Comprehensive University Biology: Cytology, Physiology, and Kingdoms

Foundations of Cytology and Cell Discovery

• Cytology is defined as the scientific study of cells. The term is derived from the Greek words "Cyto" meaning cell and "Logy" meaning study.

• The cell is characterized as the fundamental building block of life and the structural and functional basis of all living organisms.

• Historical Timeline of Discovery:

  • Robert Hooke (1665): Observed dead cells in cork. He is recognized as the Father of Cytology.

  • Antonie van Leeuwenhoek (1674): First to observe living cells in pond water.

• Cell Theory Development:

  • In 1838, Matthias Schleiden and Theodor Schwann formulated the cell theory, stating all living organisms are composed of cells and the cell is the basic unit of life.

  • In 1855, Rudolf Virchow added the principle "omnis cellula e cellula," meaning new cells are formed from pre-existing cells.

• Biological Extremes in Cell Size:

  • Largest cell in the human body: Ovum (Female sex cell).

  • Smallest cell in the human body: Sperm (Male sex cell).

  • Longest cell in the male body: Neuron.

  • Smallest cell in women: Red Blood Cell (RBC).

  • Largest cell overall: Ostrich's egg.

  • Smallest cell overall: Mycoplasma (bacteria).

The Cell Membrane and Transport Mechanisms

• The cell membrane, also known as the plasma membrane, is a thin, elastic, and flexible outer covering. In animal cells, it is the outermost layer, whereas, in plant cells, it lies directly beneath the cell wall.

• Composition of the Cell Membrane: It consists of approximately $50\%$ Proteins and $50\%$ Lipids.

• Functional Roles:

  • Acts as a protective barrier (like a "bodyguard").

  • Maintains the shape of the cell.

  • Protects internal contents.

  • Acts as a selectively permeable membrane, controlling the influx and efflux of substances.

• Movement Across the Membrane:

  • Diffusion: The spontaneous movement of molecules from a region of higher concentration to lower concentration. The rate of diffusion follows the order: Gases > Liquids > Solids.

  • Osmosis: The movement of water from higher to lower concentration through a semi-permeable membrane. This process requires no energy and continues until an equilibrium state is reached.

• Transport Types:

  • Active Transport: Movement of molecules from lower to higher concentration, requiring cellular energy ($ATP$). This is also referred to as reverse osmosis in certain contexts.

• Effects of Solutions on Cell Size:

  • Isotonic Solution: Concentrations are equal; no change in cell size.

  • Hypotonic Solution: Dilute solution (Solute < Solvent); the cell absorbs water and swells (Turgidity).

  • Hypertonic Solution: Concentrated solution (Solute > Solvent); the cell loses water and shrinks (Plasmolysis).

The Cell Wall and Chromosomal Structure

• The cell wall is a non-living, rigid structure found only in plants, bacteria, fungi, and algae. Unlike the cell membrane, it is freely permeable.

• Material Composition of Cell Walls:

  • Bacteria: Peptidoglycan (also called Peptin).

  • Fungi: Chitin.

  • Plants: Cellulose.

  • Algae: Cellulose and Pectin.

• The Glycocalyx is a slime layer that covers the cell membrane in bacteria.

• Chromosomes are thread-like structures located in the nucleus containing genetic information. They consist of DNA and Proteins (specifically Histones).

• Human Chromosomal Count: Total of $46$ chromosomes ($23$ pairs).

  • $22$ pairs are autosomal.

  • $1$ pair is the sex pair ($XX$ for female, $XY$ for male).

• DNA (Deoxyribonucleic Acid):

  • Functional segments are called genes.

  • Discovered by Friedrich Miescher in 1869.

  • The double-helical structure was proposed by Watson and Crick in 1953.

The Cytoplasm and Cellular Organelles

• Cytoplasm is the fluid filling the space between the plasma membrane and the nuclear envelope, house to various cell organelles.

• Components of Cytoplasm:

  • Cytosol: The aqueous, water-based fluid portion.

