All Free Biology MCQs with Answers

• A. α-1,4 linkages
• B. Both α-1,4 and α-1,6 linkages
• C. α-1,6 linkages
• D. All of the above

Explanation: The correct answer is that in amylose, glucose units are linked by α-1,4 glycosidic bonds. This linear structure differentiates amylose from amylopectin, which contains both α-1,4 and α-1,6 linkages, the latter of which contributes to its branched structure. Options suggesting α-1,6 linkages or a combination of linkages are incorrect for amylose. The presence of only α-1,4 linkages is a defining feature of amylose.

• A. Cellulose
• B. Glycogen
• C. Starch
• D. All of the above

Explanation: Cellulose is the correct answer because it is an unbranched polysaccharide consisting of a linear chain of glucose units linked by β-1,4-glycosidic bonds. This linear structure is crucial for its role in providing structural support to plant cells. In contrast, glycogen is highly branched, which makes it effective for energy storage in animals. Starch contains both amylose (which is mostly linear) and amylopectin (which is branched), so it is not entirely unbranched.

• A. Pyranose fructose
• B. β -D glucose
• C. Furanose
• D. α -D glucose

Explanation: The correct answer is α-D-glucose. Starch is a polysaccharide made up of glucose monomers. Specifically, it is composed of α-D-glucose units linked together. The α designation refers to the orientation of the hydroxyl group on the anomeric carbon which is important for the structure and function of starch. Other options like pyranose fructose, β-D-glucose, and furanose do not represent the monomer units of starch. Pyranose fructose and furanose are related to different sugar structures, while β-D-glucose is a different anomer of glucose not used in starch.

• A. Storage sulphur containing polysaccharide
• B. Nitrogen containing structural homopolysaccharide
• C. Mucopolysaccharide
• D. Structural oligosaccharide

Explanation: The correct answer is that chitin is a nitrogen-containing structural homopolysaccharide. Chitin is a long-chain polymer of N-acetylglucosamine, a derivative of glucose, and it is used primarily for structural purposes in the exoskeletons of arthropods. The other options are incorrect because they do not accurately describe the composition or function of chitin: it is not a storage polysaccharide, it does not contain sulfur, it is not a mucopolysaccharide, and it is not an oligosaccharide.

• A. Amylopectin
• B. Starch
• C. Cellulose
• D. None of these

Explanation: The correct answer is Starch. Starch is composed of two types of glucose polymers: amylose and amylopectin. The iodine test for starch is based on the interaction between iodine and the helical structure of amylose, resulting in a dark blue color. Amylopectin, despite being part of starch, does not produce this color change on its own due to its highly branched structure. Cellulose does not form a complex with iodine because its linear chains do not create the necessary helical structure. Therefore, the statement 'None of these' is incorrect as starch does indeed produce a dark blue color with iodine.

• A. Glycogen is analogous to starch
• B. It is a structural polysaccharide
• C. It is a non-reducing sugar
• D. It gives a red color with iodine solution

Explanation: Glycogen is a storage polysaccharide found primarily in animals, stored in the liver and muscles. It is not a structural polysaccharide, which is a category that includes materials like cellulose in plants. Glycogen's role is similar to that of starch in plants, serving as an energy reserve. Glycogen is non-reducing, meaning it doesn't have a free aldehyde or ketone group to participate in redox reactions. Additionally, glycogen gives a red color when it reacts with iodine solution, which is a classic test for its presence.

• A. Glycoproteins
• B. Flavoproteins
• C. Lipoproteins
• D. All of these

Explanation: The correct answer is Glycoproteins, as immunoglobulins (antibodies) are glycoproteins. They have specific carbohydrate groups attached to their protein structure, which is essential for their function in the immune system. The other options are incorrect: Flavoproteins involve a flavin cofactor and are unrelated to immunoglobulins. Lipoproteins are involved in lipid transport and do not share the same structural characteristics as immunoglobulins. Therefore, the option 'All of these' is also incorrect, as it inaccurately groups different molecules with distinct functions and compositions.

• A. Keratin
• B. RuBP
• C. Rubisco
• D. Fibrinogen

Explanation: Rubisco, or ribulose-1,5-bisphosphate carboxylase/oxygenase, is the most abundant protein on Earth due to its essential role in the Calvin cycle of photosynthesis. It catalyzes the fixation of carbon dioxide, which is a critical process for the synthesis of organic compounds in plants, algae, and some bacteria. While keratin, RuBP, and fibrinogen are significant in their respective roles, they do not match Rubisco in abundance or function in photosynthesis.

• A. Haemoglobin
• B. Myosin
• C. Myoglobin
• D. Actin

Explanation: Myoglobin is the correct answer because it is a protein found in muscle tissues that stores oxygen, providing a reserve that can be used during muscle contraction and periods of increased demand. While haemoglobin is involved in oxygen transport in the blood, it does not store oxygen within muscles. Myosin and actin are related to muscle contraction and cell structure, respectively, but do not have a role in oxygen storage.

• A. Polyester
• B. Lipid
• C. Protein
• D. Polysaccharide

Explanation: Silk is a natural fiber that is primarily composed of the protein fibroin, secreted by silkworms. This makes Option C, 'Protein,' the correct answer. Polyester (Option A) is a synthetic polymer, lipids (Option B) are fats and oils, and polysaccharides (Option D) are carbohydrates. None of these are the primary components of natural silk fibers.