recessive allele.

  3. Principle of Segregation: Allelic pairs separate independently during gamete formation so that each gamete carries only one allele per locus (evaluated via Monohybrid crosses).

  4. Principle of Independent Assortment: Alleles of distinct gene loci segregate independently of one another during gametes formation (evaluated via Dihybrid crosses).

• Genetics Terminology Glossary:

  • Allele: One of the alternative structural forms of a specific gene (e.g., tall vs. dwarf alleles for plant height).

  • Allelic Pair: The precise combination of two alleles occupying a gene locus in an organism.

  • Dominant Allele: An allele that expresses its phenotypic effect over a paired alternate allele (symbolized by uppercase letters, e.g., $T$).

  • Recessive Allele: An allele whose phenotypic expression is suppressed in the presence of a dominant allele (symbolized by lowercase letters, e.g., $t$).

  • Phenotype: The observable physical, physiological, or functional appearance of a trait.

  • Genotype: The specific underlying allelic composition for a gene or set of genes.

  • Homozygote: An individual possessing identical alleles at a given locus (e.g., $TT$ or $tt$).

  • Heterozygote: An individual possessing two different alleles at a given locus (e.g., $Tt$).

  • Punnett Square: Graphic diagram devised by Reginald Punnett used to calculate probabilities of offspring genotypes and phenotypes.

  • P Generation: Parental true-breeding generation.

  • F1 Generation: First filial generation resulting from parental cross.

  • F2 Generation: Second filial generation resulting from self-pollination of F1 hybrids.

  • Test Cross: Experimental cross between an individual exhibiting a dominant phenotype and a homozygous recessive individual ($tt$) to determine whether the dominant parent is homozygous or heterozygous.

  • Monohybrid Cross: A genetic cross monitoring a single character trait at one gene locus.

  • Dihybrid Cross: A genetic cross simultaneously monitoring two distinct character traits at two separate gene loci.