Exam Questions

Here are three exam questions and answers.


1. What conditions promote the Midwest plains?

Winds carry air up the windward side of the Rocky Mountains, the air cools, and water vapor condenses and precipitates. The West side of the Rocky’s is colder and wetter. The air then moves down the leeward side of the mountain, expanding and warming, thus increasing its capacity to absorb and retain water. This creates a desert like, dry ecosystem. The rain shadow effect extends 1,500 km to the East of the Rocky’s, creating a range from 300mm/yr in Colorado to 1,000 mm/yr in Illinois. The whole Midwest is within that rain shadow.

2. How does soil texture affect other soil properties? Why does it influence ecosystem processes so strongly?

The texture of the soil, which is based on the proportions of sand, clay, and silt, are indicators of the soil properties.  Soil properties include drainage, water holding capacity, aeration, susceptibility to erosion, organic matter content, cation exchange capacity, pH buffering capacity, and soil tilth. Properties like drainage and water holding capacity will determine erosion rates, nutrient leaching rates, decomposition, etc. The texture influences the properties, which have a direct effect on ecosystem processes because it determines the vegetation and natural communities that will grow.

3. How do bacteria and fungi differ in their environmental responses and their roles in decomposition?

Bacteria and Fungi are responsible for 95% of the total decomposer biomass and respiration. Fungi create networks of hyphae, which are filaments that enable them to spread and grow. This allows them to get nitrogen from one place and carbon from another. When soils are plentiful, they spread their network in search of the most labile substances. Fungi secrete enzymes which degrade cell walls, breaking down litter and extracting the nutrients. Bacteria have a small size and large surface: volume ratio that allows them to absorb soluble substrates, and to grow and divide quickly in substrate-rich areas. Bacteria often lines roots and enjoys macropores in the soil, where water movement is rapid and nutrients flow.