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Cell Structure and Function: Study Notes for General Biology

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Cell Structure and Function

Introduction to Cells

Cells are the basic unit of life in all living organisms. They carry out essential functions necessary for survival and reproduction. Understanding cell structure and function is fundamental to biology.

  • Cell Theory: All living things are composed of cells; cells are the basic unit of structure and function in living organisms; all cells arise from pre-existing cells.

  • Types of Cells: Cells are classified as prokaryotic or eukaryotic.

  • Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; examples include bacteria and archaea.

  • Eukaryotic Cells: Have a nucleus and membrane-bound organelles; examples include plant, animal, fungal, and protist cells.

Cell Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct processes.

  • Nucleus: Contains genetic material (DNA) and controls cellular activities.

  • Ribosomes: Sites of protein synthesis; found free in cytoplasm or attached to the endoplasmic reticulum.

  • Endoplasmic Reticulum (ER): Network of membranes involved in protein and lipid synthesis.

    • Rough ER: Studded with ribosomes; synthesizes proteins.

    • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies chemicals.

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

  • Mitochondria: Powerhouse of the cell; site of cellular respiration and ATP production.

  • Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.

  • Plasma Membrane: Semi-permeable barrier that controls movement of substances in and out of the cell.

  • Cytoskeleton: Network of protein filaments that provide structural support, shape, and aid in cell movement.

  • Chloroplasts: (Plant cells only) Site of photosynthesis; contain chlorophyll.

  • Cell Wall: (Plant cells, fungi, and some prokaryotes) Provides structural support and protection.

Cell Membrane Structure and Function

The cell membrane is essential for maintaining homeostasis and regulating the internal environment of the cell.

  • Phospholipid Bilayer: Composed of two layers of phospholipids with hydrophilic heads and hydrophobic tails.

  • Proteins: Embedded in the membrane; function as channels, carriers, receptors, and enzymes.

  • Fluid Mosaic Model: Describes the dynamic and flexible nature of the cell membrane.

  • Selective Permeability: Allows certain molecules to pass while restricting others.

Transport Across Cell Membranes

Cells transport substances across their membranes using various mechanisms.

  • Passive Transport: Movement of substances without energy input.

    • Diffusion: Movement of molecules from high to low concentration.

    • Osmosis: Diffusion of water across a semi-permeable membrane.

    • Facilitated Diffusion: Movement of molecules via membrane proteins.

  • Active Transport: Movement of substances against concentration gradient using energy (ATP).

    • Example: Sodium-potassium pump ( pump).

  • Bulk Transport: Movement of large particles via vesicles.

    • Endocytosis: Taking in substances by engulfing them.

    • Exocytosis: Expelling substances from the cell.

Comparison of Prokaryotic and Eukaryotic Cells

Prokaryotic and eukaryotic cells differ in structure and complexity.

Feature

Prokaryotic Cells

Eukaryotic Cells

Nucleus

Absent

Present

Membrane-bound Organelles

Absent

Present

Size

Smaller (1-10 μm)

Larger (10-100 μm)

Examples

Bacteria, Archaea

Plants, Animals, Fungi, Protists

Cellular Respiration and Energy Production

Cells obtain energy through cellular respiration, a process that converts glucose into ATP.

  • Cellular Respiration Equation:

  • Stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain.

  • ATP: Adenosine triphosphate, the main energy currency of the cell.

Photosynthesis (Plant Cells)

Photosynthesis is the process by which plants convert light energy into chemical energy.

  • Photosynthesis Equation:

  • Occurs in: Chloroplasts of plant cells.

  • Importance: Provides energy and organic molecules for most life forms.

Summary

Cells are the fundamental units of life, with complex structures and functions that enable organisms to survive and reproduce. Understanding cell structure, organelles, membrane transport, and energy production is essential for further study in biology.

Additional info: Some details were inferred based on standard General Biology curriculum and context from the handwritten notes.

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