Multiple choice

Maximum biological activities occur in ________ of the soil.

  1. horizon A

  2. horizon B

  3. horizon O

  4. horizon C

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Horizon A (topsoil) contains the highest organic matter, humus, and root density, supporting maximum biological activity including decomposition, nutrient cycling, and soil organism activity. This is where most plant roots and soil organisms are concentrated.