Excretory Products and their Elimination TS

1. Urea is more toxic than ammonia
   ❌ Incorrect – Urea is less toxic than ammonia. That’s one of the reasons organisms like humans convert ammonia into urea before excreting it.

2. Urea is produced in kidneys
   ❌ Incorrect – Urea is produced in the liver, via the urea cycle. The kidneys excrete urea from the blood, but do not produce it.

3. Urea is energetically more expensive to produce than ammonia
   ✅ Correct – The conversion of ammonia to urea requires ATP, making it energetically more expensive than directly excreting ammonia.

4. Urea is never present in human blood
   ❌ Incorrect – Urea is present in human blood and is routinely measured as Blood Urea Nitrogen (BUN). It is transported from the liver to the kidneys via the bloodstream.

✅ Correct statement:

3. Urea is energetically more expensive to produce than ammonia