Question

Absence of Mg++ ions from plant tissue result in
A. Plasmolysis
B. Necrosis
C. Chlorosis
D. Both (B) and (C)

Answer 1

Hint: Chlorophyll has a magnesium ion inside. It is a large ring structure and a heterocyclic compound that is derived from pyrrole. There are four nitrogen atoms which bind to the magnesium and it lies in the centre that defines the chlorophyll molecule.

Complete answer: Necrosis is defined as the death of plant cells. When necrosis occurs, the plant tissues will turn brown to black. Necrotic symptoms can occur in any part of the plant like food storage organs, leaves, or in woody tissues. It occurs due to deficiency of magnesium ions. There are two types of death observed in the cells of storage organs; they are dry rot and wet rot. Whereas chlorosis also occurs due to the absence of magnesium ions. It causes the yellowing of green leaves due to the lack of chlorophyll. Many factors contribute to chlorosis. Plants that are affected by this condition show symptoms in one or two branches or the whole plant. The first indication is the paling of the green colour of foliage to yellow.
a) Plasmolysis occurs when a cell is kept in a hypertonic solution the cell will lose its water content. The opposite of plasmolysis is called deplasmolysis when the cell is kept in a hypotonic solution the water will get into the cell which results in the cell becoming turgid.
Hence, the correct answer is option D.

Note: Magnesium is an important structural element present in the chlorophyll of plants. The plant will be unable to capture light energy when magnesium is absent. Thus, magnesium deficiency changes the colour of the plant parts.