Question

9/33
nitrogen-fixing bacteria are important because they:
decompose dead organisms
absorb carbon dioxide
convert nitrogen gas into ammonia usable by plants
produce oxygen during photosynthesis

Explanation:

• Decomposing dead organisms is done by decomposers like fungi and some bacteria, not nitrogen - fixing bacteria.
• Absorbing carbon dioxide is mainly related to plants during photosynthesis, not nitrogen - fixing bacteria.
• Nitrogen - fixing bacteria have the ability to convert atmospheric nitrogen gas ($N_2$) into ammonia ($NH_3$) or related compounds that plants can use.
• Producing oxygen during photosynthesis is a characteristic of plants (and some algae/cyanobacteria), not nitrogen - fixing bacteria.

Answer:

Convert nitrogen gas into ammonia usable by plants