All the following are examples of commensalism except :

Options

A. Orchid on mango branch
B. Cattle egret and grazing cattle
C. Sea anemone and clown fish
D. Cuckoo (koel ) and crow

Answer

To solve the question "All the following are examples of commensalism except:", we will analyze each option provided and determine whether it represents a commensal relationship or not.

### Step-by-Step Solution:

1. **Understanding Commensalism**:
- Commensalism is a type of symbiotic relationship where one organism benefits while the other is neither helped nor harmed.

2. **Analyzing Each Option**:
- **Option A: Orchid on Mango Branch**:
- Orchids are epiphytes that grow on mango trees. The orchid benefits by gaining support and access to sunlight, while the mango tree remains unaffected. This is a classic example of commensalism.

- **Option B: Cattle Egret and Grazing Cattle**:
- Cattle egrets follow grazing cattle to catch insects that are disturbed by the cattle. The cattle are not harmed or helped by the egrets, making this another example of commensalism.

- **Option C: Sea Anemone and Clownfish**:
- The clownfish lives among the stinging tentacles of the sea anemone, gaining protection from predators. The sea anemone is unaffected by the clownfish's presence. This is also an example of commensalism.

- **Option D: Cuckoo and Quail/Crow**:
- The cuckoo lays its eggs in the nests of other birds (like quails or crows). The cuckoo benefits as its eggs are raised by the host birds, while the host birds are harmed as they raise a chick that is not their own. This relationship is an example of brood parasitism, not commensalism.

3. **Conclusion**:
- The exception to the examples of commensalism is **Option D: Cuckoo and Quail/Crow**. This relationship is classified as brood parasitism.

### Final Answer:
**D: Cuckoo and Quail/Crow**