[BIO 11.1] E2 - The Cell

• The cell is the basic unit of structure and function in organisms. Eukaryotic cells possess a nucleus and other membrane-bound organelles.
• The cell wall is an organelle unique to plant cells, found external to the plasma membrane.
• There are two types of cell walls: primary and secondary.
• The primary cell wall is integral to growth and development.

  Found in: younger parts of the plant

  Composition: cellulose

  Observed in: onions, bell peppers, and tomatoes
• The secondary cell wall is important for structural support and rigidity.

  Found in: older parts of the plant and dead cells

  Composition: primarily of lignin

  Observed in: coconuts and pears

  Turns red when stained with 18% alcoholic phloroglucinol-sulfuric acid solution
• The middle lamella is the substance connecting adjacent primary cell walls that are glued together by pectin

  Observed in tomatoes and bell peppers
• The plasmodesmata joins the cytoplasm of adjacent plant cells

  Observed in tomatoes and bell peppers
• The lacuna (hollow space) is formed when the protoplasm dies.

  Observed in coconuts and pears
• As plant cells grow older, the secondary cell wall begins to emerge. Over time, this grows thicker and thicker, until it cuts off the plasmodesmata, disabling the cell’s ability to communicate with adjacent cells. This forms the lacuna of a plant cell.
• When a fruit ripens, the pectin holding the middle lamella together degrades due to pectinase. This causes the middle lamella to disintegrate as the fruit ripens. This is also why a ripe fruit is easy to crush, but an unripe fruit is harder.
• The protoplasm includes all the contents of a living cell bounded by the cell wall, excluding the cell wall.
• The cytoplasm is the region between the nucleus and plasma membrane.
• The cytosol is the fluid space holding the organelles.
• IKI (iodo-potassium iodide) is used to stain onions and cheek cells.
• The nucleus is the genetic library of the cell, containing its DNA.
• The nucleolus is the site of ribosome biogenesis through rRNA production.
• The central vacuole acts as storage for the cell. It is bounded by the tonoplast. It also contains pigment. The purple pigment in onions is called anthocyanin.
• Plant cells contain cytoplasmic strands while animal cells don't.
• Cytoplasmic strands provide structural support and transport. It holds the nucleus in place.
• Plastids are membrane-bound organelles in photosynthetic eukaryotes. They function for storage and photosynthesis.
• Chloroplast is the round and green dots containing the chlorophyll pigment, giving plants their green color. It is found in water thyme leaf (Hydrila sp.)
• Chromoplast are the small orange dots that contain carotenoid pigments, giving plants their orange coloration. It is found in ripe bell peppers and tomatoes. They function for photoprotection.
• Leucoplasts are dark-stained granules that appear colorless and store food.

  Starch (potatoes): Amyloplasts

  Lipids: Elaioplasts

  Proteins: Proteinoplasts
• The protozoan specimen was stained with IKI to observe its locomotory organelles.
• Cilium (singular): Short hair-like protrusions
• Flagellum (singular): Longer than cilia and whip-like
• Plant crystals function for waste storage, calcium regulation, and defense against herbivory.
• Crystals made of calcium oxalate:

  1.) Raphide: groups of short and very sharp crystals (Tradescantia spathacea leaf abaxial)

  2.) Prismatic: prism-shaped crystals (Tradescantia spathacea leaf abaxial)

  3.) Styloid: large and solitary crystal (Dieffenbachia sp. leaf back midrib)

  4.) Druse: spiky and rough crystals (Dieffenbachia sp. leaf back midrib)
• Crystals made of calcium carbonate:

  1.) Cystolith (club-like) (Ficus sp. leaf w.m.)

  2.) Cystolith (worm-like): the only extracellular crystal (Pilea micropylla leaf abaxial)