All Free Biology MCQs with Answers

4311. Which of the following is non-reducing disaccharide sugar?

• A. Mannose
• B. Sucrose
• C. Maltose
• D. Lactose

Explanation: Mannose: Mannose is a monosaccharide, not a disaccharide. It is a single sugar unit and does not fit the criteria for a non-reducing disaccharide. Sucrose: The correct option is sucrose. Sucrose is a non-reducing disaccharide composed of one molecule of glucose and one molecule of fructose linked together by a glycosidic bond. It is commonly known as table sugar and is obtained from sugarcane or sugar beets. Sucrose is non-reducing because it lacks a free aldehyde or ketone group, which is required for a sugar to be considered reducing. Both glucose and fructose have their anomeric carbon involved in the glycosidic linkage, leaving no free aldehyde or ketone group to participate in a reducing reaction. Maltose: Maltose is a reducing disaccharide composed of two glucose molecules linked together by a glycosidic bond. It is formed during the breakdown of starch into smaller carbohydrate units. Maltose is reducing because one of its glucose units has a free aldehyde group on the anomeric carbon, which can participate in a reducing reaction. Lactose: Lactose is a reducing disaccharide composed of one molecule of glucose and one molecule of galactose linked together by a glycosidic bond. It is commonly known as milk sugar and is found in milk and dairy products. Lactose is reducing because the glucose unit in lactose has a free aldehyde group on the anomeric carbon, allowing it to participate in a reducing reaction.In summary, option b) Sucrose is the correct option. Sucrose is a non-reducing disaccharide composed of glucose and fructose, lacking a free aldehyde or ketone group necessary for a reducing reaction. The other options (a) Mannose, (c) Maltose, and (d) Lactose are all reducing disaccharides.

4312. Which of the foIIowing sugar is mainly present in human blood?

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

Explanation: Glucose: The correct option is glucose. Glucose is the main sugar present in human blood and serves as a primary source of energy for the cells in the body. After consuming carbohydrates from food, the digestive system breaks down complex carbohydrates into glucose, which is then absorbed into the bloodstream. Glucose is transported through the bloodstream and taken up by various tissues and organs to provide energy for cellular processes. Sucrose: Sucrose is a disaccharide composed of one glucose molecule and one fructose molecule linked together. It is commonly known as table sugar and is found in various sweet foods. However, sucrose is not the primary sugar present in human blood.Fructose: Fructose is a monosaccharide, and while it is found in certain foods like fruits and honey, it is not the primary sugar present in human blood. Mannose: Mannose is another monosaccharide, and it is essential for various cellular processes. However, it is not the primary sugar present in human blood.In summary, the correct option is a) Glucose. Glucose is the main sugar present in human blood and serves as the primary energy source for cells and tissues throughout the body.

4313. The simplest monosaccharide containing keto group is:

• A. Glyceraldehyde
• B. Glucose
• C. Dihydroxyacetone
• D. Ribose

Explanation: Glyceraldehyde: Glyceraldehyde is a monosaccharide with three carbon atoms (a triose sugar). It contains an aldehyde functional group (a carbonyl group with a terminal -CHO). While it is a simple monosaccharide, it does not contain a keto group. Glucose: Glucose is a monosaccharide with six carbon atoms (a hexose sugar). It contains an aldehyde functional group in its linear form, known as an aldohexose. However, in its cyclic form, which is the most stable and prevalent in biological systems, it contains a hydroxyl group (-OH) on its first carbon atom (C1), making it an aldose and not a keto sugar. Dihydroxyacetone: The correct option is dihydroxyacetone. Dihydroxyacetone is the simplest monosaccharide containing a keto group. It is a three-carbon sugar with a ketone functional group (a carbonyl group within the carbon chain) on its central carbon (C2) and hydroxyl groups (-OH) on the other two carbon atoms. Ribose: Ribose is a monosaccharide with five carbon atoms (a pentose sugar). It contains an aldehyde functional group (an aldopentose) on its first carbon atom (C1), making it an aldose and not a keto sugar.In summary, the correct option is c) Dihydroxyacetone. Dihydroxyacetone is the simplest monosaccharide containing a keto group, with a ketone functional group on its central carbon atom.

4314. Which of the following type of carbohydrates has high molecular weight and is sparingly soluble in water?

• A. Monosaccharide
• B. Oligosaccharides
• C. Disaccharides
• D. Polysaccharides

Explanation: Monosaccharide: Monosaccharides are the simplest form of carbohydrates, and they cannot be hydrolyzed into smaller carbohydrates. They consist of a single sugar unit and have a relatively low molecular weight. Examples of monosaccharides include glucose, fructose, and galactose. Monosaccharides are usually highly soluble in water due to their small size and ability to form hydrogen bonds with water molecules. Oligosaccharides: Oligosaccharides are carbohydrates composed of a small number of monosaccharide units (typically 3 to 10 sugar units) linked together by glycosidic bonds. They have higher molecular weights than monosaccharides but are still relatively smaller than polysaccharides. Examples of oligosaccharides include raffinose and sucrose. Oligosaccharides can be soluble or sparingly soluble in water, depending on their size and structure. Disaccharides: Disaccharides are a type of oligosaccharide composed of two monosaccharide units linked together by a glycosidic bond. Examples of disaccharides include lactose, maltose, and sucrose. Disaccharides have higher molecular weights than monosaccharides but are still smaller than polysaccharides. They are usually soluble in water, with some exceptions like trehalose, which is less soluble. Polysaccharides: The correct option is polysaccharides. Polysaccharides are large carbohydrates composed of multiple monosaccharide units linked together by glycosidic bonds. They have very high molecular weights, making them much larger and more complex than monosaccharides, oligosaccharides, or disaccharides. Examples of polysaccharides include starch, glycogen, and cellulose. Due to their large size and complex structures, many polysaccharides are sparingly soluble or insoluble in water.In summary, option d) Polysaccharides is the correct option. Polysaccharides have high molecular weights and are sparingly soluble in water due to their large and complex structures. The other options (a) Monosaccharide, (b) Oligosaccharides, and (c) Disaccharides have lower molecular weights and are generally more soluble in water.

