In Los Angeles, California, where surrounding moutnains prevent the movement of smog-filled air, the most common type of pollution is known as "photochemical smog." Nitrogen dioxide derived from automobile exhausts is a major component of this smog, and can react with moisture in the atmosphere to produce acid rain. In the nitrogen geochemical cycle, plants and animals normally do not obtain useable nitrogen from the*1 pointN2-fixing bacteria in soil and waternitrates in rainwaterproteins and nucleic acids in the food that they consume.nitrogen gas N2 in the atmosphere

The question seems to be asking where plants and animals normally obtain usable nitrogen in the nitrogen geochemical cycle. The options are:

1. N2-fixing bacteria in soil and water
2. Nitrates in rainwater
3. Proteins and nucleic acids in the food that they consume
4. Nitrogen gas N2 in the atmosphere

The correct answer is:

3. Proteins and nucleic acids in the food that they consume.

Here's why:

Nitrogen is an essential element for all life forms as it is a fundamental component of amino acids, proteins, and DNA. However, most organisms cannot use atmospheric nitrogen (N2), which makes up about 78% of the air we breathe. This is because N2 is a very stable molecule and it takes a lot of energy to break the bonds that hold the two nitrogen atoms together.

Instead, plants and animals typically get the nitrogen they need from the consumption of proteins and nucleic acids in the food they eat. In the case of plants, they absorb nitrates from the soil through their roots. These nitrates are produced by bacteria in the soil that can fix atmospheric nitrogen.

So, while N2-fixing bacteria and nitrates in rainwater do play a role in the nitrogen cycle, the primary way that plants and animals obtain usable nitrogen is through the consumption of proteins and nucleic acids.