Final answer:
A house plant that drops its leaves suddenly may be experiencing environmental stress, disease, or damage caused by human activity such as paint obstructing the leaves' pores. External factors are critical for plant health and may lead to symptoms such as leaf drop.
Step-by-step explanation:
A house plant that suddenly drops its leaves may be suffering from various issues, such as environmental stress, drought, or disease. In the case of Mimosa pudica, the sensitive plant mentioned, the leaves droop and fold when touched, but this is a defense mechanism rather than a sign of ill health, and the plant will return to normal after a few minutes. However, when a plant like a poinsettia has its leaves painted with gold paint, it may wilt and droop because the paint can block pores preventing transpiration and gas exchange, leading to poor health or death. This is an example of how environmental changes can harm a plant. Environmental factors such as light, water, temperature, and nutrient availability critically affect a plant's health and can cause symptoms like leaf drop.