  • Cytoplasmic Inclusions: Non-living components existing as Euchromatin (loosely packed, transcriptionally active) or Heterochromatin (tightly packed, transcriptionally inactive).

• Mitochondria:

  • Dimensions: Length is $1-2\,\mu m$; Diameter is $0.1-0.6\,\mu m$.

  • Function: Known as the "Powerhouse of the cell," it synthesizes Adenosine Triphosphate ($ATP$), which is the energy currency of the cell.

  • Structural Features: Sausage-shaped, double-membraned organelle with its own DNA and ribosomes. The inner membrane is the site of energy synthesis.

  • Involved in apoptosis (programmed cell death).

• Ribosomes: Non-membrane-bound structures essential for protein synthesis. Discovered by George E. Palade in 1955.

• Endoplasmic Reticulum (ER): A network of sac-like structures acting as a transport channel between the nucleus and cytoplasm.

  • Rough ER (RER): Studded with ribosomes; site of protein synthesis.

  • Smooth ER (SER): Lacks ribosomes; synthesizes lipids/fats and detoxifies drugs/poisons in the liver via the enzyme Cytochrome $P450$.

• Golgi Bodies: Discovered by Camillo Golgi in 1898. They consist of vesicles, cisternae, and vacuoles.

  • Faces: Cis face (convex, receiving side near nucleus) and Trans face (concave, shipping side near membrane).

  • Functions: Acts as the "Post Office" for packaging/despatching proteins/lipids and forming lysosomes.

• Lysosomes: Known as "suicide bags," they contain digestive enzymes (made in RER) for waste disposal. If damaged, they may burst and digest their own cell.

• Vacuoles: Membrane-bound sacs.

  • In plants: Large, permanent, central (occupying $50-90\%$ of volume), storing cell sap (amino acids, sugars, organic acids).

  • In animals: Small, temporary, and numerous; store glucose, glycogen, and protein.

• Plastids: Exclusive to plant cells. They contain their own DNA and ribosomes.

  • Chloroplasts: Green plastids containing chlorophyll ($Mg^{2+}$ based) for photosynthesis, along with Xanthophylls (yellow) and Carotenes (orange).

  • Chromoplasts: Provide color (e.g., Lycopene in tomatoes, Capsanthin in chilli).

  • Leucoplasts: Colorless storage plastids: Amyloplast (starch/carbs), Aleuroplast (protein), and Elaioplast (fats).

The Cell Nucleus and Classification

• The nucleus is the "Brain of the Cell," discovered by Robert Brown in 1831. It is the largest, double-membraned organelle in eukaryotic cells.

• The nuclear membrane separates nucleoplasm from cytoplasm.

• Nucleoplasm is a type of protoplasm (term coined by Purkinje in 1839) containing the nucleolus (ribosome biogenesis site) and chromatin.

• Prokaryotic Cells:

  • Size: $1-10\,\mu m$.

  • Undefined nuclear region called a Nucleoid.

  • Nucleus and membrane-bound organelles are absent.

  • Single chromosome; example: Bacteria, Blue-green algae (Cyanobacteria).

• Eukaryotic Cells:

  • Size: $10-100\,\mu m$.

  • True nucleus and organelles present.

  • Multiple chromosomes; example: Plant and animal cells.

• Bacterial Appendages:

  • Flagella: Hair-like structures for locomotion made of flagellin protein. Parts: Basal body (attachment), Hook (joint), and Filament.

Cell Division and Cycle

• Reason for division: Organism growth, replacement of dead/injured cells, and gamete formation.

• The Cell Cycle:

  • $G_1$ Phase (Gap 1): Cell growth and normal function.

  • S Phase (Synthesis): DNA replication resulting in two identical copies for each chromosome.

  • $G_2$ Phase (Gap 2): Preparation for mitosis.

  • Mitotic Phase: Division of nucleus and cytoplasm.

