chapter 13

Question 1

Describe excretion and organs involved in it

Answer 1

The removal of waste substances of metabolic reactions, toxic materials and substances in excess of requirements

Organs:
lungs : excrete carbon dioxide, water vapour
Kidney : excrete urea, excess water and ions
Liver: produces urea

Question 2

Why is excretion needed , in terms of carbon dioxide ad urea

Answer 2

Carbon dioxide :
easily dissolves in water to form acidic solution, which lowers pH of cells, reducing enzyme activity that are essential

Urea also very toxic in high concentrations

Question 3

State and describe the main structures involved in the excretory system a

Answer 3

Kidney - two bean shape that filters blood to remove toxic waste
Renal artery - carry oxygenated blood to kidney , contains high concentration of waste and urea
Renal vein - Carry deoxygenated blood, contains low concentration of waste and urea
Ureter- tube connecting kidney to bladder
Bladder- organ that stores urine
Urethra - tube that connect bladder to exterior, where urine and semen released

Question 4

Describe the parts of the kidney and its functions

Answer 4

Cortex
Medulla

Functions:
- regulate water content of the blood for maintaining blood pressure
- excrete toxic waste products of metabolism and substances in excess

Question 5

Outline the structure and functions of nephrons and its blood vessels

Answer 5

Nephron starts in cortex, loops down into medulla and back up

Process 1 : Ultrafiltration
Glomerulus inside Bowman’s capsule . Smaller molecules are forced out of the capillaries and into Bowman’s capsule
Capillaries get narrow which increases blood pressure forcing small molecules out.
E.g : Glucose, water, salt, urea, amino acids

Process 2: Selective Reabsorption
1. Glucose only reabsorbed at proximal convoluted tubule by active transport ( nephrons adapted by having a lot of mitochondria

2. Salts reabsorbed at Loop of Henle by diffusion and active transport
3. Water reabsorbed at Loop of Henle and collecting duct by osmosis
4. urea not reabsorbed , but excreted

Question 6

Describe the role of liver in excretion and assimilation

Answer 6

Excess amino acids cannot be stored, so broken down by process , deamination ( removal of nitrogen containing part of amino acids to form urea )

Enzymes in liver split up amino acid molecules ( carbon into glycogen and stored. Nitrogen into ammonia and then urea )

Urea dissolved in blood and taken to kidney to be excreted

Question 7

state the consequences of high urea levels

Answer 7

• cell death
• reduced response to insulin, leading to diabetics
• deposits inside blood vessels