Cell Biology: Foundations for Anatomy & Physiology (BIOL 109)

Introduction to Cells

Cell Theory

The cell theory is a fundamental concept in biology that describes the properties of cells, the basic unit of life. It provides the foundation for understanding the structure and function of all living organisms.

• All living things are made of cells: Every organism, from bacteria to humans, is composed of one or more cells.

• All cells come from pre-existing cells: Cells reproduce by dividing, ensuring continuity of life.

• Cells are the smallest physiologic unit: The cell is the minimal unit capable of performing all life processes.

Example: Human tissues such as muscle, nerve, and skin are all composed of cells that originated from a single fertilized ovum.

Cellular Origin and Differentiation

All cells in the human body are descendants of a single cell, the fertilized ovum. Through cell division and differentiation, specialized tissues are formed.

• Cell division: The process by which a cell replicates to produce new cells.

• Cell differentiation: The process by which cells become specialized for specific functions.

• Four basic types of body tissue:

  • Epithelial tissue: Covers body surfaces and lines cavities.

  • Connective tissue: Supports, binds, and protects organs.

  • Muscle tissue: Responsible for movement.

  • Neural tissue: Conducts electrical impulses for communication.

Example: The fertilized ovum divides and differentiates to form the skin (epithelial), bones (connective), heart (muscle), and brain (neural tissue).

Cell Anatomy

Eukaryotic Cell Organization

Eukaryotic cells, which include all animal and plant cells, have a complex structure with specialized compartments called organelles.

• Genetic material stored in a central nucleus: The nucleus contains DNA, the hereditary material.

• Cell membrane (or plasma membrane): Forms the outer boundary of the cell, regulating entry and exit of substances.

• External watery environment: Called extracellular fluid or interstitial fluid.

• Internal environment: The region between the plasma membrane and nucleus is the cytoplasm.

• Cytoplasm: Contains liquid cytosol and various organelles (membranous and nonmembranous).

Example: In a typical human cell, the nucleus is centrally located, surrounded by cytoplasm and enclosed by the plasma membrane.

Cellular Components

The cell is organized into distinct regions and structures, each with specific functions.

• Plasma membrane: Separates the cell from its environment and controls movement of substances.

• Cytoplasm: The internal fluid and structures between the plasma membrane and nucleus.

• Cytosol: The liquid portion of the cytoplasm, containing dissolved ions and molecules.

• Organelles: Specialized structures within the cytoplasm that perform specific functions.

Membranous Organelles	Nonmembranous Structures
Peroxisomes Lysosomes Endoplasmic reticulum Golgi apparatus Mitochondria Nucleus	Cytoskeleton Microvilli Cilia Ribosomes Centrioles

Additional info: Membranous organelles are surrounded by lipid bilayers, allowing compartmentalization of cellular processes. Nonmembranous structures are typically protein-based and provide structural support or facilitate movement.