Nitrogen gas makes up nearly 80% of Earth's atmosphere, yet nitrogen is often a limiting factor for plant growth. Why ?
1. The atmospheric form of nitrogen cannot be used by plants.
2. Nitrifying bacteria remove usable nitrogen from the soil more repidly than plants can absorb it.
3. Atmospheric nitrogen dissolves readily in the soil but is washed out with every rainfall.
4. Plants must absorb nitrogen through their roots, which are not in contact with the atmosphere.

In general, the biomass in an ecosystem will be greatest at the trophic level comprising.

1. secondary consumers

2. primary consumers

3. producers

4. tertiary consumers

Consider the following two statements:

1. Both l and ll are correct and ll explains l

2. Both l and ll are correct but ll does not explain l

3. l is correct but ll is incorrect

4. l is incorrect but ll is correct

What percent of energy in the sunlight availble to the primary producers is converted by them into net primary productivity ?
1. 1
2. 2
3. 5
4. 10 

Both hydrach and xerarch successions:

1. Take same time

2. Have similar sere

3. Lead to mesic conditions

4. Have same pioneer species

The second trophic level in a lake is:

1. Phytoplankton

2. Zooplankton

3. Benthos

4. Fishes

The rate of formation of new organic matter by consumers is called as:

1. Secondary productivity
2. Standing crop
3. Standing state
4. Net primary productivity

The limitations of ecological pyramids include all the following except:

1. The do not take into account the same species belonging to two or more trophic levels

2. They do not represent relationships between organisms at different trophic levels

3. They assume a simple food chain and do not consider food webs

4. Saprotrophs are not given any place in the ecological pyramids

About what percent of the global carbon is contained in the atmosphere?

1. 71

2. 49

3. 17

4. about 1

Which of the following organisms will be the first to colonize a bare rock?

1. Annual plants

2. Lichens

3. Perennail plants

4. Herbs and shrubs