Прочитайте текст и выполните задания. Crop alteration and biotechnology 1. Crop alteration has bee...: ответ на тест 922853 - Английский язык

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                                Crop alteration and biotechnology
1. Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests.
2. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism. Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants.
3. Careful selection and breeding have had enormous effects on the characteristics of crop plants. The green revolution popularized the use of conventional hybridization to increase yield many folds by creating «high-yielding varieties». For example, average yields of corn (maize) in the USA have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques.
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                                Crop alteration and biotechnology
1. Crop alteration has been practiced by humankind for thousands of years, since the beginning of civilization. Altering crops through breeding practices changes the genetic make-up of a plant to develop crops with more beneficial characteristics for humans, for example, larger fruits or seeds, drought-tolerance, or resistance to pests.
2. Crop breeding includes techniques such as plant selection with desirable traits, self-pollination and cross-pollination, and molecular techniques that genetically modify the organism. Domestication of plants has, over the centuries increased yield, improved disease resistance and drought tolerance, eased harvest and improved the taste and nutritional value of crop plants.
3. Careful selection and breeding have had enormous effects on the characteristics of crop plants. The green revolution popularized the use of conventional hybridization to increase yield many folds by creating «high-yielding varieties». For example, average yields of corn (maize) in the USA have increased from around 2.5 tons per hectare (t/ha) (40 bushels per acre) in 1900 to about 9.4 t/ha (150 bushels per acre) in 2001. Variations in yields are due mainly to variation in climate, genetics, and the level of intensive farming techniques.
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                                            Forest health
1. The importance of pests and their negative impacts on forests are often underestimated. Pest outbreaks can contribute either directly or indirectly to economic and environmental losses. Insects and diseases can have adverse effects on tree growth and survival, yield and quality of wood and non-wood products, wildlife habitat, recreation and scenic and cultural value. Yet they are integral components of forests.
2. Invasive plant species can also cause damage through competition and prevention of regeneration of native tree species, posing new challenges especially to the in situ conservation of forest biological diversity. Pollution is another threat to forest health and vitality.
3. Insects and diseases influence the health of natural and planted forests, trees also outside forests and other wooded lands. Movement of insects and diseases has been facilitated by increased long-range air travel and reduced travel time, increased international trade of agricultural and forest products, and the exchange of plant material. Forest pests can be extremely destructive, as seen in recent years in both developed and developing countries.
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                                            Mangroves
1. Mangroves are the characteristic littoral plant formations of tropical and subtropical sheltered coastlines. Generally speaking, mangroves are trees and shrubs growing below the high-water level of spring tides. Their root systems are thus regularly inundated with saline water, even though it may be diluted due to freshwater surface run-offs and only flooded once or twice a year. Mangroves depend on terrestrial and tidal waters for their nourishment, and on coastal soils and silt deposits from upland erosion as substrate for support.
2. Mangroves are among the most productive terrestrial ecosystems and are a natural, renewable resource. However, the world's mangroves are beleaguered. Mangroves are losing their habitats as rivers are dammed, their waters diverted and the intertidal zone extensively developed for agriculture or aquaculture and generally dried up.
3. The depletion of mangroves is a cause of serious environmental and economic concern to many developing countries. This stems from the fact that at the interface between the sea and the land, mangroves play a pivotal role in moderating monsoonal tidal floods and in coastal protection. The continuing degradation and depletion of this vital resource will reduce not only terrestrial and aquatic production and wildlife habitats, but more importantly, the environmental stability of coastal forests that provide protection to inland agricultural crops and villages will become seriously impaired.
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                                                   Botany
1. Botany is a branch of biology that involves the scientific study of plant life. Botany covers a wide range of scientific disciplines concerned with the study of plants, algae and fungi, including structure, growth, reproduction, metabolism, development, diseases, chemical properties, and evolutionary relationships between taxonomic groups. Today botanists study over 550,000 species of living organisms.
2. The study of plants is vital as they are a fundamental part of life on Earth, which generates oxygen, food, fibres, fuel and medicine that allow humans and other life forms to exist. Through photosynthesis, plants absorb carbon dioxide, a greenhouse gas that in large amounts can affect global climate. Additionally, plants allow us to produce food to feed an expanding population, produce medicine and materials, understand environmental changes more clearly.
3. Virtually all foods eaten come from plants, either directly from staple foods and other fruit and vegetables, or indirectly through livestock or other animals, which rely on plants for their nutrition. Plants are the fundamental base of nearly all food chains because they use the energy from the sun and nutrients from the soil and atmosphere, converting them into a form that can be consumed and utilized by animals.
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                                       Factors affecting growth
1. The genotype of a plant affects its growth, for example selected varieties of wheat grow rapidly, maturing within 110 days, whereas others, in the same environmental conditions, grow more slowly and mature within 155 days.
2. Growth is also determined by environmental factors, such as temperature, available water, available light, and available nutrients in the soil. Any change in the availability of these external conditions will be reflected in the plants growth.
3. Biotic factors are also capable of affecting plant growth. Plants compete with other plants for space, water, light and nutrients. Plants can be so crowded that no single individual produces normal growth. Optimal plant growth can be hampered by grazing animals, suboptimal soil composition, lack of mycorrhizal fungi, and attacks by insects or plant diseases, including those caused by bacteria, fungi, viruses, and nematodes.
4. Some plants may be organized according to their seasonal growth pattern: annual plants live and reproduce within one growing season, biennial plants live for two growing seasons and usually reproduce in second year, and perennial plants live for many growing seasons and continue to reproduce once they are mature. These designations often depend on climate and other environmental factors; plants that are annual in alpine or temperate regions can be biennial or perennial in warmer climates.
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One of the main conditions of normal plant growth …