Meaning of the Line:

The line "accompanied by complex post fertilization development" in the NCERT refers to the process that occurs after fertilization in certain organisms. It indicates that after the fusion of male and female gametes during fertilization, these organisms undergo intricate and elaborate developmental stages before reaching maturity.

Explanation:

1. Fertilization:
Fertilization is the process of fusion of male and female gametes, resulting in the formation of a zygote. The zygote is the first cell of the new individual and contains the complete set of genetic information from both parents.

2. Post Fertilization Development:
After fertilization, the zygote undergoes a series of developmental stages, which collectively make up the post fertilization development. This development is characterized by various changes and transformations that occur within the zygote to form a mature organism. These changes include:

- Cleavage: The zygote undergoes rapid cell divisions called cleavage, where it divides into a number of smaller cells called blastomeres. These divisions lead to the formation of a solid ball of cells known as a morula.

- Blastula Formation: Further divisions of the blastomeres result in the formation of a hollow ball of cells called a blastula. The blastula consists of an outer layer of cells called the trophoblast and an inner cell mass called the embryoblast.

- Gastrulation: Gastrulation is a critical process during which the blastula undergoes reorganization to form three distinct germ layers: ectoderm, mesoderm, and endoderm. These germ layers give rise to different tissues and organs of the mature organism.

- Organogenesis: Organogenesis is the process of organ formation from the three germ layers. The germ layers differentiate and give rise to specific tissues and organs, leading to the development of a fully formed organism.

3. Complexity of Post Fertilization Development:
The line in the NCERT suggests that the post fertilization development in certain organisms is complex. This complexity arises due to the intricate processes involved in the formation of various tissues, organs, and systems in the developing organism. The specific details of post fertilization development vary among different organisms, depending on their life cycles and evolutionary adaptations.

Overall, the line highlights the significance of the post fertilization development stage in the life cycle of organisms, emphasizing the complexity and intricacy of the processes involved in shaping the final form of the mature organism.