Biology: Microscopy and Cell Theory

Microscopy

• Compound light microscopes can examine living cells but magnify up to only 1000x, insufficient for most organelles.
• Electron microscopes can magnify up to 2,000,000x, examining non-living cells and structures inside or on their surfaces.

Cell Theory

• All living things are made of cells.
• Cells are the basic unit of structure and function in an organism.
• All cells come from pre-existing cells.
• Schleiden (1838): discovered all plants are made of cells.
• Schwann (1839): discovered all animals are made of cells.
• Virchow (1855): discovered all cells come from pre-existing cells.

Cellular Organization

• Cells are the foundational units for biological organization.
• Levels of organization progress from smallest to largest: Organelle → Cell → Tissue → Organ → Organ System → Organism

Cell Membrane

• Also known as the plasma membrane or phospholipid bilayer.
• Function: Acts as a barrier between the cell's interior and the environment, with selective permeability.
• Components:
  • Phospholipids: Major membrane component.
  • Proteins: Facilitate substance transport.
  • Carbohydrates: Aid in cell recognition.

Cytoskeleton

• Function: Provides cell shape, movement, and division.
• Examples: cilia, flagella, pseudopod, and centrioles.

Centrioles

• Part of the cytoskeleton involved in cell division.
• Found only in animal cells.

Cytoplasm

• Includes cytosol (gel-like fluid), cytoskeleton, and organelles.

Nucleus

• Contains DNA (genetic information).
• Controls cell activities.
• Found only in eukaryotic cells.

Ribosomes

• Synthesize proteins.
• Can be free-floating in the cytoplasm or bound to the rough endoplasmic reticulum.

Endoplasmic Reticulum

• Smooth ER: Lacks ribosomes; produces lipids, ships to Golgi, and breaks down toxins.
• Rough ER: Contains ribosomes; produces and ships proteins to the Golgi.

Golgi Apparatus

• Receives proteins and lipids from the ER.
• Packages and distributes them throughout the cell.

Vacuoles

• Membrane-bound spaces for temporary storage (ions, nutrients, water, waste).
• Plant cells have a large central vacuole, maintaining turgor pressure.

Lysosomes

• Membrane-bound pouches with enzymes to break down waste, materials, and invaders.
• Found only in animal cells.

Mitochondria

• Found in all eukaryotic cells.
• Generates ATP (energy) during cellular respiration using glucose.

Chloroplasts

• Found in plant cells and certain protists.
• Conduct photosynthesis, converting light energy into glucose.

Cell Wall

• Rigid structure outside the cell membrane in plants, fungi, and some protists.
• Provides support and protection.

Extracellular Matrix (ECM)

• Found in animal cells.
• Functions: Supporting, adhering, moving and regulating the cell.

Cell Type Differences

• Animal cells: Contain lysosomes, centrioles, cilia, and flagella.
• Plant cells: Contain a cell wall, chloroplasts, and a large central vacuole.