- Created by: Almaaz
- Created on: 25-09-19 21:02
(I) Excretion (by Almaaz Salie)
Excretion is the removal of toxic materials, the waste products of metabolism and substances in excess to requirements in an organism.
2.70 waste products of plants
In plants, carbon dioxide and oxygen are the waste products of metabolism and they diffuse out of the leaf through the stomata. In plants, carbon dioxide is excreted through respiration;
Glucose + Oxygen → Carbon dioxide + water
C6H12O6 + 6O2 → 6CO2 + 6H2O (aerobic respiration)
And Oxygen is excreted through Photosynthesis;
Carbon dioxide + water → Glucose + Oxygen
6CO2 + 6H2O → C6H12O6 + 6O2 (photosynthesis)
2.71 Excretory products of organs in Humans
Excretion in humans enables the body to prevent build up of dangerous concentrations. The major excretory products are carbon dioxide, excess water & salts and nitrogenous compounds (amino acids, urea, uric acid, etc.).
Carbon dioxide and water are produced in the process of tissue respiration.
Nitrogenous compounds are produced by the breakdown of proteins and amino acids.
The main excretory organs are;
Lungs - remove carbon dioxide and excess water (in vapour).
Skin - provides a surface for small amounts of excess water, salts and urea to move out of the body.
Kidneys - removes substances such as urea and excess water and salts.
2.73B the structure of the urinary system (biology only in bold)
The inner part of the kidney is called the medulla and the outer part is called the cortex.
The ureter carries urine from the kidneys to the bladder to be excreted out of the body.
The kidney is supplied by the renal artery and a renal vein takes blood away.
Each kidney contains millions of kidney tubules or nephrons
2.74B the structure of a nephron
1) The renal artery transports oxygenated blood to the Bowman’s capsule under high pressure
2) In the glomerulus (ball of capillaries within the capsule) the pressure increases even further as the capillaries leaving (efferent arteriole = exiting to renal vein) is narrower than the capillary entering(afferent arteriole)
3) This pressure leads to ultrafiltration - water, salts, glucose and urea pass out of the capillary and into the Bowman’s capsule and into the tubules.
4) Proteins and blood cells are too big to leave the capillaries and so stay within the blood
5) All glucose is reabsorbed at the proximal convoluted tubule by active transport, whilst the rest of the filtrate continues through the tubules. There are many mitochondria here to provide the energy for active transport.
6) Salts are reabsorbed by the loop of Henle
7) Water is reabsorbed into the blood at the collecting ducts, depending on the water levels in the body (and therefore ADH produced)
8) The remaining filtrate (water, salts and urea) in the collecting duct will form urine
9) This is transported through the ureters to be stored in the bladder and then through the urethra to leave the body
2.72B how the kidney carries out its roles of excretion and osmoregulation
Excretion is filtering the bad…