All Free Biology MCQs with Answers

851. Which of the following is TRUE about the Na+/K+ pump?

• A. It moves 2 Na+ out and 3 K+ in
• B. It moves 3 Na+ out and 2 K+ in
• C. It is a passive transport mechanism
• D. It does not require ATP

Explanation: The Na+/K+ ATPase pump moves 3 Na+ out and 2 K+ in against their concentration gradients, using ATP.

852. Lysosomes are called 'suicide bags' because

• A. They contain digestive enzymes
• B. They can digest the cell itself when ruptured
• C. They kill bacteria
• D. They produce toxic substances

Explanation: When lysosomes rupture, their hydrolytic enzymes can digest the cell's own components, causing autolysis.

853. Which of the following has its own DNA and 70S ribosomes?

• A. Nucleus
• B. Mitochondria
• C. Golgi apparatus
• D. Peroxisomes

Explanation: Mitochondria (and chloroplasts) have their own circular DNA and 70S ribosomes, supporting the endosymbiotic theory.

854. The site of photosynthesis in eukaryotic cells is

• A. Mitochondria
• B. Chloroplast
• C. Ribosome
• D. Nucleus

Explanation: Chloroplasts contain chlorophyll and are the site of photosynthesis in plant cells and algae.

855. Which cell junction allows direct cytoplasmic communication between adjacent cells?

• A. Tight junctions
• B. Desmosomes
• C. Gap junctions
• D. Adherens junctions

Explanation: Gap junctions (or plasmodesmata in plants) form channels that allow direct exchange of ions and small molecules between cells.

856. In osmosis, water moves from

• A. High solute concentration to low solute concentration
• B. Low water potential to high water potential
• C. High water potential to low water potential
• D. Hypertonic to hypotonic solution

Explanation: Water moves from high water potential (dilute, hypotonic) to low water potential (concentrated, hypertonic).

857. The left ventricle pumps blood to the

• A. Lungs
• B. Body
• C. Right atrium
• D. Pulmonary artery

Explanation: The left ventricle pumps oxygenated blood through the aorta to the entire body (systemic circulation).

858. The SA node is the

• A. AV bundle
• B. Pacemaker of the heart
• C. Valve of the heart
• D. Coronary artery

Explanation: The sinoatrial (SA) node in the right atrium is the natural pacemaker, initiating each heartbeat.

859. Which blood vessel has the thickest muscular wall?

• A. Vena cava
• B. Pulmonary vein
• C. Aorta
• D. Capillary

Explanation: The aorta has the thickest wall to withstand the high pressure of blood ejected from the left ventricle.

860. Blood clotting requires

• A. Vitamin A
• B. Vitamin K
• C. Vitamin C
• D. Vitamin D

Explanation: Vitamin K is required for synthesis of clotting factors II, VII, IX, and X in the liver.