4315. Glycosidic bond is formed by the:

• A. Removal of water
• B. Removal of oxygen
• C. Addition of oxygen
• D. Addition of water

Explanation: Removal of water: The formation of a glycosidic bond involves the removal of a water molecule (H2O) from two hydroxyl groups of monosaccharide units. One hydroxyl group donates an -H (hydrogen atom), and the other donates an -OH (hydroxyl group). The loss of these two components (H and OH) results in the formation of a covalent bond (glycosidic bond) between the two monosaccharide units. Removal of oxygen: This option suggests that the glycosidic bond is formed by removing oxygen. However, this is not accurate. The glycosidic bond formation is related to the loss of water, not oxygen.Addition of oxygen: This option suggests that the glycosidic bond is formed by adding oxygen. However, this is not accurate. The glycosidic bond formation involves the removal of water, not the addition of oxygen. Addition of water: This option suggests that the glycosidic bond is formed by adding water. However, this is not accurate either. The glycosidic bond is formed by the removal of water, not the addition of water.In summary, option a) Removal of water is the correct option. The formation of a glycosidic bond involves the removal of a water molecule from two hydroxyl groups of monosaccharide units, leading to the covalent linkage between the two monosaccharides.

4316. The bond that is formed between two monosaccharide units is called:

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

Explanation: Ionic bond: An ionic bond is a type of chemical bond that forms between two atoms when one atom donates an electron, becoming positively charged (cation), and the other atom accepts the electron, becoming negatively charged (anion). Ionic bonds occur between atoms with significantly different electronegativities, resulting in the transfer of electrons. Hydrogen bond: A hydrogen bond is a type of weak chemical bond that occurs between a hydrogen atom in a polar covalent bond and an electronegative atom (usually oxygen, nitrogen, or fluorine) in another molecule. Hydrogen bonding is important for the structure and properties of many molecules, but it is not the bond that forms between two monosaccharide units. Peptide bond: A peptide bond is a specific type of covalent bond that forms between the carboxyl group (COOH) of one amino acid and the amino group (NH2) of another amino acid during the formation of a protein. Peptide bonds are essential for building protein chains in a process called protein synthesis.Glycosidic bond: The correct option is glycosidic bond. A glycosidic bond is a type of covalent bond that forms between two monosaccharide units during the formation of disaccharides, oligosaccharides, and polysaccharides. It is formed when a hydroxyl group (-OH) of one monosaccharide reacts with the anomeric carbon (the carbon containing the carbonyl group) of another monosaccharide. This reaction involves the removal of a water molecule (H2O), resulting in the formation of a glycosidic linkage between the two monosaccharides.In summary, option d) Glycosidic bond is the correct option. A glycosidic bond is the covalent bond that forms between two monosaccharide units during the formation of various types of saccharides like disaccharides, oligosaccharides, and polysaccharides. The other options (a) Ionic bond, (b) Hydrogen bond, and (c) Peptide bond are different types of chemical bonds with different functions and properties.

4317. C5H10O5 is the formula of _?

• A. Ribose sugar
• B. RNA
• C. DNA
• D. ATP

Explanation: C5H10O5 is the formula for the sugar molecule called ribose. Ribose is a pentose sugar, meaning it has five carbon atoms, and is classified as a monosaccharide. It is an essential component of nucleotides, which are the building blocks of RNA (ribonucleic acid) molecules. Ribose is involved in various biological processes and plays a crucial role in the synthesis of RNA and other important cellular functions.

4318. Monosaccharides have a general formula represented by:

• A. Cn(H2O)n
• B. C2(H2O)n
• C. C(H2O)n
• D. C1(H2O)n

Explanation: General fomrula of monosaccharides is Cn(H2O)n as number of carbon and oxygen is usually same in monosaccharides.

4319. _ are the major sites for the storage of glycogen in an animals body.

• A. Muscles and Liver
• B. Around Belly and Hips
• C. Around Thighs and Belly
• D. Liver and Kidney's

Explanation: Glycogen is called as animal starch and it is abundantly found in muscle and liver cells of animal tissue.

4320. All are characteristics of monosaccharides except:

• A. All carbon contain OH except carbonyl carbon
• B. Digestion by amylase enzyme
• C. Primary product of photosynthesis
• D. Very simple and very sweet in taste

Explanation: This statement is incorrect. Monosaccharides are already in their simplest form and do not require digestion by enzymes like amylase. Amylase is an enzyme that specifically breaks down polysaccharides (complex carbohydrates) like starch into smaller maltose units, which are disaccharides. Monosaccharides, being the building blocks of carbohydrates, are directly absorbed into the bloodstream without any further digestion.