There are two main systems in a plant: the reproductive and the vegetative. The reproductive parts of the plant include the flowers, fruit and seeds. The vegetative parts of the plant include the leaves, roots and stems. Just as in animals, each part of a plant has a specific function, each one geared toward the plant's survival and eventual reproduction.
This is the main reproductive organ of the plant. The petals and scent of the flowers attract pollinators, such as insects and birds. Once pollinated, the flower is no longer needed and will drop from the plant, leaving the fruit, which contains the seeds. Eventually, the seeds will also fall to the ground where they will either lie dormant until the time is right for germination, or get carried away by natural forces, birds or animals.
This is one of the most important parts of the plant as it is where the process of photosynthesis is carried out. The leaves of the plant contain chlorophyll, a substance that absorbs sunlight. The leaves will also absorb carbon dioxide from the air and water from the soil. Using the energy obtained from the sunlight, and with a little help from bacteria, the plant changes carbon dioxide and water into a type of sugar that can be used as food for the plant.
Stems have several functions. They support the upper portion of the plant away from the soil so that the plant won't absorb too much moisture and rot. Stems also act as a sort of highway, bringing water and nutrients up from the roots to the leaves and flowers, and, after photosynthesis, sending food to the roots. The stems also store food.
The roots not only anchor the plant in the soil, they absorb water and minerals from the soil. Roots can also store food for the plant's later use.