Removal of auxin source demonstrates that leaf abscission is _______by auxin, and apical dominance is________by auxin.

Options

A. promoted, promoted
B. inhibited, inhibited
C. promoted, inhibited
D. inhibited, promoted

Explanation

To answer the question regarding the effects of auxin on leaf abscission and apical dominance, we will analyze the role of auxin in both processes step by step.

### Step-by-Step Solution:

1. **Understanding Leaf Abscission**:
- Leaf abscission refers to the process of shedding mature leaves from a plant. This process is crucial for the plant's health and resource management.
- A specific layer of tissue, known as the abscission layer, forms at the base of the leaf or fruit, leading to its detachment.

**Hint**: Remember that leaf abscission is the shedding of leaves, which is an important process for plant health.

2. **Role of Auxin in Leaf Abscission**:
- Auxin is a plant hormone that plays a significant role in various growth processes.
- High concentrations of auxin inhibit the formation of the abscission layer. When auxin levels are high, the abscission layer does not form, preventing leaf drop.
- Conversely, when auxin levels decrease, the abscission layer can form, leading to leaf shedding.

**Hint**: Consider how the concentration of auxin affects the formation of the abscission layer.

3. **Understanding Apical Dominance**:
- Apical dominance is the phenomenon where the growth of lateral buds is inhibited by the presence of the apical bud. The apical bud secretes auxin, which suppresses the growth of lateral buds.
- This ensures that the plant grows taller and more efficiently, as the resources are focused on the main stem.

**Hint**: Think about how the apical bud influences the growth of other buds through auxin secretion.

4. **Role of Auxin in Apical Dominance**:
- Auxin promotes apical dominance by inhibiting the growth of lateral buds. Therefore, when auxin is present, it supports the dominance of the apical bud over lateral buds.

**Hint**: Recall that auxin's role in promoting growth is primarily seen in the context of apical dominance.

5. **Conclusion**:
- Based on the above analysis, we conclude that:
- Leaf abscission is **inhibited** by auxin (because high auxin levels prevent the formation of the abscission layer).
- Apical dominance is **promoted** by auxin (as auxin suppresses lateral bud growth).

Thus, the correct answer to the question is:
- Removal of auxin source demonstrates that leaf abscission is **inhibited** by auxin, and apical dominance is **promoted** by auxin.

### Final Answer:
Leaf abscission is **inhibited** by auxin, and apical dominance is **promoted** by auxin.