CBSE Questions for Class 11 Medical Biology Excretory Products And Their Elimination Quiz 13 - MCQExams.com

• Phloem conducts food made in the leaves to all other parts of the plant. Phloem is composed of various specialized cells called sieve tubes, companion cells, phloem fibers, and phloem parenchyma cells. 
• The nephron is the functional unit of the kidney, the structure that actually produces urine in the process of removing waste and excess substances from the blood. 
• In the circulatory system, veins are the blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. 
• Platelets, also called thrombocytes, are blood cells whose function (along with the coagulation factors) is to stop bleeding. Platelets have no nucleus, they are fragments of cytoplasm which are derived from the megakaryocytes of the bone marrow and then enter the circulation. 
• Hence, the correct answer is 'A- 2, B- 1, C- 4, D- 3'.

• In most invertebrates, the excretory structures are simple tubular forms whereas vertebrates have complex tubular organs called kidneys. The shark is a vertebrate and has kidneys as excretory structures.
• Protonephridia or flame cells are the excretory structures in Platyhelminthes (Flatworms, e.g., Planaria), rotifers, some annelids, and the cephalochordate Amphioxus. Protonephridia are primarily concerned with ionic and fluid volume regulation, i.e., osmoregulation.
• Nephridia are the tubular excretory structures of earthworms and other annelids like leech. Nephridia help to remove nitrogenous wastes and maintain a fluid and ionic balance.
• Malpighian tubules are the excretory structures of most insects including cockroaches. Malpighian tubules help in the removal of nitrogenous waste and osmoregulation.

Correct option: (D)

Explanation for correct option: (D)

The function of the kidney is to filter unwanted substances from the blood and produce urine which is excreted from the body. The nephron is the functional unit of the kidney. It filters blood and forms urine by following steps.

• Filtration of blood occurs in the glomerulus and the filtrate consists of water, wastes and useful solutes like glucose, amino acids, smaller proteins and ions.
• The filtrate now passes through proximal convoluted tubule, the loop of Henle and distal convoluted tubule present in nephron where the nutrients, ions and water from the filtrate are reabsorbed back into the blood.
• The filtrate finally becomes hypertonic to blood plasma and is termed as urine.
• 
  

Explanation for incorrect options:

Option (A): The major calyces of the kidney open into the renal pelvis. It acts as a funnel for urine to flow into the ureter.

Option (B): Sweat is made majorly of water, with tiny amounts of other chemicals like ammonia, urea, salts, and sugar. It is secreted by sweat glands.

Option (C): Urinary bladder stores the 1 % filtrate that has to be excreted as urine.