All Free Biology MCQs with Answers

4301. Water acts as universal solvent because of:

• A. Heat of vaporization
• B. High polarity
• C. Hydrogen bonding
• D. Cohesion and Adhesion

Explanation: Heat of vaporization: The heat of vaporization is the amount of heat energy required to convert a liquid into a gas at a constant temperature and pressure. While water does have a relatively high heat of vaporization, it is not the primary reason why water acts as a universal solvent. High polarity: The correct option is high polarity. Water is a polar molecule, meaning it has a partial positive charge on one end (the hydrogen atoms) and a partial negative charge on the other end (the oxygen atom). This polarity arises due to the unequal sharing of electrons in the water molecule. The oxygen atom is more electronegative than the hydrogen atoms, pulling the electrons closer to itself and creating a dipole moment.Because of its polarity, water molecules are attracted to other polar or charged molecules, including ions and other polar substances. When a solute (substance to be dissolved) is added to water, the water molecules surround and solvate the solute, effectively breaking its interactions and allowing it to disperse evenly throughout the water. This ability to dissolve a wide variety of polar and charged substances is the reason why water is often referred to as the "universal solvent." Hydrogen bonding: Hydrogen bonding is a specific type of intermolecular bonding that occurs between hydrogen atoms bonded to electronegative atoms (such as oxygen, nitrogen, or fluorine) and lone pairs on nearby electronegative atoms. Water molecules form hydrogen bonds with each other due to the polarity of the water molecule. While hydrogen bonding does contribute to water's unique properties, including its high heat of vaporization and high surface tension, it is not the primary reason why water acts as a universal solvent. Cohesion and adhesion: Cohesion refers to the attraction between water molecules, causing them to stick together, while adhesion refers to the attraction between water molecules and other substances. These properties are responsible for phenomena like surface tension and capillary action. While cohesion and adhesion play essential roles in various biological processes, they are not the primary reasons why water acts as a universal solvent.In conclusion, option b) High polarity is the correct option. Water's high polarity allows it to act as a universal solvent, enabling it to dissolve a wide range of polar and charged substances, making it an essential medium for various biological and chemical processes.

4302. Water acts as a temperature stabilizer for many organisms in the environment because of its:

• A. High surface tension
• B. Latent heat of vaporization
• C. High specific heat capacity
• D. Density

Explanation: High surface tension: Surface tension refers to the property of the surface of a liquid that allows it to resist external forces, effectively minimizing its surface area. Water does have a relatively high surface tension due to the cohesive forces between its molecules. While high surface tension has various biological implications, such as the ability of certain insects to walk on water, it is not the primary reason why water acts as a temperature stabilizer. Latent heat of vaporization: The latent heat of vaporization is the amount of heat energy required to convert a liquid into a gas at a constant temperature and pressure. Water has a particularly high latent heat of vaporization compared to many other liquids. While this property is essential for processes like evaporative cooling in organisms, it is not the main reason why water acts as a temperature stabilizer. High specific heat capacity: The correct option is high specific heat capacity. Specific heat capacity refers to the amount of heat energy required to raise the temperature of a substance by a specific amount. Water has a relatively high specific heat capacity compared to many other substances.Water's high specific heat capacity allows it to absorb and store a significant amount of heat energy without a substantial increase in temperature. As a result, water can act as a buffer against temperature fluctuations in its surroundings. During the daytime, when the environment is warmer, water absorbs heat from the sun and its surroundings. This absorption of heat prevents rapid temperature increases in the environment, helping to keep the surroundings relatively cooler.Conversely, during the nighttime, when the environment cools down, the water releases the stored heat energy, providing warmth and preventing rapid temperature drops. This property is particularly beneficial for many organisms that live in aquatic environments or have a high water content in their bodies, as it helps to maintain a relatively stable and hospitable temperature range for their biological processes. Density: Density refers to the mass of a substance per unit volume. Water has a unique property where its density decreases as it transitions from a liquid to a solid state (as in the case of ice). This property is why ice floats on water. While this property is ecologically important for aquatic ecosystems, it is not the primary reason why water acts as a temperature stabilizer. In conclusion, option c) High specific heat capacity is the correct option. Water's high specific heat capacity allows it to act as a temperature stabilizer by absorbing and storing heat, buffering against rapid temperature changes in the environment and helping to maintain a relatively stable and suitable temperature range for organisms in their surroundings.

