All Free Biology MCQs with Answers

1861. Malonic acid is an example of____________?

• A. Irreversible inhibitor
• B. Reversible inhibitor
• C. Competitive inhibitor
• D. Non-competitive inhibitor

Explanation: Malonic acid resembles succinic acid and competes with it for the active site of succinate dehydrogenase, so it is a competitive inhibitor. Students often choose reversible inhibitor because malonic acid binds reversibly, but competitive inhibition gives the more specific classification.

1862. The structure of an enzyme is altered by____________?

• A. Irreversible inhibitor
• B. Reversible inhibitor
• C. Competitive inhibitor
• D. Non-competitive inhibitor

Explanation: Irreversible inhibitors permanently alter an enzyme, often by forming strong covalent bonds with amino acids needed for its structure or active site. A common mistake is choosing non-competitive inhibitor, because it binds away from the active site, but non-competitive binding can still be reversible and need not permanently change the enzyme.

1863. A chemical substance that reacts with enzyme but is not transformed into product and thus blocking active site is called__________?

• A. Substrate
• B. Co-factor
• C. Inhibitor
• D. Promotor

Explanation: An inhibitor binds to an enzyme without being converted into the normal product and can block the active site, preventing substrate binding. A substrate is normally transformed by the enzyme, so students may choose substrate if they overlook the phrase “not transformed into product.”

1864. Production of sweat and sebum is related with ?

• A. Skin
• B. Liver
• C. Lungs
• D. GIT

Explanation: Sweat is produced by sweat glands and sebum by sebaceous glands, both located in the skin. The liver and lungs also take part in excretion, but they do not produce sweat and sebum, so option b is the likely mistaken choice.

1865. Study of liver is called _________?

• A. hepatology
• B. hematology
• C. mycology
• D. None of These

Explanation: Hepatology is the branch of medicine concerned with the liver and its diseases. Hematology studies blood, and mycology studies fungi, so those options refer to different fields. Students may choose hematology because both words begin with “hepat-” or “hemat-” in some unfamiliar spellings, but the liver is studied in hepatology.

1866. The elimination of toxic nitrogenous waste and excess water in man is by______?

• A. Excretion
• B. Circulation
• C. Reproduction
• D. Pollution

Explanation: Excretion removes metabolic wastes such as urea and also eliminates excess water and salts from the body, mainly through the kidneys. Circulation transports materials but does not remove them, and reproduction and pollution are unrelated processes. Students may choose circulation because blood carries wastes to the kidneys, but transport is not the same as elimination.

1867. Which of the following organ is responsible for body metabolism?

• A. Kidney
• B. Liver
• C. Lungs
• D. Heart

Explanation: The liver is a major metabolic organ, carrying out carbohydrate, lipid, and protein metabolism as well as detoxification and synthesis of important substances. Students may choose the kidney because it regulates body chemistry, but its main role is filtration and urine formation rather than overall metabolism.

1868. Nephrostome in earthworm opens in____________?

• A. External space
• B. Internal Body cavity
• C. In gut
• D. In Bladder

Explanation: In an earthworm, the nephrostome is the ciliated funnel that opens internally into the coelom and receives coelomic fluid. The nephridiopore is the external opening, so choosing it reverses the internal and external ends of the nephridium.

1869. The nephridia of earthworm open into the coelom by_________?

• A. Nephrostome
• B. Nephridiopore
• C. Flame cell
• D. Anus

Explanation: The nephrostome is the funnel-shaped opening through which an earthworm's nephridium receives fluid from the coelom. A nephridiopore opens to the outside, while the anus belongs to the digestive tract; students commonly choose nephridiopore by confusing entry with exit.

1870. Malphighian tubules absorb waste materials and salts from__________?

• A. Blood
• B. Lymph
• C. Gut
• D. Hemolymph

Explanation: In insects, Malpighian tubules remove nitrogenous wastes and salts from the haemolymph, the insect equivalent of blood. They do not absorb these wastes from the gut or lymph, so choosing blood reflects a generalised but imprecise use of the term blood.