All Free Biology MCQs with Answers

4641. The general formula of monosaccharides is:

• A. None of these
• B. Cx(H2O)y
• C. Cn(H2O)n
• D. Cy(H2O)n

Explanation: The general chemical formula for a monosaccharide is Cn(H2O)n. In this formula n represents the number of carbon atoms in the molecule.The ratio of carbon to hydrogen to oxygen atoms is typically 1:2:1. These are hydrated carbons i.e. having a water molecule against each carbon.

4642. Ribose forms a _ cornered ring.

• A. Three
• B. Four
• C. Six
• D. Five

Explanation: Ribose forms a five-membered ring, which is also called a furanose ring. This ring consists of four carbon atoms and one oxygen atom. Structure: In aqueous solution, ribose primarily exists in its cyclic furanose form. The ring is made up of four carbon atoms from the original five-carbon chain and one oxygen atom.Numbering: The carbon atoms in the ring are numbered 1 through 4, with the fifth carbon (C5) attached to the fourth carbon and extending outside the ring.Function: This five-membered ring structure is crucial in biological molecules like RNA, where ribose forms the backbone with a phosphate group.

4643. _ corners of glucopyranose are occupied by carbon atoms.

• A. Three
• B. Four
• C. Five
• D. Six

Explanation: One corner is occupied by oxygen and rest of the four by carbon atoms, whereas sixth carbon remaining outside the ring. So, there are 5 carbon atoms in ring of glucopyranose.

4644. Glucose is naturally produced in:

• A. Green plants
• B. Protists
• C. Animals
• D. Fungi

Explanation: The correct answer is Green plants. Green plants are capable of photosynthesis, which allows them to convert sunlight, carbon dioxide, and water into glucose and oxygen. This process is essential for their energy production and growth. Unlike green plants, Protists are a diverse group, and not all perform photosynthesis; many are heterotrophic. Animals are consumers that rely on other organisms for glucose, while Fungi absorb nutrients from organic matter and do not photosynthesize.

4645. The ones yielding two monosaccharides on hydrolysis are:

• A. Trisaccharides
• B. Tetrasaccharides
• C. Pentasaccharides
• D. Disaccharides

Explanation: The correct answer is D. Disaccharides are composed of two linked monosaccharide units, and upon hydrolysis, they yield exactly two monosaccharides. This is why they fit the description given in the question. Trisaccharides, tetrasaccharides, and pentasaccharides contain three, four, and five monosaccharide units respectively, and their hydrolysis results in the release of the corresponding number of monosaccharides, not just two.

4646. The molecular formula of sucrose is:

• A. C12H22O11
• B. C6H12O6
• C. C3H6O3
• D. C5H10O5

Explanation: Sucrose is a disaccharide formed by the condensation of glucose and fructose monomers, resulting in the removal of a water molecule (H2O). This process forms a 1,2-glycosidic bond, leading to the molecular formula C12H22O11, making Option A correct. Options B, C, and D represent different compounds: glucose, glycerol, and an undefined carbohydrate structure, respectively. They do not correspond to the molecular composition of sucrose.

4647. Starches are of _ types.

• A. One
• B. Two
• C. Three
• D. Four

Explanation: Starches consist of two major types: amylose and amylopectin. Amylose is characterized by a linear chain of glucose molecules, while amylopectin is distinguished by its highly branched structure. These two components play a critical role in determining the properties and functionality of starch. The options suggesting one, three, or four types are incorrect because they do not align with the scientific classification of starch.

4648. Cotton is a pure form of:

• A. Starch
• B. Amylopectin
• C. Cellulose
• D. Pectins

Explanation: Cotton is a pure form of cellulose, which is a polysaccharide that serves as the main structural component of plant cell walls. This makes cellulose the primary substance in cotton fibers. The other options-starch, amylopectin, and pectins-are different types of carbohydrates with distinct roles in plants. Starch, including amylopectin, is primarily used for energy storage, while pectins are involved in maintaining the structure of fruit and plant cells, not in forming fibers like cellulose does.

4649. In the herbivores, cellulose is digested because of:

• A. Bacteria
• B. Yeasts
• C. Protozoa
• D. Bacteria, Yeasts, and Protozoa

Explanation: In herbivores, the digestion of cellulose is primarily facilitated by bacteria and protozoa present in their digestive systems. These microorganisms produce enzymes that break down cellulose into simpler sugars, which the herbivores can then absorb. Bacteria and protozoa are critical for this process, residing in the rumen or cecum of animals like cows and sheep. Although yeasts are not primarily involved in cellulose digestion, they might contribute minimally. Therefore, the correct answer is Option D: Bacteria, Yeasts, and Protozoa. Options A and C are partially correct because they include either bacteria or protozoa, but not both. Option B, involving yeasts, is incorrect as yeasts are not major contributors to cellulose digestion.

4650. Lipids as hydrophobic compounds are component of:

• A. Genetic material
• B. Cell wall
• C. Cytoplasm
• D. Cellular membrane

Explanation: The correct answer is Option D: Cellular membrane. Lipids, particularly phospholipids, are integral to the structure of cellular membranes. They form a bilayer that constitutes the basic framework, ensuring membrane fluidity and selective permeability. The other options are incorrect because lipids do not constitute genetic material, are not primary components of the cell wall, and while present in the cytoplasm, do not define it.