The primary role of stems in plants is to provide support and transport nutrients and water between the roots and leaves. Stems are crucial for maintaining the plant's structural integrity and positioning leaves to maximize photosynthesis by accessing sunlight. They also serve as a conduit for hormones and growth signals, facilitating overall plant growth and adaptation. In certain species, stems can store food and water, contributing to the plant’s resilience under stress. Thus, stems are vital for plant health and development.