WATER AND SALT PHYSIOLOGY IN DIFFERENT
ENVIRONMENTS
Aim: how animals adapt to their changing environment and the mechanism employed by animals to
adapt to the range of environment in which they live in.
Various aquatic environment have different water and salt physiology:
Freshwater
Salt water-high osmotic potential and ion content compared to fish themselves but still
survive.
Brackish-mixing of salt and fresh water.
Migratory-moving from seawater to freshwater.
For animal to survive in a range of different environment they carryout activities that require an
energy input.
Although animals have evolves to live in various environment this has come with the expenses of
energy cost to maintain their blood osmotic potential.
Terrestrial animals tend to be xeric (little moisture; dry) and live in humid environment (high
level of water vapour in the environment).
Marine fish use energy to maintain their body fluid more dilute than seawater
Animals adapt to their surrounding live in:
Seawater- high concentration of ions and low concentration of water (hyperosmotic
environment)
Freshwater-very dilute with low ion content
Salt lakes- high concentration of ions
Glacial ponds-more dilute and less ion content compared to fresh water
Estuaries- high salt, low water to low salt, high water. Main problem for animals is to try not to
dry out.
Rainforests
Extreme deserts
Animals in freshwater
Evolved and moved from the ocean to freshwater and forced to adapt to life in freshwater.
Hyperosmotic regulators maintain blood that is hyperosmotic and prevent the blood from
becoming hyposmotic compared to freshwater.
,Animals have blood that is substantially (to a greater extent) more concentrated than freshwater.
The table shows that the ion concentration is very low concentration.
pared to the other aquatic animals.
However, there is an advantage of having low ion concentration, which is that less energy is
required for survival.
Fresh water animals gain water and lose ions
Freshwater animals are hyperosmotic compared to ambient environment and are at risk of
simple diffusion-passive exchange of water and ions from high to low concentration, which
requires energy and accomplished via active transport.
Energy is required to act against (counteract) these problems.
Passive exchange of ions and water
Rate of exchange depends upon :
Magnitude of gradient-the higher the gradient the faster the diffusion and vice versa.
Permeability of outer body covering-protecting animals from hyposmotic compared to
blood composition
Surface area across which exchange is occurring-large surface area increase diffusion
across exchange membrane.
, Freshwater mussel and cray fish have very high ionic concentration and therefore require more
energy for survival.
Water-salt relations in a freshwater animal
Freshwater animal is hyperosmotic.
Low ion concentration in ambient
water compared to blood plasma.
Water taken up by animal via
osmosis through the lungs.
Exchange occurs by simple diffusion,
which is a problem.
Solution: animal take up more water and
produce more dilute urine.
Loss of salt –active absorption is the major
source of sodium and chloride. The minor
source of salt is from water and salt in food.
Permeability (of water and gas) of outer body covering (skin)
Integument (outer protective layer of animal) has low permeability, which reduces rate of
passive exchange and energy cost.
Some permeability is required, particularly in gills where osmosis and diffusion of water and ions
occurs the most. It is possible to reduce the permeability’s in the gills but that is not to their
advantage as the gills need to be very permeable to respiratory gases which are important to the
animal to maintain high metabolic rate so need to take up a lot of oxygen. If these animals are
permeable to gases then they are also permeable to water and ions
High metabolic rate requires high oxygen from water.
Gills are more permeable due to large surface area and very thin membrane that allows diffusion
of gases over a short distance and thus the faster the rate of movement.
ENVIRONMENTS
Aim: how animals adapt to their changing environment and the mechanism employed by animals to
adapt to the range of environment in which they live in.
Various aquatic environment have different water and salt physiology:
Freshwater
Salt water-high osmotic potential and ion content compared to fish themselves but still
survive.
Brackish-mixing of salt and fresh water.
Migratory-moving from seawater to freshwater.
For animal to survive in a range of different environment they carryout activities that require an
energy input.
Although animals have evolves to live in various environment this has come with the expenses of
energy cost to maintain their blood osmotic potential.
Terrestrial animals tend to be xeric (little moisture; dry) and live in humid environment (high
level of water vapour in the environment).
Marine fish use energy to maintain their body fluid more dilute than seawater
Animals adapt to their surrounding live in:
Seawater- high concentration of ions and low concentration of water (hyperosmotic
environment)
Freshwater-very dilute with low ion content
Salt lakes- high concentration of ions
Glacial ponds-more dilute and less ion content compared to fresh water
Estuaries- high salt, low water to low salt, high water. Main problem for animals is to try not to
dry out.
Rainforests
Extreme deserts
Animals in freshwater
Evolved and moved from the ocean to freshwater and forced to adapt to life in freshwater.
Hyperosmotic regulators maintain blood that is hyperosmotic and prevent the blood from
becoming hyposmotic compared to freshwater.
,Animals have blood that is substantially (to a greater extent) more concentrated than freshwater.
The table shows that the ion concentration is very low concentration.
pared to the other aquatic animals.
However, there is an advantage of having low ion concentration, which is that less energy is
required for survival.
Fresh water animals gain water and lose ions
Freshwater animals are hyperosmotic compared to ambient environment and are at risk of
simple diffusion-passive exchange of water and ions from high to low concentration, which
requires energy and accomplished via active transport.
Energy is required to act against (counteract) these problems.
Passive exchange of ions and water
Rate of exchange depends upon :
Magnitude of gradient-the higher the gradient the faster the diffusion and vice versa.
Permeability of outer body covering-protecting animals from hyposmotic compared to
blood composition
Surface area across which exchange is occurring-large surface area increase diffusion
across exchange membrane.
, Freshwater mussel and cray fish have very high ionic concentration and therefore require more
energy for survival.
Water-salt relations in a freshwater animal
Freshwater animal is hyperosmotic.
Low ion concentration in ambient
water compared to blood plasma.
Water taken up by animal via
osmosis through the lungs.
Exchange occurs by simple diffusion,
which is a problem.
Solution: animal take up more water and
produce more dilute urine.
Loss of salt –active absorption is the major
source of sodium and chloride. The minor
source of salt is from water and salt in food.
Permeability (of water and gas) of outer body covering (skin)
Integument (outer protective layer of animal) has low permeability, which reduces rate of
passive exchange and energy cost.
Some permeability is required, particularly in gills where osmosis and diffusion of water and ions
occurs the most. It is possible to reduce the permeability’s in the gills but that is not to their
advantage as the gills need to be very permeable to respiratory gases which are important to the
animal to maintain high metabolic rate so need to take up a lot of oxygen. If these animals are
permeable to gases then they are also permeable to water and ions
High metabolic rate requires high oxygen from water.
Gills are more permeable due to large surface area and very thin membrane that allows diffusion
of gases over a short distance and thus the faster the rate of movement.
