With the help of a friendly scarecrow, students identify the basic needs of plants. They learn how seeds grow into plants and that the plant goes through changes called a lifecycle. They witness each step as seeds germinate and grow into flowering plants which produce seeds that eventually germinate and grow again.
Identify the basic needs of plants.
- Students will understand that a lifecycle consists of the different parts of an organism's life as it grows and changes. Lifecycles occur over and over again.
- Students will describe the four-stage lifecycle of a typical plant.
- Seeds: Most plants begin as seeds. The outside part of the seed is called the seed coat; it is a sheath that protects the seed. Inside the seed coat, there is an embryo and a food source. The embryo, a tiny plant, is made up of a small root, a small stem, and very tiny leaves. The food source provides the plant with nutrition as it begins to grow. When the conditions are right, the seed will germinate.
- Germination/seedling: Germination is the process by which a seed becomes a sprout (seedling). After the seed coat splits open, the root of the embryo grows down into the soil. Then the stem grows, bringing the tiny leaves up through the soil with it. In addition, the food sources are pushed out of the soil on the stem; they become green and look like leaves. Called "seed leaves," they will provide the plant with food until it grows new leaves. The plant's new leaves will make the food it needs to grow. The tiny plant that emerges after germination is known as a seedling, or sprout.
- Full-grown plant: As the seedling grows, it produces more leaves, roots, and stems, which get thicker and stronger. The result is an adult plant.
- Flowers/seed production: When most plants are fully-grown, they produce flowers. Flowers are the reproductive structures that make seeds. A flower consists of a pistil, several stamens that surround the pistil, and petals. The tips of each stamen make pollen, which is transferred to the tip of the pistil and on to the center of the flower (pollination). Soon, the flower dies off, but the part where the seeds develop grows into a fruit. The seeds will eventually grow into new plants.
- Cones/seed production: Some plants do not use flowers to produce seeds; they use cones instead. These plants are called conifers. A pine tree is an example of a conifer. Conifers produce two types of cones; small cones, which make pollen, and large cones which make seeds. Wind blows pollen from the small cones to the large cones (pollination), and seeds begin to grow inside the large cones. When the weather becomes dry, the woody scales of the cones open and the seeds fall out. These seeds may become new plants.
- Students will realize that a new seed needs the right conditions to start growing; that is, it needs the right amount of water, the right temperature, and the right amount of light. Not all seeds require the same conditions to germinate. Most seeds germinate in warm temperatures, but some seeds need a period of cold temperatures before they germinate. Some seeds will not grow until the intense heat of a forest fire stimulates them.
- Students will understand that some plants can pollinate themselves while others require pollination from separate individuals. The problem is moving pollen from the stamen/small cone of one individual to the pistil/large cone of another individual. Plants have solved this problem in a couple of ways. Confers, for example, developed wing-like structures on their pollen grains that allow the wind to carry the pollen from plant to plant. Flowering plants use insects, birds, and other animals to move pollen, which sticks to the animals, from one flower to another.
- Students will note that a seed will only grow into the type of plant from which it came. For example, a pine seed will not grow into an iris.
- Flowering plants vs. conifers: Obtain a large piece of butcher paper and draw a Venn diagram on it. Give one circle the heading, "Flowering Plants" and the other circle the heading, "Conifers". Write "Similarities" above the point where the two circles overlap. Tape the diagram on the board in front of the class. Have a class discussion comparing and contrasting Flowering Plants and Conifers. Here are some questions to help lead the discussion: How are their life cycles the same? How are they different? Do they have similar structures? What are their defining structures? Write the answers under their respective headings on the diagram.
- Plant lifecycle picture: Provide the students with paints, markers, or crayons and a piece of white paper. Ask them to choose a type of plant (Flowering Plant or Conifer) and illustrate its lifecycle. The students should draw a Seed stage, a Germination/Seedling stage, a Full-Grown stage, and Flower/Cone stage.
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