Water and Electrolytes

Question 1

Water Balance

Answer 1

the balance between water intake and output

Question 2

Electrolyte

Answer 2

compound that dissociates into ions when dissolved in water

They conduct electric current

Question 3

Most abundant ions of electrolytes in most animals

Answer 3

Sodium (Na+)

Chloride (Cl-)

Potassium (K+)

Calcium (Ca 2+)

Question 4

Electrolyte ion imbalances can lead to…

Answer 4

muscle spasms, confusion, irregular heart rhythms, fatigue, paralysis and even death

Question 5

Osmolarity

Answer 5

the total concentration of all solute particles in a solution

measured in osmoles per lire

Question 6

osmotic stress

Answer 6

occurs when the concentration of dissolved substances in a cell or tissue is abnormal

Question 7

Osmoregulation

Answer 7

regulation of solute concentrations and water balance by a cell or organism

Question 8

Osmoconformers

Answer 8

marine animals which maintain the osmolarity of their body fluids such that it is always equal to the surrounding seawater.
(sharks, jellyfish, dogfish)

Question 9

Osmoregulators

Answer 9

An organism that controls its internal salt concentration
(most fish, vertebrates and terrestrial invertebrates

Question 10

hyperosmotic

Answer 10

the solution outside the body has a higher solute concentration than solution inside

Question 11

hyposomotic

Answer 11

A term describing organisms with body fluids with a higher concentration of water and lower solute concentration than the external environment.

Question 12

Hyperosmotic Sea Creatures…

Answer 12

Live in seawater, Higher concentration outside than inside

Water tends to flow out by osmosis (cells will shrivel)

Drink water to regain balance, but Gain excess electrolytes.

use Membrane proteins to actively pump out ions

and Excrete small # of electrolytes through urine to achieve balance

Question 13

Hyposomotic Sea Creatures…

Answer 13

Live in freshwater, Higher concentration inside than outside

Water tends to flow in by osmosis (cell will lyse)

Excrete water to regain balance, but Lose electrolytes.

Actively transport ions in from the environment to gain electrolytes (through gills)

Question 14

epithelial cells

Answer 14

skin cells that cover the outside of the body and line the internal surfaces of organs

Question 15

primary active transport

Answer 15

source of energy like ATP is used to move ions against their concentration gradient

Ex. Sodium-Potassium Pump

Question 16

secondary active transport (cotransport)

Answer 16

relies on membrane proteins that use an electrochemical gradient established by a pump during primary active transport

Question 17

symporter

Answer 17

cotransporter that carries two different ions or small molecules, both in the same direction

Question 18

antiporter

Answer 18

cotransporter that carries two ions or small molecules in different directions

Question 19

Aquaporins

Answer 19

A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane

cells use pumps to set up an osmotic gradient that allows this.

Question 20

Ammonia (NH3)

Answer 20

toxic to cells because at high concentrations it can raise the pH of intracellular fluids enough to inactivate enzymes.

(made by the breakdown of excess amino and nucleic acids)

Question 21

How is electrolyte balance maintained?

What drives the movement of ions across membranes?

Answer 21

Ions are moved either by active transport or passive transport (ion pumps, co- transporters, ion channels)

Question 22

How is water balance maintained?

What drives the movement of water across membranes?

Answer 22

Water movement is driven by osmosis (differences in osmolarity). Water movement is facilitated through some proteins (aquaporins) that make the membrane more permeable to water.

Question 23

How is nitrogenous waste eliminated?

What is the reason for the different elimination products (ammonia, uric acid, urea)?

Answer 23

The removal strategy depends on water availability.Ammonia: easy to make, but is toxic and requires lots of water

Uric acid: most energy-consuming synthesis; minimal water (solid waste)

Urea: some energy required; water soluble but harmless; contributes to osmolarity

Question 24

What are the advantages of urea in sharks to help maintain salt balance?

Answer 24

Urea is a very inert substance that doesn’t really do any damage to proteins or cells therefore you can accumulate very high concentrations without any negative effects

Question 25

What happens if you starve a shark or dogfish?

Answer 25

if you starve dogfish or sharks they will not get enough food to create enough nitrogenous waste to maintain the urea concentration

as a consequence, they will actively break down their own proteins and they will break down their muscles,

because it’s better for them to be skinny and weak than to have the wrong osmolarity

Question 26

How do sharks secrete concentrated salt solutions?

Answer 26

The rectal gland

Question 27

What are the steps involved in salt excretion through the rectal gland in sharks? (4)
ABC
AB
AB
A

Answer 27

1. A) Na+/K+ - ATPase pump actively pumps Na+ ions out of the epithelial cells and into the interstitial fluid. (3 out, 2 in)
   B) This creates an electrochemical gradient which allows Na+ ions to enter the cell.
   C) This gradient also allows for other ions to enter the cell w/o the expenditure of extra energy.

2.
A) Due to Na+ master gradient, Na+, Cl- and K+ all move into the cell via a cotransporter (secondary transport)
B) Na+ moves ALONG its chemical gradient, whereas, Cl- and K+ move AGAINST their chemical gradients
(with Na+ through cotransporter)

3. A) As Cl- build-ups inside the cell, it exists through chloride channels in the APICAL membrane; into the rectal gland lumen (down its concentration gradient)
   B) K+ diffuses back into the interstitial fluid through potassium channels in the BASOLATERAL membrane
4. A) Access amount of Na+ diffuses into the lumen along its chemical gradient from the interstitial fluid through SPACES in between the cells.

Question 28

Where is the Na+/K+ - ATPase pump located in freshwater fish? Why?

Answer 28

It is located in the APICAL membrane instead of the Basolateral membrane.
This is because freshwater fish need to bring salt in not remove salt.

Question 29

How do terrestrial (not marine) animals maintain water and electrolyte balance?

Answer 29

Question 30

What are the advantages and disadvantages of uric acid

Answer 30

The big advantage of uric acid is it’s water-insoluble so you don’t lose any water or very little water if you excrete it

However,

the big disadvantage is that it’s a very complex molecule making this compound requires a lot of ATP and energy

Question 31

Which of the following mechanisms contributes to osmoregulation in both marine and freshwater bony fish?

Answer 31

gain of water through food

Question 32

The intercellular concentration of three electrolytes is compared with the concentration of these electrolytes in fluid eliminated from the shark rectal gland in the Table. Based on the data, which of the following is a likely function of the rectal gland?

Answer 32

The rectal gland is able to concentrate Na+, K+, and Cl-.

Question 33

Why do birds secrete uric acid as their nitrogenous waste? Because uric acid…

Answer 33

requires little water for nitrogenous waste disposal, thus conserving water and reducing body mass.