• Mitosis vs. Meiosis:

  • Mitosis: Occurs in somatic cells; results in two diploid ($2n$) daughter cells genetically identical to the parent. Used for growth and repair.

  • Meiosis: Occurs in germ cells; involves two nuclear divisions resulting in four haploid ($n$) daughter cells that are genetically diverse. Malfunctions lead to disorders like Down's, Klinefelter's, or Turner's syndrome.

• Cytoskeleton and Centrosome:

  • Cytoskeleton: Provides structural support (microfilaments, microtubules, intermediate filaments).

  • Centrosome: Made of two centrioles ($9+0$ or $9+2$ microtubule arrangement) used in cell division.

DNA Replication and Transport Processes

• DNA Replication: Semi-conservative process where each new double-stranded DNA contains one original parent strand and one new daughter strand.

• Enzymes for Replication:

  • Helicase: Unwinds or "unzips" the DNA double strand.

  • Topoisomerase: Prevents tangling and supercoiling.

  • DNA Primase: Initiates the production of new strands.

  • DNA Polymerase: The "builder" enzyme that doubles DNA content.

  • DNA Ligase: The "gluer" enzyme that joins DNA strands.

  • Reverse Transcriptase: Creates complementary DNA from an RNA template.

• Endocytosis and Exocytosis:

  • Endocytosis: Cell engulfs external materials (e.g., Phagocytosis for "cell eating," Pinocytosis for "cell drinking"). Example: Amoeba using pseudopodia.

  • Exocytosis: Cell transports molecules out using vesicles (known as "cell vomiting"), releasing enzymes or hormones.

Plant Tissues

• Histology is the study of tissues. Tissues are groups of cells working together to perform specific functions.

• Hierarchy: Cell $\rightarrow$ Tissue $\rightarrow$ Organ $\rightarrow$ Organ System $\rightarrow$ Organism.

• Meristematic Tissue (Actively dividing cells found in growth regions):

  • Apical Meristem: Located at root and shoot tips; increases length.

  • Lateral Meristem (Cambium): Located beneath the bark; increases thickness.

  • Intercalary Meristem: Located at the base of leaves or internodes (e.g., in grasses/sugarcane); increases internode length.

• Permanent Tissue (Non-dividing, mature cells):

  • Simple Permanent Tissue (Homogenous cells):

    • Parenchyma: Living cells used for food storage. Chlorenchyma contains chlorophyll; Aerenchyma contains air spaces for buoyancy.

    • Collenchyma: Living cells with thickened corners; provides mechanical strength and flexibility (found in stalks/stems of climbers).

    • Sclerenchyma: Dead, rigid tissue with lignin-thickened walls; provides toughness (found in bark, husk of coconut, and walnut shells via Sclereids).

  • Complex Permanent Tissue (Various cells working as a unit):

    • Xylem: Conducts water and nutrients upward (one-way flow) via transpiration pull. Comprised of tracheids, vessels, xylem fibers (dead), and xylem parenchyma (living).

    • Phloem: Translocates food bidirectional. Composed of sieve tubes, companion cells, phloem parenchyma (living), and phloem fibers (dead).

• Protective Tissues:

  • Epidermis: Outermost layer. Desert plants have a waxy "cuticle" made of cutin to prevent water loss. Stomata on leaves are regulated by kidney-shaped guard cells.

  • Cork: External dead tissue with walls coated in Suberin, which is impermeable to water and gases.

• Transpiration occurs through stomata as water vapor (leads to cooling and loss of turgidity), whereas Guttation occurs at night as water droplets through Hydathodes.

Animal Tissues

• Epithelial Tissue (Protective covering/lining):

  • Squamous: Thin and flat. Simple Squamous (mouth/oesophagus) vs. Stratified Squamous (skin).

  • Cuboidal: Cube-like cells in glands and kidney tubules.

  • Columnar: Pillar-like tall cells in intestine and stomach. Ciliated Columnar (respiratory tract) has hair-like projections to move mucus.

