BIOL 2390 - Topic 6 (part 2)

Water balance in aquatic animals

They face the constant exchange of water with their environment, via osmosis, but the exchange is different depending on whether they are freshwater or marine organisms

Freshwater organisms’ water balance issues

They have a higher solute concentration inside their body, causing them to passively gain water

Marine organisms’ water balance issues

They have a lower concentration of solutes inside their body, causing them to passively lose water.

Freshwater organisms solving water balance issues

It depends on the species, but generally, they limit drinking and undergo constant urination

Marine organisms solving water balance issues

They drink water and then filters out the salt from the seawater (ex. turtules)

Terrestrial animals compensating for water loss

It usually depends on the environment that they are in, as different environments will be drier and others will be more wet

Terrestrial animals compensating for water loss (methods)

1.) Directly drinking water

2.) Obtaining moisture from food

3.) Metabolic production of water

Metabolic production of water

Certain organisms, such as desert rodents, don’t have access to liquid sources, therefore they have to make their own water via cellular respiration

Kidney’s

It recovers water during waste filtration of the bloodstream, reducing water the amount of water lost in waste in the process

Kidney parts

1.) Nephron, which is where waste is pushed out

2.) Loop of henle, which is the part that absorbs water

Modified loop of henle

1.) Certain animals, usually those in dry environments like desert rodents, have a longer loop of Henle, which allows for greater water absorption efficiency

2.) This requires minimal energy, but it does require specific selection pressures to be present for the adaptation to develop

Nasal systems that helps with water balance

Nasal evaporators/condensers reduce water loss when exhaling, while also somewhat helping cool desert animals when inhaling?

How nasal evaporators/condensers work

1.) Air temp is cooler than body temp and the exhaled air is warmer than the cool nasal cavity, therefore causing condensation in the nasal passage

2.) This is absorbed in the nasal cavity, resulting in reduced water loss

Nasal evaporators/condensers cooling desert animals?

1.) When air comes in, it goes through well-hydrated passages, therefore causing evaporation

2.) This results in a cooling effect that hydrates the air during inhalation

Plant evolution to variability in environments

Plants have evolved a wide range of responses to the variability of precipitation and soil moisture

Plant adaptations to variable precipitation and soil moisture patterns

1.) Closing their leaf stomata

2.) Intentionally curling or wilting their leaves

3.) Losing their leaves entirely

Closing leaf stomata

It is a good response for short-term water loss, but it can eventually cause more damage if left closed for too long

Closed leaf stomata disadvantages

1.) It can lead to high heat levels

2.) It can’t take in CO2, therefore photorespiration and photodamage eventually occurs

Photo damage

When the light ends up causing damage to the plant, because it can’t carry out photosynthesis (occurs when stomata are closed)

Plants curling or wilting their leaves

It reduces light absorption, by increasing light reflection

Plants losing their leaves entirely

1.) This is more for long-term cases, where the water loss is so severe that it is better to lose their leaves entirely

2.) It is usually a drought or seasonal-specific response

Why do we lose leaves during the winter?

Because it is so cold and there is no water available for the plant, therefore the plant purposely loses the leaves, to prevent any further damage