PPT basd on excretion topic of life processes biology (Science). By Tushar Jain

2. Excretion is the process by which the
waste products produced during metabolic
activities is removed from the body.
 In unicellular organism, the waste products
are removed from the cells into the
surroundings by diffusion.
 In multicellular organism, the waste products
are removed through specialized organs.
 Excretion takes place in all organisms.

3. Compared to animals, plants do not have a
well-developed excretory system to throw out
nitrogenous waste materials. This is because of
the differences in their physiology. Therefore,
plants use different for excretion.
The gaseous waste material produced during
respiration (CO2) and photosynthesis (O2) diffuse
out through stomata in the leaves and through
lenticels in other part of the plants. Excess water
evaporates mostly from stomata and also from the
outer surface of the stem, fruits, etc., throughout
the day. This process of getting rid of excess
water is called transpiration.

4. Waste products may be stored in
leaves that fall off. Other waste materials
that are exuded by some – resins, saps,
latexes, etc. are forced from the interior of
the plant and by absorptive forces of plant
cells. Plants also excrete some waste
substances into the soil around them.

5. Plants do not have mechanism to collect,
transport and throw out their waste products.
They have adopted varied strategies to protect
their living cells from waste products.
Old leaves : Waste products are stored in
older leaves which soon fall off.
Old Xylem : Resins, gums, tannins and other
waste products are deposited in the old xylem
which soon becomes non-functional , e.g.,
heart wood.

6. Bark : Bark consists of dead cells which is peeled off
periodically. Tannins and other wastes are deposited in
the bark. Incidentally, tannins are raw material for dyes
and inks.
Central Vacuole : Most plant waste product are stored in
central vacuole of their cells. They are unable to influence
the working of cytoplasm due to presence of a selectively
permeable membrane called tonoplast.
Root Excretion : Some wastes substances are actually
excreted by the plant in the region of their root.
Detoxification : The toxic oxalic acid is detoxified by
formation calcium oxalate which gets crystallized into
needles, prisms, stars and crystal sand. Excess of
calcium is also precipitated as calcium carbonate crystals.
Salt Glands : They excrete excess salts obtained from
the habitat. Hydathodes also have an excretory function.

8. Many unicellular organism like Amoeba throw
out their wastes by diffusion from their body
surface. Protozoan’s have no organs for excretion.
As they live in an aquatic habitat, their wastes are
eliminated by diffusion through the plasma
membrane.
Simple multicellular organisms like Hydra throw
out their solid waste matter through mouth. High
multicellular organism have well defined specialized
excretory organs. Those organs could be simple
tubular structures as in flatworms and leech.

9. The excretory organs of insects (e.g.,
grasshopper, cockroach and housefly) are also
tubular. They remove nitrogenous wastes from
the body fluid and help in maintaining the water
balance in the body.
In vertebrates, the main organs of
excretion and maintenance of water balance
are the kidneys.

10. The excretory system of human
beings includes pair of kidneys, a pair
of ureters, a urinary bladder and a
urethra. Kidneys are located in the
abdomen, one on either side of the
backbone, Urine produced in the
kidneys passes through the ureters into
the urinary bladder where it is stored
until it is released through the urethra.

12. Our Excretory system consists of kidneys,
blood vessels that join them, ureters, urinary
bladder and urethra. They help produce and
excrete urine.
There are two bean-shaped kidneys that
lie in the abdominal cavity, one on either side
of the vertebral column. The kidneys are
reddish brown, Each of them is about 10 cm
long and weighs about 150 g. Although they
weigh less, they receive a lot f blood for
filtration.

13. A volume of blood nearly equivalent to
that in the whole body passes through the
kidneys every four or five minutes. The kidneys
produce urine to filter out the waste products,
like urea and the uric acid, from the blood.
Urine leaves each kidney through a tube
called ureters. The ureters from both the
kidneys are corrected to the urinary bladder
that collects and stores urine. Ureters carry
urine from the kidneys into the urinary bladder.
The urethra is a canal that carries urine from
the bladder and expels it outside the body.

15. Each kidney is enclosed in a thin fibrous covering
called the capsule. A renal artery brings blood into the
kidney, along with nitrogenous waste materials, After
filtration in the kidney, the purified blood leaves the kidney
through a renal vein.
Two distinct regions can be seen in the section of a
kidney :
(1) An outer, dark, granular cortex and (2) an inner, lighter
medulla.
The hollow space from where the ureter leaves the kidney
is called the pelvis. Each kidney is made up of numerous
(about one million) coiled excretory tubules, known as
nephrons, and collecting ducts associated with tiny blood
vessels. A nephron is the structural unit of a kidney, having
three functions – filtration, absorption and secretion.

16. A cluster of thin-walled blood capillaries
remains associated with the cup-shaped end of
each nephron tubule. These capillaries bring
blood from the body to the nephron for
filtration. The network of capillaries spreads
over the nephron tubules also. These
capillaries finally carry purified blood to the
body.

18. A nephron consists of a long coiled tubule
and the Malpighian corpuscle. The tubule of
the nephron is differentiated into the proximal
convoluted tubule. Henle’s loop and the distal
tubule opens into the collecting duct.
At the proximal end of the nephron is the
Malpighian corpuscle, which consists of
Bowman’s capsule is a double-walled cuplike
structure which surrounds the dense network
of blood capillaries called the glomerulus.

19. Glomerular filtration - When the blood enters into the
glomerular through the afferent arteriole, a part of the
water and some dissolved constituent of the blood of low
molecular weight like nitrogenous waste, glucose and
mineral salts filter out through the capillary walls into the
surrounding Bowman’s capsule by a process referred to
as glomerular filtration. The filtered fluid or glomerular
filtrate resembles the blood plasma in its chemical
composition except for the absence of large molecules.
In man, about 180 liters of fluid is filtered from the
blood plasma through glomerular capillary walls every 24
hours.

20. Tabular Reabsorption - The glomerular filtrate flows on
through the convoluted tube, collecting tubule and then
into the pelvis of the kidney and down the ureter into the
urinary bladder. As the filtrate flows the proximal
convoluted tubule some water and physiologically
important salts like glucose, amino acids, sodium chloride
and sodium bicarbonate are reabsorbed into the blood
through the capillaries around this portion leaving only the
wastes to be excreted out.
Active secretion – As the glomerular filtrate flows through
the distal convoluted tubes, the unwanted substances,
which could not be filtered out in the glomerular are
actively secreted out by the tubular walls into the filtrate
from the blood.
As the result of this entire process, homeostasis of the
blood is maintained and all the waste products remained in
the tubular fluid constitute the urine, which is ready for
excretion from the body.