• Muscular Tissue (Contraction/relaxation for movement):

  • Skeletal Muscle: Elongated, cylindrical, striated, multinucleated, voluntary, and easily fatigued (attached to bones).

  • Smooth Muscle: Spindle-shaped, non-striated, uninucleated, involuntary, and non-fatiguing (found in internal organs/vessels).

  • Cardiac Muscle: Cylindrical, branched, striated, uninucleated, involuntary, and non-fatiguing (found in heart walls).

• Connective Tissue (Binding and support):

  • Areolar: Loose network between skin and muscles.

  • Adipose: Stores fat in adipocytes; acts as an insulator/shock absorber.

  • Dense Connective: Tendons (Muscle to Bone) and Ligaments (Bone to Bone).

  • Skeletal Connective: Cartilage (flexible, matrix of gel) vs. Bone (hard, matrix of Calcium and Phosphorous).

  • Fluid Connective: Blood and Lymph.

• Nervous Tissue: Found in the Brain, Spinal Cord, and Nerves.

  • Neuron Anatomy: Cell body (Soma) contains nucleus; Dendrites receive signals; Axon transmits signals (covered by Myelin sheath made of Schwann cells); Axon terminals release neurotransmitters across a gap called a Synapse.

Blood and Lymph Components

• Blood Study: Hematology.

• Composition: $55\%$ Liquid (Plasma) and $45\%$ Solid (Cells).

  • Plasma: $92\%$ water; contains proteins like Fibrinogen/Heparin (anticoagulants), Globulin (defense), and Albumin (osmotic balance).

  • Serum: Clear liquid remaining after clotting proteins are removed from blood.

  • Red Blood Cells (Erythrocytes): Count of $4.5-5.5$ million per $mm^3$. Biconcave, lack nucleus when mature, lifespan of $120$ days, formed in bone marrow. Destroyed in the Spleen ("Graveyard of RBC").

  • White Blood Cells (Leukocytes): Count of $5000-8000$ per $mm^3$. Lifespan $13-20$ days. Types: Monocytes, Lymphocytes, Neutrophils, Basophils, Eosinophils.

  • Platelets (Thrombocytes): Count of $1,50,000-3,50,000$ per $mm^3$. Essential for coagulation/clotting.

• Lymph: Colorless/yellowish fluid similar to plasma but lacking RBCs and blood proteins; maintains fluid balance.

Biological Kingdoms and Taxonomy

• Taxonomy: The science of naming and classifying organisms. Carolus Linnaeus is the Father of Taxonomy (published "Systema Naturae" in 1735).

• Order of Classification: Kingdom $\rightarrow$ Phylum $\rightarrow$ Class $\rightarrow$ Order $\rightarrow$ Family $\rightarrow$ Genus $\rightarrow$ Species.

• Classification Schemes:

  • Two Kingdom (Linnaeus): Plantae and Animalia.

  • Three Kingdom (Ernst Haeckel): Added Protista.

  • Five Kingdom (R.H. Whittaker, 1969): Monera, Protista, Fungi, Plantae, Animalia. Based on cell structure, nutrition, and organization.

  • Three Domain (Carl Woese): Bacteria, Archaea, Eukarya.

• Kingdom Monera: Unicellular prokaryotes with peptidoglycan walls. Includes Eubacteria and Archaebacteria (live in extreme conditions).

• Kingdom Protista: Eukaryotic unicellular organisms. Includes Protozoans like Amoeba (pseudopodia), Euglena (flagellum), Paramecium (cilia), and Plasmodium.

• Kingdom Fungi: Eukaryotic, mostly multicellular heterotrophs with chitin walls. Examples: Yeast (unicellular), mushrooms, bread moulds. Lichens represent a symbiotic relationship between Fungi and Blue-green Algae.

• Kingdom Plantae:

  • Cryptogamae (Hidden reproduction): Thallophyta (Algae - study called Phycology), Bryophyta (Amphibians of plant kingdom; Mosses/Liverworts), Pteridophyta (First terrestrial vascular plants; Ferns).

