All Free Biology MCQs with Answers

891. Trypsin is activated by

• A. HCl
• B. Enterokinase/Enteropeptidase
• C. Pepsin
• D. Bile

Explanation: Enterokinase (enteropeptidase) from intestinal brush border activates trypsinogen to trypsin, which then activates other pancreatic enzymes.

892. Lactase deficiency causes

• A. Diabetes
• B. Lactose intolerance
• C. Celiac disease
• D. Pernicious anemia

Explanation: Lactase deficiency leads to lactose intolerance, causing bloating, gas, and diarrhea when dairy is consumed.

893. Intrinsic factor is required for absorption of

• A. Iron
• B. Vitamin B12
• C. Calcium
• D. Vitamin D

Explanation: Intrinsic factor from gastric parietal cells binds vitamin B12 for absorption in the ileum; its deficiency causes pernicious anemia.

894. The hepatic portal vein carries blood from the

• A. Liver to heart
• B. Intestines to liver
• C. Liver to kidneys
• D. Spleen to liver

Explanation: The hepatic portal vein carries nutrient-rich blood from the digestive organs to the liver for processing.

895. Pancreatic juice is alkaline due to

• A. HCl
• B. Bicarbonate
• C. Pepsin
• D. Bile

Explanation: Sodium bicarbonate in pancreatic juice neutralizes acidic chyme from the stomach, creating optimal pH for enzymes.

896. Chylomicrons are formed in

• A. Liver
• B. Intestinal epithelial cells
• C. Blood
• D. Adipose tissue

Explanation: Chylomicrons (lipoprotein particles containing triglycerides) are formed in intestinal epithelial cells after fat absorption.

897. The active site of an enzyme is

• A. The entire enzyme surface
• B. A specific region where substrate binds
• C. The coenzyme binding site
• D. Where allosteric regulators bind

Explanation: The active site is a specific pocket or cleft on the enzyme where the substrate binds and catalysis occurs.

898. According to the induced fit model

• A. The active site is rigid
• B. The enzyme changes shape to fit the substrate
• C. The substrate is unchanged
• D. No conformational changes occur

Explanation: Koshland's induced fit model proposes that the enzyme's active site is flexible and changes shape to better accommodate the substrate.

899. Competitive inhibitors

• A. Bind to allosteric site
• B. Cannot be overcome by increasing substrate
• C. Bind to active site
• D. Change Vmax but not Km

Explanation: Competitive inhibitors bind to the active site, competing with substrate. They can be overcome by increasing substrate concentration.

900. The optimum pH for pepsin is approximately

• A. 2
• B. 7
• C. 8
• D. 10

Explanation: Pepsin works optimally at pH 1.5-2 in the stomach, where it is activated by HCl.