Microscope and Onion Peel Mount Quiz

Microscopy and Temporary Mounts

• Use a thin camel hair paintbrush to transfer onion peel for observation.
• Safranin solution is applied to the peel before adding a coverslip; prevent air bubbles.
• Temporary mounts allow for observation under low and high power of a compound microscope.
• Similar structures in onion bulbs of different sizes indicate that cells are uniform regardless of onion size.

Cells and Their Characteristics

• Cells are the basic building units of all organisms, including onions.
• The cell membrane acts as a selectively permeable barrier, regulating substance movement.
• Diffusion facilitates the movement of substances from high to low concentration areas.
• CO2 diffuses out of cells when its concentration is higher inside than outside, while O2 enters when its concentration decreases inside the cell.

Diffusion and Osmosis

• Diffusion is vital for gas exchange between cells and their external environment.
• Osmosis describes the diffusion of water across a selectively permeable membrane towards higher solute concentration.
• The effect of surrounding solutions on cells:
  • Hypotonic Solution: Cell gains water, causing swelling.
  • Isotonic Solution: No net water movement; cell remains the same size.
  • Hypertonic Solution: Cell loses water, potentially leading to shrinkage.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells are generally small (1-10 µm); eukaryotic cells are larger (5-100 µm).
• Prokaryotic nuclear regions lack a defined membrane; eukaryotic nuclear regions are well-defined and membrane-bound.
• Prokaryotic cells typically have a single chromosome; eukaryotic cells contain multiple chromosomes.
• Membrane-bound organelles are absent in prokaryotic cells but present in eukaryotic cells.

Endoplasmic Reticulum (ER)

• The ER is a network of membranes, comprising two types: rough (RER) and smooth (SER).
• RER appears rough due to ribosomes attached, which are essential for protein synthesis.
• Proteins synthesized in RER are distributed throughout the cell as needed.
• SER is involved in lipid production, vital for cell function and membrane biogenesis, along with synthesis of enzymes and hormones.