Overview
This lecture introduces the cell as the fundamental unit of life, detailing its discovery, structure, types, and the specific roles of its components in living organisms.
Discovery and Definition of Cells
- Robert Hooke discovered cells in 1665 while examining cork under a microscope.
- Cells are the basic building units of all living organisms.
- Leeuwenhoek observed living cells in pond water in 1674.
- Schleiden and Schwann proposed the cell theory: all plants and animals are made of cells; cells are the basic unit of life.
- Virchow suggested that all cells arise from pre-existing cells.
Types of Organisms and Cells
- Unicellular organisms (e.g., Amoeba, bacteria) consist of a single cell.
- Multicellular organisms are made up of many cells with specialized functions.
- Cells differ in shape, size, and function based on their roles.
Structure and Organization of Cells
- All cells have three main structures: plasma membrane, nucleus, and cytoplasm.
- The plasma membrane is selectively permeable, allowing certain substances in/out via diffusion and osmosis.
- Plant cells have an extra rigid cell wall made of cellulose for support and protection.
- The nucleus contains genetic material (chromosomes, DNA) and controls cell activities.
- Prokaryotic cells lack a defined nucleus and membrane-bound organelles; eukaryotic cells have both.
Cell Organelles and Their Functions
- Endoplasmic Reticulum (ER): RER makes proteins; SER makes lipids.
- Golgi Apparatus: Modifies, stores, and packages materials; forms lysosomes.
- Lysosomes: Contain digestive enzymes; break down waste and foreign materials; known as "suicide bags".
- Mitochondria: Powerhouse of the cell; generates energy (ATP); has its own DNA.
- Plastids: Present in plant cells; chloroplasts (photosynthesis), chromoplasts (color), leucoplasts (storage).
- Vacuoles: Storage sacs; large and numerous in plant cells, small in animal cells; maintain cell turgidity.
Cell Division
- Mitosis produces two identical daughter cells for growth and repair.
- Meiosis produces four cells with half the chromosome number for reproduction (gametes).
Key Terms & Definitions
- Cell — Basic structural and functional unit of life.
- Plasma membrane — Selectively permeable outer covering of a cell.
- Cell wall — Rigid outer layer in plant cells made of cellulose.
- Nucleus — Organelle containing genetic material (DNA).
- Prokaryote — Cell without a nucleus or membrane-bound organelles.
- Eukaryote — Cell with a nucleus and organelles.
- Osmosis — Diffusion of water through a selectively permeable membrane.
- Mitochondria — Organelle producing cellular energy (ATP).
- Lysosome — Organelle with digestive enzymes for waste removal.
Action Items / Next Steps
- Prepare temporary mounts of plant and animal cells for observation.
- Complete exercises comparing plant and animal cells and prokaryotic and eukaryotic cells.
- Research electron microscopes and their role in cell discovery.
- Conduct osmosis experiments as described in activities.