All Free Biology MCQs with Answers

4291. The covalent bond or bridge between two monosaccharides to form a disaccharide is called a:

• A. Carboxyl bond
• B. Hydroxyl bond
• C. Hydrogen bond
• D. Glycosidic bond

Explanation: When two monosaccharides join through dehydration condensation process they form disaccharide with glycosidic linkage and release water molecules.

4292. Most proteins are made up of:

• A. 16 types of Amino acids
• B. 10 types of Amino acids
• C. 170 types of Amino acids
• D. 20 types of Amino acids

Explanation: About 170 types of amino acids have been found to occur in cells and tissues. Of these about 25 are constituents of proteins. Most of the proteins are however, made of 20 types of amino acids.

4293. In glycine R is _.

• A. Fatty acid
• B. Ethane
• C. Hydrogen
• D. Methane

Explanation: Amino acids Fibrous mainly differ due to the type or nature of R group. R may be a hydrogen atom as in glycine, or CH3 as in alanine, or any other group.

4294. Lipid contains double the amount of energy as compared to the same amount of carbohydrates due to the presence of?

• A. Lower proportion of C-H bonds
• B. Higher proportion of C-H bonds
• C. Higher proportion of C-O bonds
• D. Glycerol and sulfuric acid

Explanation: C-H bond is a potential source of energy. Lipids have a higher proportion of C-H bonds as compared to carbohydrates and proteins.

4295. Which one is an example of nucleotides?

• A. Adenosine
• B. ATP
• C. Guanine
• D. NAD

Explanation: Adenosine is a nucleoside while guanine is a nitrogenous base. NAD is a dinucleotide. Only ATP is a nucleotide among all options.

4296. The sum of all chemical reactions taking place within a cell is called:

• A. Thermoregulation
• B. Osmoregulation
• C. Metabolism
• D. Isomerism

Explanation: Word metabolism is derived from Greek word which means "Changes". Temperature regulation, water and salt regulation respectively called thermoregulation and osmoregulation, while isomerism is the phenomenon in which more than one compounds have the same chemical formula but different structures.

4297. Water is a very good solvent for substance due to its _ nature and act as _ due to its higher heat capacity.

• A. Dipole nature, Thermo-stabilizer
• B. Polar, Bipolar
• C. Organic, Inorganic
• D. Ionic, Covalent

Explanation: Water is an excellent solvent for polar substances due to its dipole nature. Ions and molecules move randomly and are in a more favourable state to react with other molecules and ions when in solution and water have great ability to absorb heat due to higher heat capacity and act as thermo-stabilizer.

4298. The water molecules remain attached together and do not separate because of this bonding:

• A. Non-covalent
• B. Ionic
• C. Hydrogen
• D. Hydrophobic

Explanation: Non-covalent: Non-covalent bonds are a class of chemical interactions that do not involve the sharing of electrons between atoms. Instead, they are relatively weaker interactions, including hydrogen bonds, van der Waals forces, and electrostatic interactions. While hydrogen bonds are a type of non-covalent bond, it is more specific to mention "hydrogen bonds" rather than the broader term "non-covalent. Ionic: Ionic bonds involve the complete transfer of electrons from one atom to another, resulting in the formation of positively charged ions (cations) and negatively charged ions (anions). These oppositely charged ions are held together by electrostatic attractions, forming a strong bond. Water does not form ionic bonds with itself, so this option is not the correct one. Hydrogen: The correct option is hydrogen bonds. Water molecules are held together by hydrogen bonds. A hydrogen bond is a type of non-covalent bond formed between a partially positive hydrogen atom and a partially negative atom of another molecule or within the same molecule. In water, each water molecule contains two hydrogen atoms covalently bonded to a central oxygen atom. The oxygen atom is more electronegative than hydrogen, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms. These partial charges allow water molecules to form hydrogen bonds with each other. The hydrogen of one water molecule is attracted to the oxygen of another water molecule, creating a network of hydrogen bonds that hold the water molecules together in a cohesive structure. Hydrophobic: Hydrophobic interactions are interactions between nonpolar molecules that exclude water. Water molecules tend to cluster together to minimize their contact with nonpolar substances. While hydrophobic interactions play a role in the self-assembly of nonpolar molecules, they do not directly account for the cohesion of water molecules. In conclusion, water molecules remain attached together primarily due to the bonding of hydrogen bonds (c). These hydrogen bonds are responsible for the unique properties of water, including its high surface tension, cohesion, and the ability to dissolve various substances.

