Plants are eukaryotes that use the Sun's light for energy. They include algae, which live in water, and land plants. All land plants have two forms during their life cycle, called alternation of generations. One form is diploid, where the cells have two copies of their chromosomes, and the other form is haploid, where the cells have one copy of their chromosomes. In land plants, both diploid and haploid forms have many cells. Two kinds of land plants are vascular plants and bryophytes. Vascular plants have long tissues that stretch from end to end of the plant. These tissues carry water and food. Most plants have roots and leaves. 