The Cell: Structure and Function

Foundations of Cytology

  • Definition: Cytology is the study of cellular structure and function.

  • General Principles:     * Cells are the basic unit of living organisms.     * All cells descend from earlier cells.     * Cellular structure is directly correlated to cellular function.

  • Fundamental Features of All Cells:     * Plasma membrane: The outer covering of the cell.     * Cytosol: The semifluid substance containing organelles.     * Chromosomes: Carry genetic information (genes).     * Ribosomes: The site for protein synthesis.

Prokaryotic Cells

  • Organisms: Single-celled organisms such as Bacteria and Cyanobacteria.

  • Characteristics:     * Lack a nucleus and membrane-bound organelles.     * Do not reproduce sexually.

  • Structural Components:     * Nucleoid: Region in the cytoplasm where DNA is concentrated.     * Cell Wall: Commonly composed of peptidoglycan.     * Flagella: Used for motility.     * Pili: Used for attachment or exchange of genetic material.     * Envelope: May include a gelatinous capsule or slime capsule (glycocalyx).

Cyanobacteria

  • Photosynthesis: Contain chlorophyll a and accessory pigments within thylakoids.

  • Historical Impact: Primary contributors to the early oxygenation of the ancient atmosphere.

  • Envelope: Enveloped by a mucilaginous sheath.

Eukaryotic Cells

  • Organization: Contain membrane-bound nuclei and organelles.

  • Protoplast: A broad term for all material and organelles enclosed by the plasma membrane.

  • Key Organelles:     * Mitochondria: Site of aerobic respiration.     * Endoplasmic Reticulum (ER): Includes Rough (with ribosomes) and Smooth versions.     * Golgi Apparatus: Involved in processing and packaging (Golgi body/vesicles).     * Cytoskeleton: Composed of Macrotubules, Intermediate filaments, and Microfilaments.

  • Plant-Specific Structures: Cell wall, Chloroplasts, Plasmodesmata, and a large Vacuole limited by the Tonoplast.

Protists and Amoeboid Movement

  • General: Single-celled eukaryotes including Amoeba, Paramecium, Spirogyra, and Euglena.

  • Amoeba:     * Irregularly shaped heterotrophs.     * Pseudopodia: Protrusions of cytoplasm used for "amoeboid movement" and capturing food to create food vacuoles.     * Contractile Vacuoles: Accumulate and expel water and waste.

  • Paramecium Structures: Includes Cillia, Oral groove (vestibulum), Cytostome (cell mouth), Anal pore (cytoproct), Macronucleus, and Micronucleus.