Water Balance

Question 1

Homeostasis for water balance 3 points:

Answer 1

• all life depends on aqueous environment
• Animals must maintain water and electrolyte balance in different environments
• Balance: depends on intake and removal

Question 2

Water and solutes are linked:

Answer 2

• osmolarity controls water flow
• Osmolarity: concentration of solutes in a solution (e.g ions, sugar, urea)
• Precise concentration of ions (electrolytes) required

Question 3

Jellyfishes…

Answer 3

• Jelly fish is a osmoconfromer
• Most vertebrates and terrestrial invertebrates are osmoregulatory

Question 4

Fish in salt water osmolarity in…
Gill tissue?
Seawater?

Answer 4

Gill tissue: lower osmolarity

Seawater: higher osmolarity

Urine has low water but some salt

Question 5

Fish: Fresh water osmolarity in…
Gill tissue?
Freshwater?

Answer 5

Gill tissue: higher osmolarity

Freshwater: lower osmolarity

Metabolic waste is excreted into the surrounding water

Urine has low salt but large volumes of water

Question 6

What do the Seawater/gill tissue gain/lose in fish in seawater

Answer 6

Gill tissues: Gain electrolytes by diffusion
Seawater: Lose electrolytes by active transport

Question 7

What do the seawater/gill tissue gain/lose in fish in fresh water

Answer 7

Gill tissues: Gain electrolytes by active transport
Freshwater: Lose electrolytes by diffusion

Question 8

Sharks are…

Answer 8

• are osmoconformers

Question 9

Shark tissues have…

Answer 9

• Their tissues have a similar osmolarity as the surrounding seawater
• Relatively low salt concentration; high osmolarity due to high concentration of urea
• Salt is removed through the rectal gland

Question 10

Bony fishes (salmon or sea bass) are…

Answer 10

• are osmoregulators

Question 11

Bony fishe tissues maintains..

Answer 11

• Their tissues maintains lower osmolarity as the surrounding seawater
• Salt is removed by the same mechanism through chloride cells in their gills

Question 12

The desert locust must conserve what?

Answer 12

• Locust must conserve water: must minimize water loss through the cuticle, as well as through breathing, or excretion

Question 13

Desert locust parts and explain:

Answer 13

• Cuticle is very hydrophobic
• Organs are bathe in hemolymph: “open circulatory system
• Alimentary canal: fore, mid and hind gut
• Spiracle: opening that connects to tracheal system. Spiracles can be closed to prevent water loss
• Malpighian tubules filter hemolymph, releases filtrate into hind gut, water and minerals are reabsorbed

Question 14

What are the 4 Common mechanisms

Answer 14

• Ions pumps build up osmotic pressure (active transport); water follows by osmosis
• Filtration is not very selective (size-based)
• Selective ion channels allow re-absorption
• Reabsorption is tightly regulated (response to hydration status)

Question 15

How is electrolyte balance maintained?

Answer 15

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

Question 16

How is water balance maintained?

Answer 16

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

Question 17

How is nitrogenous waste eliminated?

Answer 17

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 18

Terrestrial vertebrates: osmoregulation through the kidney

Answer 18

• The kidney is composed of numerous nephrons
• A nephron is a tubular system that starts in the cortex and ends in the medulla

Question 19

Nephron parts

Answer 19

Bowman’s capsule
Distal and proximal tube
Loop of henle

Question 20

Loop of Henle parts

Answer 20

Descending/ascending limb
Has thin and thick ascending limb

Question 21

Loop of Henle…

Answer 21

• extends from the cortex into the medulla and goes back up into the cortex
• Important feature: it has a gradient in osmolarity

Question 22

Aldosterone is… and explain what it does

Answer 22

• is a steroid hormone
• released from the adrenal gland: lat. ad renam next to the kidney
• central role in the regulation of blood
• Na+ and K+ levels (→ of blood pressure)

Question 23

Antidiuretic hormone (ADH) is also called… and is…

Answer 23

• also called vasopressin
• is a peptide hormone
• released from pituitary gland
• controls water retention

Question 24

Diabetes Insipidus

Answer 24

Pituitary gland produces insufficient ADH, hence the kidneys make a lot of urine