Which of the following is not true for a species :

Options

A. Members of a species can interbreed
B. Variations occur among members of a species
C. Gene flow does not occur between the populations of a species
D. Each species is reproductively isolated from every other species

Answer

To determine which statement is not true for a species, let's analyze the given options step by step:

1. **Understanding the Definition of Species**:
- A species is defined as a group of organisms that can interbreed and produce fertile offspring. Members of the same species share common characteristics and genetic makeup.

2. **Analyzing Each Statement**:
- **Option A: Members of species can interbreed**:
- This statement is true. Members of the same species have the ability to mate and produce offspring.

- **Option B: Variations occur among the members of species**:
- This statement is also true. Within a species, individuals can exhibit variations due to genetic differences, environmental factors, and mutations.

- **Option C: Gene flow does not occur between the population of species**:
- This statement is not true. Gene flow refers to the transfer of genetic material between populations of the same species. It is essential for maintaining genetic diversity and can occur through migration, mating, and reproduction. Therefore, this statement is false.

- **Option D: Each species is reproductively isolated from every other species**:
- This statement is true. Reproductive isolation is a key characteristic of species, meaning that members of different species do not typically interbreed.

3. **Conclusion**:
- The statement that is not true for a species is **Option C: Gene flow does not occur between the population of species**.

### Final Answer:
The correct answer is **Option C**.