Chapter 19, Problem 26A

Summary Introduction

Introduction :

Silica is a group of minerals that made up of silicon and oxygen. These two elements are most abundant elements found in the earth’s crust. Silica is generally found in crystalline state and rarely found in the amorphous state. Silica contains 1 atom of silicon and 2 atoms of the oxygen and results in chemical formula SiO₂. Silica is formed by the process of complex inorganic polymerization.

Answer to Problem 26A

Correct answer :

The correct answer is option (B) diatom.

Explanation of Solution

Explanation/justification for the correct answer :

Option (B) diatoms. Diatoms are autotrophs that produce their food by performing photosynthesis. They are unicellular algae and specifically known for the illustrious design of their cell walls. Their cell walls are composed of transparent, biogenic silica that known as frustule. This is a unique feature of diatoms. The frustule is composed of two valves known as thecae that usually overlap one another. The biogenic opaline silica that makes the cell wall of diatoms is synthesized by the polymerization of the monomers of silicic acid. So, the correct answer is option (B).

Explanation for incorrect answer :

Option (A) brown alga. Brown algae are multicellular algae comprise the class Phaeophyceae. The cell walls of brown algae are composed of cellulose with the alginic acid. They also have polysaccharide fucoidan in their cell wall’s amorphous section. So, this is an incorrect option.

Option (C) dinoflagellate. Dinoflagellates are unicellular eukaryotic marine planktons that constitute phylum Dinoflagellata. They have a membrane bound cell wall called as theca. The cell walls of dinoflagellates are composed of cellulose and divided into the plates of the cellulose within the membrane vesicles. So, this is an incorrect answer.

Option (D) euglenoid. Euglenoids are unicellular plantlike protists. They are usually found in shallow freshwater but some also found in saltwater. Euglenoids have characteristics of both animals and plants. They don’t have a cell wall and in place of that they have a pellicle which is composed of protein layer with the substructure of microtubules. So, option (D) is also incorrect.