Onion Cell Labelling Quiz

Cell Structures in Onion Cells

• Nuclear membrane/envelope: Composed of phospholipid bilayers with pores that facilitate transport.
• Nucleus: Contains the nucleolus and is central to genetic material.
• Nucleolus: A condensed region responsible for ribosomal RNA (rRNA) synthesis.

Unique Features of Onion and Other Cells

• Onion cells lack chloroplasts: Grown underground, thus do not perform photosynthesis.
• Reaction to iodine: Stains onion cells yellowish, enhancing visibility of organelles.
• Vacuole: Occupies the center of each cell, storing substances and maintaining turgor pressure.

Organelles and Their Functions

• Inside the nucleus: Nucleoli are visible; crucial for ribosome assembly.
• Cell wall: Surrounds each cell, providing structural support.
• Plasma membrane: Found just within the cell wall, regulates what enters and exits the cell.

Elodea Cell Characteristics

• Chloroplasts: Present in Elodea, containing chlorophyll, about 30-50 per cell.
• Layer observation: Two layers of cells detected; top layer receives more sunlight, showing more chloroplasts.
• Cell sizes: Larger cells found in the upper layer, smaller in the lower layer.

Cytoplasm and Vacuoles

• Cyclosis: Describes the movement of cytoplasm within the cell.
• Vacuole functions:
  • Stores organic compounds and pigments.
  • Provides protection by storing poisons.
  • Maintains turgor pressure to keep plants upright.

Eggplant Cell Structures

• Shape of eggplant cells: Spherically shaped, accommodating storage.
• Pigment presence: Anthocyanin, a water-soluble pigment found in vacuoles, gives color.
• Amyloplasts in potato cells: Oval structures responsible for starch storage (amylose and amylopectin).

Chemical Reactions and Cell Types

• Iodine interaction: Turns starch in amyloplasts purple, indicating presence of carbohydrates.
• Stone cells: Composed largely of cell walls made of lignin, providing structural support and are dead at maturity.
• Plasmodesmata: Channels in cell walls allowing nutrient and waste transport, facilitating cell communication.

Summary of Cell Functions

• Purpose of stone cells: Provide structure and support, contributing to the crunchiness of fruits like pears.
• Nuclear envelope: Functions to protect the nucleus while controlling substance passage.
• Stroma: The fluid within chloroplasts where photosynthesis reactions take place.