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Chapter 8: Cell Structure & Function

1. Cell Theory

• Fundamentals:

  • All living things are composed of cells.

  • Cells are the basic unit of structure and function.

  • New cells arise from existing cells.

2. Scale of Cells and Microscopy

2.2 Types of Microscopes

• Light Microscopes:

  • Samples can be alive.

  • Uses light and lenses to magnify images.

  • Requires dyes or fluorescent labels for visibility.

• Electron Microscopes:

  • Samples must be dead and chemically fixed.

  • Uses electrons for high magnification.

  • Two types:

    • Scanning Electron Microscopy (SEM): Surface examination.

    • Transmission Electron Microscopy (TEM): Examines thin cross-sections.

3. Basic Cell Structure

• General Features:

  • Enclosed by a membrane.

  • Contains cytoplasm, which includes water, salts, ions, macromolecules, and organelles.

• Organelles:

  • Specialized components that perform specific functions.

  • Can be membrane-bound or non-bound.

• Types of Cells:

  • Prokaryotes: Smaller, lack a nucleus.

  • Eukaryotes: Larger, possess a nucleus.

4. Key Organelles and Their Functions

• Cell Wall: Provides structure and protection (plants).

• Chloroplast: Site of photosynthesis (plants).

• Central Vacuole: Stores materials and helps maintain cell structure (plants).

• Nucleus: Contains DNA; controls cellular activity.

• Ribosomes: Sites of protein synthesis.

• Endoplasmic Reticulum (ER):

  • Rough ER: Synthesizes proteins.

  • Smooth ER: Synthesizes lipids; detoxifies.

• Mitochondrion: Produces ATP through cellular respiration.

• Golgi Body: Modifies and sorts proteins and lipids for secretion.

• Lysosomes: Digest waste materials.

5. Cell Transport Mechanisms

5.1 Importance of Transport

• Maintenance of homeostasis through selective permeability.

• Transport proteins and vesicles are used for materials that cannot pass freely.

5.2 Types of Transport

• Passive Transport:

  • Does not use energy; moves substances down the concentration gradient.

  • Diffusion: Movement from high to low concentration.

  • Facilitated Diffusion: Requires special proteins for larger molecules.

  • Osmosis: Diffusion of water through selectively permeable membranes.

• Active Transport:

  • Uses energy; moves substances against their concentration gradient.

  • Protein Pumps: Transport ions using ATP.

  • Bulk Transport: Vesicles move large molecules in/out of cells;

    • Endocytosis: Materials into the cell.

    • Exocytosis: Materials out of the cell.

6. Homeostasis in Living Organisms

• Organisms maintain a relatively stable internal environment.

• Unicellular Organisms: Grow, respond to stimuli, and reproduce independently.

• Multicellular Organisms: Specialized cells that communicate and collaborate for overall organism function.

7. Biological Organization

• Levels of Organization:

  • Atoms → Molecules → Cells → Tissues → Organs → Organ Systems → Organisms → Populations → Communities → Ecosystems → Biosphere

8. Cell Communication

• Chemical Signals: Cells communicate through chemical signals and proteins.

• Cell Junctions: Physical connections facilitating communication between cells.

• Receptor Proteins: Translate external signals into cellular responses, altering cellular activity based on the stimulus.