  • Phanerogamae (Exposed reproduction): Gymnosperms (Naked seeds; Pines/Deodar) and Angiosperms (Flowering plants with seeds in fruit).

  • Angiosperms split into Monocots (1 cotyledon, parallel veins, fibrous roots) and Dicots (2 cotyledons, net veins, taproot).

• Kingdom Animalia:

  • Invertebrates: Porifera (sponges), Cnidaria (jellyfish), Platyhelminthes (flatworms), Aschelminthes (roundworms), Annelida (segmented worms), Arthropoda (jointed legs - largest phylum), Mollusca (soft bodied - second largest), Echinodermata (spiny skin).

  • Vertebrates: Pisces ($2$-chambered heart), Amphibians ($3$-chambered heart), Reptiles ($3$-chambered, exception crocodile), Aves (Birds, $4$-chambered, warm-blooded), Mammals ($4$-chambered, mammary glands).

Human Physiology: Nervous and Endocrine Systems

• Central Nervous System (CNS): Brain and Spinal Cord.

  • Human Brain: Protected by skull ($22$ bones: $14$ facial, $8$ cranial) and three layers of meninges (Dura Mater, Arachnoid Mater, Pia Mater). Consumes $20\%$ of total oxygen and $20-25\%$ of glucose.

  • Forebrain: Cerebrum (largest part, memory/learning), Thalamus (sensory relay), Hypothalamus (base of thalamus, controls hunger, thirst, temperature, and pituitary).

  • Midbrain: Vision and hearing processing.

  • Hindbrain: Pons (facial sensation), Cerebellum (body balance, "little brain"), Medulla Oblongata (involuntary heart/respiration control).

  • Spinal Cord: $31$ pairs of nerves (Cervical-$8$, Thoracic-$12$, Lumbar-$5$, Sacral-$5$, Coccygeal-$1$ bundle called Cauda Equina).

• Peripheral Nervous System (PNS):

  • Somatic: Voluntary control (Sensory/Afferent vs Motor/Efferent).

  • Autonomic: Involuntary control. Sympathetic ("Fight or Flight") and Parasympathetic ("Rest and Digest").

• Endocrine System (Ductless glands secreting hormones into blood):

  • Pituitary: Master gland. Anterior (Growth Hormone, Prolactin) and Posterior (ADH/Vasopressin - water balance, Oxytocin - milk secretion/labor).

  • Pineal: Secretes Melatonin (regulates sleep-wake circadian rhythm).

  • Thyroid: Requires iodine to produce Thyroxine (metabolism). Deficiency causes goitre.

  • Adrenal: Located above kidneys; secretes Adrenaline (stress response). Deficiency causes Addison's disease.

  • Pancreas: Mixed/Heterocrine gland. Islets of Langerhans contain $\alpha$-cells (Glucagon) and $\beta$-cells (Insulin). Deficiency of insulin causes Diabetes Mellitus.

Human Physiology: Digestion and Respiration

• Digestive System:

  • Mouth: Salivary amylase breaks starch.

  • Oesophagus: $25\,cm$ tube, uses peristalsis.

  • Stomach: J-shaped; secretes Hydrochloric Acid ($HCl$, pH $1.6$), Pepsin (protein digestion), and Mucus.

  • Small Intestine: Longest part ($6.5-7.5\,m$). Duodenum receives Bile (from Liver/Gallbladder for fat emulsification) and Pancreatic juice (Amylase, Lipase, Trypsin). Inner walls have Villi to increase absorption area.

  • Large Intestine: Absorb water and electrolytes. Parts: Cecum, Colon, Rectum.

  • Liver: Study called Hepatology. Largest gland. Converts glucose to glycogen (Glycogenesis) and detoxifies blood via Hepatocytes and Kupffer cells.

