Page 90 - Biology_Form_3
P. 90
Excretion
blood cells are excreted through bile and
Exercise 4.1
its elimination is via the digestive system.
1. Explain the meaning of excretion.
2. Why must metabolic wastes be Major excretory products in animals
removed from the body? The major excretory products in animals
FOR ONLINE READING ONLY
are nitrogenous compounds such as urea,
3. How does excretion help maintain ammonia, and uric acid from breakdown of
homeostasis? proteins and nucleic acids, carbon dioxide
Excretion in humans and water from cellular respiration.
Task 4.2 (a) Nitrogenous waste products
Search for information from internet and Breakdown of nitrogen containing
library sources on the excretory organs molecules such as amino acids results in
in humans with their corresponding excess accumulation of Nitrogen that must
excretory products. Summarise the be removed from the body. Amino acids
important points from your search. are broken down by the body in order to
generate energy or be converted into fats or
There are four main excretory organs in carbohydrates. Amino acids as byproducts
humans namely; kidneys, lungs, skin and must be removed because they are highly
liver. The kidneys excrete nitrogenous toxic to the body. Excess nitrogen may be
wastes in the form of urine. Nitrogenous excreted in the form of ammonia, urea, or
wastes such as urea, ammonia, and uric uric acid.
acid result from breakdown of proteins
and nucleic acids. Excretes such as carbon Urea
dioxide and water vapour are produced
as a result of cellular respiration through Humans remove excess nitrogenous
lungs. Excretion of mineral salts, small waste in form of urea. Urea is a product
amount of urea and water in the form of of ammonia metabolism. Other animals like
sweat is carried out by the skin through sharks, adult amphibians, and mammals
sweat glands. The liver excretes bile made including humans also excrete urea as
from the breakdown of cholesterol and their nitrogenous wastes. Urea is less
dead or old red blood cells in the liver. toxic and less soluble in water compared to
Excretory organs work in coordination with ammonia. It can be excreted in a moderately
other systems to maintain homeostasis. concentrated solution. Excretion of urea
For example, the kidneys regulate blood allows body water to be conserved. This
pressure through the renin-angiotensin is an important advantage for terrestrial
system, and the liver detoxifies blood by animals with limited access to water. The
metabolising drugs and toxins. The liver animals which excrete ammonia in the form
work in coordination with the kidneys in of urea are termed as ureotelic.
filtering such toxins. The worn out red
83
23/10/2025 11:52:43
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 83 KAMISHNA 23/10/2025 11:52:43
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 83
KAMISHNA
