Chapter 3: Cells – The Living Units (Anatomy & Physiology Study Notes)

Chapter 3: Cells – The Living Units

3-1 Cell Theory

The cell theory is a foundational concept in biology, stating that cells are the basic structural and functional units of life. All physiological functions of organisms depend on the activities of individual and collective cells.

• Cell Theory Principles:

  • All living things are composed of cells.

  • The cell is the basic unit of structure and function in organisms.

  • All cells arise from pre-existing cells.

• Cell Diversity:

  • Over 200 different types of human cells exist.

  • Cells differ in size, shape, subcellular components, and functions.

  • Examples include fibroblasts (connective tissue), erythrocytes (red blood cells), epithelial cells (lining and transport), muscle cells (movement), fat cells (nutrient storage), macrophages (defense), nerve cells (information processing), and sperm (reproduction).

• Cell Specialization: The mechanical activities of cells are determined by their shapes and specific subcellular structures.

3-2 Generalized Cell Structures

Despite their diversity, most cells share common structures and functions. The three basic parts of a cell are the plasma membrane, cytoplasm, and nucleus.

• Plasma Membrane: A flexible outer boundary that separates the cell from its environment. It includes the glycocalyx (cell surface sugars) and cell junctions (connections between cells).

• Cytoplasm: The intracellular fluid containing organelles, which are specialized structures that perform various cellular functions.

• Nucleus: The control center of the cell, containing genetic material (DNA).

Key Organelles and Structures:

• Nuclear envelope: Surrounds the nucleus and regulates passage of materials.

• Chromatin: DNA and associated proteins; condenses to form chromosomes during cell division.

• Rough Endoplasmic Reticulum (ER): Studded with ribosomes; site of protein synthesis.

• Smooth Endoplasmic Reticulum (ER): Lacks ribosomes; involved in lipid synthesis and detoxification.

• Ribosomes: Sites of protein synthesis; can be free in cytosol or attached to rough ER.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes for breaking down waste and cellular debris.

• Peroxisomes: Contain enzymes for detoxifying harmful substances.

• Mitochondria: Powerhouse of the cell; site of ATP production via aerobic respiration.

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structural support and facilitate movement.

• Centrosome and Centrioles: Organize microtubules and are important in cell division.

Example: The diagram provided shows a typical animal cell with labeled organelles, illustrating the spatial organization and relationships among cellular structures.

*Additional info: The notes are based on standard college-level Anatomy & Physiology content, and the images support identification of cell types and organelles as required for foundational understanding in the course.*