How do nitrogen-fixing bacteria help cycle nitrogen through ecosystems?

A. They release nitrogen into the atmosphere when they replicate their DNA.

B. They capture nitrogen from the atmosphere and convert it into forms that plants can use, like ammonia.

C. They convert sunlight into chemical energy which is then stored in the nitrogen.

D. They convert ammonia from animal feces and urine into forms that plants can use.

Forces that are equal in strength but opposite in direction are a.) balanced b.) unbalanced c.) always result in motion d.) do not exist

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area