Correct option is D
Explanation:
Let's evaluate each statement regarding cell toxicity due to heavy metals in plants:
A. The uptake of heavy metals does not lead to accumulation of ROS.
This statement is incorrect.
The uptake of heavy metals in plants often leads to the accumulation of reactive oxygen species (ROS), which is a key mechanism by which heavy metals induce cell toxicity. ROS can damage cellular components such as lipids, proteins, and DNA. Hence, this statement is false.
B. They usually mimic essential metals (e.g., Ca²⁺, Mg²⁺, etc.) and take their place in essential reactions.
This statement is correct.
Heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) can mimic essential metals like Ca²⁺, Mg²⁺, and Fe²⁺, and thus interfere with vital processes in plants. For example, cadmium can replace calcium in cellular processes, disrupting normal function. This mimicking is a key aspect of the toxicity of heavy metals. Hence, this statement is true.
C. Ion channels that transport essential metals do not participate in transport of heavy metals.
This statement is incorrect.
Ion channels that normally transport essential metals (such as Ca²⁺ and Mg²⁺) can also transport heavy metals like cadmium (Cd²⁺), lead (Pb²⁺), and others. This contributes to the toxic effects of heavy metals in plants. Therefore, this statement is false.
D. Heavy metals can directly interact with oxygen to form ROS.
This statement is correct.
Heavy metals can directly interact with oxygen molecules, leading to the formation of reactive oxygen species (ROS). For example, copper and iron can catalyze reactions that produce ROS, contributing to oxidative stress and cell damage in plants. Thus, this statement is true.
Conclusion:
Statement A is incorrect because the uptake of heavy metals does lead to ROS accumulation.
Statement B is correct as heavy metals mimic essential metals and interfere with essential processes.
Statement C is incorrect because ion channels that transport essential metals can also transport heavy metals.
Statement D is correct because heavy metals can directly interact with oxygen to form ROS, leading to oxidative damage.
