Answer:

The primary factor controlling the environment and the associated plant and animal life in a wetland is water. Wetlands are characterized by the presence of water, which plays a crucial role in shaping the physical and biological components of the ecosystem. Here's a detailed explanation of why water is the primary factor:

1. Water availability:
- Wetlands are typically saturated or inundated with water for a significant part of the year, creating a unique habitat.
- The presence of water provides a suitable environment for various wetland plants and animals to thrive.

2. Hydrology:
- Water controls the hydrology of wetlands, including the water table, flooding, and drainage patterns.
- The fluctuation in water levels influences the distribution of different plant and animal species within the wetland.
- Some species are adapted to thrive in areas with frequent flooding, while others prefer drier areas.

3. Nutrient cycling:
- Water in wetlands transports and cycles nutrients, such as nitrogen and phosphorus, which are essential for plant growth.
- Wetland plants take up these nutrients from the water, and the cycling process supports a diverse range of plant species.
- The availability of nutrients also affects the growth of algae and other microscopic organisms, which form the base of the wetland food chain.

4. Water chemistry:
- The chemical composition of the water, including factors like pH and salinity, affects the types of plants and animals that can survive in the wetland.
- Some wetlands have brackish water with higher salinity, while others have freshwater.
- The water chemistry can dictate the presence of specific plant species and influence the overall biodiversity of the wetland.

5. Water temperature:
- Water temperature is closely linked to the overall climate and seasonality in a wetland.
- It affects the growth and physiological processes of aquatic plants and animals.
- Certain species may be adapted to specific temperature ranges, and changes in water temperature can impact their survival and reproductive success.

In conclusion, while other factors like temperature, soil, and light also play important roles, water is the primary factor controlling the environment and associated plant and animal life in a wetland. Its availability, hydrology, nutrient cycling, chemistry, and temperature collectively shape the unique characteristics and biodiversity of wetland ecosystems.