Lab 3: Cells, Diffusion/Osmosis, Tissues

Cellular Structure and Function

• Cell Overview: Smallest structural and functional unit of living organisms, consisting of a plasma membrane enclosing cytoplasm (cytosol and organelles).

• Key Organelle Functions:

  • Plasma Membrane: Controls movement of substances into and out of the cell.

  • Microvilli: Membrane folds that increase surface area for absorption or secretion.

  • Nucleus & Nucleolus: Houses DNA; nucleolus serves as assembly site for ribosomes.

  • Mitochondria: Synthesizes ATP via aerobic cellular respiration.

  • Ribosomes: Primary site of protein synthesis.

  • Rough Endoplasmic Reticulum (RER): Processes and transports proteins from attached ribosomes; synthesizes phospholipids.

  • Smooth Endoplasmic Reticulum (SER): Synthesizes fatty acids and steroids; detoxifies toxic substances.

  • Golgi Complex: Modifies, sorts, and packages proteins received from RER.

  • Lysosomes: Contain enzymes that digest and recycle worn-out organelles and substances.

  • Peroxisomes: Produce hydrogen peroxide and detoxify harmful substances.

  • Cytoskeleton: Three types of protein filaments maintaining cell shape and driving movement.

  • Centrosomes (Centrioles): Form the mitotic spindle, cilia, and flagella.

Somatic Cell Cycle

• Interphase: Period of growth and normal metabolic activity where DNA replicates.

  • G1 Phase ($8\text{--}10\text{ hours}$): Cell is metabolically active, duplicates organelles, and begins centrosome replication.

  • S Phase ($8\text{ hours}$): DNA is replicated.

  • G2 Phase ($4\text{--}6\text{ hours}$): Growth continues, enzymes and proteins are synthesized, and centrosome replication completes.

• Mitotic (M) Phase: Period of cell division.

  • Prophase: Nucleolus and nuclear membrane disappear; chromatin condenses into chromosomes; centrioles move to opposite poles; spindle fibers form.

  • Metaphase: Chromosomes align at the metaphasal plate; spindle fibers attach to centromeres.

  • Anaphase: Chromatids separate and move toward opposite poles.

  • Telophase: Prophase activities reverse to re-form nuclear structures.

  • Cytokinesis: Division of cytoplasm resulting in two genetically identical daughter cells.

Transport Across the Plasma Membrane

• Simple Diffusion: Net movement of solute down a concentration gradient from high to low concentration.

  • Diffusion rate depends on molecular weight (e.g., Methylene blue dye crystal at $\text{MW } 320$ vs. Potassium permanganate dye crystal at $\text{MW } 158$).

• Osmosis: Diffusion of solvent (water) across a selectively permeable membrane toward higher solute concentration.

  • Osmotic Pressure: The amount of hydrostatic pressure required to stop osmotic flow.

• Tonicity Concepts:

  • Isotonic Solution: Equal solute concentration relative to cytosol; cell volume remains unchanged.

  • Hypotonic Solution: Lower solute concentration; water enters the cell, causing swelling and potential rupture (hemolysis in red blood cells).

  • Hypertonic Solution: Higher solute concentration; water leaves the cell, causing it to shrink (crenation in red blood cells).

Histology and Epithelial Tissue

• Histology: Study of the microscopic anatomy of cells and tissues.

• Epithelial Tissue Features:

  • High cellularity with closely packed cells and minimal extracellular matrix.

  • Avascular nature; receives nutrients via diffusion from underlying connective tissue across a basement membrane.

  • Classified into covering/lining epithelia and glandular epithelia.

• Cell Shapes:

  • Squamous: Thin, flattened cells with flat nuclei.

  • Cuboidal: Cube-shaped cells with central round nuclei.

  • Columnar: Tall cells with oval nuclei near the base.

  • Transitional: Variable shape (cuboidal when relaxed, squamous when stretched).

• Layering Arrangements:

  • Simple Epithelium: Single cell layer functioning in diffusion, filtration, secretion, or absorption (includes

  • Simple Squamous: A single layer of flattened cells that allows for the diffusion of gases and serves as a filtration barrier, commonly found in places like the alveoli of lungs and the lining of blood vessels.

  • Simple cuboidal: A single layer of cube-shaped cells that plays a role in secretion and absorption, typically located in glands, the kidney tubules, and the surface of ovaries.

  • Simple columnar: A single layer of tall, column-like cells that is involved in absorption and secretion, prominently found in the lining of the digestive tract and the uterus.

  • Stratified Epithelium: Multiple cell layers providing protection against abrasion, often found in the skin, mouth, and esophagus.

  • Pseudostratified Columnar: A type of epithelium that appears to have multiple layers due to varying cell heights but is actually a single layer, mainly involved in secretion and the movement of mucus, commonly found in the respiratory tract lining.

  • Simple Columnar: Contains cilia on the surface to help move substances across the epithelial surface, commonly found in the respiratory tract and fallopian tubes.

  • Stratified Epithelium: Multiple cell layers forming a protective barrier against wear and pathogens (includes stratified squamous, stratified cuboidal, stratified columnar, transitional).

  • Pseudostratified Columnar: Single cell layer with varied cell heights and nuclear levels giving a false stratified appearance; all cells touch the basement membrane.