As vascular plants, trees are organized into three major organs: the roots, the stems, and the leaves. The leaves are the principal photosynthetic organs of most higher vascular plants. They are attached by a continuous vascular system to the rest of the plant so that free exchange of nutrients, water, and end products of photosynthesis (oxygen and carbohydrates in particular) can be carried to its various parts.The stem is divided into nodes (points where leaves are or were attached) and internodes (the length of the stem between nodes). The leaves and stem together are called the shoot. Shoots can be separated into long shoots and short shoots on the basis of the distance between buds (internode length). The stem provides support, water and food conduction, and storage.
The two chromatids of a duplicated chromosome are held together at a region of DNA called the centromere. Centromeres are the attachment points for microtubules, which are responsible for the guiding the movement of chromosomes during mitosis and meiosis.
