IB Biology 1.2 - Ultrastructure of Cells - Interactive Lecture

Key Concepts:

• Prokaryotic cells vs. Eukaryotic cells
• Scale and magnification in cell images
• Binary fission
• Organelles (nucleus, mitochondria, ribosomes, endoplasmic reticulum (ER), Golgi apparatus, lysosomes, chloroplasts, vacuoles, centrioles, peroxisomes)
• Cell membrane and cell wall
• Light microscope vs. Electron microscope (TEM & SEM)

1. Prokaryotic vs. Eukaryotic Cells:

• Prokaryotic Cells:
  • Small size (0.1-5.0 micrometers).
  • Simple structure with fewer internal components.
  • Lack membrane-bound organelles.
  • Single, circular DNA chromosome.
  • May contain plasmids (small DNA fragments).
  • Cell wall and plasma membrane; some have a capsule.
  • May have flagella or pili for locomotion.
  • Single-celled organisms.
  • Reproduce via binary fission (cloning).
• Eukaryotic Cells:
  • Larger size (10-100 micrometers).
  • Complex structure with compartmentalized organelles.
  • Membrane-bound organelles (nucleus, mitochondria, ER, Golgi, etc.).
  • DNA in multiple linear chromosomes within the nucleus.
  • Cell membrane (all) and cell wall (plant cells).

2. Importance of Scale:

• Images of cells often lack scale bars, leading to misinterpretations of size.
• Prokaryotic cells are significantly smaller than eukaryotic cells.
• Prokaryotic cells are similar in size to some eukaryotic organelles.

3. Prokaryotic Cell Details:

• Binary Fission: Asexual reproduction where a cell copies its DNA and splits into two identical daughter cells.
  • Fast and efficient process.
  • Results in clones (identical copies).

4. Eukaryotic Cell Details:

• Organelles: Membrane-bound structures with specific functions.
• Nucleus:
  • Double-layered nuclear envelope with pores.
  • Contains DNA organized into chromosomes via chromatin.
  • Nucleolus: Site of ribosome production.
• Mitochondria:
  • "Powerhouse of the cell" - produces ATP (cellular energy).
  • Double membrane; inner membrane folded into cristae.
  • Matrix: Aqueous solution within cristae containing enzymes.
• Ribosomes:
  • Build proteins.
  • Two subunits (large and small).
  • Not membrane-bound.
• Endoplasmic Reticulum (ER):
  • Network of folded membranes.
  • Forms vesicles for transport.
  • Rough ER (RER): Contains ribosomes for protein synthesis, packaging, and shipping.
  • Smooth ER (SER): Synthesizes lipids, stores calcium.
• Golgi Apparatus:
  • Receives vesicles from ER, modifies and sorts contents.
  • Repackages and sends vesicles to different locations.
• Lysosomes:
  • Unique to animal cells.
  • Contain hydrolytic enzymes for breaking down food and cellular debris.
• Cell Membrane:
  • Defines cell shape and space.
  • Controls movement of substances in and out of the cell.

5. Plant Cell Specifics:

• Chloroplasts:
  • Unique to plant cells.
  • Site of photosynthesis (conversion of sunlight into sugar).
• Cell Wall:
  • Provides support and strength.
  • Made of cellulose.
• Central Water Vacuole:
  • Maintains turgor pressure (static pressure against the cell wall).
  • Supports plant structure.

6. Structures in Both Plant and Animal Cells:

• Centrioles:
  • Aid in cell division.
  • Form spindle fibers to separate chromosomes.
  • Animal cells have centrosomes (attachment sites for centrioles).
• Peroxisomes:
  • Contain digestive enzymes.
  • Break down specific substances like hydrogen peroxide.

7. Microscopy:

• Light Microscope:
  • Uses light to illuminate the specimen.
  • Magnification in the thousands.
  • Shows natural or stained colors.
• Electron Microscope:
  • Uses electrons to generate an image.
  • Higher magnification and resolution than light microscopes.
  • Transmission Electron Microscope (TEM): Electrons pass through the specimen (2D image).
  • Scanning Electron Microscope (SEM): Electrons bounce off the specimen (3D image).
  • Images lack natural color.

8. Synthesis/Conclusion:

Understanding the differences between prokaryotic and eukaryotic cells, the functions of various organelles, and the tools used to study cells (microscopes) are fundamental to biology. The video emphasizes the importance of considering scale in cell images and provides a detailed overview of cell structures and their functions.