Question

Which of the following refers to the early earth?

• A. Planula
• B. Nebula
• C. Morula
• D. Blastula

Answer 1

Answer: (B)

Nebula

Solar system was born around 4600 million years ago by collapsing of gaseous cloud called solar nebula under influence of its own force of gravity. It produced several cold, spinning and cloudy masses of cosmic dust and gases which are termed as nebulae. The central mass of nebula formed Sun which got hotter by conversion of its gravitational energy into heat. The rotational movement of nebula separated a ring of cloud which condensed into planets and earth was one of them. Planula is free swimming larval stage of coelenterates. Morula and blastula are the embryonic stages in pre natal embryonic development of human. First cleavage in zygote produces two cells which then divide to form four cells and so on. The 16-celled embryonic stage is referred to as morula. Rapid cell divisions in zygote, without increase in cell mass, results in formation of blastocyst/blastula which in turn consists of blastocoel, the centrally placed cavity which is surrounded by spherical cell layer, the blastoderm and inner cell mass.