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Plant Life Unit 2: Life Science This multimedia product and its contents are protected under copyright law. The following are prohibited by law: • any public performance or display, including transmission of any image over a network; • preparation of any derivative work, including the extraction, in whole or in part, of any images; • any rental, lease, or lending of the program. In This Section: We consider seeds and how they grow, how new plants can be started from plant parts, how environmental conditions affect plants, how plant parts work, and how plants respond to their environment. A brief, final section takes up the tiny plantlike organisms called molds. Copyright (c) 2011 by Pearson Education, Inc. Children and Plants Throughout the elementary years, it is important that children build an understanding of biological concepts through direct experiences with living things. Plants are excellent sources for observational activities, classification tasks, and experimentation. Copyright (c) 2011 by Pearson Education, Inc. Seeds “Where do seeds come from?” Seeds are produced in the ovary, in the central part of the flower. As the ovary ripens, its seeds become enveloped either by a fruity pulp, a pod, or a shell, depending on the kind of plant. “What are some examples of seeds?” Pears and peaches are fruits whose pulp we eat. Beans, peas, and peanuts are examples of seeds enclosed in pods. When we “shell” string beans, lima beans, peas, or peanuts, we are removing these seeds from their pods. Walnuts, pecans, and coconuts have hard outer shells. Copyright (c) 2011 by Pearson Education, Inc. Seed Plants Seeds come in many shapes, colors, and sizes. Still, they have three things in common: A protective seed cover A baby plant (embryo) A food supply that nourishes the seed as it pushes up through the soil and grows into a young plant. The growth process from seed to seedling is called germination. Copyright (c) 2011 by Pearson Education, Inc. Survival Conditions Some flowering plants produce thousands of seeds a year. However, a variety of factors enable only a small percentage of wild seeds to grow: Birds, insects, bacteria, and other organisms destroy seeds. Unless proper conditions of moisture, temperature, and oxygen are present, seeds remain dormant. Copyright (c) 2011 by Pearson Education, Inc. How Seeds Travel Children can learn that seeds travel in several ways. Some are scattered through the actions of animals and people. The wind blows many seeds. Water can carry seeds from place to place because many seeds float. The capacity of seeds to disperse widely and in different ways is another survival feature. Copyright (c) 2011 by Pearson Education, Inc. Sprouting Seeds Some easy-to-grow seeds are kidney beans, lima beans, pinto beans, whole green peas, and yellow peas. To ensure that only live, healthy seeds are planted, make sure you soak them and plant them while still moist. A method for treating seeds can be found in the textbook. Copyright (c) 2011 by Pearson Education, Inc. Soil Instruct students to plant seeds only slightly deeper than the seed length. But always follow instructions on the seed package for seed store varieties. Because it takes energy to push through the soil, a small seed planted too deeply runs out of food before it reaches the surface. Keep the soil somewhat loose so that air can get to the roots. Ensure that there is proper drainage by either using a container with small holes, placed in a saucer or placing a layer of rocks in a container before adding soil. Copyright (c) 2011 by Pearson Education, Inc. Vegetative Reproduction Many people think that only seeds produce new flowering plants. Yet, some of the most useful and interesting ways to grow new plants are through the propagation of roots, stems, and even leaves. This technique is called vegetative reproduction. Why not just use seeds? Vegetative reproduction results in faster growth. Some plants do not have seeds (ex: seedless oranges). Quality control (a seedling’s growth is unpredictable; however, if vegetative reproduction is used, we can ensure that the new plant will be very similar to its parents). Copyright (c) 2011 by Pearson Education, Inc. Roots Consider the orange-colored taproot of the carrot plant (the part we eat): If left in sunlight, the taproot will sprout leaves, stems, flowers, and seeds. Parsnips and beets grow in the same way. New plants may be grown from taproots in the classroom by embedding them in moist sand or garden soil. Copyright (c) 2011 by Pearson Education, Inc. Stems Most ground-cover plants, such as grass, strawberry, and ivy, spread quickly after planting. These plants send out stems or runners that take root, push up shoots, and develop into new plants. These lateral stems may spread above ground, as the strawberry plant and Bermuda grass do, or below ground, as quack grass does. Copyright (c) 2011 by Pearson Education, Inc. Leaves Even some leaves may develop into whole plants. Suggestions for using an African violet, echeveria, and bryophyllum plant are in the textbook. Copyright (c) 2011 by