Birds excrete nitrogenous wastes in form of

Step 1: Analyze the question The question asks which form of nitrogenous waste birds excrete. Nitrogenous wastes come from the breakdown of proteins and nucleic acids.

Step 2: The concept Animals excrete nitrogenous waste in three main forms, depending on their habitat and water availability:

| Form | Toxicity | Water needed | Examples | |---|---|---|---| | Ammonia | Very toxic | A lot | Aquatic animals, e.g. fish, tadpoles | | Urea | Less toxic | Moderate | Mammals, adult amphibians | | Uric acid | Least toxic | Very little | Birds, reptiles, insects |

Step 3: Apply it to birds

• Birds lay eggs with hard shells, so the embryo cannot get rid of liquid waste. Uric acid is insoluble and stays as a solid paste inside the egg.
• Birds are also built for flight, so they save body weight by not storing or carrying much water. Excreting uric acid conserves water.
• This is why bird droppings have a white, pasty part. That white part is uric acid.

Step 4: Check the other options

• A. Ammonia: excreted by aquatic animals such as fish, not birds.
• B. Sweat: this is a fluid from sweat glands. Birds do not have sweat glands.
• C. Urea: the main waste of mammals, including humans.
• E. Urine: this is a fluid that carries waste, not the chemical form of the nitrogenous waste itself.

Answer: D. uric acid

Exam tip: Remember "Birds, Reptiles, and Insects = Uric acid", the water-savers. Fish excrete ammonia, and mammals excrete urea.