IGCSE Biology Chapter 13 : excretion and homeostasis

Excretion

What gas is excreted through the lungs?

Carbon dioxide

What does kidney excrete ?

urea and excess water and ions

Define Excretion

the removal of toxic materials from organisms, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements.

What is the function of liver ?

• assimilation of amino acids by converting them to proteins.

• Deamination

• Alcohol, drugs & hormones are broken down in the liver.

What is assimilation ?

uptake and use of nutrients by body cells

What is deamination ?

removal of the nitrogen-containing part of amino acids to form urea.

Where and how is urea formed?

• formed in liver

• from excess amino acids

Parts of kidney ?

• Medulla - inner part

• Cortex - outer layer (contains Bowman’s capsules and coiled tubules )

• Ureter

• Bladder

• Urethra

• Renal artery and vein

What does renal artery do ?

brings wastes and water from the blood

What does bladder do ?

stores urine

What does renal vein do ?

reabsorbs water and functional molecules and leaves wastes behind

What is the role of glomerulus ?

• ultrafiltration from the blood of water, glucose , urea and ions

What is the function of nephron ?

• reabsorption of all the glucose, some of the ions, most of the water ( none of the urea) back into the blood.

What does urine contains ?

• urea, excess water and ions

Explain the process of ultrafiltration

• : blood from the renal artery enters the glomerulus.

• Water, urea, salts, and glucose are forced into the Bowman’s capsule.

• . Blood cells and large proteins cannot pass through.

Explain the process of selective reabsorption

in the tubule, two-thirds of the salt and water and all the glucose move out of the nephron by active transport.

Why is urea toxic ?

• can lower the pH of the body and denature the enzyme

• it can lead to the dead of individual