Which of the following statements regarding fertilization and implantation is incorrect ?

Options

A. Fertilization can occur only if sperm and ovum simultaneously reach the ampullary isthmic junction of the fallopian tube .
B. During fertilization , the sperm comes in contact with the corona radiata cells of the ovum first and start degrading it.
C. The division of the morula leads to the formation of blastocyst.
D. The embryo is formed by the differentiation of inner cell mass.

Answer

To determine which statement regarding fertilization and implantation is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Fertilization Location**:
- Fertilization occurs in the ampullary isthmic junction of the fallopian tube, where the sperm and ovum meet.
- The statement: "Fertilization can occur only if the sperm and ovum simultaneously reach the ampullary isthmic junction of the fallopian tube" is **correct**.

2. **Sperm Interaction with Ovum**:
- The sperm first comes into contact with the outer layer of the ovum, known as the corona radiata.
- The statement: "During fertilization, the sperm comes in contact with the corona radiata cells of the ovum first and then starts degrading it" is **incorrect**.
- The sperm does not degrade the corona radiata; instead, it binds to it, which triggers the acrosomal reaction. This reaction releases enzymes that degrade the zona pellucida, which is the layer beneath the corona radiata.

3. **Formation of Blastocyst**:
- After fertilization, the zygote undergoes several divisions to form a morula, which then develops into a blastocyst.
- The statement: "The division of morula leads to the formation of blastocyst" is **correct**.

4. **Embryo Formation**:
- The inner cell mass of the blastocyst differentiates to form the embryo.
- The statement: "The embryo is formed by the differentiation of the inner cell mass" is **correct**.

### Conclusion:
The incorrect statement regarding fertilization and implantation is the second statement: "During fertilization, the sperm comes in contact with the corona radiata cells of the ovum first and then starts degrading it."