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5 - Excretion
100
2 (i) When proteins are digested they are broken down into amino ac
Any unused amino acids are deaminated (broken down) to form
new substances. One such substance is urea,
(a) What does the body use these amino acids for?
(b) Where in the body does deamination occur?
(©) Copy the diagram and draw a box around part of the amino
acid (in diagram) that is removed to form urea.
if
HO—— Cc —— C ——NHp
H
(d)_ What happens to the remaining portion of the amino acid a
the urea group is removed?
(©) Which organ is responsible for eliminating urea from the bo
(ii) (@) Which structures filter the blood as it passes through the
kidney?
(b) Below is a diagram of the filtering unit in the kidney. Name
structures A-D.
(©) Which substances are filtered at structure A?
(@) Which substances are re-absorbed by the blood vessels
surrounding structure D?
(e) After re-absorption at structure D, what is the name of the
remaining mixture?
()_ Where does structure € lead to?
(ii) When there is a high salt concentration in the blood the
pituitary gland secretes a hormone that dictates to the kidne
to re-absorb water. What is this hormone called?
(iv) Explain how someone with malfunctioning kidneys can hay
their blood filtered.
Va
