Mechanism fo breathing vary among different groups of animals depending mainly on _____ and _____.

Answer

To answer the question regarding the mechanism of breathing in different groups of animals, we need to identify the two main factors that influence these variations.

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks us to identify two main factors that cause the variation in the mechanism of breathing among different groups of animals.

2. **Identifying Different Groups of Animals**: Different groups of animals include vertebrates like fish, amphibians, reptiles, birds, and mammals. Each of these groups has a unique mechanism for breathing.

3. **Analyzing the Factors**: The mechanisms of breathing vary primarily due to:
- **Habitat of the Organism**: The environment in which an organism lives plays a crucial role in determining how it breathes. For example, aquatic animals like fish have gills to extract oxygen from water, while terrestrial animals have lungs to breathe air.
- **Level of Organization**: This refers to the complexity of the organism's body structure. For instance, simpler organisms may rely on diffusion for gas exchange, while more complex organisms have specialized respiratory systems.

4. **Filling in the Blanks**: Based on the analysis, we can fill in the blanks:
- The mechanism of breathing varies among different groups of animals depending mainly on **habitat** and **level of organization**.

### Final Answer:
The mechanism of breathing varies among different groups of animals depending mainly on **habitat** and **level of organization**.