Q10(b):

Which of the following statements are true? If false, correct them: (b) Every mineral element that is present in a cell is needed by the cell.

Step 1: Evaluation of the Proposition

The statement "Every mineral element that is present in a cell is needed by the cell" is False.

Logical Justification: Biological systems, particularly plant cells, exhibit a high degree of permeability and uptake mechanisms that are not perfectly selective. Plants absorb nutrients from the soil solution via active and passive transport mechanisms [Per the Transmembrane Transport Theory]. Because these mechanisms operate based on electrochemical gradients and the presence of transporter proteins, they frequently facilitate the uptake of non-essential elements or heavy metals that happen to be present in the rhizosphere.

Step 2: Analytical Evidence and Mechanisms

To understand why this statement is incorrect, consider the following biological realities:

• Non-Essential Accumulation: Plants often accumulate elements such as Selenium, Gold, or heavy metals like Lead ($Pb^{2+}$) and Cadmium ($Cd^{2+}$) from the soil if these elements are present, even though they serve no known physiological or metabolic function for the plant [Based on Studies in Phytoremediation and Bioaccumulation].
• Chemical Analogy: Plants may mistakenly transport elements into their system due to chemical similarities between essential nutrients and non-essential ions (e.g., $Sr^{2+}$ behaving similarly to $Ca^{2+}$), leading to the presence of elements that are not required for survival.
• Threshold vs. Presence: The definition of an "essential" element requires that the plant cannot complete its life cycle without it and that the element is directly involved in metabolism [Per Arnon and Stout's Criteria for Essentiality]. Mere presence in the tissue does not equate to nutritional requirement.

Step 3: Correcting the Statement

The corrected statement should reflect the distinction between accumulation and essentiality.

Corrected Statement: "Only the essential mineral elements present in a cell are strictly needed by the cell; plants may accumulate many non-essential mineral elements through passive or active uptake without those elements being required for their metabolic processes."

Visual Representation of Mineral Uptake Selectivity

Final Solution: The statement is False. Corrected: Plants frequently take up non-essential elements from their environment that are not required for their life cycle or metabolic function; therefore, the mere presence of a mineral element in a cell does not confirm that the cell requires it.