Energy Distribution in Plants
Annuals are plants that go through their entire life cycle within a single year.Annuals begin their life cycles in the spring when seeds that survived the winter germinate (begin to grow).In regions with distinct dry and wet seasons,germination occurs with the onset of the rainy season.Because it has only one growing season,an annual has to distribute its photosynthates (energy-rich molecules)first to leaves.Leaves,in turn,become involved in photosynthesis,which replenishes the supply of photosynthates and increases overall plant biomass.At the time of flowering,the plant decreases the amount of energy distributed to leaves and diverts most of its photosynthate to reproduction.For example,in the sunflower,the biomass of leaves declines from approximately 60 percent of the total plant weight during the period of growth to 10 to 20 percent by the time the seeds are ripe.When in bloom,the sunflower distributes 90 percent of its photosynthate to the flower head and the remainder to the leaves, stem,and roots.
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