Fall 2022 Class Test Solutions on Fats and Carbohydrates – Baylor University
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Explain The Importance of Fats in The Human Body
Broadly speaking, fats have two roles in the body. First, they are essential ingredients of every cell, being vital to innumerable cell mechanisms. As such they weigh about 1% of the body's total and are not appreciably consumed during periods of starvation. That kind of consumption is limited to the second role of fats; their use as a store of energy. Weight for weight 1 lb. (0-45 kgs.) of depot fat - as it is called - will yield over twice as much energy as either 1 lb. of protein or 1 lb. of carbohydrate. The ratio, roughly 9:4, is due to the straightforward nature of the typical fat molecule. Essentially it is just a chain of carbon atoms tied, except at one end, to an unvarying series of hydrogen atoms. Except for the occasional oxygen atom at the end, there are no more; hence no water is locked up within the molecules, hence its greater capacity to act as a fuel. Water cannot serve as a fuel, and molecules rich in H2O are less effective as energy liberators when oxidized. Fortunately for creatures like the camel not only is fat such a well-compressed store of energy but when it is oxidized it also liberates water. Nature is frequently adept at gaining on both swings and roundabouts, and the camel rides on both. (The animal can also allow its body temperature to rise: thus obviating some water loss.)
Depot fat-and more about it under starvation and obesity-is not a fixed entity, like a spare tin of lard in the kitchen. However constant an abdominal outline may be, the fat within is being perpetually removed and replaced. Only about half of depot fat is stored beneath the skin. A lot is attached to the mesentery, the membrane supporting the small intestine, and a lot more is around the kidneys. Some depot fat is entirely normal; obesity is often defined as the condition where over 30% of the body weight is fat. This depot fat also acts as a good insulator due to the relative lack of blood vessels ramifying through this kind of tissue. It consists essentially of cells, which are just droplets of fat each surrounded by a thin membranous shell of protoplasm.
Unlike beef fat, and various other animal fats, human fat melts at quite low temperatures: its melting point is 63°F (17°C), or normal room temperature, and much less than body heat, as against 121°F (49 5°C) for beef fat. Although many fats that are liquid at normal temperatures are called oils, there is no distin- guishing difference; olive oil is strictly olive fat. Fats also have a low specific gravity. Consequently, fat people float in water more readily than thin This is one advantage of growing old, a time of greater fatness, for one's specific gravity decreases as the proportion of fat increases. Even thin old people have more fat in them than in their youth and therefore float more readily without the exertion of swimming.
Fat needs are very obscure. They are mainly hidden by the organic changes going on within the body. It is all very well to talk of proteins, fats, and carbohydrates as if they were entirely separate from each other, but to some extent, they can be made from each other. Potatoes only have 0.1% fat, but they are undeniably fattening: much of their carbohydrate is turned into fat by the body. Similarly, some fat can be turned into carbo- hydrate and many proteins can be turned into sugar. However, although both carbohydrates and fat can go some way towards forming proteins, the essential amino-acids already referred to are essential to the formation of new proteins; the fats and carbo- hydrates cannot do all the conversion by themselves.
Such interchangeability complicates the issue of dietary fat needs. Certainly, some mammals survive on outstandingly little fat, and the human species as a whole is remarkable in its ability to eat either a little or a lot of it. In Britain, the average fat intake is 4 ozs. (113 gms.) per person per day. (One should perhaps remember again that wartime ration of 8 ozs. (227 gms.) of fat a week, and remember the enthusiasm of the medical profession for a war-time diet to be feasible once again.) A Kikuyu of Eastern Africa eats less than a quarter of this, while an Eskimo eats on average double the British amount. Extra fat is not always beneficial if the diet is too one-sided: too great an intake of fat with insufficient carbohydrates in the diet can lead to ketosis, a dangerous affliction that is a kind of internal poisoning. The general opinion on fat intake is that, whereas a high carbohydrate intake can do much to maintain high-fat stores, it is probably necessary to eat at least a small amount of fat, particularly if it contains what are called unsaturated fats. (They are called unsaturated because not every carbon atom has its full potential of hydrogen atoms around it; instead, there are some double bonds in the carbon chain.) Quite apart from actual fat needs, but integral to them, is the need for vitamins. Animal fats to a large degree, and vegetable oils to a smaller degree, are rich in vitamins A, D, and E.
