Excretion in Humans

Ureter

Step 1: The excretory system has several parts connected to each other. Step 2: The ureter is a narrow tube that runs from the inner side of each kidney down to the urinary bladder. Step 3: The urethra is different — it leads from the urinary bladder to the outside of the body. Step 4: The renal artery carries blood into the kidney, and the collecting duct is a part inside the kidney. Step 5: Therefore, the tube that connects the kidney to the urinary bladder is the ureter.

A muscular bag that stores urine temporarily

Step 1: After urine is formed in the kidneys, it passes through the ureters. Step 2: The urine then collects in the urinary bladder. Step 3: The urinary bladder is a muscular bag situated in the lower abdomen that stores urine temporarily. Step 4: When the bladder is full, urine is expelled outside through the urethra. Step 5: Option A describes the urethra, Option C describes the kidney, and Option D describes sweat glands — so the correct answer is Option B.

Nephron

Step 1: Just like a neuron is the unit of the nervous system, the kidney has its own unit. Step 2: Inside each kidney, there are millions of microscopic tubular structures called nephrons (also called renal tubules). Step 3: Each nephron filters the blood, removes waste, and helps form urine — making it the working unit of the kidney. Step 4: A neuron is the unit of the nervous system, not the kidney. Ureters and renal pelvis are parts of the excretory system but not the functional unit of the kidney. Step 5: Therefore, the nephron is the structural and functional unit of the kidney.

Urea

Step 1: Our body breaks down excess amino acids (building blocks of proteins) in the liver. Step 2: This breakdown process produces a nitrogenous waste called urea. Step 3: Urea is carried through the blood to the kidneys, which then filter it out and remove it through urine. Step 4: Carbon dioxide is a waste product of respiration (not amino acid breakdown). Oxygen is not a waste product. Glucose is a useful sugar, not a waste. Step 5: Therefore, the correct answer is Urea.