a) excretion is the removal or metabolic waste from the body.
Metabolic waste consists of waste substances that may be toxic or are produced n excess by reactions inside cells.
b) Explain the importance of removing metabolic wastes, including carbon dioxide and nitrogenous waste, from the body.
The are many substances that need to be excreted - almost any cell product that is formed in excess by the chemical process occurring in the cells must be excreted. However there are two products that are produced in very large amounts.
Carbon dioxide from respiration.
Nitrogen containing compounds such as urea.
Where are these substances produced.
Carbon dioxide is produced by every living cell in the body as a result of respiration.
Urea is produced in the liver from excess amino acids.
Where are the substances excreted?
Carbon dioxide is passed from the cells of respiring tissues into the blood stream. It is transported in the blood (mostly in the form of hydrogen carbonate ions) to the lung. In the lungs the carbon dioxide diffuses into the alveoli to be excreted as we breathe out.
Urea is produced by breaking down excess amino acids in the liver. This process is known as deamination. The urea is then passed through the blood stream to be transported to the kidneys It is transported in solution - dissolved in the plasma. In the kidneys the urea is removed from the blood to become part of urine. Urine is stored in the bladder until it is removed.
Why must the substances be removed?
Carbon dioxide.
Excess CO2 is very toxic. A high level of carbon dioxide has three main effects.
Majority of carbon dioxide is carried in the blood as hydrogen carbonate ions. However, forming hydrogen carbonate ions forms hydrogen ions. This occurs inside the red blood cells, under the haemoglobin. They compete with oxygen for space on the haemoglobin. If there is too much carbon dioxide in the blood it can reduce oxygen transport.
The carbon