Cells, Membrane, and Transport

Cell Theory

  • All organisms are made of cells.

  • Cells are the basic unit of life and structure.

  • All cells come from pre-existing cells.

Cell Size and Shape

  • Cells must be large enough to house components and carry out functions but small enough to maintain a sufficient surface area to volume ratio for nutrient absorption and waste disposal.

  • Size variations: 10 m to 1 nm (nanometers) scale.

Structure and Function of Cells

Prokaryotic vs Eukaryotic Cells

  • Prokaryotic cells are structurally simpler than eukaryotic cells.

    • Types:

      1. Prokaryotic: bacteria, archaea

      2. Eukaryotic: protists, plants, fungi, animals

  • Common features among all cells:

    • Plasma membrane

    • DNA

    • Ribosomes

Differences between Prokaryotic and Eukaryotic Cells

Prokaryotic Cells

  • Typically small and simple.

  • Lack a membrane-bound nucleus; DNA is found in the nucleoid region.

  • Contains ribosomes.

Eukaryotic Cells

  • Larger (10-100 µm in diameter).

  • Contains a true nucleus.

  • Comprise membranous (e.g., rough and smooth ER, Golgi apparatus) and non-membranous organelles.

  • Metabolism compartmentalized, increasing membrane surface area for reactions.

Cell Structures

Prokaryotic Cell Structure

  • Components:

    • Ribosomes

    • Capsule

    • Cell wall

    • Plasma membrane

    • Pili

    • Flagella

    • Nucleoid region (DNA)

Eukaryotic Cell Structure (Animal)

  • Components:

    • Rough and smooth endoplasmic reticulum

    • Flagellum

    • Lysosome

    • Nucleus

    • Ribosomes

    • Golgi apparatus

    • Mitochondrion

    • Plasma membrane

Eukaryotic Cell Structure (Plant)

  • Components:

    • Central vacuole

    • Chloroplast

    • Cell wall

    • Plasmodesmata

Functions of Cell Components

  • Cell Wall: Protects cell, maintains shape.

  • Cell Membrane: Selective barrier controlling material in and out.

  • Nucleus: Houses genetic material and controls gene expression.

  • Endoplasmic Reticulum (ER):

    • Rough ER: Synthesizes proteins and membranes.

    • Smooth ER: Synthesizes lipids and stores calcium ions, detoxifies.

  • Mitochondria: Converts food into ATP (energy).

  • Chloroplasts: Site of photosynthesis in plant cells.

  • Ribosomes: Translate RNA to protein.

  • Lysosomes: Digestion of nutrients and recycling materials.

  • Golgi Apparatus: Modifies, stores, and transports cellular molecules.

  • Vacuoles: Maintain water balance and store nutrients.

Membrane Structure

  • Phospholipid Bilayer:

    • Composed of hydrophilic heads and hydrophobic tails.

    • Selectively permeable, allowing certain molecules to pass while blocking others.

  • Fluid Mosaic Model:

    • Proteins embedded in the phospholipid bilayer perform various functions, including acting as enzymes, signal transduction, and transporters.

Transport Mechanisms Across Cell Membranes

  • Passive Transport: Diffusion across a membrane without using energy.

    • Diffusion: Movement from high to low concentration.

    • Facilitated Diffusion: Requires transport proteins to help substances cross a membrane.

  • Osmosis: Diffusion of water across a membrane, balancing solute concentrations on either side.

    • Types of Tonicity:

      • Isotonic: Equal solute concentration; no net movement of water.

      • Hypotonic: Lower solute concentration outside the cell; cells swell (turgid in plants, lysed in animals).

      • Hypertonic: Higher concentration outside the cell; cells shrink (plasmolysis in plants, crenation in animals).

  • Active Transport: Requires energy (ATP) to move solutes against their concentration gradient.

  • Endocytosis & Exocytosis: Mechanisms for large molecules: vesicles transport substances into (endocytosis) and out of (exocytosis) the cell.

    • Types of endocytosis: Phagocytosis, pinocytosis, receptor-mediated endocytosis.

Endomembrane System

  • Interconnected membranes include ER, Golgi apparatus, lysosomes, and plasma membrane. Form transport vesicles and communicate through physical contact and vesicle movement.

Study Tips

  • Create flashcards for each cell component and its function.

  • Fill in structures on a printed diagram of a cell without labels.