1、1. A 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 be adequate for normal bodily functioning, yet may not be a balanced diet.CarbohydratesCarbohydrates are a rapid source of energy, they are the
2、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.An average adult requires about 12,000kJ of energy a day,
3、 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 oxidised to release energy for active transport, macromolecule synthesis, cell division and muscle contraction. Carbohydrates are digested in the duod
4、enum 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 la
5、cks carbohydrate stores of fat are mobilised and used as an energy source.ProteinsProtein is not a direct source of energy in the body, it is used primarily 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.
6、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 diet must provide Essential Amino Acids (EAAs) which are synthesised into proteins which can be structural, i.e. collagen in bone, keratin in ha
7、ir, myosin and actin in muscle; metabolic enzymes, hemoglobin, protective antibodies and communicative hormones.Sources of protein include meat, fish, eggs 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 synthe
8、sised 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 converted to cysteine. Cells draw upon a pool of amino acids for protein synthesis which either come from dietary protein digested and absorbed
9、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, any amino acid in excess of immediate bodily requirements is broken down into urea and excreted. It is therefore important to maintain the dietar
10、y 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 kwashiorkor which is caused when high levels of carbohydrates are eaten to overcome the lack of protein in the diet. One symptom of kwashiorkor is
11、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 in tissues causing them to become waterlogged.VitaminsVitamins cannot be synthesised by the body so must be supplied by diet. Vitamins have no co
12、mmon structure or function but are essential in small amounts for the body to be able to utilise other dietary components efficiently.Vitamins fall 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 gro
13、up vitamins and vitamin C. Vitamins are known as micronutrients because only small quantities are required for a healthy diet, in fact fat soluble 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 concentratio
14、ns 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 vitamins can be excreted in the urine if in excess in the diet.Vitamins carry out a wide range of functions and prevent specific deficiency diseases. A diet
15、that lacks a certain vitamin is not a balanced diet, vitamins have vital roles in the maintenance of a healthy body.An example of a deficiency is when the diet does not contain enough, or any vitamin A. Vitamin A is found in some animal foods such as milk, eggs, liver and fish liver oils, related co
16、mpounds such as carotenoids e.g. b carotene, are in a wide variety of vegetables such as cabbages, carrots and spinach.Vitamin 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 dry
17、ing or scarring of the cornea - xerophthalmia, which 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 blindn
18、ess - an inability to see in dim light can also 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 ce
19、lls can no longer function and the result is night 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, par
20、ticularly measles and infections of the respiratory 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.Vitamin D, or calciferol, is another fat soluble ste
21、roid vitamin which functions to stimulate 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 t
22、herefore essential in growing childrens 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 os
23、teomalacia, a progressive softening of the 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
24、and oily fish are all rich in vitamin D.Vitamin 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
25、vitamin K. Without vitamin K cuts can fail to heal and internal bleeding can occur.Vitamin 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 c
26、onnective tissues such 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 gum
27、s. As vitamin C is water soluble, it is not toxic in high doses as it can be excreted in the urine, very high doses can however cause diarrhea.B 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 metabolis
28、m, therefore 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. When we have too much of carbohydrates, they are most likely be stored as sugar units.2. In the process of di
29、gestion, carbohydrates are finally turned into cells.3. The Essential Amino Acids which build part of proteins can be formed by human body.4. The ultimate cause of kwashiorkor is lack of protein, rather than lack of carbohydrates.5. There are generally two different kinds of vitamins, they are _.6.
