Biology Chapter: Cell Theory and Size (hard)

Cell Theory and Surface Area to Volume Ratio

• All living organisms consist of one or more cells; cells are fundamental units of life.
• Every function in an organism operates at the cellular level, emphasizing cells' importance.
• As cell size increases, volume grows faster than surface area, limiting cell size due to nutrient and waste exchange challenges.
• Smaller cells have a higher surface area-to-volume ratio, enhancing nutrient absorption and waste removal efficiency.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack a nucleus; DNA is not enclosed and is found in the cytoplasm.
• Prokaryotes lack membrane-bound organelles, are generally smaller, and simpler compared to eukaryotes.
• Bacterial cell walls are made of peptidoglycan; archaeal cell walls use pseudomurein.
• Eukaryotic cells have a membrane-bound nucleus and organelles (mitochondria, ER, Golgi apparatus).
• Eukaryotic cells are larger, more complex, and possess cell walls made of cellulose (in plants) or chitin (in fungi).

Evolution of the Five Kingdoms of Life

• Monera: Comprised of prokaryotes (bacteria and archaea); single-celled organisms without a nucleus.
• Protista: Eukaryotic, mainly single-celled organisms like protozoa and algae, with diverse nutritional modes (autotrophic and heterotrophic).
• Fungi: Primarily multicellular eukaryotes that absorb nutrients through external digestion (molds, mushrooms, yeasts).
• Plantae: Multicellular autotrophic eukaryotes with cellulose-based cell walls; include trees, flowers, and grasses.
• Animalia: Multicellular heterotrophic organisms lacking cell walls; comprises humans, animals, and insects.

Prokaryotic Cell Structures and Functions

• Plasma membrane: Phospholipid bilayer with proteins that regulate substance movement and protect the cell; carbohydrates aid in cell recognition.
• Cell wall: Provides structure and protection; in bacteria, comprised of peptidoglycan, with variations in thickness and membranes based on Gram classification.
• Flagella: Long, whip-like structures for motility, capable of rotating 360 degrees in response to environmental signals (chemotaxis).
• Axial filament: Provides corkscrew movement in spirochetes, contains endoflagella.
• Fimbriae: Hair-like projections aiding in adherence and colonization.
• Pili: Longer than fimbriae, used in DNA transfer during conjugation.
• Capsule: Gelatinous outer layer providing protection and assisting in virulence by evading the immune system.
• Endospore: Resistant structures formed in adverse conditions, capable of withstanding heat and desiccation.
• Chromosome: Single, circular DNA molecule containing essential genetic information, located freely in the cytoplasm.

Flagella Arrangements

• Monotrichous: A single flagellum at one end of the cell.
• Lophotrichous: A tuft of flagella at one or both ends of the cell.
• Amphitrichous: A single flagellum or cluster at both ends of the cell.
• Peritrichous: Flagella are distributed around the cell's surface.

Plasma Membrane Components

• Phospholipids: Form the bilayer with hydrophobic tails inward and hydrophilic heads outward.
• Proteins: Embedded or surface-associated, facilitating transport, signaling, and enzyme functions.
• Cholesterol: Maintains fluidity and stability in eukaryotic membranes.
• Carbohydrates: Involved in cell recognition and communication, often in glycoproteins and glycolipids.

Movement Across Plasma Membranes

• Simple diffusion: Movement of molecules from high to low concentration without energy; ideal for small molecules like gases.
• Facilitated diffusion: Requires transport proteins for larger molecules (e.g., glucose) to pass the membrane.
• Osmosis: Water movement across a semi-permeable membrane based on solute concentration; results in isotonic, hypertonic, or hypotonic conditions affecting cell shape and function.
• Active transport: Movement of molecules against the concentration gradient (low to high) requiring energy (ATP) and transport proteins.

Bacterial and Archaeal Cell Walls

• Bacterial cell wall: Composed of peptidoglycan; provides shape and protection against osmotic pressure.
• Archaeal cell wall: Lacks peptidoglycan; composed of pseudomurein or other polymers suited for extreme environments.
• Gram-positive: Thick peptidoglycan retains crystal violet dye, appears purple, contains teichoic acids, lacks outer membrane.
• Gram-negative: Thin peptidoglycan layer covered by an outer membrane with lipopolysaccharides (LPS); does not retain crystal violet but stains pink with counterstain.

Explore the fundamental concepts of cell theory and the importance of the surface area to volume ratio in relation to cell size. This quiz will help you understand how these principles apply to the structure and function of living organisms. Test your knowledge and grasp the significance of these cellular concepts.