All Free Biology MCQs with Answers

3741. The chlorophyll head is made up of:

• A. Four joined porphyrin rings
• B. Four joined tetrapyrrole rings
• C. Four joined pyrrole rings
• D. Two joined pyrrole rings

Explanation: The chlorophyll molecule has a head known as the porphyrin ring, which is made up of four pyrrole rings linked together. This tetrapyrrole structure is fundamental to the function of chlorophyll in photosynthesis. Option C is correct, as it accurately describes this arrangement. Options A and B incorrectly emphasize the term 'porphyrin' without specifying the pyrrole structure, while Option D underestimates the number of pyrrole rings involved.

3742. In the chlorophyll head, an atom of magnesium is coordinated with the:

• A. Carbon of each porphyrin ring
• B. Hydrogen of each pyrrole ring
• C. Nitrogen of each porphyrin ring
• D. Oxygen atoms of the phytol tail

Explanation: The magnesium atom in the chlorophyll head is coordinated with the nitrogen atoms of the porphyrin ring. These nitrogen atoms form a square planar arrangement around the magnesium, stabilizing it in the center of the ring. This coordination is essential for the porphyrin ring to absorb light effectively, while the phytol tail anchors the molecule into the membrane and hydrogen and carbon atoms do not participate directly in magnesium coordination.

3743. _ of hemoglobin is also a porphyrin ring.

• A. α - chain
• B. β - chain
• C. Haem group
• D. Protein

Explanation: The correct answer is the heam group. Hemoglobin is composed of protein chains and a non-protein component, the haem group, which contains a porphyrin ring. This ring is central to the function of hemoglobin, as it binds iron ions that facilitate oxygen transport. The α and β chains are protein subunits and do not contain the porphyrin ring. The term 'protein' is too broad and does not specifically identify the part of hemoglobin that includes the porphyrin structure.

3744. The heme group of hemoglobin differs from the porphyrin of chlorophyll in having:

• A. Iron as central atom
• B. Magnesium as central atom
• C. Four pyrrole rings
• D. Central atom coordinated with nitrogen of each pyrrole ring

Explanation: The haem group of hemoglobin is characterized by having iron as its central metal atom. In contrast, the porphyrin of chlorophyll has magnesium as its central atom. This distinction is crucial in differentiating the two compounds. While both structures feature four pyrrole rings and have their central atom coordinated with the nitrogen of each pyrrole ring, it is the type of metal atom that sets them apart.

3745. The long tail of chlorophyll, which is attached to one of the pyrroles, is

• A. Hydrocarbon tail
• B. Phytol
• C. Hydrophilic tail
• D. Carotenoid tail

Explanation: The correct answer is phytol. Phytol is the specific name for the long-chain alcohol that constitutes the hydrocarbon tail of chlorophyll, essential for anchoring it within the thylakoid membrane due to its hydrophobic properties. The option 'Hydrocarbon tail' is too broad and nonspecific, as it doesn't uniquely identify the tail as phytol. 'Hydrophilic tail' is incorrect because it describes a water-attracting structure, which does not apply to the hydrophobic nature of chlorophyll's tail. 'Carotenoid tail' is unrelated because carotenoids are different pigments that do not form part of chlorophyll's structure.

3746. The chlorophyll molecule is embedded in the hydrophobic core of:

• A. Thylakoid membrane by its head
• B. Lamellar membrane by its head
• C. Thylakoid membrane by its tail
• D. Lamellar membrane by its tail

Explanation: The chlorophyll molecule is embedded in the hydrophobic core of the thylakoid membrane by its hydrophobic tail. This orientation allows the hydrophilic head of chlorophyll to face the aqueous environment, which is essential for its role in capturing light energy during photosynthesis. The thylakoid membrane is a specific site where the light-dependent reactions of photosynthesis occur, making it the correct answer. The other options incorrectly suggest an association with either the head of the chlorophyll molecule or a different type of membrane.

3747. Chlorophyll a and chlorophyll b differ from each other in only one of the following:

• A. Atoms
• B. Elements
• C. Functional groups
• D. Carbon atoms

Explanation: The primary difference between chlorophyll a and chlorophyll b is in their functional groups. Chlorophyll a contains a methyl group (CH₃), while chlorophyll b contains a carbonyl group (CHO). This difference in functional groups affects their absorption properties and roles in photosynthesis. Options A, B, and D are incorrect, as they do not accurately describe the structural difference between the two types of chlorophyll.

3748. Chlorophyll a and chlorophyll b differ from each other with respect to the number of:

• A. Carbon atoms
• B. Oxygen atoms
• C. Hydrogen atoms
• D. Hydrogen and oxygen atoms

Explanation: Chlorophyll a and chlorophyll b have the same basic structure, but they differ in the number of hydrogen and oxygen atoms. Specifically, chlorophyll a has two additional hydrogen atoms and one less oxygen atom compared to chlorophyll b. This difference in atomic composition influences their absorption spectra and roles in photosynthesis. The incorrect options fail to account for the differences in both hydrogen and oxygen atoms.

3749. As compared to chlorophyll a, chlorophyll b has:

• A. Two more hydrogen atoms
• B. One less oxygen atom
• C. Two less hydrogen atoms and one more oxygen atom
• D. Two more hydrogen atoms and one less oxygen atom

Explanation: Chlorophyll a and chlorophyll b differ primarily in one functional group attached to the porphyrin ring. In chlorophyll a, there is a methyl group (-CH₃), whereas in chlorophyll b, this group is replaced by a carbonyl group (-CHO). This difference accounts for chlorophyll b having two fewer hydrogen atoms and one more oxygen atom compared to chlorophyll a. The incorrect options either add hydrogen or remove oxygen, which are not characteristic of chlorophyll b's structure.

3750. As compared to chlorophyll b, chlorophyll a has:

• A. Two more hydrogen atoms
• B. One less oxygen atom
• C. Two less hydrogen atoms
• D. Two more hydrogen atoms and one less oxygen atom

Explanation: Chlorophyll a differs from chlorophyll b in its chemical structure: it contains a methyl group (-CH₃) instead of a carbonyl group (-CHO). This difference accounts for chlorophyll a having two more hydrogen atoms and one less oxygen atom than chlorophyll b. Options A and B are partially correct but incomplete, as they each address only one of the differences. Option C is incorrect because chlorophyll a does not have fewer hydrogen atoms than chlorophyll b.