Comprehensive Notes – Cells, Tissues, & Biological Organization
Prokaryotic and Eukaryotic Cells
• Age & Complexity
– Prokaryotes = oldest, small, simple; first life forms.
– Eukaryotes evolved later from prokaryotes; larger, structurally complex.
• Genetic Material
– Prokaryote: DNA found in an un-bound nucleoid; usually a single circular chromosome.
– Eukaryote: DNA enclosed by a true nucleus; multiple linear chromosomes.
• Internal Compartments
– Prokaryotes lack membrane-bound organelles.
– Eukaryotes possess membrane-bound organelles (nucleus, ER, Golgi, mitochondria, chloroplasts, lysosomes, peroxisomes, etc.).
• Shared Universal Features
– \text{DNA}, \text{cytoplasm}, \text{ribosomes}, \text{plasma\ membrane} present in both.
– Ribosome function (protein synthesis) the same, but eukaryotic ribosomes are larger (80 S vs. 70 S).
• Cell Boundary Structures
– Capsule (glycocalyx) = extra polysaccharide layer in some prokaryotes; protection, adherence, virulence.
– Cell wall: peptidoglycan in bacteria; cellulose/chitin/cellulose-pectin in some eukaryotes (plants, fungi, some protists).
– Plasma membrane in all cells; phospholipid bilayer regulating transport.
• Motility & Surface Extensions
– Prokaryotic flagellum: simple protein filament spun by basal motor.
– Eukaryotic flagellum/cilium: 9!+!2 microtubule pattern, whiplike motion.
– Pili/Fimbriae (prokaryotes): attachment, conjugation.
• Organelle Matrix (fill-in table guidance)
– Nucleus → eukaryotes only → information storage/protection.
– Ribosome → both → protein synthesis.
– Endoplasmic reticulum → eukaryote → protein (rough) & lipid (smooth) processing.
– Golgi apparatus → eukaryote → modification, sorting, packaging.
– Mitochondrion → eukaryote → ATP production via aerobic respiration.
– Chloroplast → plant/algal eukaryote → photosynthesis.
– Capsule → some prokaryotes → virulence & desiccation resistance.
– Cell wall → most prokaryotes & some eukaryotes → support/shape.
– Flagellum → both (structure differs) → motility.
Hierarchy of Biological Organization
• Levels (smallest → largest)
- Chemical level: atoms, molecules, four biomolecule classes (carbohydrates, proteins, lipids, nucleic acids).
- Organelle level: mitochondria, nucleus, ER, Golgi, etc.—membrane-bound structures in eukaryotes.
- Cell: smallest functional unit of life (e.g., skin cell, neuron, RBC).
- Tissue: groups of similar cells performing a specialized function.
- Organ: groups of tissues working together (heart, lungs, skin).
- Organ System: organs coordinating for a process (respiratory, circulatory).
- Organism: integrated organ-system network maintaining homeostasis (human, cat, mushroom).
- Population: same-species organisms in an area.
- Community: multiple populations in the same locale.
- Ecosystem: communities + abiotic environment interactions.
- Biosphere: global sum of all ecosystems.
Animal Tissues
1. Epithelial Tissue
• Sheet of tightly packed cells; covers body surfaces, lines organs/cavities, forms glands.
• Cell junctions (tight, desmosome, gap) create selective barriers.
• Classified by layers (simple, stratified, pseudostratified) & cell shape (squamous, cuboidal, columnar).
| Type | Key Features | Typical Location | Function |
|---|---|---|---|
| Simple squamous | Single flat layer | Alveoli, capillaries | Diffusion, secretion |
| Simple cuboidal | Single cube layer | Kidney tubules, ovaries, glands | Absorption, secretion |
| Simple columnar | Single tall layer; goblet cells | Digestive tract, gall bladder | Absorption, mucus secretion |
| Pseudo-stratified columnar | One layer; nuclei at varying heights; often ciliated | Trachea, bronchi, uterine tubes | Secretion, propulsion |
| Stratified squamous | Many flat layers | Epidermis, mouth, vagina | Protection vs. abrasion |
| Stratified cuboidal | ≥2 cube layers | Sweat, salivary, mammary ducts | Protection, secretion |
| Stratified columnar | ≥2 tall layers | Male urethra, some gland ducts | Protection, secretion |
2. Connective Tissue
• Universal roles: bind, support, protect, insulate, store energy, transport.
