All Free Biology MCQs with Answers

• A. Membrane potential
• B. Accumulation of Na ions
• C. Accumulation of K ions
• D. Proton gradient

Explanation: The chemiosmotic theory, proposed by Peter Mitchell, suggests that a proton gradient across the membrane is used to generate ATP. This gradient is created by the accumulation of hydrogen ions (protons) on one side of the membrane, driving ATP synthesis as protons flow back across the membrane through ATP synthase.

• A. Thylakoids - flattened membranous sacs forming the grana of chloroplasts
• B. Centrioles - sites for active RNA synthesis
• C. Ribosomes - those on chloroplasts are larger (80S) while those in the cytoplasm are smaller (70S)
• D. Lysosomes - optimally active at a pH of about 8.5

Explanation: Thylakoids are flattened membranous sacs forming the grana of chloroplasts. These are essential components of chloroplasts, playing a critical role in photosynthesis by housing pigments necessary for capturing light energy.

• A. Outer membrane
• B. Inner membrane
• C. Thylakoids
• D. Stroma

Explanation: Thylakoids are the flattened sac-like membranous structures within chloroplasts. Chlorophyll is embedded in the thylakoid membranes, where it plays a crucial role in the light-dependent reactions of photosynthesis, capturing and converting light energy.

• A. Oxidative enzymes
• B. Hydrolytic enzymes
• C. Reductive enzymes
• D. Anabolic enzymes

Explanation: Hydrolytic enzymes are responsible for breaking down various biomolecules and are the primary components of lysosomes, facilitating cellular digestion.

• A. Ribosomes which occur on the nuclear membrane and ER
• B. Ribosomes of only cytosol
• C. Ribosomes of only nucleolus and cytosol
• D. Ribosomes of only mitochondria and cytosol

Explanation: Ribosomes attached to the nuclear membrane and endoplasmic reticulum (ER) are involved in synthesizing proteins destined for secretion or for use in the cell membrane. These ribosomes, often referred to as membrane-bound ribosomes, work in conjunction with the ER to ensure proteins are properly synthesized and transported.

• A. Ribosome
• B. Peroxisome
• C. Golgi apparatus
• D. Mitochondria

Explanation: The Golgi apparatus is essential for modifying, sorting, and packaging proteins and lipids. It completes protein glycosylation by adding sugar moieties, which are critical for the protein's functionality.

• A. Centrosomes
• B. Golgi bodies
• C. Ribosomes
• D. Mitochondria

Explanation: Ribosomes are the site of protein synthesis in the cell, where amino acids are assembled into proteins, earning them the nickname "protein factories."

• A. Chemiosmotic theory
• B. Munch's hypothesis (mass flow model)
• C. Relay pump theory of Godlewski
• D. Cholodny­-Went model

Explanation: The chemiosmotic theory, proposed by Peter Mitchell, is the most widely accepted explanation for ATP synthesis in mitochondria and chloroplasts. It involves the creation of a proton gradient across a membrane, which drives ATP synthesis as protons flow back across the membrane through ATP synthase.

• A. Only in the cytoplasm
• B. In the cytoplasm as well as in the mitochondria
• C. In the nucleolus as well as in the cytoplasm
• D. Only on ribose attached to nucleus

Explanation: In the cytoplasm, ribosomes are present and mitochondria also have its own DNA and ribosomes. Ribosomes are responsible for protein synthesis so wherever ribosomes are present protein synthesis occurs.

• A. Protein synthesis
• B. Phosphorylation of flavoprotein.
• C. Breakdown of macromolecules.
• D. Oxidation-reduction reaction.

Explanation: The cristae of mitochondria house the electron transport chain, where oxidation-reduction reactions occur as part of cellular respiration, facilitating ATP production.