Senescence is

Options

A. Terminal irreversible phase of ageing
B. Combined deteriorative processes in mature plant
C. A period between complete maturity and final death of an organ
D. All of these

Answer

**Step-by-Step Text Solution:**

1. **Definition of Senescence**: Senescence is defined as a gradual deteriorating process that occurs in plants throughout their lifespan.

2. **Occurrence**: This process happens after a cell or tissue has matured. It signifies the transition from maturity to the eventual death of the organ.

3. **Cellular Changes**: During senescence, there is an increase in the number of senescent cells, indicating that the cells are undergoing aging and decline in function.

4. **Final Phase**: Senescence marks the period between the complete maturity of the plant organ and its final death. This phase is characterized by irreversible changes.

5. **Options Analysis**:
- The first option states that senescence is a terminal irreversible phase of aging, which is true.
- The second option describes it as a combined deteriorative process, which is also accurate.
- The third option refers to it as a period between complete maturity and final death, which is correct as well.

6. **Conclusion**: All the provided options correctly describe aspects of senescence, confirming that they are valid statements regarding the process.