Vertebrate Adaptions For Terrestrial Life


AP-Biology Essay on vertebrate structural adaptations for terrestrial life.
(From an actual past AP-BIOLOGY test)
The problems of survival of animals on land are very different from
those of survival of animals in aquatic environment. Describe four problems
associated with animal survival in terrestrial environments but not in aquatic
environments. For each problem, explain a physiological of structural solution.

Four problems faced by animals on land are breathing (respiration),
water conservation in excretions, successful reproduction, and the producing an
egg which can survive outside of the water.

All animals need to respire, but I have no idea why. Maybe you would
like to answer that? Aquatic animals use gills, which are outgrowths from the
body which increase surface area over which gas exchange can occur. Inside the
gills of aquatic animals, the circulatory system removes oxygen, and delivers
waste carbon dioxide. Land vertebrates have developed a different approach to
the problem of gas exchange, as water is not present in all of the terrestrial
environment. Terrestrial vertebrates have developed lungs to solve this problem.
Air enters through the nasal passages, or the mouth, passes through the trachea,
then branches off at the two bronchi, and goes through many branching passages
called bronchioles, which end in alveoli. Alveoli are sack-like structures where
the circulatory system meets the respiratory system.

Since terrestrial vertebrates do not live in water, they need to develop
a means of conserving water. One way we do this is through our excretions.
Nitrogen forms a major waste product in animals. When amino acids and nucleic
acids are broken down, they release toxic ammonia (NH3). To rid the body of this
toxin, several mechanisms have evolved, each appropriate to the habitat or
survival of the animal. Aquatic animals secrete NH3 directly into the
surrounding water. Land animals cannot do this because of the toxicity of NH3.
Instead, NH3 is converted into urea in our livers. Urea is significantly less
toxic than NH3, and thus requires less water to excrete in the urine. The reason
we need the water to excrete this is because the water is needed to dilute the
urea (or NH3 if we did excrete it in that form), in order to make it less toxic.
Birds excrete ammonia in the form of uric acid, that’s what they’re always
dropping on our heads. Those mangy little rats with wings… have you ever
wondered why we let those little pests run free in the cities, but we wont let
dogs and cats free, even though most people consider the birds more of a
nuisance? I didn’t think so, anyways:

A third adaptation to terrestrial life is internal fertilization. In
aquatic animals, many eggs are laid, usually allowing the water, and chance to
fertilize the eggs. We can’t do this on land, because the eggs and sperm would
dry out, and would stay in the same place, unless they could walk (he he he). To
solve this problem, we have developed a system of internal fertilization. The
sperm are released directly inside the female, providing an increased chance of
fertilization.
The amniotic egg of birds and reptiles represents a transition to
terrestrial life. The egg provides conditions similar in some ways to the
aquatic environment. In the aquatic environment, eggs have soft, usually
permeable shells, which do not have to worry about losing water. The amniotic
cavity formed by the amnion is fluid-filled, protecting the embryo. The egg case
often leathery in reptiles, and calcified in birds protects the contents, while
permitting gas to be exchanged with the surroundings. This egg also prevents the
evaporation of water from the embryo, since the egg cannot walk to the store and
buy some Evian, it needs all to water it has.

Category: Science