The seed
A seed is the reproductive organ of seed plants; it consists of an embryo, endosperm and seed coat. The embryo has a radicle, a small stem, a bud and cotyledons — the first organs of the future plant. In dicots (cotton, bean, pea) the embryo has two cotyledons, which often store the food; when the seed germinates, two cotyledon leaves come above ground. A cotton seed has a thick woody coat whose cells grow long hairs — cotton fibre. In monocots (wheat, barley, maize, rice, oats) the embryo has one cotyledon and most food is stored in the endosperm. In a wheat grain the fruit wall and seed coat are fused, and inside are the endosperm and embryo. A seed contains water, mineral substances (ash remains when it is burned) and organic substances — starch (wheat, maize), protein (bean, mung bean, pea) and oil (walnut, almond, sunflower, cottonseed, peanut). Cumin and dill seeds contain essential oils; bitter almond and peach kernels contain a poisonous substance.
| Group | Cotyledons | Food store |
|---|---|---|
| Dicot | 2 | in the cotyledons |
| Monocot | 1 | in the endosperm |
Experiments: (1) soak bean and wheat seeds for 12 hours, open them, draw and compare the parts (two and one cotyledon). (2) Test for starch: touch wheat or maize flour with a drop of weak iodine (it turns blue-black). (3) Test for oil: crush a sunflower seed or walnut kernel on white paper — a greasy stain remains. (4) Water and ash: heating seeds in a dry test tube is done by the teacher only (safety goggles, tongs) while pupils watch from a distance. Safety: iodine is not to be swallowed; open flame only for the teacher; do not eat bitter almond, peach or apricot kernels — they are poisonous; pupils with nut allergy take care.