最新大学英语四级模拟试题附答案Word格式.docx

1、2.大学生考证的利弊3.考证面前，我的选择The Popularity of Getting Certificates on CampusPart Reading Comprehension （Skimming and Scanning） （15 minutes） In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1.For questions 1-7, choose the best answer from the fou

2、r choices marked A）, B）, C） and D）. For questions 8-10, complete the sentences with the information given in the passage.Main Energies for the BodyA balanced diet is one that provides an adequate intake of energy and nutrients for maintenance of the body and therefore good health. A diet can easily

3、be adequate for normal bodily functioning, yet may not be a balanced diet.CarbohydratesCarbohydrates 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

4、 as fats in the cells, although carbohydrate is the first source of energy in the body. An average adult requires about 12,000kJ of energy a day, most of this is supplied by the respiration of carbohydrates in the cells.Carbohydrates are used principally as a respiratory substrates, i.e. to be oxidi

5、zed 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 car

6、bohydrates, 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 mobilized and used as an energy source.ProteinsProtein is not a direct source of energy in the body, it is used primaril

7、y for growth and repair of body tissues while remaining an energy source as a last resort. Proteins fulfill a wide variety of roles in the body. They are broken down in the stomach and intestines to amino acids which are then absorbed. The body can only form 8 amino acids to build proteins from, the

8、 diet must provide Essential Amino Acids （EAAs） which are synthesized into proteins which can be structural, i.e. collagen in bone, keratin in hair, myosin and actin in muscle; metabolic enzymes, hemoglobin, protective antibodies and communicative hormones.Sources of protein include meat, fish, eggs

9、 and pulses. The diet needs to provide 8 EAAs as the body is unable to synthesis proteins without these molecules. 2 other amino acids are synthesized from EAAs so if the diet lacks the original EAAs these other two will not be present either. Phenylalanine is converted to tyrosine and methionine is

10、 converted to cysteine. Cells draw upon a pool of amino acids for protein synthesis which either come from dietary protein digested and absorbed in the gut and the breakdown of body protein such as muscle. However, unlike fats and carbohydrates there is no store of amino acids for cells to draw on,

11、any amino acid in excess of immediate bodily requirements is broken down into urea and excreted. It is therefore important to maintain the dietary intake of protein everyday. If the body lacks protein, muscle wasting occurs as muscle is broken down.If protein is lacked in a diet a person develops kw

12、ashiorkor which is caused when high levels of carbohydrates are eaten to overcome the lack of protein in the diet. One symptom of kwashiorkor is the abnormal collection of fluid around the abdomen due to the lack of protein in the blood. The body cannot retain water by osmosis and fluid accumulates

13、in tissues causing them to become waterlogged.Vitamin CategoriesVitamins cannot be synthesized by the body so must be supplied by diet. Vitamins have no common structure or function but are essential in small amounts for the body to be able to utilize other dietary components efficiently.Vitamins fa

14、ll into two categories, fat soluble vitamins such as vitamin A, D, E and K which are ingested with fatty foods and water soluble vitamins such as the B group vitamins and vitamin C. Vitamins are known as micronutrients because only small quantities are required for a healthy diet, in fact fat solubl

15、e vitamins can be toxic in high concentrations, for example the body stores vitamin A, or retinol, in the liver as it is toxic if kept in high concentrations in the blood stream, a dose of more than 3300mg of vitamin A can be considered toxic. Water soluble vitamins such as vitamin C and B groups vi

16、tamins can be excreted in the urine if in excess in the diet.Vitamins AVitamin A is essential to the proper functioning of the retina in the eye and the epithelial tissues. A lack of vitamin A results in dry, rough skin, inflammation of the eyes, a drying or scarring of the cornea - xerophthalmia, w

17、hich occurs when the secretion of lubricating tears is stopped, the eyelids become swollen and sticky with pus. Mucous surfaces of the eye may become eroded allowing infection to set in, leading to ulceration and destruction of the cornea. Night blindness - an inability to see in dim light can also

