To solve the question regarding the dichotomous key and identify the incorrect statement about tissues P, Q, R, S, T, and U, we will follow these steps:
### Step-by-Step Solution:
1. **Identify the Type of Tissue:**
- The first part of the key states: "The cells of tissue have walls." This indicates we are dealing with plant tissues. If the cells have no walls, we would be dealing with animal tissues.
2. **Classify Plant Tissues:**
- If the tissue is made of only one type of cell, it is classified as **simple tissue**. If it is made of more than one type of cell, it is classified as **complex tissue**.
3. **Classify Animal Tissues:**
- If the tissue lines the fallopian tubes, it is identified as **R (ciliated epithelium)**. If it transports nutrients, it is identified as **S (blood)**.
4. **Identify Simple Tissues:**
- For simple tissues, if the cells store air, it is classified as **P (aerenchyma)**. If it is mainly a mechanical tissue, it is classified as **U (sclerenchyma)**.
5. **Identify Complex Tissues:**
- If the tissue conducts water, it is classified as **T (xylem)**. If it conducts organic nutrients, it is classified as **Q (phloem)**.
6. **Evaluate the Statements:**
- Now we need to evaluate the statements regarding P, Q, R, S, T, and U to find the incorrect one:
- **P**: Aerenchyma is found in aquatic floating plants.
- **Q**: Phloem conducts organic nutrients.
- **R**: Ciliated epithelium lines the fallopian tubes.
- **S**: Blood transports nutrients.
- **T**: Xylem conducts water.
- **U**: Sclerenchyma possesses uniform thickening of lignin.
7. **Identify the Incorrect Statement:**
- The statement that "S can be xylem" is incorrect because S is identified as blood, not xylem. Therefore, the incorrect statement is regarding tissue S.
### Conclusion:
The incorrect statement regarding tissues P, Q, R, S, T, and U is that **S is xylem** when it is actually blood.
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