4303. Ice floats on water due to which property of water:

• A. Low density
• B. Heat of vaporization
• C. Ionization
• D. Hydrophobic exclusion

Explanation: Low density: The correct option is low density. Water is one of the few substances where the solid form (ice) is less dense than the liquid form. When water cools down and freezes, its molecules arrange themselves in a hexagonal lattice structure, creating open spaces between the molecules. This unique arrangement leads to a decrease in the overall density of ice compared to liquid water. As a result, ice is lighter and less dense than the surrounding liquid water, causing it to float on the water's surface.This property of ice floating on water is crucial for aquatic ecosystems. When lakes and rivers freeze during colder temperatures, the layer of ice that forms on the surface acts as an insulating barrier, protecting the aquatic life beneath from extreme temperature fluctuations. If ice were denser than water, it would sink, leading to the freezing of entire water bodies from the bottom up, which would have severe consequences for the organisms living in these environments. Heat of vaporization: The heat of vaporization is the amount of heat energy required to convert a liquid into a gas at a constant temperature and pressure. While this property is important for processes like evaporative cooling, it is not directly related to why ice floats on water. Ionization: Ionization refers to the process by which a molecule or atom gains or loses electrons, becoming charged. Water can undergo ionization, where a small fraction of water molecules dissociate into positively charged hydrogen ions (H+) and negatively charged hydroxide ions (OH-). However, this process is not related to the floating of ice on water. Hydrophobic exclusion: Hydrophobic exclusion is the tendency of nonpolar substances to aggregate and minimize their contact with water. This phenomenon is not directly related to the property of ice floating on water. In conclusion, option a) Low density is the correct option. The low density of ice compared to liquid water is the reason why ice floats on water, and this property is ecologically important for the survival of aquatic life during freezing temperatures.

4304. Most abundant carbohydrate in nature is:

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

Explanation: Cellulose: Cellulose is the most abundant carbohydrate in nature. It is a complex polysaccharide made up of glucose molecules linked together in a linear chain. Cellulose is the primary structural component of plant cell walls, providing rigidity and strength to the cell. As one of the most abundant biopolymers on Earth, cellulose plays a crucial role in providing structural support to plants, contributing to their form and overall growth. Polysaccharides: Polysaccharides are a class of carbohydrates composed of multiple sugar units (monosaccharides) linked together. Cellulose, starch, and glycogen are all examples of polysaccharides. While they are essential carbohydrates, the question specifically asks for the most abundant carbohydrate in nature, which is cellulose (option a). Starch: Starch is another polysaccharide made up of glucose units but with a branched or helical structure. It serves as a major energy storage polysaccharide in plants. Plants store excess glucose in the form of starch, mainly in roots and seeds, to be used as a source of energy when needed. Glycogen: Glycogen is a highly branched polysaccharide made up of glucose units. It is the primary energy storage polysaccharide in animals, found primarily in the liver and muscles. Glycogen serves as a readily available source of glucose, which can be broken down to provide energy during times of high energy demand, such as physical activity or fasting.In summary, the most abundant carbohydrate in nature is a) Cellulose. It is a complex polysaccharide found in the cell walls of plants, providing structural support and rigidity to plant cells. While polysaccharides like starch and glycogen are also important carbohydrates, they are not as abundant as cellulose in nature.

4305. All of the following yield glucose on complete hydrolysis except:

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

Explanation: Starch: Starch is a polysaccharide composed of glucose units linked together in a branched or helical structure. It is the primary energy storage polysaccharide in plants. Complete hydrolysis of starch breaks down the glycosidic bonds between the glucose units, yielding individual glucose molecules. Cellulose: Cellulose is another polysaccharide made up of glucose units, but it has a linear arrangement. It is the primary structural component of plant cell walls, providing rigidity and strength to the cell. Unlike starch, cellulose is not easily hydrolyzed by most organisms due to the specific arrangement of its glucose units. However, certain microorganisms and animals possess cellulase enzymes that can break down cellulose into glucose units through hydrolysis. Glycogen: Glycogen is a highly branched polysaccharide composed of glucose units. It serves as the primary energy storage polysaccharide in animals, found primarily in the liver and muscles. Similar to starch, complete hydrolysis of glycogen breaks down the glycosidic bonds between the glucose units, yielding individual glucose molecules. Chitin: Chitin is a polysaccharide composed of N-acetylglucosamine units linked together. It is a structural component found in the exoskeletons of arthropods (e.g., insects, spiders, crustaceans) and the cell walls of fungi. Chitin is not composed of glucose units, so it does not yield glucose on complete hydrolysis. Instead, it breaks down into N-acetylglucosamine monomers.In summary, all options (a) Starch, (b) Cellulose, and (c) Glycogen yield glucose on complete hydrolysis because they are composed of glucose units. Option (d) Chitin is the correct option as it does not yield glucose on hydrolysis since it is composed of N-acetylglucosamine units, not glucose units.

4306. Glucose combines with _ to form milk sugar.

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

Explanation: Glucose: Glucose is a monosaccharide, which means it is a single sugar unit. While glucose is an important carbohydrate and serves as a source of energy for the body, it does not combine with itself to form milk sugar. Galactose: Galactose is another monosaccharide and is crucial for the formation of lactose, which is the milk sugar. Lactose is a disaccharide composed of one molecule of glucose and one molecule of galactose linked together by a glycosidic bond. When lactose is hydrolyzed, it breaks down into its constituent monosaccharides, glucose, and galactose. Fructose: Fructose is a monosaccharide, and it is the sweetest of all naturally occurring sugars. While fructose is commonly found in fruits and honey, it does not combine with glucose to form milk sugar. Mannose: Mannose is another monosaccharide, and it is important for various cellular processes in the body. However, it does not combine with glucose to form milk sugar. In summary, the correct option is b) Galactose. Glucose combines with galactose to form lactose, which is the milk sugar found in the milk of mammals.

