2.9 Exercise: Biological Molecules Quiz-1 (Copy)

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Unit 2: Biological Molecules
2.1 Introduction to Biochemistry
2.2 Properties of Carbon
2.3 Chemical Nature and Importance of Water
2.4 Carbohydrates | 15 MCQs

1. A student analyzes a sample of protoplasm and finds that roughly 99% of its mass consists of six primary bio-elements. Which of the following elements is found in the highest percentage by mass?

Carbon
Hydrogen
Oxygen
Nitrogen

Check Answer

Correct: Oxygen
Explanation: Oxygen makes up approximately 65% of the total mass of the human body (and protoplasm), primarily because of its presence in water ($H_2O$), which is the most abundant compound in living things.

2. During the folding of a protein, nonpolar side chains tend to cluster together in the interior of the molecule to avoid contact with water. This phenomenon is an application of:

Covalent bonding
Hydrophobic exclusion
Specific heat capacity
High density of ice

Check Answer

Correct: Hydrophobic exclusion
Explanation: Hydrophobic exclusion is the property where non-polar molecules are forced together in an aqueous environment to minimize their contact with water, a critical factor in the stability of membranes and protein structures.

3. Carbon is considered the “backbone of life” because it can form long, stable chains and rings by bonding with other carbon atoms. This specific property is known as:

Tetra-valency
Isomerism
Catenation
Electronegativity

Check Answer

Correct: Catenation
Explanation: Catenation is the ability of carbon atoms to link together to form long chains or rings, allowing for the vast diversity and complexity of organic molecules.

4. If a lake in a cold climate did not have the unique density property of water, how would aquatic life most likely be affected during winter?

Life would thrive as water remains liquid throughout.
The lake would freeze from the bottom up, killing most organisms.
Water would evaporate faster, causing the lake to dry out.
The oxygen levels would increase due to increased light penetration.

Check Answer

Correct: The lake would freeze from the bottom up
Explanation: Ice is less dense than liquid water, so it floats and insulates the water below. If ice were denser, it would sink, eventually freezing the entire lake from the bottom up and destroying the habitat.

5. Large bodies of water, such as the Arabian Sea near Karachi, help maintain a relatively stable temperature in the surrounding air. This is due to water’s high:

Cohesion
Specific heat capacity
Heat of vapourisation
Surface tension

Check Answer

Correct: Specific heat capacity
Explanation: Water can absorb or release a large amount of heat with only a slight change in its own temperature, acting as a “heat buffer” for the environment.

6. During intense exercise, humans sweat to cool down. This cooling effect is primarily a result of which property of water?

High specific heat
High heat of vapourisation
High surface tension
Low density of ice

Check Answer

Correct: High heat of vapourisation
Explanation: As sweat evaporates from the skin, it absorbs a significant amount of heat energy from the body, providing an effective cooling mechanism.

7. When a plant cell synthesizes a disaccharide like sucrose from two monosaccharides, the reaction involves the removal of a water molecule. This process is called:

Hydrolysis
Oxidation
Condensation
Isomerization

Check Answer

Correct: Condensation
Explanation: Condensation (or dehydration synthesis) is the chemical reaction where two molecules are joined together with the loss of a water molecule.

8. Which of the following disaccharides is correctly matched with its constituent monosaccharides?

Maltose = Glucose + Fructose
Sucrose = Glucose + Galactose
Lactose = Glucose + Galactose
Sucrose = Glucose + Glucose

Check Answer

Correct: Lactose = Glucose + Galactose
Explanation: Lactose (milk sugar) is formed by the linkage of glucose and galactose. Sucrose is Glucose + Fructose, and Maltose is Glucose + Glucose.

9. A researcher identifies a polysaccharide that provides structural support to the cell walls of fungi and the exoskeletons of arthropods. This molecule is most likely:

Starch
Glycogen
Cellulose
Chitin

Check Answer

Correct: Chitin
Explanation: Chitin is a structural polysaccharide found in the exoskeletons of insects and the cell walls of fungi.

10. Starch and glycogen are both storage polysaccharides. Why is glycogen often referred to as “animal starch”?

It is found in the chloroplasts of animals.
It is the primary storage form of glucose in animals, similar to starch in plants.
It has the exact same linear structure as amylose.
It is indigestible by human enzymes.

Check Answer

Correct: It is the primary storage form of glucose in animals
Explanation: Glycogen is stored in the liver and muscles of animals to provide a quick source of energy, performing a function identical to starch in plants.

11. The $alpha$-glucose and $beta$-glucose molecules have the same molecular formula ($C_6H_{12}O_6$) but differ in the orientation of the hydroxyl group on Carbon-1. This is an example of:

Catenation
Isomerism
Tetra-valency
Condensation

Check Answer

Correct: Isomerism
Explanation: Isomers are molecules with the same molecular formula but different structural arrangements, such as $alpha$ and $beta$ glucose.

12. Water molecules are polar because oxygen is more electronegative than hydrogen. This polarity results in the formation of:

Ionic bonds within the water molecule
Hydrogen bonds between adjacent water molecules
Covalent bonds between different water molecules
Non-polar covalent bonds

Check Answer

Correct: Hydrogen bonds between adjacent water molecules
Explanation: The partial positive charge of hydrogen in one molecule is attracted to the partial negative charge of oxygen in another, forming a hydrogen bond.

13. Which property of water allows it to move upward through a 100-meter tall Sequoia tree against gravity?

Hydrophobic exclusion
Specific heat
Cohesion and Adhesion
Low density of ice

Check Answer

Correct: Cohesion and Adhesion
Explanation: Cohesion (water sticking to water) and Adhesion (water sticking to xylem walls) create a continuous column of water that can be pulled up the plant.

14. Humans can digest starch but cannot digest cellulose, even though both are made of glucose. This is because:

Cellulose is an inorganic molecule.
Human enzymes cannot break the $beta$-1,4-glycosidic linkages in cellulose.
Cellulose does not contain any hydrogen bonds.
Starch is only found in animals.

Check Answer

Correct: Human enzymes cannot break the $beta$-1,4-glycosidic linkages
Explanation: Enzymes are shape-specific. Humans have enzymes for the $alpha$-linkages in starch but lack the cellulase enzyme required to hydrolyze the $beta$-linkages in cellulose.

15. Which of the following is an example of an inorganic biological molecule found within the protoplasm?

Glucose
Carbon dioxide
Cellulose
Adenosine triphosphate (ATP)

Check Answer

Correct: Carbon dioxide
Explanation: Inorganic molecules generally lack a C-H bond. Carbon dioxide ($CO_2$) and water ($H_2O$) are key inorganic molecules essential for life processes.

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2.9 Exercise: Biological Molecules Quiz-1 (Copy)

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