There is next to no difference between animal and vegetable fats in their energy values, but there is an eternal dispute over their respective merits. The principal villain is alleged to be cholesterol, a sterol (after the Greek for solid. As chole is Greek for bile, the word cholesterol means solid bile or gall stone) which is found in animal fats and which can also be manufac tured by the body. Each of us has about 6 oz. (170 gms.) of cholesterol within us at the best of times. Gall stones are largely cholesterol (up to 97%) and evidence of an association has sometimes been found between high cholesterol levels in the blood and the incidence of heart disease and arterial degenera- tion. However, an association between two factors does not indicate a causal relationship; the cholesterol may well be in the blood because of some breakdown in fat metabolism which is also affecting the arteries. Whether cause or effect the proportion of cholesterol is at the center of the storm and of countless contradictory statements about animal and vegetable fats.
In 1961 the American Heart Association said: "There is no final proof that changing the fat content of the diet will prevent cardiovascular disease...In 1965 the same Association turned round and said 'atherosclerosis could originate as a result of high-fat diets': it recommended increased consumption of vegetable oils and a decrease in foods and fats rich in cholesterol. Conversely, only a few months beforehand, a professor of food science from California had said that too great a reliance on vegetable oils would greatly increase aging and decay. Conversely again, the National Academy of Sciences produced a report in 1966 recommending no general decrease in fat consumption: 'Any drastic reduction... would alter the body metabolism in unpredictable, possibly deleterious ways." With such a complex and little-understood subject as the ingestion of polyunsaturated fatty acids, triglycerides, and all the rest, and with the equally tricky problem of arterial decay, it is a small wonder that no hard and fast answer can be given. In summary, therefore, cholesterol had a bad press in the late 1950s, but its reputation is now better, vegetable oils boomed in the 1950s and have done well ever since. However, there is a see-saw character to the perpetual skirmishing between the animal fat brigades and the contingents supporting vegetable oils. Sometimes butter forges ahead, follow- ing a medical report in its favor or just the whim of the buying public. Sometimes margarine does better for similar reasons (or the lack of them) and no doubt this mercurial warfare will continue.
Where Are Fats Found?
Roughly speaking, meats have a comparable weight percentage of fat and protein, although something like lean pork has rather more protein and something like rump steak has rather more fat. Rabbit, duck, and chicken all have extremely modest amounts of fat in their meat. Fish vary considerably, with eel, salmon, and herring having quite a bit, with cod and haddock having virtually none at all. Human and cow milk has a little, and all the condensed milk and cheeses have far more. Egg white has scarcely any (about 1%), and egg yolk has a lot (over 30%). Substances like lard, dripping, olive oil, and fish liver oil have 100%; butter and margarine have less as they contain some water. Most of the cereals are extremely low in fat, and the sugars, jams, treacles, and honey have none. Nuts have a lot, Brazil (70%), hazel (62%), walnut (60%), and peanuts (48%). Fruit and vegetables have less than 1% fat.
Discuss The Structure and Importance of Carbohydrates in Humans
These include all sugars and starches. Chemical they are built up of carbon, hydrogen, and oxygen, and they follow a general ruling: there are two hydrogen atoms for each atom of oxygen - as in water. The general formula can be written as Cx (H2O)y and this is called a hydrated carbon or carbohydrate.
British people eat carbohydrates, fats, and proteins roughly in the proportion of 4:1:1. This means, bearing in mind that a given weight of fat yields over twice as much energy as a given weight of either protein or carbohydrate, that 55% of British energy comes from carbohydrate. Many other societies, because of the universal cheapness of carbohydrates over fats and proteins, eat an even greater proportion of sugars and starches. It is customarily that carbohydrate should not supply more than 66% of anyone's energy, but it frequently does so.
The total weight of carbohydrates within an lb. (70 kg.) man is about 13 oz. (368 gms.), with some two-thirds of this being in the muscles. Carbohydrate is steadily being used by the body, but can only be stored to a very limited degree. Within thirteen hours of the last replacement, even assuming a sedentary occupation, all available supplies have been consumed, and fat stores will be called upon to bridge the gap. The body's method of dealing with the various forms of ingested carbohydrates is to try and turn them all into glucose. No starches can be absorbed into the blood: the enzymes amylase and maltase must work on them to produce glucose. The sucrose of cane or beet sugar is turned by sucrase into glucose and fructose, and the fructose is turned into glucose both by the liver cells and other cells. The lactose of milk is turned by lactase into glucose and galactose, but the liver soon turns the galactose into glucose.