4299. Which property of water plays an important role in regulation of heat produced by oxidation?

• A. Heat capacity
• B. Heat of vaporization
• C. Dipole nature
• D. lonization of water

Explanation: Heat capacity: Heat capacity refers to the amount of heat energy required to raise the temperature of a substance. Water does have a relatively high heat capacity, which allows it to absorb and store a significant amount of heat energy without a substantial increase in temperature. This property contributes to water's role as a thermo-stabilizer, as discussed in a previous question, but it is not directly related to the regulation of heat produced by oxidation. 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. Water has a particularly high heat of vaporization compared to many other liquids. When water absorbs heat and undergoes vaporization, it takes a considerable amount of heat from its surroundings to break the hydrogen bonds and transition from a liquid to a gaseous state. This process is highly endothermic and results in a cooling effect on the surrounding environment.In the context of oxidation, heat of vaporization plays a crucial role in the regulation of heat produced by exothermic oxidation reactions. Exothermic reactions release heat energy, and if left unchecked, they can lead to an increase in temperature in the surrounding environment. However, in the presence of water, as the temperature rises due to oxidation, water absorbs this excess heat and undergoes vaporization. This endothermic process helps to moderate the temperature rise, preventing the system from overheating. Dipole nature: Water's dipole nature, resulting from its polar covalent bonds and hydrogen bonding, is responsible for many of its unique properties, including its ability to dissolve polar and charged substances, its high surface tension, and its cohesive properties. However, the dipole nature of water is not directly related to the regulation of heat produced by oxidation. Ionization of water: Water can undergo a process of ionization, where a small fraction of water molecules dissociate into positively charged hydrogen ions (H+) and negatively charged hydroxide ions (OH-). This process is responsible for water's ability to act as a weak electrolyte. However, the ionization of water does not play a significant role in the regulation of heat produced by oxidation. In summary, option b) Heat of vaporization is the correct option, as the high heat of vaporization of water helps to regulate the heat produced by oxidation reactions by absorbing and dissipating excess heat.High specific heat capacity: Water has a high specific heat capacity, which means that it can absorb or release large amounts of heat energy without changing temperature significantly. This makes water an excellent temperature buffer, helping to regulate temperature in living organisms and environments.

4300. Which property of water helps to maintain the integrity of lipid membranes?

• A. Specific heat capacity
• B. Cohesion and adhesion
• C. Hydrogen bonding
• D. Hydrophobic exclusion

Explanation: 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. While water does have a high specific heat capacity, this property is not directly related to maintaining the integrity of lipid membranes. 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. Both cohesion and adhesion are important properties of water, contributing to phenomena like surface tension and capillary action. However, they are not directly involved in maintaining the integrity of lipid membranes. Hydrogen bonding: Hydrogen bonding is a type of non-covalent bonding between water molecules, which gives water many of its unique properties, such as high heat of vaporization, high surface tension, and solvent capabilities. While hydrogen bonding is crucial for various functions in living organisms, it is not the primary property that helps maintain the integrity of lipid membranes. Hydrophobic exclusion: The correct option is hydrophobic exclusion. This property arises due to the hydrophobic nature of lipid molecules. Lipids are nonpolar molecules and do not mix well with water, which is a polar molecule. When lipid molecules are exposed to water, they tend to cluster together, minimizing their contact with water molecules. This clustering effect is known as hydrophobic exclusion.In biological systems, such as cell membranes, lipids play a fundamental role in forming a barrier that separates the aqueous environments inside and outside the cell. The hydrophobic exclusion property of lipids helps maintain the integrity of lipid membranes by preventing water from permeating through the hydrophobic core of the membrane. This exclusion of water ensures that the lipid bilayer remains intact and impermeable to water-soluble substances while allowing the passage of hydrophobic molecules and small nonpolar molecules necessary for cell function.In summary, option d) Hydrophobic exclusion is the correct option as it describes the property of water that helps maintain the integrity of lipid membranes by minimizing the interaction between water molecules and hydrophobic lipid molecules.