5.2.1(Excretion)

Define the term excretion

• The removal of metabolic waste from the body

State what substances need to be excreted from the body

• CO2 from respiration

• Urea

• Uric acid

• Ammonia

Describe the importance of excretion in the human body

• prevents the build of metabolites which could be fatal

• They alter the pH, which affects enzymes and reduces their activity

• Metabolites may also act as inhibitors and reduce enzyme activity

Describe the importance of the lungs in excretion

• CO2 is produced by respiration in all cells

• CO2 is transported in the blood as hydrogen carbonate ions to the lungs

• In the lungs, the carbon dioxide then diffuses into the alveoli to be extracted during expiration

Describe the importance of the liver in excretion

• Converts excess amino acids into urea which are broken down during the process of deamination

• The urea then travels in the blood to the kidneys where it is filtered out and removed from the body in urine

Describe the importance of the skin in excretion

• Urea, Uric acid and ammonia can all be excreted from the blood via sweat

Describe the importance of exertion of CO2 in the body

• CO2 reacts with H2O to form carbonic acid which dissociates to form a hydrogen ion a hydrogen carbonate ion.

• The hydrogen ion, decreases the pH in the blood. which causes the change in many proteins around the body

• CO2 needs to be removed to ensure that the pH of the blood doesn’t decrease so enzyme activity isn’t affected

Describe the importance of excreting nitrogenous compounds from the body

• Excess amino acids cannot be stored in the body, therefore they are broken down into ammonia by removing the amino group during deamination

• Ammonia is very toxic and can cause damage to cells and in high concentrations can be fatal