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Biology for Secondary Schools

Other animals also have kidneys but they Urinary system
excrete other forms of nitrogenous waste.
For example fishes excrete nitrogenous Task 4.3
waste in form of ammonia whereas birds Search from library and online sources
and reptiles excrete nitrogenous waste in about the concept of urinary system in
FOR ONLINE READING ONLY
form of uric acid. human. Summarize important points
from your search.
(b) Carbon dioxide

Respiration process results into the Urinary system refers to all organs
production of carbon dioxide gas which is responsible for production, storage and
toxic to the body if allowed to accumulate. excretion of urine. It consists of the
Thus, it is removed from the body to avoid kidneys, ureters, urinary bladder, and the
blood acidosis, a condition caused by urethra. Its major functions are to eliminate
excessive carbon dioxide in the blood which metabolic waste products and maintaining
affect enzymatic and cellular functions. The the correct concentration of water and salt
carbon dioxide is carried in the bloodstream in the body fluids. The urinary system also
in the form of carbonic acid. As the blood plays a significant role in controlling blood
reaches the lungs, the carbonic acid is composition, blood pressure, and the pH
converted to carbon dioxide and diffuses in of body fluids.
the alveoli. It is excreted during exhalation
via nose and mouth. The kidneys
Are a pair of reddish-brown bean-shaped
(c) Excess water organs found on each side of the back of
Different metabolic activities such as the lower portion of the abdominal cavity.
cellular respiration, produce excess water. The left kidney is located a bit higher than
This excess metabolic waste in the form the right kidney. The kidneys are well
of water is removed from the body in the protected by muscles and ribs as well as the
form of water vapour from lungs during fats that surround them. There is an adrenal
exhalation, as sweat through sweat glands in gland above each kidney which secretes
the skin, and as urine though kidneys after adrenaline hormone. For each kidney, there
temporary storage in the urinary bladder. is a renal artery that supplies oxygenated
blood to it and renal vein which carries
Exercise 4.2 deoxygenated blood to the vena cava. The
1. Describe various organs involved in function of the kidneys is to excrete urine
excretion in human. by filtering wastes and excess water from
2. Briefly describe different metabolic the blood. The kidneys with its nephrones,
wastes excreted by humans and their renal artery and renal vein constitutes the
sources. renal system.
3. Why kidney is considered the main
excretory organ?

84 Student’s Book - Form Three

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