Unit 9 Test
1. Gases – most animals require O for2metabolism and release CO as the 2espiratory waste product.
2. Nutrients – animals utilize many different types of food, obtaining carbohydrates, fats, and proteins in
3. Wastes – fluid and solid wastes from digestion and metabolism are released. Organisms must also
balance the ion composition of their internal fluids. Ions are obtained from food or directly from the
environment (especially in aquatic animals).
The fluid surrounding cells is called the interstitial fluid
All organisms need to exchange molecules with their environment. In small animals this occurs directly
from the external medium to the internal cell or cells. However, for larger multicellular animals the
circulatory system delivers and carries away substances from the interstitial fluid bathing the cells.
Exchange occurs directly between the interstitial fluid and the cells. Body systems are dependent on the
circulatory system for gases, nutrients and waste removal.
Complex animals must also have a circulatory fluid that carries gases, wastes, and nutrients to the
interstitial fluid. As well, respiratory systems and digestive systems have direct contact with the external
To varying degrees, animals maintain relatively constant internal conditions in the face of a fluctuating
external environment, a process known as homeostasis.
Neural and/or hormonal processes are involved in keeping internal variables relatively constant.
Organisms have built-in regulatory systems that are usually based on negative feedback.
Thermoreceptors send information to the hypothalamus in the brain if the skin and body temperature is
below or above the set point. This information is integrated in the brain to bring about a response that will
regulate body temperature back to the set point. In this way a stimulus brings about a response that
compensates for the disturbance. In other words, negative feedback results in lowering a variab