4307. Formation of a tri-saccharide involves release of _ water molecule.

• A. 1
• B. 3
• C. 2
• D. 4

Explanation: 1: This option suggests that the formation of a tri-saccharide involves the release of only one water molecule. However, the correct answer requires considering the number of water molecules released during the formation of each glycosidic bond in a tri-saccharide. 3: This option suggests that the formation of a tri-saccharide involves the release of three water molecules. However, this is not accurate. The number of water molecules released during the formation of a glycosidic bond depends on the type of glycosidic linkage being formed. 2: The correct option is 2. The formation of a tri-saccharide involves the linking of three sugar units (monosaccharides) through two glycosidic bonds. When a glycosidic bond is formed, a molecule of water (H2O) is released as a byproduct. This is a condensation reaction, where the hydroxyl group (-OH) from one sugar and a hydrogen atom from another sugar combine to form water (H2O), while the remaining oxygen and carbon atoms form the glycosidic bond between the two sugars. Since two glycosidic bonds are formed in a tri-saccharide, two water molecules are released during the process. 4: This option suggests that the formation of a tri-saccharide involves the release of four water molecules. However, this is not accurate, as explained above. The formation of two glycosidic bonds in a tri-saccharide results in the release of two water molecules. In summary, option c) 2 is the correct option. The formation of a tri-saccharide involves the release of two water molecules during the creation of two glycosidic bonds between three sugar units.

4308. Which of the following polysaccharide is present in human muscles abundantly?

• A. Myoglobin
• B. Actin and myosin
• C. Collagen
• D. Glycogen

Explanation: Myoglobin: Myoglobin is a protein found in muscle tissues that is responsible for storing and transporting oxygen within muscle cells. While myoglobin is abundant in muscle tissues, it is not a polysaccharide. Actin and myosin: Actin and myosin are proteins that are major components of muscle fibers and are involved in muscle contraction. They are not polysaccharides. Collagen: Collagen is the most abundant protein in the human body and is a major component of connective tissues, such as tendons, ligaments, and skin. While it plays a crucial role in supporting and connecting tissues, collagen is not a polysaccharide. Glycogen: The correct option is d) Glycogen. Glycogen is a highly branched polysaccharide made up of glucose units and serves as the primary energy storage polysaccharide in animals, including humans. In human muscles, glycogen is stored in large amounts and acts as a readily available source of glucose during periods of increased energy demand, such as exercise. When energy is needed, glycogen is broken down into glucose units, which can be further utilized through cellular respiration to produce energy for muscle contraction and other cellular functions.In summary, the polysaccharide present in human muscles abundantly is d) Glycogen. It serves as an essential energy reserve that can be mobilized to meet the energy needs of muscle cells during physical activity and other energy-demanding processes.

4309. Which of the following sugars is the sweetest?

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

Explanation: Glucose: Glucose is a monosaccharide and an essential source of energy for living organisms. While glucose is crucial for cellular metabolism and energy production, it is not the sweetest among the sugars listed. Fructose: The correct option is fructose. Fructose is also a monosaccharide and is known to be the sweetest naturally occurring sugar. It is commonly found in fruits, honey, and certain vegetables. Because of its high sweetness, fructose is often used as a sweetener in various food products and beverages. 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 obtained from sugarcane or sugar beets. While sucrose is sweet, it is not as sweet as fructose, which is the sweeter component of the sucrose molecule.Maltose: Maltose is a disaccharide composed of two glucose molecules linked together. It is not as sweet as fructose and is less sweet than sucrose. In summary, among the given options, b) Fructose is the sweetest sugar. It is naturally occurring and is commonly used as a sweetener due to its high sweetness level.

4310. ln a disaccharide, if carbon atoms are 12 then how many OH groups will be present?

• A. 11
• B. 10
• C. 8
• D. 12

Explanation: 11: This option suggests that there are 11 OH groups present in the disaccharide with 12 carbon atoms. However, this is not accurate. 10: This option suggests that there are 10 OH groups present in the disaccharide with 12 carbon atoms. However, this is not accurate either. 8: The correct option is 8. In a disaccharide, there are two sugar units (monosaccharides) linked together by a glycosidic bond. Each monosaccharide has several hydroxyl groups (-OH) attached to its carbon atoms.If a disaccharide has 12 carbon atoms in total, then each monosaccharide has six carbon atoms. In the two monosaccharide units, there are five carbon atoms with hydroxyl group (-OH) and one carbonyl group. The two monosccharides have 10 hydroxyl groups (-OH) in total. Now, to become a disaccharide, a glycosidic bond needs to form. This requires two hydroxyl groups. A water molecule is released while C-O forms the glycosidic bond.Therefore, in the disaccharide, the total number of hydroxyl groups will be 10 - 2 = 8. 12: This option suggests that there are 12 OH groups present in the disaccharide with 12 carbon atoms. However, this is not accurate. The correct answer is 8 hydroxyl groups.In summary, option c) 8 is the correct option. In a disaccharide with 12 carbon atoms, there are 8 hydroxyl groups, which are part of the two monosaccharide units linked together by a glycosidic bond.