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O-level Biology: Nutrition

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O-level Biology: Nutrition
« on: September 08, 2014, 09:42:58 AM »
Nutrition Nutrition is taking in nutrients  which are organic substances and mineral ions, containing raw materials and  energy for growth and tissue repair, absorbing and assimilating them. Nutrition  is one of the characteristics of living organisms. All organisms do it, they do  it to obtain energy for vital activities and raw materials needed for growth and repair.
Every Individual needs to take in a certain amount of each nutrient daily, depending on their age, size, sex and activity.
There are 7 Types of nutrients,  these are:
  • Carbohydrates
  • Proteins
  • Fats
  • Vitamins
  • Minerals
  • Roughages
  • Water
  Carbohydrates, proteins, fats and vitamins are all organic substances. This means that they are made by living organisms (plants) and  contain carbon atoms in their structures. Plants make organic substances from  inorganic materials like carbon dioxide, water and inorganic minerals. Animals  are unable to do this.
  Carbohydrates:  This nutrient is an organic compound composed of carbon,  hydrogen and oxygen.
 Function: It is used as an energy resource, essential in respiration to release energy.
 It is  used in creating the cellulose, the substance forming cell walls of plant cells.
Carbohydrates are 3 types:
  • The smallest and simplest  form
  • Water soluble
  • Chemical formula C6H12O6
  • Examples: Glucose-Fructose-Galactose
  • Sources:  Fruits-Honey
  • Each molecule consists of two Monosaccharide  joined together
  • Water soluble
  • Examples: Lactose-Sucrose-Maltose
  • Sources: Table sugar- Milk
  • Each molecule  has many joined  monosaccharide forming a long chain.
  • Insoluble in water
  • Examples: Starch-Glycogen-Cellulose
  • Sources: Bread-Potatoes-Pasta, Cellulose in plant cells and Glycogen  in livers.
Monosaccharide and Disaccharides are sugars, they are  reducing for Benedict’s reagent, except for the disaccharide sucrose, it is  non-reducing.
Polysaccharides are not considered as sugars and don’t have  a sweet taste. Excess polysaccharides are stored in the liver and muscles.
 Lipids (Fats):  These are composed of carbon, hydrogen and oxygen. But their  ratios are different than that of carbohydrates. One fat molecule is made of a glycerol unit and three molecules of fatty acids.
Fats are essential in a diet because they are needed to:
  • Release high amounts of energy
  • Make cell membranes
  • Store them under the skin to insulate heat.
  • Forming a layer of fats around organs to protect them from damage
  • Storing energy (better than glycogen)
When fats are respired, they produce about twice as much  energy as carbohydrates.
   Proteins:  These are also organic compounds; they contain the elements  Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Phosphorus or Sulfur.
 A molecule of protein is a long chain of simpler units  called amino acids. 
These amino acids are linked together by what's called  “peptide bond”.
Types of protein:
  • Animal Protein: It contains the most biological value because it contains all essential amino acids (Meat, Milk, Fish, Eggs etc).
  • Plant Protein: It contains a lower biological value to humans because it contains fewer essential amino acids (Cereals, Peas, Beans etc).
Needs of proteins:
  • Making and new body cells
  • Growth and repair
  • Making enzymes (they are proteins in nature)
  • Build up hormones
  • Making antibodies
Although proteins are needed in high amounts, the body will  only absorb as much as needed, so excess protein is delaminated in the liver and  excreted as urea.
Vitamins: These are organic, soluble substances that should be present  in small amount in our diets, they are very important though.
 Most of the amount of vitamins in our bodies was taken in as nutrients, the body its self can only make few Vitamins, so we have to have to  get them from organisms that make them, such as plants.
 Each type of Vitamin helps in chemical reactions that take  place in our cells.
 Types Of Vitamins: Vitamin C: This is present in most fruits and vegetables specially citrus fruits like lemon and oranges, however, it is damaged by heating so it these foods have no value of Vitamin
C if they are eaten cooked.
Vitamin C is essential for the formation of Collagen, a protein that functions as cementing layer between cells, Vitamin C also increases immunity.
Vitamin D: This is present in fish oils, egg yolk, milk and liver. Unlike Vitamin C, Vitamin D is made by animals as well as plants, this occurs when the skin is exposed to the Ultra Violet Rays of the sun. Vitamin D plays a big role in absorbing Calcium from the small intestine and depositing it in bones. So it is responsible for having healthy bones.
   Minerals (Inorganic Ions):  These are a lot of types, each needed in small quantities.  Iron and Calcium are the most important minerals, and they are needed in higher amounts.
Types Of Minerals:
  • Calcium: This mineral is needed for the formation of bones and teeth as they are made of calcium salts, it also helps in blood clotting and transmission of nerve impulses. Good sources of the mineral Calcium are milk, dairy products and hard water.
  • Iron: This mineral is needed for the formation of the red pigment haemoglobin which is essential for the transport of oxygen around the body in red blood cells. Good sources of Iron include red meat specially liver and green leafy vegetables.
