Biology: The Cell: The Fundamental Unit of Life

Cell Types

  • Prokaryotic Cells

    • Small, simple, unicellular, no organelles.

    • First appeared 3.5 billion years ago.

  • Eukaryotic Cells

    • Larger, complex, unicellular or multicellular, contain membrane-enclosed organelles.

    • First appeared 2.1 billion years ago.

Prokaryotic Domains

  • Bacteria and Archaea

    • All prokaryotes are unicellular.

    • Fossils date back to at least 3.5 billion years.

Eukaryotic Cell Structure

  • Common features: Plasma membrane, nucleus, mitochondria.

  • Animal cells have unique organelles such as lysosomes.

  • Plant cells have unique organelles such as chloroplasts and cell walls.

Plasma Membrane

  • Surrounds all cells; regulates material passage.

  • Composed of a phospholipid bilayer and proteins.

Transport Mechanisms

  • Passive Transport (no energy required):

    • Diffusion: Molecules move from high to low concentration.

    • Osmosis: Water moves from areas of high to low water concentration.

    • Facilitated Diffusion: Large molecules pass through transport proteins.

  • Active Transport (energy required):

    • Moves substances from low to high concentration, against the gradient.

Membrane Function

  • Selectively permeable, regulating entry/exit of substances.

Nucleus

  • Contains the cell's DNA and directs cell activities.

  • Surrounded by a nuclear envelope with pores for molecule passage.

Protein Synthesis

  • Transcription in the nucleus produces RNA from DNA.

  • Translation occurs at ribosomes, producing proteins.

Golgi Apparatus

  • Modifies, sorts, and ships cellular products, including proteins.

Energy Organelles

  • Chloroplasts: Site of photosynthesis in plant cells.

  • Mitochondria: Site of cellular respiration in both plant and animal cells, producing ATP.

Vacuoles

  • Intracellular sacs for storage (e.g., nutrients, pigments).

  • Plant cells typically have a large central vacuole.

Cell Walls and Cytoskeleton

  • Cell walls provide support in plants and fungi; absent in animal cells.

  • Animal cells use a cytoskeleton for support and flexibility.

Extracellular Matrix

  • In animal cells, facilitates adhesion and tissue formation.