18、occur. Rod cells in the retina of the eye detect light of low intensity, they convert vitamin A into a pigment, rhodopsin, which is bleached when light enters the eye. Rod cells resynthesis rhodopsin, but if there is a deficiency of the vitamin, rod cells can no longer function and the result is nig

19、ht blindness. Epithelial cells use retinol to make retinoic acid, an intracellular messenger used in cell differentiation and growth. Without retinoic acid epithelial cells are not maintained properly and the body becomes susceptible to infections, particularly measles and infections of the respirat

20、ory system and gut.Xenophthalmia is common among children whos diets consist of mainly cereals with little meat or fresh vegetables, this is common in Indonesia, Bangladesh, India and the Philippines.Vitamins DVitamin D, or calciferol, is another fat soluble steroid vitamin which functions to stimul

21、ate calcium uptake from the gut and its deposition in bone. vitamin D acts as a hormone when converted by enzymes in the gut and liver into an active form of active vitamin D, which stimulates epithelial cells in the intestine to absorb calcium. vitamin D is therefore essential in growing childrens

22、diets to enable the growth of strong bones. Without adequate amounts of vitamin D children can develop rickets, which is the deformation of the legs caused when they lack calcium to strengthen the bones. In adults a lack of vitamin D in the diet can lead to osteomalacia, a progressive softening of t

23、he bones which can make them highly susceptible to fracture.Vitamin D is made by the body when exposed to sunlight and is stored in the muscles, however, if the skin is rarely exposed to the sunlight or is dark little vitamin D is produced. Foods such as eggs and oily fish are all rich in vitamin D.

24、Vitamins KVitamin K, phylloquinone, is found in dark green leafy vegetables such as spinach and kale. It is a fat soluble vitamin which is involved in the clotting process of blood. In the intestines bacteria synthesize a number of important clotting factors which need vitamin K. Without vitamin K c

25、uts can fail to heal and internal bleeding can occur.Vitamins CVitamin C is a water soluble vitamin, known chemically as ascorbic acid. It is found in citrus fruits such as oranges and lemons, and also in potatoes and tomatoes. The main function of vitamin C is the formation of connective tissues su

26、ch as collagen. It is also known to be an antioxidant which helps to remove toxins and aids the immune system. A lack of vitamin C leads to Scurvy, a condition experienced by sailors on long journeys when they did not have fruit in their diets. Scurvy causes painful, bleeding gums. As vitamin C is w

27、ater soluble, it is not toxic in high doses as it can be excreted in the urine, very high doses can however cause diarrhea.Vitamins BB group vitamins have a wide range of roles acting as co-enzymes in metabolic pathways. They are found in most plant and animal tissues involved in metabolism, therefo

28、re foods such as liver, yeast and dairy products are all rich in B group vitamins. Deficiency of B group vitamins include dermatitis, fatigue and malformation of red blood cells.1. An adult needs about 12,000kJ of energy a day from _.A. the cell B. the respiring process of carbohydratesC. fats in th

29、e cell D. a balanced diet2. Carbohydrates are ultimately absorbed into cells in the process of _.A. digestion B. respirationC. oxidization D. mobilization3. The Essential Amino Acids which build part of proteins can be obtained from_.A. stomach B. body tissuesC. the body D. the diet4. The ultimate c

30、ause of kwashiorkor is lack of _.A. protein B. carbohydratesC. vitamins D. diet5. Vitamins are called “micronutrients” in that _.A. excessive fat soluble vitamins can be excreted in the urine B. the body only requires small amount of vitaminsC. a dose of 3300mg of vitamins can be considered toxic D.

31、 the high concentrations of water soluble vitamins are toxic6. Night blindness is a disease normally caused by lack of _.A. fat soluble vitamins B. water soluble vitaminsC. vitamin A D. innate disability7. The main function of vitamin D is to prevent adults from _.A. the growth of strong bones B. fractureC. a progressive softening of the bones D. calcium uptake from the gut8. Although the human body produces vitamin D normally, i