Question

Silica incrustation is found on the leaf surfaces of
A) Mango
B) Grasses
C) Castor
D) Oleander

Answer 1

Hint: Many species of plants metabolise silicon and incorporate it into the cell walls. In some cases, as a structural component, it may be even more important that lignin. However, silica can also be found on the external surfaces.

Complete Answer:
- Silica is found to help plants in various protective ways. Its presence in the cell walls protects plants against fungal pathogens. In addition, it is also seen to help plants with various stresses like drought and soil salinity though it is not clear how it does so. However, as a simple incrustation, silica is also seen to physically play a protective role.
- As silicon dioxide, silica is found as a physical structure called a phytolith. The kind of phytolith can also be used as a tool to classify plants, and is one of the most common structures found in fossils of plants. Plants that never produce phytoliths, cannot be stimulated to do so, while those that do, will produce them in varying amounts depending on the conditions.
- For grasses, phytoliths or silica incrustations are seen to play a protective role against herbivores. Because of the stiff, poky feel of these incrustations, herbivores tend to avoid eating these plants. They are most commonly found in many members of the grass family. Option B is the correct answer.
- Silica incrustations are not found in many trees, members of the potato family, and several herbaceous plants. A, C, and D are all incorrect answers. Other than the defence aspect against other organisms the presence of this material decreases digestibility of that plant.

Hence the correct answer is option B.

Note: Plants are also known to deposit other minerals within their cell walls for a number of purposes. Phytolith as a term also included the calcareous minerals that may be found in cell walls, commonly found in cacti. Calcium oxalate is an example.