Cell Structure and Function

Cell Structure and Function

• Cell Theory: Cells are the fundamental unit of structure, function, and organization in all living organisms.
• Differentiation: Stem cells specialize into specific cell types (e.g., muscle, neuron).
• Tissues: Groups of similar cells performing a function (e.g., epithelial, muscle, nervous).
• Organs: Tissues working together to perform a function (e.g., heart, lungs).
• Systems: Collections of organs performing a specific function (e.g., cardiovascular, respiratory).
• Prokaryotic Cells (e.g., Bacteria): Nucleoid, plasmids, 70S ribosomes, capsule, cell wall. Example: E. coli.
• Eukaryotic Cells (e.g., Plant and Animal): Plasma membrane, cytoplasm, nucleus, nucleolus, endoplasmic reticulum (smooth and rough), Golgi apparatus, vesicles, lysosomes, 80S ribosomes, mitochondria, centrioles.
• Plant-Specific Organelles: Cell wall, chloroplasts, vacuole, tonoplast, amyloplasts, plasmodesmata, pits. Example: Palisade mesophyll.
• Microscopy: Different types of microscopes (light, electron) allow viewing of cell structures.
• Light Microscopes: Advantages: Easy to use, affordable, can observe living cells. Limitations: Lower magnification, resolution than electron microscopes.
• Gram Staining: Distinguishes Gram-positive (thick peptidoglycan layer, penicillin-susceptible) and Gram-negative (thin peptidoglycan, outer membrane, resistant to some antibiotics) bacteria. Procedure: Crystal violet, iodine, alcohol wash, safranin.
• Cell Measurement: Magnification = Measured Size / Actual Size. Convert units (e.g., mm to µm).

Cell Specialization

• Palisade Mesophyll Cells: Photosynthesis, cylindrical shape, many chloroplasts, large vacuole, thin walls. Located in leaves.
• Sperm Cells: Haploid nucleus, acrosome (enzymes), mid-section (mitochondria), tail (motility). Male reproductive cell.
• Egg Cells: Haploid nucleus, large cytoplasm, zona pellucida and corona radiata (protection). Female reproductive cell.
• Root Hair Cells: Large surface area for water and nutrient absorption, partially permeable membrane, mitochondria for active transport.
• White Blood Cells (WBCs): Lymphocytes (T cells, B cells), Neutrophils (phagocytic). Immune response cells.
• Red Blood Cells (RBCs): Biconcave shape, no nucleus, maximizes hemoglobin, small and flexible.

Tissue Structure and Function

• Epithelial Tissue: Squamous epithelium (thin, efficient diffusion, found in alveoli, COPD affects it). Columnar epithelium (contains goblet cells, cilia move mucus/pathogens, found in trachea).
• Endothelial Tissue: Blood vessels (single squamous layer reduces friction, regulates blood flow/pressure, Atherosclerosis).
• Muscular Tissue: Skeletal muscle (multinucleated, striated, sliding filament theory: actin, myosin, calcium, ATP). Fast-twitch vs. slow-twitch fibers.
• Nervous Tissue: Neurons (myelinated, non-myelinated axons, synaptic transmission: neurotransmitters). Neurotransmitter imbalances affect health (e.g., Parkinson's, depression).