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Transcript
IB Biology / IHS NAME: _________________________________________________ go all the way through the seed coat. Activity: a Seed Adapted from “Seeds of Flowering Plants,” © Allyn & Bacon Directions: The seed of a bean plant (= a bean!) has two cotyledons. (See Fig. 2) That makes a bean plant a dicotyledonous plant, or dicot for short. Other flowering plants’ seeds have only one cotyledon, so they are called monocotyledonous plants, or monocots. Beans are produced in a pod, the fruit of the bean plant. Like all fruits, the pod was once the ovary of the flower. √ Check off the tasks below as you complete them. 1. Percent gain in mass Prior to the activity today you should have massed a dry bean and put it in a cup of water. Take the bean out of the water, pat it dry, and re-mass it. Then calculate its % gain in mass. This is the formula: % change = (new – old) old x 100 In some cases a seed coat needs to be tough enough to withstand the digestive juices of animals that eat the seeds, carry them a distance, and then disperse them with their wastes into a new environment! 4. The inner seed The inner seed of a bean is made entirely of embryo. The embryo consists of two large cotyledons (*what we just called "seed halves") and the tiny future plant. The cotyledons contain stored food. Slowly and gently pull the cotyledons apart until you feel a point of attachment break. Then, lay the two halves flat on a paper towel, like an open book, with the tissues of the embryo at the top. I have separated the two cotyledons of my seed. 5. The future plant The tiny future plant may still be attached to one of the cotyledons, or part of it may have broken off in step 3 when the seed coat was removed. You should be able to see the plumule, or embryonic shoot, and the radicle, or embryonic root. Use Neil 9e figure 38.8(a) on p. 808, and the third ¶ on p. 808, to help you! The radicle is the first structure to emerge when a seed germinates. Space for calculation & answer: 2. Exterior of a bean A bean is covered by a protective seed coat (testa). Find the place it was attached to its pod, a scar called the hilum. Close to the hilum is the much smaller micropyle, the pore where the pollen tube entered the ovule! When you soaked the seed overnight, it imbibed water through its micropyle. I see my seed's plumule & radicle. 6. Future leaves On the plumule are the first true leaves of the future plant. Use a stereoscope or hand lens to examine and count 'em. I count (how many?) ________ tiny future leaves. On my soaked bean, I see the hilum, seed coat, & micropyle. 7. View of a seed, without its coat, from behind. Fig. 1 3. Seed coat Remove the seed coat. If the two halves* of the seed start to come apart, hold them together. Use a hand lens or stereoscope to examine the seed coat: I can tell that the micropyle (circle one) does/does not I understand this diagram enough to label it by drawing lines to these labels: cotyledons plumule point of attachment Fig. 2 radicle well IB Biology / IHS 8. No endosperm. Mature dicot seeds do not contain endosperm. The endosperm was transferred to the embryo’s cotyledons as the seed developed in its pod. Scratch the surface of one of the cotyledons with a dissecting needle. Then, put a drop of Lugol’s iodine on it. What happens? Under the stereoscope, observe the cotyledon cells – they are very easy to see because of the stained amyloplasts (starch-containing plastids) within them!! I see cotyledon cells! The end! "Seed" you later! Hope this has "bean" fun! NAME: _________________________________________________