• Structural elements: living cells + extracellular matrix (ECM of fibers & ground substance).
| Category | Subtype & Description | Location / Example | Main Function |
|---|---|---|---|
| Loose CT | Areolar, adipose, reticular; fewer fibers, more ground | Subcutaneous layers, lymph nodes, fat | Cushion, insulation, nutrient reserve |
| Dense CT | Dense regular (tendons), dense irregular (dermis) | Tendons, ligaments | Strong flexible support |
| Adipose | Fat droplets in adipocytes | Hypodermis, around organs | Energy storage, insulation |
| Cartilage | Hyaline, fibrocartilage, elastic; matrix of chondroitin sulfate; chondrocytes | Nose, epiglottis, intervertebral discs | Flexible support, cushioning |
| Bone (osseous) | Collagen + mineral salts; osteoblasts/osteocytes | Skeleton | Protection, support, Ca^{2+} storage, hematopoiesis |
| Blood | Plasma + RBC + WBC + platelets | Vessels, heart | Transport gases/nutrients, immunity, clotting |
3. Muscle Tissue
| Type | Cells | Location | Control | Function |
|---|---|---|---|---|
| Skeletal | Long, cylindrical, multinucleate, striated | Attached to bones | Voluntary | Body movement, posture, heat |
| Cardiac | Branched, uni-nucleate, striated, intercalated discs | Heart wall | Involuntary | Pump blood |
| Smooth | Spindle-shaped, non-striated, uni-nucleate | Walls of hollow organs (GI, vessels, bladder, uterus) | Involuntary | Propel substances, regulate diameter |
4. Nervous Tissue
• Primary cell: Neuron—dendrites, soma, axon—conducts electro-chemical impulses.
• Glial (support) cells:
– Astrocytes (CNS): chemical environment upkeep.
– Microglia (CNS): phagocytic defense.
– Ependymal (CNS): ciliated, circulate cerebrospinal fluid.
– Oligodendrocytes (CNS): myelin production.
– Satellite cells (PNS): support neuron cell bodies.
– Schwann cells (PNS): myelinate peripheral axons.
Plant Tissues
Meristematic Tissue (dividing)
• Apical meristem: located at root & shoot tips; primary growth (height).
• Lateral meristem: vascular cambium & cork cambium; secondary growth (girth).
– Vascular cambium → secondary xylem (wood) + secondary phloem.
– Cork cambium → cork cells; with phloem forms bark.
Permanent Tissue (non-dividing)
Simple Permanent
• Epidermis: outer covering; waxy cuticle minimizes water loss, blocks pathogens; guard cells around stomata regulate gas exchange.
• Ground tissue / Fundamental tissue
– Parenchyma: thin-walled; storage & photosynthesis.
– Collenchyma: uneven cell walls; flexible support to young organs.
– Sclerenchyma: thick lignified walls; includes fibers (commercial rope, flax) & sclereids (seed coats, gritty pear texture); rigid support.
Complex Permanent (Vascular)
• Xylem: tracheids + vessel elements; water/mineral conduction upward; secondary xylem = wood.
• Phloem: sieve-tube elements + companion cells; translocates organic nutrients bidirectionally.
Cell Modifications & Adaptations
• Microvilli on intestinal epithelium ↑ surface area for absorption.
• Cilia on respiratory pseudostratified epithelium sweep mucus.
• Flagella enable sperm motility.
• Root hairs (plants) enlarge absorptive area for water/minerals.
• Tracheary element perforations (vessel plates) speed water flow.
• Cuticle & cork bark reduce desiccation, pathogen entry.
• Myelin sheath insulates axons, accelerating impulse conduction.
Numerical & Statistical References
• Levels of organization in multicellular organisms = 5 (cell → tissue → organ → organ system → organism).
• Microtubule arrangement in eukaryotic flagella/cilia = 9!+!2 pattern.
Ethical, Philosophical & Practical Implications
• Understanding cellular differences underpins antibiotic selectivity (targeting peptidoglycan in bacteria without harming human cells).
• Knowledge of tissue regeneration (meristems, stem cells) informs agriculture & medical therapies.
• Recognizing tissue specialization guides pathology (e.g., epithelial dysplasia in cancer, connective tissue disorders, neurodegeneration).
Quick Review Practice (Based on Activity)
• Brain & spinal cord → Nervous tissue.
• Epidermis → Stratified squamous epithelium.
• Ligaments, tendons, fat, bone → Connective tissue (dense & supportive).
• Heart wall → Cardiac muscle tissue.
• Vessel walls & respiratory tract lining → Vascular tissue (smooth muscle + pseudostratified epithelium).