Which statements accurately describe why the body converts NH₄⁺ to urea? (Select all that apply)

I. Urea is less toxic than NH₄⁺ and can be safely excreted in urine.

II. NH₄⁺ is readily eliminated from the body without conversion.

III. The conversion of NH₄⁺ to urea helps in maintaining the body's acid-base balance.

IV. Urea formation allows the body to excrete excess nitrogen while conserving water.

Which is true about the structure of urea? (Select all that apply)

I. Urea contains a carbonyl group (C=O).

II. Urea contains two amine groups (-NH₂).

III. Urea contains a hydroxyl group (-OH).

IV. Urea contains only single bonds between carbon and nitrogen.

In which of the following organs does the urea cycle occur?