Question

A lack of micronutrients affects not only plant growth but also vital functions, such as photosynthetic and mitochondrial electron flow. Which of the following group of elements shall have the greatest impact on both photosynthetic and mitochondrial electron transport?

• A. Co, Ni and Mo
• B. Ca, K and Na
• C. Mn, Co and Ca
• D. Cu, Mn and Fe

Hint:

Look for the metals that sit directly inside cytochromes, plastocyanin and the water-splitting complex.

Answer 1

The Correct Option is D

Step 1: Understanding the Question.
We need the group of micronutrients that plays the biggest direct part in both the photosynthetic electron transport chain in the chloroplast and the mitochondrial electron transport chain.

Step 2: Key Concept.
Electron transport chains pass electrons through carrier molecules, many built around metal ions. Iron (Fe) forms iron-sulfur clusters and cytochromes used in both chloroplasts and mitochondria. Copper (Cu) is the metal center of plastocyanin, a photosynthetic electron carrier, and of cytochrome c oxidase, the last enzyme of the mitochondrial chain. Manganese (Mn) forms the oxygen-evolving complex of Photosystem II, where water is split to release electrons.

Step 3: Detailed Explanation.
Since Fe, Cu and Mn are each built directly into these carrier proteins, a shortage of any one slows electron flow in both photosynthesis and respiration, matching option 4, Cu, Mn and Fe. Option 1, Co, Ni and Mo, matters for other jobs, cobalt for vitamin B12 and nitrogen fixation, nickel for urease, molybdenum for nitrate reductase and nitrogenase, not for the transport chains directly. Option 2, Ca, K and Na, is mainly involved in signaling, osmotic balance and stomatal movement, not electron carriers. Option 3, Mn, Co and Ca, has Mn right but pairs it with Co and Ca, which are not core transport chain metals.

Step 4: Final Answer.
Cu, Mn and Fe together have the greatest direct impact on both electron transport chains. \[ \boxed{\text{Cu, Mn and Fe}} \]