Excretion
CAPE Biology Unit 2
What is Excretion?
 Excretion
is the process by which waste
products of metabolism and other non-
useful substances are eliminated from an
organism
 The
elimination of waste products by an
organism, that results from metabolic
processes. In plants, waste is minimal and
is eliminated primarily by diffusion to the
outside environment.
 Animals have specific organs of excretion.
In vertebrates, the kidney filters blood,
conserving water and producing urea
and other waste products in the form of
urine.
What is Osmoregulation?
 Osmoregulation
is the physiological
processes that an organism uses to
maintain water balance; that is, to
compensate for water loss, avoid excess
water gain, and maintain the proper
osmotic concentration (osmolarity) of the
body fluids.
 Most
humans are about 55 to 60 percent
water by weight (45 percent in elderly
and obese people and up to 75 percent
in newborn ). Many jellyfish are 95 percent
or more water.
 Another definition of osmoregulation is:
The process by which the water content
and the ion concentration is regulated
and kept constant in the cells.
The need to remove
nitrogenous waste from the
body
 Perhaps
the most troublesome by-product
of metabolism is nitrogen-containing
waste. Nitrogen is removed from proteins
and nucleic acids when they are broken
down for energy or converted to
carbohydrates and/or fats. The
nitrogenous waste product is Ammonia.
This is a very small, but very toxic byproduct of the metabolic removal of
nitrogen from proteins and nucleic acids.
 The
human body cannot utilize the
Ammonia; therefore it has to be excreted
before its toxic properties damage the
body.
 The
two physiological processes,
excretion and osmoregulation are
interconnected as they both are
responsible for bringing about
homeostasis in the body. The
physiological mechanisms involved are
intimately bound with each other, so
much so, in higher vertebrates like
mammals, kidneys perform functions,
excretion and osmoregulation.
 Excretion
gets rid of the waste in or body.
For this to work, the waste, especially
nitrogenous waste, has to be diluted into
the blood stream so that is may be
transported to the kidneys. The water from
the blood is used-up to facilitate the
diffusion of the waste to the blood stream.
 Osmoregulation
is now “activated” and
then replenishes the water content of the
blood. This water comes from the kidneys,
as it extracts the excess water and waste
from the blood stream. Osmoregulation is
a homeostatic mechanism. It is activated
when the body recognises that it is
lacking in water or essential ions, or there
is too much in the blood stream.
Major excretory products of
Animals and Plants




Nitrogenous compounds such as urea, uric
acid and ammonia (these come from the
breakdown of proteins, nucleic acids and
excess amino acids)
Oxygen from photosynthesis in plants-some of
this may be used in respiration
Carbon dioxide from cellular respiration in
autotrophic organisms
Bile pigments from the breakdown of ‘heam’
in the liver
Excretory structures in Animals
 THE
KIDNEYS : Has many functions. It
servers essential regulatory roles in most
animals. They are essential in the urinary
system, and serves haemolytic functions in
maintaining the blood pressure by
maintaining salt and water balance, etc.
 Ureter : Tubular structure that carries urine
from kidneys to bladder
 Urinary
Bladder : Stores and releases urine
 Urethra : Excretes urine from bladder to
the outside of the body
 Skin : Excretes water, sodium chloride,
and urea.
 Lungs : expels useless gasses.
Deamination


Deamination is the removal of an amine group
from a molecule. Enzymes which catalyse this
reaction are called deaminases.
In the human body, deamination takes place
primarily in the liver, however glutamate is also
deaminated in the kidneys. Deamination is the
process by which amino acids are broken down if
there is an excess of protein intake. The amino
group is removed from the amino acid and
converted to ammonia. The rest of the amino acid
is made up of mostly carbon and hydrogen, and is
recycled or oxidized for energy.