All Free Biology MCQs with Answers

• A. Chitin
• B. Starch
• C. Cellulose
• D. Glycogen

Explanation: Cellulose is the correct answer because it is the most abundant organic polymer on Earth. It forms the cell walls of plants, which are present in vast quantities, making it a major component of the carbon found in the biosphere. This abundance of cellulose in plant cell walls contributes significantly to the Earth's carbon cycle.Chitin, though abundant in certain organisms like arthropods and fungi, is not as widespread as cellulose. Starch, while an important energy storage molecule in plants, does not contribute as extensively to the biosphere's carbon. Glycogen, being primarily found in animals, is not as prevalent as cellulose in the biosphere.

• A. Glycosidic bond
• B. Peptide bond
• C. Ester bond
• D. Hydrogen bond

Explanation: The correct answer is a glycosidic bond. This is the type of covalent bond that specifically forms between two monosaccharides in carbohydrates. While peptide bonds link amino acids, ester bonds are found in lipids, and hydrogen bonds, although important in the structure of many biological molecules, do not form the primary bonds between monosaccharides.

• A. Amino group
• B. Hydrogen atom
• C. Carboxyl group
• D. Hydroxyl group

Explanation: Monosaccharides are the simplest form of carbohydrates and typically contain multiple hydroxyl groups. Each carbon atom in a monosaccharide is bonded to a hydroxyl group, except for one that is bonded to a carbonyl group, forming either an aldehyde or a ketone. This is why the correct answer is the hydroxyl group. The other options, such as amino groups and carboxyl groups, are not typically found in simple sugar structures.

• A. Glucose
• B. Fructose
• C. Mannose
• D. Ribose

Explanation: Cellulose is a polysaccharide that consists of long chains of glucose molecules. Specifically, it is made up of β-D-glucose units linked by β-1,4-glycosidic bonds. This structure provides the rigidity and strength of plant cell walls. The other options, fructose, mannose, and ribose, are monosaccharides that do not form cellulose. Fructose is found in sucrose, mannose is involved in other polysaccharide structures, and ribose is a component of RNA, not cellulose.

• A. 1,4
• B. 1,6
• C. Both 1,4 and 1,6
• D. 1,2

Explanation: Glycogen is a highly branched polysaccharide that serves as a form of energy storage in animals and fungi. It is composed of glucose molecules linked together primarily by 1,4-glycosidic bonds, which form the linear chains. Additionally, 1,6-glycosidic bonds are present at the branch points, occurring approximately every 10 glucose units along the linear chain. Therefore, glycogen contains both types of linkages. Options A and B highlight only one type of linkage each, which is incorrect, and Option D refers to a linkage not found in glycogen. The correct answer is Option C: 'Both.'

• A. It is a stored form of glucose
• B. In glycogen, the right end is reducing and the left end is non-reducing
• C. It is a branched polymer of glucose
• D. It is a stored form of glucose in plants

Explanation: The correct answer is Option D: 'It is a stored form of glucose in plants.' This statement is incorrect because glycogen is the storage form of glucose in animals, not plants. Plants store glucose as starch, not glycogen.Option A is correct because glycogen serves as a glucose reserve, primarily in animals.Option B is correct because the structural arrangement of glycogen allows for both reducing and non-reducing ends, with the non-reducing ends being more numerous.Option C is correct because glycogen is indeed a branched polymer of glucose, which allows rapid release of glucose when needed.

• A. They are conjugated molecules of carbohydrates
• B. They have a role in the extracellular matrix of animals
• C. They are components of biological membranes
• D. They are found in both plants and animals

Explanation: Connective tissues are specific to animals, providing structure and support. Glycoproteins and glycolipids are found in cell membranes of both plants and animals, where they perform functions like cell recognition and signalling. Therefore, the statement that these molecules are found in both plants and animals is not true for connective tissues, making Option D the correct answer. Options A, B, and C correctly describe characteristics or roles of glycoproteins and glycolipids in biological systems and are not the answer.

• A. Maltose
• B. Sucrose
• C. Lactose
• D. Ribose 5- ­phosphate

Explanation: In non­-reducing sugars, a free aldehyde or ketonic group is absent. Sucrose is a non­-reducing sugar formed by condensation of one molecule each of glucose and fructose with the release of a water molecule. A glycosidic bond is established between carbon atom 1 of glucose and carbon atom 2 of fructose.

• A. Help in regulating metabolism
• B. Are exclusively synthesized in the body of living organism as at present
• C. Are conjugated proteins
• D. Enhance oxidative metabolism.

Explanation: Enzymes control all the life processes. They increase the rate of a biological reaction. The magnitude of increase may be greater than those affected by other catalysts.Vitamins are accessory indispensable food factor, organic in nature (organic acid, amino acid esters, alcohols, steroids, etc.) required by an organism in small amounts to maintain normal growth and regulate the metabolic processes. Hormones are a biologically active organic substance that is produced in minute quantities by some specialized organs and exert physiological effects at sites remote from their origin.

• A. Lipoprotein
• B. Polysacchiride
• C. Glycoprotein
• D. Phospholipid

Explanation: Lipoproteins and glycoproteins are conjugated molecules. Phospholipids are class of lipids that form basic structure of biological membrane. Chitin in only polysaccharide that contain nitrogen and it component of fungal cell wall as well as exoskeleton of insects.