Choose the ODD one out of the following terms given and name the CATEGORY to which the others belong:
Bile, Urea, Uric acid, Ammonia
Topic: Nitrogenous wastes
Answer
Odd term: BILE. Category of the others: NITROGENOUS WASTES (excretory substances).
Urea, uric acid and ammonia are all NITROGENOUS WASTES — the products of breaking down excess amino acids and nucleotides, containing nitrogen.
BILE is a DIGESTIVE JUICE secreted by the liver and stored in the gall bladder. It emulsifies fats and contains no nitrogen as a waste product.
THE NEAR-MISS worth noticing: bile does carry the BILE PIGMENTS (bilirubin and biliverdin), which are genuine excretory products from the breakdown of haemoglobin — so bile has an excretory role. But bile ITSELF is a digestive secretion, and it is not nitrogenous, so it fails the category.
The three correct terms follow a pattern worth knowing: AMMONIA (most toxic, needs most water — fishes), UREA (mammals), URIC ACID (least soluble, needs least water — birds and insects).