All Free Biology MCQs with Answers

1121. The cell wall is usually composed of two overlapping halves called epitheca and hypotheca in__________?

• A. Diatoms
• B. Desmids
• C. Pyrrophyta
• D. Chlorophyta

Explanation: Diatoms have a frustule made of two overlapping silica halves: the larger epitheca and the smaller hypotheca. Desmids and most green algae have cell walls, but this distinctive epitheca-hypotheca arrangement is characteristic of diatoms.

1122. Cell wall is richly impregnated with silica in__________?

• A. Rhodophyta
• B. Phaeophyta
• C. Baciliariophyta
• D. Euglenophyta

Explanation: Bacillariophyta, the diatom group, has cell walls richly impregnated with silica, forming durable frustules. Phaeophyta are brown algae and may contain alginates, but their walls are not characteristically silica-impregnated like diatoms.

1123. Microfossile often present in petroleum producing formationsare those of__________?

• A. Diatioms
• B. Heliozoans
• C. Radiolarians
• D. Foraminiferans

Explanation: Diatom frustules are siliceous and resist decay, allowing them to become abundant microfossils in sedimentary and petroleum-associated formations. Foraminiferans are also important marine microfossils, so they may seem plausible, but this question specifically identifies the silica-preserved diatom remains.

1124. Centric discoid form of diatoms is__________?

• A. Diplaneis
• B. Coscinodiscus
• C. Camphyloneiscus
• D. Stephanodis

Explanation: Coscinodiscus is a well-known centric diatom with a circular or discoid frustule. Diploneis and related names refer to other diatom forms, so selecting them confuses different genera rather than recognizing the classic discoid example.

1125. Diatoms are found in__________?

• A. Phytoplanktonic population
• B. Freshwater lakes and ponds
• C. Marine environment
• D. All of the above

Explanation: Diatoms occur as major members of phytoplankton and live in both freshwater habitats such as lakes and ponds and marine environments. Choosing only marine environments overlooks the many freshwater diatoms, while choosing only freshwater overlooks their major role in oceans.

1126. Which one of the following is representing the group of diatoms?

• A. Pinnularia, Navicula, Cymbella, Melosira
• B. Euglenamorpha, Hedneria , Heteronema, Colacium
• C. Nostoc, Anabaena, Aulosira, Cylindrospermum
• D. Cochlodinium, Gymnodinium, Lenodinium, Peridinium

Explanation: Pinnularia, Navicula, Cymbella and Melosira are all recognised diatom genera. The other groups contain euglenoids, cyanobacteria or dinoflagellates, so the trap is grouping aquatic microorganisms together without checking their classification.

1127. Diatoms belong to___________?

• A. Chrysophyta
• B. Bacillariophyceae
• C. Xanthophyceae
• D. Both A. and B.

Explanation: Diatoms have traditionally been placed within Chrysophyta and are more specifically classified in Bacillariophyceae, so both descriptions can apply under common textbook classifications. Choosing only one ignores the difference between a broader group and the more specific diatom class.

1128. Which organisms are sometimes called the " pastures of the sea"?

• A. Diatoms
• B. Radiolarians
• C. Dinoflagellates
• D. Foraminiferans

Explanation: Diatoms are called the “pastures of the sea” because they are abundant photosynthetic producers that form the base of many marine food chains. Dinoflagellates are also phytoplankton, but some produce harmful blooms, and the traditional phrase specifically refers to diatoms.

1129. The wax present on the body of cockroach is secreted:

• A. Mucocytes
• B. Leucocytes
• C. Oenocytes
• D. Granulocytes

Explanation: In cockroaches, oenocytes are specialised cells associated with producing lipids and waxes that contribute to the waterproofing of the cuticle. Mucocytes secrete mucus, while leucocytes and granulocytes are immune-related terms and do not produce the cuticular wax.

1130. The bristles on the body of the cockroach arise from__________?

• A. Epidermis
• B. Trichogen cell
• C. Basement membrane
• D. Malpighian cell

Explanation: A cockroach bristle develops from a specialised epidermal hair-forming cell called a trichogen cell. The basement membrane lies beneath the epidermis, and Malpighian cells belong to the excretory system, so neither forms the external bristle.