All animals begin life as a _.
Correct answer: B. Single fertilised egg
- A. Multicellular fertilised egg
- B. Single fertilised egg
- C. Hollow blastula
- D. Gastrula
Explanation
All animals, from simple sponges to complex humans, begin their lives as a single fertilized egg cell, also known as a zygote. This zygote is formed when a sperm fertilizes an egg cell, resulting in a single cell with a unique combination of genetic material from both parents.From this single cell, the embryo develops through various stages, including:1. Cleavage: The zygote divides into multiple cells.2. Blastula: A hollow ball of cells forms.3. Gastrula: The blastula undergoes invagination, forming a multilayered embryo.So, while all animals do pass through the blastula and gastrula stages, they all begin life as a single fertilized egg.
This question appeared on the KMU MDCAT 2023 (retake) paper, which you can sit online with every answer explained.
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About Embryonic Development
Embryonic development begins after fertilization with cleavage and formation of the morula and blastula, followed by gastrulation and the establishment of germ layers. It includes organ formation, tissue differentiation and early growth, rather than the later increase in size associated with postnatal development.
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