Pearson Education, Inc. Environmental Conditions Plants grow and flourish only when the environment provides proper amounts of minerals, water, light, temperature, and—more indirectly—space. Because the classroom is an artificial habitat, or home, for plants, children will need to furnish the conditions the plants need for survival. Copyright (c) 2011 by Pearson Education, Inc. Growth Conditions Excess watering causes plants to die of oxygen deprivation or disease. Not enough watering usually results in droopy, malnourished plants. The absence of vital soil minerals and extremes in temperature also has a weakening, or even fatal, effect on plants. Crowding of plants is harmful to growth largely because competition deprives individual plants of enough of what they need for good growth. Green plants need light energy, but not necessarily sunshine, to manufacture their own food. Electric lights may be substituted. Plants generally grow faster when exposed to light for increased time periods, but overexposure retards growth and delays normal blooming times. Copyright (c) 2011 by Pearson Education, Inc. Three Habitats It may be difficult for us to take children directly to different habitats such as deserts and woodlands. It is possible, though, to bring several habitats to the classroom in miniature form. The terrarium is a managed habitat for small land plants and, if desired, small animals likely to be found with the plants. Three basic kinds are the woodland, the marsh, and the desert terrariums. Teachers can create these terrariums with any large clear container such as an aquarium. Copyright (c) 2011 by Pearson Education, Inc. Plant Roots Roots: Anchor the plant Absorb soil water Store food Root hairs absorb all of the water for the plant because they are able to grow in the tiny spaces between soil particles and make direct contact with water and air trapped within the soil. Copyright (c) 2011 by Pearson Education, Inc. Stem Water absorbed by the roots goes into the stems, through which it is transported by narrow tubes to all parts of the plant. Cohesion and adhesion work together to move water molecules through the plant. Copyright (c) 2011 by Pearson Education, Inc. Leaves Inside leaves is a green chemical called chlorophyll. Chlorophyll enables a leaf to chemically combine carbon dioxide from air with water to form a simple sugar. The energy needed to power this process, Photosynthesis, comes from sunlight, which is absorbed by the chlorophyll. Copyright (c) 2011 by Pearson Education, Inc. Leaves, cont’d Carbon dioxide is taken up in photosynthesis, and oxygen is released as a waste product. But when a plant consumes the food stored in its cells, it takes up oxygen and gives off carbon dioxide as a waste product. Fortunately for us, much more oxygen is released to the air through photosynthesis than is used by plants in oxidizing their stored food. In fact, green plants are the chief source of the world’s current oxygen supply. Copyright (c) 2011 by Pearson Education, Inc. Stomata How do these gases enter and leave the leaf? Thousands of microscopic openings, called stomata, may be found in a green leaf. In land plants, these are largely, but not exclusively, located in the leaf’s underside. Water in the leaf evaporates into the air through the stomata, a process called transpiration. Regulation of these openings has great survival value. In dry spells and at night, the stomata stay closed, thereby preventing any appreciable loss of water. Copyright (c) 2011 by Pearson Education, Inc. Flowers The flower is the reproductive system of a flowering plant. Its two principal organs are the pistil, which contains unfertilized egg cells, and stamens, which produce dust-like pollen cells. It is best to examine single flowers, such as tulips and sweet peas, with children rather than composite flowers, such as daisies and sunflowers which have very minute parts that are difficult to observe. Copyright (c) 2011 by Pearson Education, Inc. Pollination Self-pollination happens when pollen from a flower’s own stamens fertilize its ovules. Cross-pollination occurs when pollen from another flower perform this function. Pollen must be from the same type of flower, however, for fertilization to take place. Pollen may travel through wind, insects, or even just gravity. Copyright (c) 2011 by Pearson Education, Inc. Life Cycles Many garden flowers and vegetables grow from seeds, then blossom, produce seeds, and die in one growing season. These are known as annuals. Examples are petunias, zinnias, beans, and tomatoes. Those that live two seasons are biennials. Examples are hollyhocks, forget-me-nots, carrots, and turnips. Plants that live more than two growing seasons are perennials. Trees and most shrubs fit into this classification. Copyright (c) 2011 by Pearson Education, Inc. Tropisms A plant’s responses to environmental stimuli are called plant tropisms. Geotropism- The plant’s response to gravity. Example: A plant grows towards a light source. Hydrotropism- The plant’s response to water. Example: A plant’s roots growing towards a water source. Copyright (c) 2011 by Pearson Education, Inc.