The Fundamental Unit of Life

Introduction to Cells

• Definition: Cells are the basic building blocks of all living organisms.
• Discovery: Robert Hooke discovered cells in 1665 by observing a cork slice under a microscope. He described cells as small box-like structures, resembling honeycomb.

Types of Organisms

• Unicellular Organisms: Made up of a single cell. Examples include amoeba, chlamydomonas, paramecium, and bacteria.
• Multicellular Organisms: Consist of multiple cells and develop from a single cell, with various cell types performing different functions.

Cell Types and Functions

• Different types of cells include muscle cells, blood cells, nerve cells, bone cells, ovum, sperm cells, and fat cells.
• Shape and size of cells are determined by their function.
• Cells exhibit division of labor, similar to organs and systems in the body.

Cell Structure

Cell Organelles

• Cytoplasm: Semi-transparent fluid inside the cell where biochemical reactions occur, contains organelles.
• Organelles:
  • Rough Endoplasmic Reticulum (RER): Protein factory.
  • Smooth Endoplasmic Reticulum (SER): Fat factory.
  • Golgi Apparatus: Dispatch center for materials processed by the ER.
  • Mitochondria: Powerhouse of the cell, produces energy.
  • Vacuoles: Storage bags for materials.
  • Lysosomes: Suicide bags, contain digestive enzymes.
  • Plastids (in plants): Store pigments and aid in photosynthesis.

Plasma Membrane

• Function: Protects cell components, controls entry and exit of materials (selectively permeable).
• Processes:
  • Diffusion: Movement of gas molecules from high to low concentration.
  • Osmosis: Movement of water through a selectively permeable membrane.
  • Active Transport: Requires energy for material transfer.

Cell Wall and Nucleus

• Cell Wall: Rigid structure in plant cells made of cellulose.
• Nucleus: Contains chromatin and DNA, controls cell functions, and facilitates cell division.
• Prokaryotes vs. Eukaryotes: Prokaryotes lack a nuclear membrane and membrane-bound organelles, unlike eukaryotes.

Endoplasmic Reticulum

• Structure: Network of tubes and sheets near the nucleus.
• Types: Rough (with ribosomes) and Smooth (without ribosomes).
• Functions:
  • Protein and lipid synthesis.
  • Transport of materials within the cell.
  • Surface for biochemical reactions.
  • Detoxification in vertebrates.

Golgi Apparatus

• Structure: Flattened vesicles arranged in stacks (cisterns).
• Functions:
  • Storage, modification, and packaging of materials.
  • Formation of lysosomes.

Lysosomes and Mitochondria

• Lysosomes: Clean waste materials, digest foreign substances, and damaged organelles.
• Mitochondria:
  • Double membrane structure; inner membrane is folded for more surface area.
  • Produces ATP, the energy currency of the cell.
  • Contains its own DNA and ribosomes.

Plastids and Vacuoles

Plastids (in plants)

• Types:
  • Chromoplasts: Contain pigments, perform photosynthesis (Chloroplasts).
  • Leucoplasts: Colorless, store materials.
• Structure: Similar to mitochondria, with DNA and ribosomes.

Vacuoles

• Function: Storage of materials (solids or liquids).
• Size: Larger in plant cells, providing turgidity and rigidity.

Cell Division

• Importance: Growth, repair, and reproduction.
• Types:
  • Mitosis: Produces two identical daughter cells for growth and repair.
  • Meiosis: Produces gametes with half the chromosome number for reproduction.

Conclusion

• The lecture highlighted the complexity of cell structures and the intricate roles each component plays in maintaining life processes.
• Emphasized the importance of understanding cell functions for further studies in biology.