Q.47 Raphides are deposits of
(A) calcium oxalate
(B) calcium carbonate
(C) silica bodies
(D) protein bodies
Raphides represent needle-like crystal deposits commonly found in plant tissues, playing key roles in calcium regulation and defense. The correct answer to the multiple-choice question is option (A) calcium oxalate, as confirmed across botanical studies.
Correct Answer: Calcium Oxalate
Raphides consist of needle-shaped crystals of calcium oxalate monohydrate, formed in specialized vacuolated cells called idioblasts within plant organs like leaves, stems, and roots. These crystals precipitate from oxalic acid and calcium ions, aiding in detoxification of excess calcium and potentially deterring herbivores due to their sharp structure. Plants such as Colocasia, Pistia, and Eichhornia prominently feature raphides in cortical and pith tissues.
Option Analysis
Each option describes distinct plant inclusions, differentiated by chemical composition and morphology:
| Option | Description | Why Incorrect for Raphides |
|---|---|---|
| (A) Calcium oxalate | Needle-like (raphides), prismatic druse, or styloid crystals in idioblasts; stores calcium, defends against herbivores. | Correct – Matches raphide structure exactly. |
| (B) Calcium carbonate | Forms cystoliths (knobby) or druses in epidermal cells; seen in plants like Ficus. | Incorrect – Differs in shape and chemistry from needle-like raphides. |
| (C) Silica bodies | Opal phytoliths (microscopic silica deposits) for structural support; found in grasses. | Incorrect – Silica-based, not calcium compounds. |
| (D) Protein bodies | Aleurone grains storing proteins and enzymes in seeds; non-crystalline. | Incorrect – Organic proteins, not mineral crystals. |
Biological Significance
Raphides form via biomineralization in vacuoles, where calcium ions from xylem combine with oxalic acid from surrounding cells, ensuring controlled growth to avoid cell damage. Beyond storage, they contribute to programmed cell death and mechanical defense, making plants less palatable. Understanding these helps in botany exams and research on plant physiology.
