In-Depth Biology Notes

UNIT 3: CELL BIOLOGY

  • Biology Overview

    • Study of living organisms that emphasizes both diversity and cellular organization.
    • Cell Theory
    • States that all life forms are cellular, creating a fundamental unity.
    • Investigates how cells function and interact with their environment.

  • Reductionist Biology

    • Physico-chemical approach used to study living organisms.
    • Utilizes cell-free systems and analysis of organelles and biomolecules to understand physiological functions.

CELL: STRUCTURE AND FUNCTIONS

  • Definition of a Cell

    • Basic structural and functional unit of life.
    • Exists as unicellular (one cell) or multicellular (many cells) organisms.

  • Cell Discovery

    • Antonie Von Leeuwenhoek first described live cells.
    • Robert Brown discovered the nucleus.

  • Cell Theory Development

    • Matthias Schleiden (1838) noted all plants made of cells.
    • Theodore Schwann (1839) proposed that all animals consist of cells, culminating the Cell Theory:
    1. All living organisms are composed of cells.
    2. All cells arise from pre-existing cells.

CELL TYPES

  • Eukaryotic vs. Prokaryotic Cells

    • Eukaryotic cells: have a defined nucleus and organelles (Animal & Plant).
    • Prokaryotic cells: lack membrane-bound organelles and a defined nucleus (Bacteria, Blue-green algae).

  • Prokaryotic Cells Features

    • Generally smaller, simpler.
    • Genetic material is not enclosed in a membrane.
    • Cell wall present (except Mycoplasma).

  • Eukaryotic Cells

    • More complex with a variety of organelles.
    • Organelles include:
    • Nucleus, mitochondria, chloroplasts, endoplasmic reticulum (ER), Golgi apparatus, lysosomes.

CELL ORGANELLES

  1. Cell Membrane

    • Structure: Fluid mosaic model comprising lipid bilayer (phospholipids and proteins).
    • Functions: Selective permeability, transport molecules via passive and active transport.

  2. Cell Wall

    • Present in plants and fungi, composed of cellulose, provides structure and protection.

  3. Endoplasmic Reticulum (ER)

    • Rough ER: covered with ribosomes, synthesizes proteins.
    • Smooth ER: synthesizes lipids, involved in detoxification.

  4. Golgi Apparatus

    • Processes and packages proteins for transport within/outside the cell.

  5. Lysosomes

    • Contain hydrolytic enzymes for digestion of waste materials.

  6. Mitochondria

    • Double-membrane organelle, site of ATP production through cellular respiration.

  7. Chloroplasts

    • Found in plant cells, site of photosynthesis, contain chlorophyll.

  8. Ribosomes

    • Non-membrane-bound organelles; sites of protein synthesis, may be free or attached to ER.

  9. Cytoskeleton

    • Network of protein filaments providing structural support, facilitating movement.

  10. Centrosome/Centriole

    • Organizes microtubules, important for cell division.

THE NUCLEUS

  • Structure: Enclosed by a double membrane (nuclear envelope); contains chromatin (DNA) and nucleolus.
    • Functions in genetic control and cellular processes.
    • Nuclear pores allow transport of RNA and proteins between the nucleus and cytoplasm.

SUMMARY

  • All organisms consist of cells. Cells exhibit diversity in form, function, and activities.
  • Eukaryotic and prokaryotic cells differ significantly in structure and organization.
  • Organelles perform specific functions.
  • The nucleus manages cellular activities and heredity.
  • The cell wall offers support in plants while the plasma membrane regulates interactions with the environment.