Unit 3. Cell Size, Membrane, and Osmoregulation

Question 1

Cell sizes are limited by

Answer 1

• Requirement for adequate surface area relative to volume
• Rates at which molecules can diffuse
• Need to maintain adequate local concentrations of substances required for necessary cellular functions.

Question 2

Surface Area / Volume Ratio

Answer 2

Surface area is important because exchanges between the cell and its surroundings take place at the cell surface.

The cell’s volume determines the amount of exchange that takes place across available surface area.

Question 3

Maintaining adequate surface area / volume ratio

Answer 3

Volume of cell increases with the cube of its length. Surface area of cell increases with the square of its length.

Thus, larger cells have proportionally smaller surface areas. Thus, cells which are too large (in volume) would have not enough surface area to sufficiently intake nutrients or release wastes.

Question 4

Diffusion

Answer 4

Unassisted movement of a substance from a region of high concentration to a region of low concentration

Question 5

Rate of Diffusion with respect to cell size

Answer 5

Rate of diffusion decreases as size of molecule increases, so limitation is important for macromolecules (proteins and nucleic acids)

Question 6

Carrier Proteins

Answer 6

Used by eukaryotic cells to avoid slow diffusion rates. Actively transport materials through the cytoplasm.

Question 7

Passive Transport / Diffusion

Answer 7

Diffusion - Movement of molecules for the purpose of spreading out evenly through the space allotted.

Substances diffuse from more concentrated areas to less concentrated areas.

Question 8

Osmosis

Answer 8

Diffusion of water across selectively permeable membrane.

Movement of water across cell membranes and the balance between cell and its environment.

Question 9

Osmosis Effect on Water Balance

Answer 9

Water moves through a semipermeable membrane from low to high concentration of solutes

Water diffuses across membrane until solute concentrations on both sides are equal.

Question 10

Tonicity

Answer 10

Ability of a solution to gain or lose water

Based on concentration of solutes that cannot cross membrane in comparison to those inside the cell (solute concentration and membrane permeability).

Question 11

Water balance

Answer 11

Isotonic - same concentrations (just right)
Hypotonic - water move into cell (outside lower concentration than inside cell)
Hypertonic - water move out of cell (outside concentration than inside cell)

Question 12

Isotonic

Answer 12

No net movement of water across the membrane; stable environment; same rate in both directions.

Question 13

Hypotonic

Answer 13

Water enters the cell at a high rate, causing the cell to swell and burst

Question 14

Hypertonic

Answer 14

Water leaves the inside of the cell, causing it to shrivel and probably die

Question 15

Plasma Membrane

Answer 15

Surrounds every cell, ensures cell contents are retained.

Consists of lipids, including phospholipids and membrane proteins, organized into two layers.

Question 16

Amphipathic Membrane Components

Answer 16

Each phospholipid molecule has two hydrophobic “tails” and a hydrophilic “head” ; amphipathic molecule.

Lipid bilayer is formed when hydrophilic heads face outward and tails inward.

Question 17

Glycoproteins

Answer 17

Membrane proteins that are amphipathic and with polysaccharides attached to them.

Question 18

Proteins in Plasma Membrane

Answer 18

Enzymes
Anchors
Transport Proteins
Receptor

Question 19

Enzymes (in plasma membranes)

Answer 19

In the plasma membrane, they catalyze reactions associated with the membranes, such as cell wall synthesis

Question 20

Anchors (in plasma membranes)

Answer 20

Serve as structural components of the cytoskeleton

Question 21

Transport Proteins (in plasma membranes)

Answer 21

Move substances across the membrane

Question 22

Receptors

Answer 22

Receptors for external signals trigger processes within the cell.