Life Cycle
- Plants (1B) |
OBJECTIVES:
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Students experiment with stems. |
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The basic parts of flowering plants include the roots, stems, leaves, and flowers. Stems are important in water and food transportation, and provide support for the leaves, flowers and fruit. Some plants store food (potatoes) or water (cactus) in stems. Flowers are necessary for seed production, without which many species would die out. The main parts of a flower are drawn on the right. A plant with colored petals and/or a pleasant scent is usually pollinated by insects or birds. Wind or self-pollinated plants usually have rudimentary, inconspicuous flowers. Seeds develop in the ovary, and the ovary may develop into a fruit. Flowers that we eat include broccoli, cauliflower and artichokes, although the last one is actually the flower bud. Tree trunks are a special kind of stem, and the age of a tree can be determined by counting the rings of a tree trunk. A ring is actually the new water-conducting tissue that is made each year. Thick rings mean that the tree grew a lot in the spring and summer. Thin rings reflect bad growing conditions, like drought, or just the fact that the tree grows slowly. Concentric rings mean that the tree grew straight up, and rings that are off-center, with one side wider than the other, mean that the tree grew on a slope (look at diagram to the left). The downhill side has wider rings. Seasonal variations in conditions may cause color variations inside a ring. There are many different kinds of stems. They may be underground or above-ground, woody or soft, stiff or flexible. Stems that we eat include asparagus and potatoes. (Potatoes are very specialized stems that help to reproduce the plant. Small semi-circular leaf scars near the eyes show that they are stems.) Brussels sprouts are stem buds. PROCEDURE:
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