Step 1: Build the renin-angiotensin cascade from the start.
This pathway begins with a protein made in the liver called angiotensinogen. It sits in the blood plasma, waiting to be activated.
Step 2: Trace what activates it.
When blood pressure drops, the kidney releases the enzyme renin into the blood. Renin acts on angiotensinogen and cuts it down into angiotensin I.
Step 3: Follow the next conversion step.
Angiotensin I then gets converted into angiotensin II by an enzyme called ACE, found mainly in the lungs. Angiotensin II is the active hormone that narrows blood vessels and pushes blood pressure back up.
Step 4: Identify where the source protein actually comes from.
Even though the final hormone is activated by the kidney and lungs, its precursor molecule, angiotensinogen, is made and released by the liver. That is why the liver is credited as the organ behind angiotensin in this chain.
Step 5: Rule out the other organs.
The kidney supplies renin, not angiotensinogen. The heart and pituitary gland play no part in making any protein in this pathway.
Final Answer:
Angiotensin traces back to a liver made precursor, so the liver is the answer, option (2).