Which of the following is an agent of biological weathering?

Correct answer: Tree roots

Correct answer: A, tree roots. Biological weathering is the breakdown or alteration of rock caused by living organisms such as plants, animals, and microorganisms. Tree roots may enter tiny cracks and enlarge them as the roots grow. This can physically split or loosen the rock without transporting it away. A is therefore the only option that names a living biological agent. B, salt crystals, can grow in pores and cracks and exert pressure, but that is generally treated as a physical weathering process. C, temperature difference, causes expansion and contraction and is also a physical process. D, ice pressure is related to freeze-thaw action, in which water freezes, expands, and widens cracks; it is physical weathering, not biological weathering. Memory cue: ask “Is a living organism doing the work?” If yes, think biological weathering.