3. Which of the following statements regarding chlorophyll is NOT correct?
(1) Chlorophyll-a has a —CH₃ group in its porphyrin-like ring structure.
(2) Chlorophyll-b has -CHO group in its porphyrin-like ring structure.
(3) Only chlorophyll-a, but not chlorophyll-b, has a Mg⁺⁺ coordinated at the centre of the porphyrin ­like ring structure.
(4) The long hydrocarbon tails of chlorophyll anchors them in the photosynthetic membrane.

Option (3) is NOT correct: Both chlorophyll-a and chlorophyll-b have magnesium (Mg++) coordinated at the center of their porphyrin-like ring structure, not just chlorophyll-a. Here’s a detailed breakdown of all statements with an SEO-optimized article.

Chlorophyll Structure: True and False Statements

Introduction

Key phrase: chlorophyll chemical structure Mg porphyrin ring features

Understanding the chemical structure of chlorophyll molecules is essential for grasping their function in photosynthesis and solving biology exam questions. Chlorophyll-a and chlorophyll-b share core similarities but differ in small side-group substitutions, helping plants absorb a wider spectrum of light for energy conversion.​

Detailed Analysis of Each Statement

• (1) Chlorophyll-a has a —CH₃ group in its porphyrin-like ring structure.

  • Correct. Chlorophyll-a contains a methyl group (-CH₃) at the third carbon of its porphyrin ring, which is a major chemical difference from chlorophyll-b.​

• (2) Chlorophyll-b has -CHO group in its porphyrin-like ring structure.

  • Correct. Chlorophyll-b features an aldehyde group (-CHO) at the equivalent position where chlorophyll-a has a methyl group. This change slightly alters its absorption spectrum.​

• (3) Only chlorophyll-a, but not chlorophyll-b, has a Mg++ coordinated at the centre of the porphyrin ­like ring structure.

  • Incorrect. Both chlorophyll-a and chlorophyll-b have a magnesium ion (Mg++) at the center of their porphyrin ring, which is fundamental to their photochemical function and electron transfer abilities.​

• (4) The long hydrocarbon tails of chlorophyll anchors them in the photosynthetic membrane.

  • Correct. Both types have a long phytyl hydrocarbon tail that embeds the molecule securely within the hydrophobic core of the thylakoid membrane in chloroplasts.​

Key Facts About Chlorophyll-a and Chlorophyll-b

• Both molecules have Mg++ at the center of their tetrapyrrole ring.

• Chlorophyll-a has a methyl (-CH₃), while chlorophyll-b has an aldehyde (-CHO) group at the third position.

• The phytyl tail ensures membrane attachment and functional orientation in photosystems.