Biology Tutorials >适应教程 >Animal Water Regulation

Animal Water Regulation



Homeostatic control, a set environment, and how evolution and natural selection drives a species to adapt to its environment are crucial to its survival. In more extreme ecosystems, these laws of nature are essential. These types of evolutionary changes are described below.


These types of changes in an organism affect its actual structure, for example, birds occupying islands further away from its natural habitat may evolve to grow longer wings over time due to its more remote nature.




Kangaroo rat hibernates during hot periods of the day to conserve water. (Image credit: National Park Service,

Changes in the way an organism responds and interacts with its external environment. This is illustrated by the kangaroo water rat, an organism that hibernates during hot periods of the day to conserve water. This is an example of a behavioural adaptation in response to the prevailing conditions of the environment



All in all, these changes are necessary for an organism, and its species to survive in a particular ecosystem. Animals (and plants) that live in an aquatic environment over time have become suited to their habitat. To other animals, this would be a problem, you may notice if you stay in the bath or swim underwater for a long period of time that your hands and feet become wrinkled. This is because osmosis is occurring between you and the aquatic environment.

The higher concentration in the external environment means that the concentration gradient of osmosis must even out, therefore the cells in our hands and feet become turgid (a higher than normal concentration of water). With this in hand, aquatic animals must perform渗透调节以确保他们身体的内部环境保持在最佳水平。请注意osmosiswill always occur until there is an equilibrium between the internal and external environment (isotonic concentration). Our genomes’ are used to dry environments, so this deviation from our body’s norm can indeed indicate that we are less suited to surviving in a water environment because we are not adapted to do so anymore, unlike our distant ancestors.

关于生物的淡水栖息地,they face the problem of continuous osmosis of water into their bodies, because their body is hypotonic in comparison to their external environment. This means that water will continue to diffuse into the fish until there is an isotonic concentration between the two environments. Since the fish would not be able to operate with such a high concentration of water in their system, evolutionary adaptations have overcome this problem. The kidneys which deal with the uptake of water are suited to their function, as the glomerulus’ of the kidney has a large surface area to reduce the concentration of water in the blood. As these kidney tubules allow a large scale movements of ions out of the bloodstream, the organism needs to reabsorb some important ions such as salt back into the bloodstream via active transport.


The opposite problem exists in animals that live in the ocean, where the salty water means that water is at a lower concentration than most organisms. The result here is that the organism is hypertonic to its external environment (has a higher water concentration), and must re-absorb water to remain in a healthy state. Evolutionary adaptation has also favoured these animals, and the kidneys have been anatomically altered over time to ensure the long-term survival of such organisms. The glomeruli in such organisms have a much smaller surface area, because the need to excrete ions into its external environment is not as extreme, because most water needs to be retained for survival, unlike freshwater organisms. Little salt needs to be re-absorbed due to the fact the salt-water environment can be drunk, and therefore is not as scarce as it would be for a freshwater organism.

The key point is that these organisms need to maintain an optimum water concentration in their internal environment to continue to function normally and optimally.

In more extreme environments, such as the desert, water is scarce and water must be stored in times of need, hence a camel humps.

Excretion via urine and faeces also accounts for much of our water loss

行为的adaptations come into play here, as some species, such as the kangaroo rat lay in long periods of dormancy when the weather is hot, which would result in the rat losing more water through respiration than it can afford. The rat lays dormant underground in moist conditions where the concentration in water in the air and the rat’s lungs are at their minimum, therefore the least amount of water is lost to the external environment.

All these adaptations are designed for the organisms to survive more tolerably in their present habitat, and without these evolutionary changes, some of the species on the planet may not have survived to this point.



Choose the best answer.

1. A type of change involving the physical or bodily structure
2.A change that entails the biological process
4. A kangaroo rat hibernating during hot periods of the day to conserve water is an example of this type of change

Send Your Results (Optional)

To Email
Biology Tutorials >适应教程 >Animal Water Regulation


DNA molecule
Genetic Control – On and Off Genes

Genes are the blueprint of our bodies, a blueprint that creates a variety of proteins essential to any organism's surviv..



Passive and Active Types of Immunity

Lymphocytes are a type of white blood cell capable of producing a specific immune response to unique antigens. In thi..

Community Patterns

Learn about community patterns and the ecological factors influencing these patterns. Revisit some of the ecosystems you..

green plant cells

Plant cells have plastids essential in photosynthesis. They also have an additional layer called cell wall on their cell..

Independent Assortment and Crossing Over
Independent Assortment and Crossing Over

This tutorial describes the independent assortment of chromosomes and crossing over as important events in meiosis. Read..