BIOLOGY · Stage 9 · Chapter 10: Excretion in Humans
Biology 10.5 Kidneys work everywhere! — Osmoregulation Across Animals — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
5 min read 7 parts Lesson 5 of 6
Lesson summary
10.5 Kidneys work everywhere!
- Osmoregulation
- Water transport
- Concentrated blood
- Large drink
- Urea problem
- Kangaroo rats
Section 1 of 7What osmoregulation is
- Osmoregulation = the control of the water and salt content of the body so that cells remain in a suitable solution.
- Osmosis
- water moves across cell membranes from a dilute solution to a more concentrated one through a partially permeable membrane.
- If the surroundings are more dilute than the body fluids, water tends to enter the animal.
- If they are more concentrated, water tends to leave.
- Kidneys
- in vertebrates they control how much water and salt is lost in urine, so they are the key organs of osmoregulation.
Section 2 of 7Humans
- Water transport
- humans can transport water, so we always have water to drink and our kidneys are not put under stress.
- Concentrated blood
- the hormone ADH makes the kidneys reabsorb more water, so a small volume of concentrated urine is produced.
- Large drink
- urine is dilute and plentiful.
Section 3 of 7Hot and dry environments
- Urea problem
- desert mammals make toxic urea like all mammals, and need water to make urine.
- Camels
- their kidneys filter less water from the blood than those of cows and reabsorb much more.
- When short of water they produce only 500-1000 cm3 of thick, syrupy urine a day.
- Camels also tolerate large changes in body temperature and water content, which reduces sweating.
- Kangaroo rats
- they are very small mammals in some of the driest environments.
- Their kidneys make urine much more concentrated than camel urine.
- They do not need to drink, because they make water from digesting the seeds they eat.
- They produce dry faeces, are active at night and shelter in cool burrows by day.
Section 4 of 7Fresh water and salt water mammals
1Beavers2 points
- they live in fresh water and have as much water as they want.
- Their kidneys produce large amounts of very dilute urine and do not use energy to conserve water.
2Porpoises2 points
- they live in the sea, where water is plentiful but very salty.
- The more salty water they take in, the more salt they must remove, so their kidneys make large quantities of concentrated urine.
Section 5 of 7Urine concentration of mammals
| Mammal | Urine concentration (arbitrary units) |
|---|---|
| Beaver | 5.2 |
| Human | 14.0 |
| Porpoise | 18.0 |
| Camel | 28.0 |
| Kangaroo rat | 55.0 |
Section 6 of 7Marine birds
- Drinking seawater
- penguins, pelicans, gulls and albatrosses drink seawater, but their kidneys cannot make highly concentrated urine.
- Salt glands
- specialised glands connected to the bill remove excess salt from the blood.
- In black-backed gulls the salt glands removed 10 times more salt than the kidneys.
Section 7 of 7Fish
- Freshwater fish
- water enters constantly by osmosis across the gills and skin and salts tend to be lost.
- They do not drink, they produce large volumes of dilute urine, and gills take up salts by active transport.
- Marine bony fish
- water tends to leave by osmosis and salt enters.
- They drink seawater, produce small volumes of concentrated urine, and gill cells pump out salt by active transport.
- Sharks and rays
- they keep urea in their blood, which raises its concentration close to that of seawater and reduces water loss.
Last updated: