2009年6月英语六级考试快速阅读的实战练习5
<p> <span word="A">A</span> <span word="balanced">balanced</span> <span word="diet">diet</span> <span word="is">is</span> <span word="one">one</span> <span word="that">that</span> <span word="provides">provides</span> <span word="an">an</span> <span word="adequate">adequate</span> <span word="intake">intake</span> <span word="of">of</span> <span word="energy">energy</span> <span word="and">and</span> <span word="nutrients">nutrients</span> <span word="for">for</span> <span word="maintenance">maintenance</span> <span word="of">of</span> <span word="the">the</span> <span word="body">body</span> <span word="and">and</span> <span word="therefore">therefore</span> <span word="good">good</span> <span word="health">health</span>. <span word="A">A</span> <span word="diet">diet</span> <span word="can">can</span> <span word="easily">easily</span> <span word="be">be</span> <span word="adequate">adequate</span> <span word="for">for</span> <span word="normal">normal</span> <span word="bodily">bodily</span> <span word="functioning">functioning</span>, <span word="yet">yet</span> <span word="may">may</span> <span word="not">not</span> <span word="be">be</span> <span word="a">a</span> <span word="balanced">balanced</span> <span word="diet">diet</span>.</p><p> <span word="Carbohydrates">Carbohydrates</span></p><p> <span word="Carbohydrates">Carbohydrates</span> are a rapid source of energy, they are the bodys fuel. The bulk of a balanced diet should be made from carbohydrates. If eaten in an excess of the dietary requirements carbohydrates are easily stored as fats in the cells, although carbohydrate is the first source of energy in the body.</p><p> <span word="An">An</span> <span word="average">average</span> <span word="adult">adult</span> <span word="requires">requires</span> <span word="about">about</span> 12,000<span word="kJ">kJ</span> <span word="of">of</span> <span word="energy">energy</span> <span word="a">a</span> <span word="day">day</span>, <span word="most">most</span> <span word="of">of</span> <span word="this">this</span> <span word="is">is</span> <span word="supplied">supplied</span> <span word="by">by</span> <span word="the">the</span> <span word="respiration">respiration</span> <span word="of">of</span> <span word="carbohydrates">carbohydrates</span> <span word="in">in</span> <span word="the">the</span> <span word="cells">cells</span>.</p><p> <span word="Carbohydrates">Carbohydrates</span> are used principally as a respiratory substrates, i.e. to be oxidised to release energy for active transport, macromolecule synthesis, cell division and muscle contraction. Carbohydrates are digested in the duodenum and ileum and absorbed as glucose into cells. Sources of carbohydrates such as starch are rice, potatoes, wheat and other cereals. Sugars are also carbohydrates, sources of sugars are refined sugar - sucrose, which is a food sweetener and preservative and fruit sugars - fructose. If the diet lacks carbohydrate stores of fat are mobilised and used as an energy source.</p><p> <span word="Proteins">Proteins</span></p><p> <span word="Protein">Protein</span> <span word="is">is</span> <span word="not">not</span> <span word="a">a</span> <span word="direct">direct</span> <span word="source">source</span> <span word="of">of</span> <span word="energy">energy</span> <span word="in">in</span> <span word="the">the</span> <span word="body">body</span>, <span word="it">it</span> <span word="is">is</span> <span word="used">used</span> <span word="primarily">primarily</span> <span word="for">for</span> <span word="growth">growth</span> <span word="and">and</span> <span word="repair">repair</span> <span word="of">of</span> <span word="body">body</span> <span word="tissues">tissues</span> <span word="while">while</span> <span word="remaining">remaining</span> <span word="an">an</span> <span word="energy">energy</span> <span word="source">source</span> <span word="as">as</span> <span word="a">a</span> <span word="last">last</span> <span word="resort">resort</span>. <span word="Proteins">Proteins</span> <span word="fulfill">fulfill</span> <span word="a">a</span> <span word="wide">wide</span> <span word="variety">variety</span> <span word="of">of</span> <span word="roles">roles</span> <span word="in">in</span> <span word="the">the</span> <span word="body">body</span>. <span word="They">They</span> <span word="are">are</span> <span word="broken">broken</span> <span word="down">down</span> <span word="in">in</span> <span word="the">the</span> <span word="stomach">stomach</span> <span word="and">and</span> <span word="intestines">intestines</span> <span word="to">to</span> <span word="amino">amino</span> <span word="acids">acids</span> <span word="which">which</span> <span word="are">are</span> <span word="then">then</span> <span word="absorbed">absorbed</span>. <span word="The">The</span> <span word="body">body</span> <span word="can">can</span> <span word="only">only</span> <span word="form">form</span> 8 <span word="amino">amino</span> <span word="acids">acids</span> <span word="to">to</span> <span word="build">build</span> <span word="proteins">proteins</span> <span word="from">from</span>, <span word="the">the</span> <span word="diet">diet</span> <span word="must">must</span> <span word="provide">provide</span> <span word="Essential">Essential</span> <span word="Amino">Amino</span> <span word="Acids">Acids</span> <span word="which">which</span> <span word="are">are</span> <span word="synthesised">synthesised</span> <span word="into">into</span> <span word="proteins">proteins</span> <span word="which">which</span> <span word="can">can</span> <span word="be">be</span> <span word="structural">structural</span>, <span word="i">i</span>.<span word="e">e</span>. <span word="collagen">collagen</span> <span word="in">in</span> <span word="bone">bone</span>, <span word="keratin">keratin</span> <span word="in">in</span> <span word="hair">hair</span>, <span word="myosin">myosin</span> <span word="and">and</span> <span word="actin">actin</span> <span word="in">in</span> <span word="muscle">muscle</span>; <span word="metabolic">metabolic</span> <span word="enzymes">enzymes</span>, <span word="hemoglobin">hemoglobin</span>, <span word="protective">protective</span> <span word="antibodies">antibodies</span> <span word="and">and</span> <span word="communicative">communicative</span> <span word="hormones">hormones</span>.</p>
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