BIOL 365: Water & Ion Balance

Question 1

What are the 3 homeostatic processes involved in water & ion balance?

Answer 1

• Osmotic regulation
• Ionic regulation
• Nitrogen excretion

Question 2

What parameter determines the direction of water movement across biological membranes?

Answer 2

Osmotic pressure (determined by solute concentration on either side of the membrane).

Question 3

Why do animals rely on solute movement to control water flux across membranes?

Answer 3

Water can’t be actively transported; it only moves passively with solutes.

Question 4

What are the 2 types of transport that allow movement of molecules across epithelial cell membranes?

Answer 4

• Paracellular transport
• Transcellular transport

Question 5

What 4 basic features do all transport epithelia have in common?

Answer 5

• High surface area
• Abundant mitochondria
• Asymmetric distribution of transporters
• Cell-to-cell interactions

Question 6

What are the most abundant ions in most animals’ extracellular space?

Answer 6

• Na⁺
• Cl^-

Question 7

Where do ionoconformers typically live?

Answer 7

In seawater.

Question 8

What are stenohaline animals?

Answer 8

Aquatic animals that can only tolerate a narrow range of salt concentrations in surrounding water.

Question 9

What are euryhaline animals?

Answer 9

Aquatic animals that can tolerate a wide range of salt concentrations in surrounding water.

Question 10

What is metabolic water?

Answer 10

Water molecules formed by oxidative phosphorylation as byproducts of metabolic reactions during digestion.

Question 11

What are the most common methylamines used by animals as compatible solutes?

Answer 11

• TMAO (trimethylamine oxide)
• Betaine
• Sarcosine

Question 12

What are the most common perturbing solutes in animals?

Answer 12

• Inorganic ions (K⁺, Na⁺, Cl^-, SO₄²⁺)
• Organic solutes (charged amino acids)

Question 13

What are the most common compatible solutes in animal body fluids?

Answer 13

• Polyols (trehalose, glycerol, glucose)
• Uncharged amino acids
• Taurine

Question 14

How do urea and TMAO act as counteracting solutes?

Answer 14

Urea disrupts hydrophobic interactions and TMAO strengthens them, so they cancel each other out.

Question 16

What are the most common ions in the cytoplasm of most animals?

Answer 16

• K⁺
• SO₄²⁺
• Acetate
• Cl^-

Question 17

What type of animals have the greatest abundance of organic solutes in their body fluids?

Answer 17

Marine osmoconformers.

Question 18

What is the difference in water permeability between epithelial cells with and without aquaporins?

Answer 18

Cells with aquaporins can be 100 times more permeable to water than cells without aquaporins.

Question 19

What 2 factors affect aquaporin levels within a cell membrane?

Answer 19

• Expression of genes encoding aquaporins
• Vesicular traffic pathways transporting aquaporins to the plasma membrane

Question 20

What is the major function of mucus layers on respiratory and GI tract surfaces?

Answer 20

To reduce water loss across epithelia.

Question 21

What are keratinocytes?

Answer 21

Epithelial cells in the skin of terrestrial vertebrates that secrete proteins and lipids to form a dense, hydrophobic extracellular matrix to prevent water loss across the skin.

Question 22

What are corneocytes?

Answer 22

Differentiated keratinocytes that produce a complex protein matrix before undergoing apoptosis, leaving a cornified envelope to protect the underlying keratinocytes.

Question 23

What is the insect cuticle?

Answer 23

A complex network of hydrophobic molecules that covers all external surfaces of insects.