All Free Biology MCQs with Answers

1871. Which of the following openings have cilia?

• A. Nephrostome
• B. Nephridiopore
• C. Both of these
• D. None of these

Explanation: The nephrostome of an earthworm has cilia that create a current and draw coelomic fluid into the nephridium. The nephridiopore is an external outlet and is not the ciliated funnel, so choosing both confuses the two openings.

1872. Which of the following animal excrete nitrogenous waste mainly as uric acid?

• A. Hydra
• B. Planaria.
• C. Humans
• D. Birds.

Explanation: Birds excrete nitrogen mainly as uric acid, which requires little water and forms a semi-solid paste, an adaptation useful for flight and reproduction within the egg. Humans excrete urea, while hydra and planaria mainly release ammonia; students may choose humans because urea is the best-known nitrogenous waste.

1873. Which of the following is most toxic?

• A. Ammonia
• B. Urea
• C. Uric acid
• D. Trimethylamine oxide

Explanation: Ammonia is the most toxic of these nitrogenous wastes because it interferes rapidly with cellular metabolism and must be diluted with large amounts of water for safe removal. Urea and uric acid are less toxic forms produced by converting ammonia, while trimethylamine oxide is not the usual answer in this comparison; students may choose urea because it is the main human waste.

1874. Protonephridia are present in____________?

• A. Round worms
• B. Flateworm
• C. Tape worms
• D. Segmented worms

Explanation: Protonephridia are flame-cell excretory systems found in flatworms, including planarians and tapeworms. Students may choose roundworms because they also have a simple excretory system, but roundworms possess excretory canals or gland cells rather than protonephridia.

1875. Aquatic animals excrete nitrogenous waste commonly in the form of_____________?

• A. Ammonia
• B. Urea
• C. Uric acid
• D. Trimethylamine oxide

Explanation: Aquatic animals commonly excrete ammonia because it is highly toxic but can be rapidly diluted and removed in abundant water. Students may choose urea because it is a common nitrogenous waste in mammals, but urea formation is more useful where water conservation is necessary.

1876. Marine fish can keep their internal environment hypertonic with respect to the surrounding salty water by retaining.

• A. Excessive urea which will increase their internal solute concentration and prevent body shrinkage in hypertonic environment
• B. Trimethyl alanine
• C. Ammonia
• D. Trimethylamine oxide

Explanation: Trimethylamine oxide, commonly called TMAO, acts as an important osmolyte in marine animals and helps maintain internal solute balance in salty surroundings. Students may choose trimethyl alanine because its name resembles TMAO, but trimethylamine oxide is the relevant compound.

1877. Which of the following fishes excrete large volume of diluted urine?

• A. Bony Marine fishes
• B. Fresh water fishes
• C. Both depending upon the surrounding water
• D. None of these

Explanation: Freshwater fishes gain water by osmosis because their body fluids are more concentrated than the surrounding water, so they excrete a large volume of dilute urine. Students may choose marine bony fishes, but they lose water to seawater and therefore produce smaller volumes of more concentrated urine.

1878. The characteristic which enable animals to tolerate dehydration is called__________?

• A. Osmoconformation
• B. Osmoregulaton
• C. Anhydrobiosis
• D. Anhydrosis

Explanation: Anhydrobiosis is a state in which an organism tolerates extreme dehydration by greatly reducing metabolic activity until water returns. Students may choose osmoregulation because it controls water and solute balance, but osmoregulation does not mean surviving almost complete drying.

1879. Which of the following structure in plant's body is called excretophores?

• A. Stem
• B. Leaves
• C. Flowers
• D. Roots

Explanation: Leaves are called excretophores because plants commonly remove or store wastes in leaves that later fall, carrying those wastes away. Students may choose roots because roots can release some substances into soil, but leaves are the principal excretory structures referred to by this term.

1880. Hydra has no specialized excretory system because:

• A. It does not produce waste material
• B. Due to absence of mesoderm
• C. The whole body cells are in contact with water
• D. It has pseudocoelom.

Explanation: Hydra has no specialised excretory organs because its simple body is surrounded by water and its cells can lose soluble wastes directly by diffusion. The likely mistake is pseudocoelom, but Hydra is a diploblastic animal and does not possess a pseudocoelom.