How is primary selection different from secondary succession?

Explanation:

Primary and secondary succession occur after both human and natural events that cause drastic change in the makeup of an area. Primary succession occurs in areas where there is no soil and secondary succession occurs in areas where there is soil.

In primary succession, newly exposed or newly formed rock is colonized by living things for the first time. In secondary succession, an area previously occupied by living things is disturbed—disrupted—then recolonized following the disturbance.

Hope this helped :)

-Akito

your answer would be a. 12.5 kg

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.