Which of the following processes is NOT affected by herbicidal activity?

In the context of herbicidal activity, water absorption is not directly influenced by the mechanisms of action of most herbicides. Herbicides primarily target metabolic processes that are critical to plant growth and development, such as cell division, tissue development, and respiration.

Cell division is vital for plant growth and is often targeted by herbicides that disrupt the mitotic process within plant cells. Tissue development also relies on hormonal and metabolic pathways that many herbicides interfere with. Respiration, the process through which plants convert sugars into energy, can be inhibited by certain herbicides, affecting overall plant health.

While water absorption is an essential function for plant survival, it is generally regulated by the plant's physiological responses to its environment rather than directly impacted by herbicides. Therefore, the activity of herbicides does not typically interfere with how plants absorb water, making it the correct response to the question.