Which of the following organisms are known as chief producers in the oceans?
| 1. | Dinoflagellates | 2. | Diatoms |
| 3. | Cyanobacteria | 4. | Euglenoids |

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In which group of organisms the cell walls form two thin overlapping shells which fit together?
| 1. | Chrysophytes | 2. | Euglenoids |
| 3. | Dinoflagellates | 4. | Slime moulds |

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Diatomaceous earth is used as heat insulator in boilers and steam pipes because the cell wall of diatom is:
| 1. | composed of iron | 2. | composed of silicon dioxide |
| 3. | conductor of heat | 4. | bad conductor of electricity |

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