Excretion is the removal of waste from the body. The waste comes from chemical reactions. Two wastes are very important. One is carbon dioxide from respirat...
Question 1 Report
Excretion is the removal of waste from the body. The waste comes from chemical reactions. Two wastes are very important. One is carbon dioxide from respiration. The other is urea. Urea is made in the liver. It forms when the liver breaks down extra amino acids. The amino acids come from protein in the diet. Carbon dioxide is removed by the lungs. Urea is removed by the kidneys in the urine. If these wastes built up, they would harm the cells. A student ate a meal rich in protein. They were asked what happens to the extra amino acids.
(a) State what is meant by the term excretion. [1]
(b) Name the organ that removes carbon dioxide from the body. [1]
(c) Explain what the liver does with the excess amino acids from a protein-rich meal. [3]
(d) Explain why urea must be removed from the body. [2]
(e) Name the organ that removes urea from the blood and describe how the urea leaves the body. [3]
Answer Details
(a) Excretion is the removal from the body of the toxic waste products of metabolism / chemical reactions [1] (for example carbon dioxide and urea). It is different from egestion of undigested food.
(b) The organ that removes carbon dioxide is the lungs [1].
(c) With excess amino acids the liver breaks down the extra amino acids [1] in a process called deamination [1], which forms urea (from the amino part), while the rest can be used for respiration/energy [1]. The body cannot store extra amino acids, so the surplus must be dealt with.
(d) Urea must be removed because it is toxic / poisonous [1], so if it built up in the blood it would damage cells and harm the body [1].
(e) The organ that removes urea from the blood is the kidney [1]; the urea passes (dissolved in urine) down the ureter to the bladder [1], where the urine is stored before being released from the body through the urethra [1].
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