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Biology for Advanced Level Secondary Schools
Exercise 7.2 Consequently, this will lead to failure in
many physiological processes. Excretion
1. How do endothermic organisms utilise also helps to regulate water content of the
metabolic heat production to maintain body fluids. Excretory nitrogenous wastes
a stable internal temperature and what are removed from the bodies of living
are the key adaptations that aid in this organisms in a form which is determined
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thermoregulatory process? by the availability of water. The pH of
blood is regulated by excretion. For
2. Outline the symptoms that a person example, organisms tend to excrete ions
with hypothalamic dysfunction can such as hydrogen ions (H ) and hydrogen
+
show when he/she have shifted from carbonate ions (HCO ), which have major
-
an area with moderate temperature to influence on the pH. 3
the area with extremely cold weather
7.3.2 Major excretory products in animals
3. Describe the adaptations of mammals The major excretory products in animals
to cold and hot climatic conditions.
are nitrogenous compounds such as urea,
ammonia, and uric acid from breakdown
7.3 Excretion
of proteins and nucleic acids, carbon
Task 7.4 dioxide from cellular respiration and bile
Search from the library and internet pigments from breaking down of worn out
sources on excretion including major red blood cells in the liver.
excretory products. Write short notes Nitrogenous waste products
on the searched information. Breakdown of nitrogen containing
The maintenance of homeostasis in molecules, such as amino acids results in
animals involves osmoregulation or excess nitrogen that must be removed from
balancing the levels of water and salt in the body. When amino acids are broken
the body. It also involves the removal of down by the body to generate energy or
metabolic wastes from the body through converted into fats or carbohydrates, the
excretion; the process by which metabolic amino (NH ) group must be removed
2
waste is eliminated from an organism’s because it is not needed, as it may be toxic.
body. In vertebrates, this is primarily This excess nitrogen may be excreted in
carried out by the lungs, kidneys and skin. the form of ammonia, urea or uric acid.
Ammonia
7.3.1 Significance of excretion Ammonia is quite toxic and highly
It is important that living organisms must soluble; hence it can be a nitrogenous
get rid of excretory wastes from their excretory product if sufficient water is
bodies, because the removal of wastes available to wash it from the body. It is
prevents unbalanced body’s chemical excreted by most fish and other aquatic
equilibria. Moreover, it is a means for animals whose gills or body surface are in
removal of toxic wastes, which if allowed direct contact with water. These animals
to accumulate inhibit action of many are called ammonotelic.
enzymes involved in metabolic pathways.
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