All Free Biology MCQs with Answers

1111. Golden brown colour of diatoms is due to presence of__________?

• A. Mycoxanthin, mucoxanthin and myxoxanthophylls
• B. Alpha and beta carotenes and myxoxanthin
• C. Fucoxanthin, diatoxanthin, diadinoxanthin
• D. None of the above

Explanation: Diatoms have golden-brown colour because their plastids contain accessory xanthophyll pigments, especially fucoxanthin, along with diatoxanthin and diadinoxanthin. Students may choose a carotene-containing option because carotenes are also accessory pigments, but it does not give the characteristic diatom pigment combination listed in option c.

1112. Locomotion in diatoms is carried out with the help of__________?

• A. Valve
• B. Raphe
• C. Pseudopodium
• D. Cilia or flagella

Explanation: Many diatoms move by secreting mucilage through a longitudinal slit called the raphe; the mucilage provides the traction for gliding. Students may choose cilia or flagella because these structures produce movement in many unicellular organisms, but typical diatoms lack them and use the raphe instead.

1113. Diatomaceous earth is used for making __________?

• A. Fertilizers
• B. Weedicides
• C. Insecticides
• D. Fire proof bricks

Explanation: Diatomaceous earth consists of the accumulated silica shells of diatoms and can withstand high temperatures, so it is used in insulation and fireproof bricks. Students may choose insecticides because the powder can have abrasive insect-killing uses, but fireproof bricks are the intended application here.

1114. Diatoms stay afloat due to___________?

• A. Flagella
• B. Stored lpids
• C. Pseudopodia
• D. All of these

Explanation: Diatoms remain suspended more easily because they store lipids, which are less dense than water and reduce their sinking rate. Students may choose flagella or pseudopodia because these structures can aid movement in other organisms, but they are not the usual mechanism responsible for diatom flotation.

1115. Oil body is found in the cells of___________?

• A. Diatoms
• B. Slime moulds
• C. Chlorophycean forms
• D. None of the these

Explanation: Diatom cells commonly contain oil bodies that act as reserve food and also help reduce density, supporting flotation. Students may choose chlorophycean algae because many algae store oils, but oil bodies are a characteristic reserve feature emphasized for diatoms in this question.

1116. The chloroplasts of diatoms and chrysophycean algae do not possess____________?

• A. Chloryphyllpigments
• B. Enzymes for photolysis
• C. Defined grana and stroma
• D. Carotenes with chlorophylls

Explanation: Diatom and chrysophycean chloroplasts have a distinctive internal organization and do not show the clearly defined grana and stroma arrangement typical of higher-plant chloroplasts. Students may choose the chlorophyll option because pigment composition differs among algae, but these algae do contain chlorophyll pigments.

1117. Diatom frustule/ shell is made of_____________?

• A. Silica
• B. Calcium carbonate
• C. Manesium carbonate
• D. Both B. and C.

Explanation: A diatom frustule is a rigid shell made mainly of hydrated silica, forming the two overlapping halves of the cell wall. Students may choose calcium carbonate because it forms shells in many aquatic organisms, but diatom shells are siliceous rather than calcareous.

1118. Empty diatom cells are called___________?

• A. Raphe
• B. Valves
• C. Frustule
• D. Girdles

Explanation: A diatom’s rigid silica cell wall is called a frustule, and after the cell contents disappear, the empty frustule remains. The likely mistake is choosing valves, which are only the two overlapping halves that make up the frustule.

1119. Cell wall is extremely well preserved in fossil specimens in__________?

• A. Diatoms
• B. Dinoflagellates
• C. Slime moulds
• D. None of these

Explanation: Diatom cell walls contain hydrated silica, which resists decomposition and can remain preserved as a fossil. A student may choose dinoflagellates, but their coverings are generally organic cellulose plates rather than strongly mineralized silica walls.

1120. Unlike other algae, diatoms do not readily decay due to___________?

• A. Nonliving cells
• B. Siliceous wall
• C. Mucilaginous wall
• D. Water proof cell

Explanation: The siliceous wall of a diatom is resistant to decay, so empty frustules can accumulate after the organic cell material decomposes. The mucilaginous wall is a tempting choice because mucus may protect some organisms, but it does not provide the same durable mineral support.