30、Night blindness is a disease normally caused by lack of _.7. One of the main function of vitamin D is to prevent adults from _.8. Although the human body produces vitamin D normally, it fails to do so if there is not enough _.9. The reason why vitamin C is seen as an antioxidant is that it drives _
31、out of the body.10. If you are in lack of B group vitamins, you should turn to _.2.Our galaxy is a gigantic agglomeration of stars and planets whose numbers will probably never been known. Currently we estimate this number to be about thirty billion. Scientists have estimated that the diameter of ou
32、r galaxy, if it were to be traveled, would take us about fifty thousand light years and the thickness to be about fifteen to twenty light years.We live in small part of the Milky Way Galaxy, which is referred to as a solar system. Our solar system is made up of nine planets and 31 moons, which orbit
33、 the center of galaxy. At the center of our galaxy is our Sun, which is approximately twenty-five thousand light years from our solar system.These nine major planets in order from the center are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.Mercury is the planet nearest to
34、 the Sun. As it orbits the Sun, it does not rotate, keeping the same face of the planet toward the Sun at all times. This means that one side of the planet has a continual burning day of 900 F, and the other side a continual night and a deadly cold of 450F below zero. Mercury is the fastest travelin
35、g of the nine planets making one full orbit around the Sun in only eight days. Life on mercury would be impossible. If you could live where the night meets the day and survive the extreme conditions, you would need dark goggles to protect you eyes from the extreme light. Mercury has little or no atm
36、osphere to diffuse the sunlight. You would also weigh considerable less due to the lack of gravity. A person weighting 100 pounds on Earth would weigh 27 pounds on Mercury.Looking into the night sky you will notice Venus, the brightest star in the sky, and the second planet from the Sun. Venus can o
37、nly be seen at certain times of the day either at dawn or at Sunset. In physical characteristics, Venus is most like earth with a diameter of seven thousand six hundred miles, and gravity the same as earth. It is located a distance of sixty-seven million miles from the Sun and makes one complete orb
38、it around the Sun in two hundred twenty five days. A single day on Venus can last up to two hundred and twenty five earth days due to its slow rotation. The atmosphere appears to consist of mostly nitrogen and carbon dioxide. This is due to the lack of life on the planet.The best time to view Venus
39、comes every one hundred and twenty years as it passes between the Earth and the Sun. The last time to best view it was on June 7, 2004.Earth, the third planet form the Sun is our home planet. Earth is the only planet in our solar system known to sustain life. Under the layer of atmosphere that surro
40、unds the planet we are able to provide all the necessary components to make life sustainable. Earth is the fifth larges planet in the solar system. Its diameter is just a few hundred kilometers larger than Venus. Earth rotates on its axis one complete revolution in a twenty-four hour period and orbi
41、ts the Sun in three hundred and sixty five days.Mars is the fourth planet from the Sun and is the closest neighbor to earth. Every seventeen years Mars reaches its closest point to earth in its orbit around the Sun at thirty-five million miles.Mars is a small planet that has a red glow. It makes one
42、 complete orbit around the Sun in six hundred and eighty seven days. Oxygen and water vapor have been detected in the atmosphere of Mars, and a yellowish fog and clouds move around the planet indicating that the planet has different types of weather and seasons like the earth. A single day on Mars i
43、s very much like a day on earth lasting twenty-four hours and thirty-seven minutes, however, a year on Mars is twice as long as one year on earth.Jupiter the fifth planet from the Sun gets its name from the Father of the Greek Gods. Jupiter, which orbits four hundred eighty-three million miles from
44、the Sun, is the biggest of all the planets in our solar system. It has a diameter of eighty-nine thousand miles and a volume of thirteen times that of earth. Jupiter orbits the Sun every twelve years. Its atmosphere is thousands of miles thick and is made up of mainly hydrogen. The surface temperatu
45、re is about -205F. There are no seasons on Jupiter, but it has floating clouds of ammonia and methane gas.Jupiter has a bright red distinctive spot that is more than twice as wide as Earth. This mark has astronomers puzzled because there is no reason for the bright spot due to the fact that it does
46、not receive much Sunlight. This spot enables us to see that Jupiter has a very fast rotation. One rotation is completed every ten hours. The forces placed on the planet due to this quick rotation cause the clouds at the equator to bulge like a tire, but due to the gravitational forces of the planet
47、keep the clouds from being cast into space.Saturn, even though it is the sixth planet form the Sun, it shines so brightly because of its size. Its diameter is seventy-one thousand five hundred miles. The planet itself is golden in color and is the brightest yellow star in the night sky.Saturn makes
48、one complete revolution on its axis every ten hours and takes twenty-nine and one half days to complete one orbit around the Sun. The gravitational pull of this planet is most like that of Jupiter. It has a volume that is eight hundred times that of earth, but has a volume that is one hundred times
49、lighter than earth.Saturn has two rings that surround the planet, but never touch it. They are located outside the atmosphere and above the equator. These rings are only about ten miles thick, which makes them transparent, only being seen with the use of a telescope. The ring closest to the planet is about seven thousand miles and very thin. A black band separates the inner ring from the outer ring, which is wider and brighter. It is believed that the rings are made up of crystals of ice or
