Overview
This lecture covers the cell as the fundamental unit of life, cell theory, types of cells, structure and functions of cell organelles, and cell division processes.
The Cell: Fundamental Unit of Life
- The cell is the basic building block of all living organisms.
- Robert Hooke discovered the cell in 1665 by observing cork under a microscope.
- The term "cell" means "little room".
Types of Organisms Based on Cells
- Unicellular organisms have only one cell (e.g., bacteria, amoeba, paramecium).
- Multicellular organisms have many cells (e.g., plants, animals, humans).
- In multicellular organisms, different cells perform specialized functions.
Cell Theory
- All living organisms are composed of cells.
- The cell is the basic structural and functional unit of life.
- Cells arise from pre-existing cells (given by Rudolf Virchow).
Diversity of Cells and Division of Labor
- Multicellular organisms have various cell types (muscle, blood, nerve, etc.) with different shapes and functions.
- Different cell parts perform distinct functions, termed division of labor.
Basic Structure of Cells
- Main parts: cell membrane (plasma membrane), nucleus, and cytoplasm.
- The cell membrane controls entry and exit of substances and is selectively permeable.
- Diffusion is the movement of molecules from higher to lower concentration.
- Osmosis is the movement of water through a semi-permeable membrane from low to high solute concentration.
Special Cell Structures
- Active transport requires energy for material movement into the cell.
- The plasma membrane is made of lipids and proteins and visible only with an electron microscope.
- Endocytosis is the engulfing of materials by the membrane, seen in amoeba.
Plant Cell Wall
- Plant cells have an extra covering called the cell wall, made of cellulose.
- Cell wall provides structural strength and resists bursting in watery environments.
- Plasmolysis occurs when a plant cell loses water, causing the cell contents to shrink from the wall.
Nucleus
- Nucleus is surrounded by a double-layered nuclear membrane with pores.
- Contains chromatin (thread-like) that condenses into chromosomes with DNA and genes.
- Prokaryotes lack a defined nucleus (have a nucleoid); eukaryotes have a true nucleus.
Cytoplasm and Cell Organelles
- Cytoplasm is a jelly-like substance containing water, minerals, enzymes, and organelles.
- Cell organelles perform various tasks:
- Rough Endoplasmic Reticulum: protein synthesis
- Smooth Endoplasmic Reticulum: fat synthesis
- Golgi Apparatus: modification, packaging, and dispatch of materials
- Lysosomes: digestion and waste removal ("suicide bags")
- Mitochondria: energy production ("powerhouse"), own DNA
- Plastids (plants only): pigment storage and photosynthesis
- Vacuoles: storage; large in plants for support
Cell Division
- Cell division forms new cells for growth, repair, and reproduction.
- Two types: mitosis (growth and repair; two identical daughter cells) and meiosis (formation of reproductive cells; four cells with half chromosome number).
- Sex cells (gametes) have half the chromosomes to maintain chromosome number upon fertilization.
Key Terms & Definitions
- Cell — Fundamental unit of life.
- Unicellular — Organism with one cell.
- Multicellular — Organism with many cells.
- Cell Theory — Three principles about cells and life.
- Osmosis — Water movement across a semi-permeable membrane.
- Diffusion — Movement of molecules from high to low concentration.
- Plasmolysis — Shrinking of cell contents due to water loss.
- Prokaryote — Cell without a defined nucleus.
- Eukaryote — Cell with a defined nucleus.
- Mitosis — Cell division producing two identical cells.
- Meiosis — Cell division producing reproductive cells with half chromosomes.
- ATP — Energy currency of the cell.
Action Items / Next Steps
- Review diagrams of cell structure and organelles.
- Prepare a table comparing prokaryotic and eukaryotic cells.
- Read more about types and functions of cell organelles.