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IB Biology NAME: _________________________________________________ Activity: a Seed Adapted from “Seeds of Flowering Plants,” © Allyn & Bacon Directions: The seed of a bean plant (or, a bean!) has two cotyledons. (You will learn what those are in step 3.) That makes a bean plant a dicotyledonous plant, or dicot for short. Other flowering plants’ seeds have only one cotyledon, so they are nicknamed monocotyledonous plants, or monocots. Beans are produced in a pod, the fruit of the bean plant. Check off the tasks below as you complete them. 1. Exterior of a bean: Each bean is covered by a protective seed coat. Find the place it was attached to the pod (formerly ovary) – it leaves a scar called the hilum. Close to the hilum is the much smaller micropyle, a pore where the pollen tube entered the ovule. Water is imbibed through the micropyle at germination. On a soaked bean, find the hilum, seed coat, and micropyle. break. Then, lay the two halves flat on a paper towel, like an open book, with the tissues of the embryo at the top. 4. The tissues of the embryo. The primary tissues of the embryo may still be attached to one of the cotyledons, or parts may have broken off in step 2 when the seed coat was removed. You should be able to see the plumule, or embryonic shoot, at one end, and the radicle, or embryonic root, at the other end. Use Neil 9e figure 38.8 (a) on p. 808, and the third paragraph on p. 808, to help you! Find the plumule and the radicle. 5. The radicle. Inside the intact seed, the radicle is very close to the micropyle. The radicle is the first tissue to break through the seed coat when germination occurs. Identify a germinating seed’s priorities: is it more important to start making food first, or to start taking up water? Hilum 2. Seed coat. Peel off the seed coat from the seed. If the two halves of the seed start to come apart, hold them together. Place these items on a paper towel. Use a hand lens or stereoscope to examine the seed coat. Does the micropyle go all the way through? In some cases the seed coat needs to be tough enough to withstand the digestive juices of animals that eat the seeds, carry them a distance, and then drop them with their wastes into a new environment (seed dispersal!). 6. The plumule. The plumule or embryonic shoot contains the future first leaves of the baby plant. Use a stereoscope or hand lens to examine the plumule. How many leaves can you see? This diagram shows a seed from behind. Label its: cotyledons 3. The inner seed. The inner seed of a bean is made up entirely of embryo. The embryo consists of two large cotyledons and the primary tissues of the “baby” plant. The cotyledons contain stored food. Slowly and gently pull apart and separate the cotyledons until you feel a point of attachment plumule point of attachment radicle IB Biology 7. No endosperm. Mature dicot seeds do not contain endosperm. The endosperm was transferred to the embryo’s cotyledons as the seed developed. Scratch the surface of one of the cotyledons with a dissecting needle. Then, put a drop of Lugol’s iodine on the scratched cotyledon. What happens? Under the stereoscope, observe the cotyledon cells – they are easy to see because of the stained amyloplasts (starch-containing plastids) within them. 8. On the back of this handout, outline the germination process using the three passages from Neil 9e: p. 809, “Seed germination and seedling development.” Use bullet points. NAME: _________________________________________________