1. CHAPTER 3 EXCRETION

2. HUMAN EXCRETION
• Excretion: process of removing substances that are of no use or
in excess from the body.
• Urea, carbon dioxide, excess mineral salts and excess
water are examples of excretory products.
• eliminated through specific excretory organs, like the
skin, lungs and kidneys.
• If these excretory products are allowed to accumulate in the
body, it will become poisonous (toxic) and endanger health.

3. SKIN

4. • skin excretes waste products in the form of sweat.
• The sweat gland absorbs excretory products like
water, mineral salts and urea from blood capillaries
around it.
• Sweat is eliminated from the sweat gland through
sweat pores to the surface of the skin.

5. LUNG
• eliminate carbon dioxide and water.
• Carbon dioxide in the blood capillaries diffuses into the
alveolus and is eliminated from the lungs when
exhaling.
• Water is eliminated from the lungs in the form of water
vapour.

6. KIDNEY
• many substances are eliminated in large quantities
through kidney
• Filter blood and produce urine
• Urine: yellowish liquid that contains water, mineral
salts and urea

7. URINARY SYSTEM IN HUMAN BEINGS
• consists of
(a) a pair of kidneys (c) a urinary bladder
(b) a pair of ureters (d) urethra

8. • Blood is carried to each kidney by renal artery and away from it
by renal vein
• Blood is filtered within kidney
• Waste products (e.g. urea) and excess substances (e.g. mineral
salts and water) are converted into urine
• Ureters carry the urine from kidneys to the urinary bladder
• Urinary bladder stores urine and gradually expands like balloon
• When muscle in the wall of bladder contract, urine is expelled to
exterior via urethra. This process is called urination

9. KIDNEY

10. • dark red in color and are bean-shaped.
• internal structure of the kidney is kidney divided into
(a) the outer part which is dark red in colour named cortex
(b) the inner part which is light red in colour named medulla.
• Functions of the kidney
• eliminating excess water and mineral salts from the body
• Keep the amount of water and mineral salts in the body in
balance
• regulating the blood concentration
• helping to remove nitrogenous substances like urea and uric
acid from the body

11. KIDNEY FAILURE
• Maybe due to:
• Bacterial infection
• Injury
• High blood pressure
• 2 ways to treat kidney failure:
• Dialysis machine
• Kidney transplant

12. KIDNEY HEALTH
• Ways to maintain healthy kidneys include:
• Limiting salt and protein intake
• Maintaining blood sugar control for diabetics
• Drinking at least 8 glasses of water a day

13. EXCRETION IN PLANTS
Excretory product Source Use
Latex Rubber tree To make vehicle tyres
Rennin Certain tree stems like the To make varnish and gum
casuarina tree
Gum Certain tree stems like the To make cough medicine
acacia tree
Acid (tannic acids or Bark of plants like the tea, To make ink
tannin) coffee and mangrove tree
Quinine Bark of cinchona To make medicine to treat
malaria
Oil Flowers or leaves of certain To make perfume and
trees ointment for insect bites

14. Excretory product Source Reason for danger
Opium Flowers of the poppy plant Are drugs that ruin health
Morphine Made from opium
Heroin Made from morphine
Cocaine Leaves of coca plant
Ganja Leaves and dried flowers of
the cannabis sativa plant
Caffeine Coffee beans Causes addiction
Nicotine Tobacco leaves Smoking damages the
lungs and the breathing
channel