Lecture Notes for Ecology

• Chapter 3, How Animals Work
  • Pathways of heat exchange
  • Flow of nitrogen in animals
• Biological molecules

Chapter 3, How Animals Work

Pathways of heat exchange

Solar absorption

absorption of sunlight (solar radiation) as major source of heat.

Infrared radiation

adsorption of heat from ground, vegetation, and other animals without direct, physical contact.

Convection

heat transfer from an object to the fluid (typically air or water) that surrounds it.

Conduction

transfer of heat through direct, physical contact between solid objects such as rocks, ground, vegetation, and other animals.

Evaporation

heat transfer due to change in phase from liquid to vapor (e.g. heat loss due to release and evaporation of water on the surface of the skin through sweat glands).

Metabolic production of heat

production of heat due to respiration (oxidation of carbohydrates such as glucose to produce CO2, water, heat, and useful energy in the form of ATP).

Flow of nitrogen in animals
The supply of nitrogen for plants is often limiting for plants; however, for animals, especially carnivores, nitrogen is often present in excess.

Plants obtain carbon in the form of CO2 from the atomosphere and nitrogen from the soil.

Animals usually obtain carbon and nitrogen together from the same source (mostly protein for carnivores).

Nitrogen is used in the synthesis of proteins and nucleic acids but not as an energy source in animals.

When the amount of nitrogen taken in exceeds the amount needed for biosynthetic purposes, the excess nitrogen must be excreted.

Forms of excreted nitrogen:

1. NH4+, ammonium ion; produced during the deamination of proteins which does not require expendature of energy; is highly reactive and generally toxic to animals; typically diluted out by solublization in large quantities of water. It may be used as the main nitrogen excretory compound when the animal can afford to excrete a large amount of water as in freshwater fish and other aquatic animals.
2. Urea; has one carbon atom and two nitrogen atoms; the synthesis of urea does require energy expendature; is not nearly as toxic as ammonium, and high concentrations of this compound are found in some animals. In sharks it is used in the regulation of osmotic balance. Urea is soluble in water, but it does not need to be diluted out as much as ammonium. Urea, therefore, can be excreted from animals in high concentration without the loss of large amounts of water. Some carbon is lost, but at a ratio of only one carbon atom to every two nitrogen atoms.
3. uric acid; requires lots of energy expense, but can be excreted as a semisolid past, requiring only very small amounts of water for excretion. Major excreted form of nitrogenous waste by birds.