Which one of the following is initiated by secretions of trophoblast?
(a) Blastulation
(b) Implantation
(c) Cleavage
(d) Gastrulation

Options

A. Blastulation
B. Implanatation
C. Cleavage
D. Gastrualtion

Answer

To solve the question "Which one of the following is initiated by secretions of trophoblast?", we will analyze each option provided:

1. **Understanding Trophoblast**:
- The trophoblast is the outer layer of the blastocyst, which forms after fertilization and is crucial for implantation into the uterine wall.

2. **Analyzing the Options**:
- **(a) Blastulation**: This is the process that leads to the formation of the blastula. It occurs before the trophoblast is formed, so it cannot be initiated by the secretions of the trophoblast.
- **(b) Implantation**: This is the process where the blastocyst attaches to the uterine wall. The secretions from the trophoblast play a key role in facilitating this process, making this option a strong candidate.
- **(c) Cleavage**: Cleavage refers to the series of rapid cell divisions that occur after fertilization, leading to the formation of the blastula. This process occurs before the trophoblast is formed, so it is not initiated by trophoblast secretions.
- **(d) Gastrulation**: Gastrulation is the process that follows blastulation and involves the formation of the three germ layers. This process is not initiated by trophoblast secretions.

3. **Conclusion**:
- After analyzing all the options, we find that the correct answer is **(b) Implantation**, as it is the process initiated by the secretions of the trophoblast.

### Final Answer:
(b) Implantation