There is a stubborn persistence in the body's attitude towards carbohydrates. Glucose is always the result. Unfortunately, the ability does not always match this persistence. A notable exception is a cellulose. Was the human body able to absorb this sugar the world would not go short of carbohydrates because cellulose is omnipresent in the vegetation all around us. We do cat cellulose in large quantities with leafy vegetables and most forms of plant food, but nothing happens to it and the undigested raw material is expelled in the feces. It may have suffered somewhat from decomposition by bacteria, but they have not had time to break it down into a form that human enzymes can work upon. The greater length or capacity or complexity of the herbivore's alimentary canal permits the greater opportunity for the bacteria, and therefore absorption of the valuable glucose locked within cellulose. Some human beings claim to have the key and eat a lot of grass, and possibly they do extract some nourishment from their lawn mowings; but a human being is, in general, incapable of benefiting from the universality of cellulose. He can starve in a forest of vegetative profusion.
There is an argument that cellulose supplies beneficial roughage. No such argument can be applied to refined sugars which form an increasingly large lump of our diet. Sugars have been receiving bad notices for quite a while. A writer in The Lancet in 1964 said 'the refining of sugar may yet prove to have been a greater tragedy for a civilized man than the discovery of tobacco. Refined sugar used to be listed with spices as a rare and expensive delicacy. Colonization of the new world with cheap labor from the old led to huge sugar cane plantations, and by 1837 the average consumption of refined sugar in Britain had risen to 20 lbs. (9 kgs.) per man per year (or about an ounce a day). By 1850 it was 30 lbs. (13.6 kgs.) per man per year, by 1900 82 lbs. (37-2 kgs.), by 1936 100 lbs. (45-4 kgs.)- and then came the war with its enforced ration of only 26 lbs. (11-8 kgs.) per man per year, but by 1961 it was up to 118 lbs. (53-5 kgs.) (over 5 ozs. (142 gms.) a day) and it is now even higher. In the United States, the recent rise has been steeper still, going up 120% in the past seventy years.
In 1964, Professor John Yudkin and Mrs. Janet Roddy published an exceptionally important paper entitled 'Levels of Dietary Sucrose in Patients with Occlusive Arteriosclerotic Disease. For years the fats had been harangued for their suspected role in arterial disease, and for years the sugars had been relatively free of such insinuations. The joint paper presented evidence that "sugar rather than fat is responsible', and it added that sugar was the more likely culprit on both evolutionary and historical grounds Not only had the authors discovered evidence of an association between high sugar intake and arterial and heart disease but also the increasing consumption of sugar mirrored the increasing incidence of cardiovascular diseases. The rise in fat consumption where such a rise even exists - is much less positive than the meteoric rise in sugar intake.
Many authors supported Yudkin and Roddy with similar findings of their own. Various others (for such is the meat and drink of scientific argument) took issue either with the paper's conclusions or with how the evidence had been collected. All in all, with sugars now indicted, with fats still criticized, with protein always expensive, and with any form of gluttony deplored, the latest revelations add weight to a remark made by Alistair Cooke about the United States Food and Nutrition Board. He pictured them 'haunted by the fear that someone, somewhere, may be happy eating'.
Where Do We Find Carbohydrates?
Meats, in general, do not possess any, but there is some in the liver, and quite a bit in such artifacts as pork pies, sausages, and fish paste. Milk is about 5% carbohydrate; therefore, by weight, the condensed and dried milk possess much greater percentages of carbohydrates, although the cheeses either contain the same amount as milk or less. Egg contains a little (less than 5%) and chocolate a lot (some 55% on average). Of course, the cereals contain massive amounts, with white flour being 75% carbohydrate, rice even more, and sago and tapioca more still. Sugar is 100% carbohydrate, but brown sugars contain 2% or so of impurities, such as a few minerals and possibly some vitamins which do not contribute any significant advantages to a normal diet. Nuts all contain carbohydrates. So do all fruits and vegetables it is their greatest constituent after water. As a generalization, albeit with exceptions, starvation happens in the world when carbohydrate supplies are exhausted, and malnutrition happens when carbohydrate is available but either protein or fat is not.