• Respiratory System:

  • Passage: Nose $\rightarrow$ Pharynx $\rightarrow$ Larynx (Adam's apple) $\rightarrow$ Trachea (C-shaped cartilage) $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli (gas exchange site).

  • Diaphragm: Inhalation (moves down, ribs up) vs Exhalation (moves up, ribs down).

  • Cellular Respiration: Oxygen splits glucose to release energy ($ATP$).

    • Aerobic: Requires oxygen, $38\,ATP$ molecules produced, occurs in mitochondria/cytoplasm.

    • Anaerobic: No oxygen, $2\,ATP$ molecules produced, end products are Ethanol (yeast) or Lactic Acid (muscles - causes cramps).

Cardiovascular and Excretory Systems

• Heart: $4$ chambers. Sound is "Lub-Dub" (closing of valves). Normal cardiac output is about $5\,L/min$. Pulse rate $60-100\,bpm$.

  • Vessels: Arteries (thick-walled, oxygenated blood except pulmonary) vs Veins (thin-walled, deoxygenated blood except pulmonary).

  • Pacemaker: Sinoatrial (SA) Node initiates electrical signals.

• Excretory System: Maintains homeostasis. Main organ: Kidneys ($10-12\,cm$ length).

  • Nephron: Structural unit ($1$ million per kidney). Filters about $1100-1200\,mL$ of blood per minute via Glomerulus and Bowman's capsule.

  • Urine: $95\%$ water, $2\%$ urea. Color yellow due to Urochrome. Excreted via Ureters $\rightarrow$ Bladder $\rightarrow$ Urethra.

  • Excretion Modes: Ammonotelism (ammonia), Ureotelism (urea; mammals), Uricotelism (uric acid; insects/lizards).

Human Health and Nutrition

• Pathogens: Viruses (genetic material in Capsid), Bacteria (prokaryotic, treated by antibiotics), Protozoa, and Fungi.

• Viral Diseases: Dengue (Flavivirus, Aedes Aegypti carrier), Measles, Rabies (Lyssavirus, causes hydrophobia), AIDS (HIV, ELISA test), Polio (Jonas Salk vaccine).

• Bacterial Diseases: Plague (Yersinia pestis, "Black Death"), Cholera (Vibrio cholerae, "Blue Death"), Tuberculosis (Mycobacterium tuberculosis, BCG vaccine), Typhoid (Salmonella typhi, Widal test).

• Macronutrients:

  • Carbohydrates: Quick energy ($4\,cal/g$). Glucose, Fructose, Starch, Cellulose.

  • Fats: Highest energy ($9\,cal/g$). Adipose storage.

  • Proteins: Polymer of amino acids ($20$ total, $9$ essential). Deficiency causes Kwashiorkor (swollen abdomen) or Marasmus (body wasting).

• Vitamins:

  • Water Soluble: Vitamin B (B1-Thiamine, B12-Cyanocobalamin) and Vitamin C (Ascorbic acid - scurvy).

  • Fat Soluble: Vitamin A (Retinol - night blindness), D (Calciferol - rickets), E (Tocopherol), K (Phylloquinone - blood clotting).

Heredity and Genetics

• Gregor Mendel: Father of Genetics. Experimented with Pea Plants (Pisum sativum).

  • Monohybrid Cross: Phenotypic ratio of $3:1$ (Tall:Dwarf) in the second generation ($F_2$).

  • Dihybrid Cross: Phenotypic ratio of $9:3:3:1$ in the second generation.

• Inheritance Laws: Dominance, Segregation, and Independent Assortment.

• Human Skeletal System: $80$ Axial bones and $126$ Appendicular bones. Total $206$ (adult) or $300$ (child).

  • Bones: Femur (longest/strongest), Stapes (smallest in ear). Skull has $22$ bones; Rib cage has $25$ bones including sternum.

  • Teeth: Enamel is the hardest part. Adult formula: $2,1,2,3/2,1,2,3$ (Incisors, Canines, Premolars, Molars). Total $32$. Children lack premolars ($20$ total).