1、英语：Unit4 Exploring plants背景知识教案（1）（新 人教版选修 9） Teaching Resources Background information for Unit 4 Exploring plants 1. Importance of Plants Plants form the basic food staple for all life forms. They are the major source of food and oxygen on earth, since no animal can supply these necessary componen
2、ts without plants. The cattle we eat as beef, feed on grasses and the fish we eat, consume algae and are therefore dependent on plants for well being. Other important uses of plants include, providing shelter for animals, providing materials for clothing (cotton fibers), paper products, medicines an
3、d other chemicals, producing coal from once living plant material, reducing wind speed and noise levels, and reducing soil erosion and water runoff. There are many different types of cash crops that produce money for farmers. Olive oil comes from olives, corn oil comes from corn, and peanut oil come
4、s from peanuts. Typical agricultural products like corn, wheat, rye, and rice are all considered cash crops. Coffee plants produce beans that are used to make coffee; coca plants give us chocolate; vanilla plants grow long thin beans that are used to produce vanilla flavoring. Many drinks and bevera
5、ges, like cola and tea, come from plants. Rubber from trees is also a cash crop, as is lumber, fruit, vegetables, and cotton. Plants are also used in agriculture to help reduce wind speed. Planting trees in a row prevents the wind from blowing away the valuable topsoil. In the forest, trees act as s
6、helter for many organisms. Plants are also important for the overall ecology of an area. Roots help to stabilize soil and prevent erosion by water run off (soil conservation). Plants are also important in our atmosphere because they use carbon dioxide and give off oxygen while they undergo photosynt
7、hesis. Plants are also used in the urban setting to reduce noise, produce shade, and to beautify an area. Trees add value to homes and communities. Plants are essential to the balance of nature and in peoples lives. Green plants, i.e., those possessing chlorophyll, manufacture their own food and giv
8、e off oxygen in the process called photosynthesis, in which water and carbon dioxide are combined by the energy of light. Plants are the ultimate source of food and metabolic energy for nearly all animals, which cannot manufacture their own food. Besides foods (e.g., grains, fruits, and vegetables),
9、 plant products vital to humans include wood and wood products, fibers, drugs, oils, latex, pigments, and resins. Coal and petroleum are fossil substances of plant origin. Thus plants provide people not only sustenance but shelter, clothing, medicines, fuels, and the raw materials from which innumer
10、able other products are made. 2. The life cycle of a plant The life cycle of a plant varies depending on the individual species. There are, however, certain requirements for life that most plants need. The growth of a plant is dependent upon light, water, oxygen, carbon dioxide, minerals in the soil
11、, temperature and microbes in the soil. Light, water, and carbon dioxide are needed for photosynthesis which produces food for the plant. Oxygen is needed when it is dark, because the plant then needs oxygen to maintain itself. The correct temperature, soil, and minerals are all needed when the plan
12、t first germinates and subsequently grows. Soil helps bind the roots so the plant can anchor itself. Microbes in the soil include a number that are beneficial to plants. Microbial activity helps bring about the decay of organic material (dead plant material and animals) necessary for the production
13、of soil. Temperature or light intensity varies for each type of plant, and this helps explain global plant distribution; light intensity or temperature also effects the rate of photosynthesis in plants; the time at which a plant flowers and the rate at which water loss occurs in a plant (transpirati
14、on.) When these requirements are static for a seed, it will begin to grow or germinate. Sufficient food and minerals are stored in almost all seeds, so that these factors do not limit germination. As water is absorbed by a seed, the inner tissue swells more rapidly than the seed coat. The penetratio
15、n of water allows the tissues to become hydrated and enzyme activity increases. The food that is stored in the cotyledons or the endosperms are now digested and used. 3.The growth requirements of plants All plants need light, water, air, moderate temperatures and most need soil. Some plants, such as
16、 mistletoe and duckweed, do not require soil for growth and life but they do not constitute the majority of plants. There are wide variations in the amount of light and water that plants require. A mature Joshua tree, for example can store enough water to last three years or until another rainy seas
17、on. Most plants, however, need water on a more regular schedule. Some plants require a full days hot sun, and others cannot be taken out of deep shade. Temperature tolerance also varies tremendously. Tundra and lichens can survive near the Arctic, but many tropical plants cannot survive being carrie
18、d from the store to a car when it is near freezing. 4. Growing plants from cuttings Many plants can reproduce either sexually (seeds) or vegetatively (asexual), utilizing other plant parts. Whole plants can be grown from stems, leaves or roots, if the right plant is chosen. The following are some su
19、ggestions that can be used to illustrate vegetative reproduction. Stems: Ivy, potato tubers, bamboo and iris rhizome, bulbs of various kinds (bulbs are actually modified shoots), crocus or gladiolus, corn, Philodendron, Monstera (split-leaf philodendron), strawberry and spider plant offsets. (Many o
20、thers will grow, even hardwoods, but they take a lot of time and effort.) Roots: Japanese anemone, Oriental poppy, trumpet creeper, blackberry, raspberry, lily of the Nile, and any other plant that produces sprouts from roots. (The roots you plant will show no visible growth buds, the buds develop after the root cutting is planted.) Leaves: Begonias, African violets, various succulents, sansevieria, piggy back plant (if leaf has plantlet), and Bryophyllum.