   Roughages (Fibre):  Although roughages are not even  absorbed by the body, they are a very important nutrient in our diet. Roughages  are mostly cellulose, which is the substance that makes up the cell walls of  plants we eat. We humans, have no enzyme that could digest cellulose, that  means that roughages enter the body from the mouth, go through the digestive system, and out through the anus unchanged. But as it goes through the digestive system, roughages take space in the gut to give the gut muscles  something to push against, this process of pushing the food through the gut is  called peristalsis, without roughages peristalsis is very slow and weak. Quick  and strong peristalsis means that food stays in the alimentary canal for a  shorter period, this prevents harmful chemicals of certain foods from changing  the DNA of cells of the alimentary canal causing cancer, so roughages also  helps stay away from cancer. Roughages are found in leafy vegetables.
About 70% of your weight is water. Water is perhaps a very  essential nutrient we should take in. The functions of water include:
  • As a solvent which reactants of metabolic reactions are  dissolved in.
  • It makes up most of the blood plasma which red blood cells,  nutrients, hormones and other materials are carried in.
  • It helps in lowering the body temperature in hot conditions by secreting it as sweat on the skin, the sweat evaporates using heat energy  from the body, thus lowering the temperature.
Balanced Diet:  A perfect diet contains all of the  nutrients in reasonable proportions, not too much and not too little. The  perfect diet should also contain energy as much as the total energy used by the  individual.
 Unbalanced Diet (Malnutrition): Malnutrition is eating inadequate proportions of food. In other words, an unbalanced diet means it is rich in a nutrient and low in  another, or even lacking of a substance. There are lots of effects of  malnutrition, such as starvation, obesity or deficiency diseases.
   Starvation: Starvationis a severe reduction in vitamin, nutrient and energy intake. It is the most extreme form of malnutrition. In humans, prolonged starvation can cause permanent organ damage and eventually, death. The term inanition refers to the symptoms and effects of starvation. In case of starvation the body tends to feed on its own self.  When the glucose level is decreased in the body, the liver breaks down fats to  respire for energy, when the body is out of fats, it starts respiring proteins  from the muscles to release energy.
   Obesity: is the opposite of starvation.  It is eating too much of every nutrient, especially carbohydrates and fats.  Obesity doesn’t strike alone, it brings with it several other diseases such as  high blood pressure, cardiac diseases, diabetes, stress on joints and bones as well as other psychological issues like low self esteem and lack of confidence. To prevent obesity, you have to control your carbohydrates and fats intake and exercise regularly.
Another consequence of malnutrition is deficiency diseases.
 These are results of a certain nutrient in the diet:
  • Scurvy is the deficiency disease of vitamin C. Its symptoms  include bleeding gums.
  • Rickets is the deficiency disease of both Vitamin D and  Calcium. Bones are made of calcium which Vitamin D helps in depositing in the  bones, if any of both is lacking in the diet, rickets is developed.
  • Anemia is the deficiency disease of iron. The amount of  haemoglobin decreases causes short breath and tiredness.
  • Kwashiorkor affects children whose diets are lacking in  protein. It causes weakness and tiredness.
   Special Needs:  There are certain types of people whose diets need to be  different to normal ones.
 Such as pregnant women, breast-feeding women or  children going through puberty.
 Pregnant Women:  The diet of a pregnant woman needs to be very rich of  certain nutrients because she is not only feeding her self, she is feeding her baby as well. In order for the fetus to develop well, it needs extra Protein,  Iron, Calcium and Vitamin D. Proteins are to develop the tissues of the fetus,  Iron is to make haemoglobin and to store in the liver, while Calcium and  Vitamin D are to develop the baby’s bones.
 Breast-Feeding Women (Lactation):  Lactation means the production of breast milk. After  pregnancy, the mother breast-feeds the baby for about 6 months or more. Breast  milk needs to be high in Proteins, Calcium, and Vitamins to guarantee a healthy  growth for the infant.
 Growing Children (Passing Puberty):  At some point, each child gets a growing spurt. This is a  very high growth rate that increases the child’s size and mass in a short  period of time. A growing child’s diet needs extra Proteins to develop cells and enzymes because their metabolic rate is higher, Calcium and Vitamin D to  develop bones and Iron to make hemoglobin.
 Food Additives:  These are chemical compounded added to foods by the  manufacturer because they have some benefits such as increasing the lifespan, prevent rotting etc.
 Most food additives are good, such as ones that add colors  or flavors to foods. But there are others which have been proven hazardous to humans.
Good food additives include flavorings and colorings which  are used to make the food more appealing, antioxidants which prevent foods from combining with oxygen and rot, and stabilizers which stops foods like ice-cream  from separating into water and fatty components.
Food preservatives though, are a widely used food additives  which increase the lifespan of foods, making it cheaper to store and transport.  However, scientists claim that some preservatives contain nitrites which  combine with chemicals making a substance (nitrosamines) that causes cancer in  animals.
Food Additives[/t][/t]
  • Prevents rotting
  • Improve color
  • Improve flavor
  • Keeps texture
  • Increases lifespan
  • Prevents poisoning
  • Allergic reactions
  • Cause hyperactivity
  • Damages liver/kidney
  • Carcinogenic
  • Makes bad food look good
    Microorganisms And Food Industry:  Production of Single Celled Protein (Mycoprotein):  Mycoprotein is a protein made from microscopic fungus.  Humans need large amounts of proteins in their diets, in some poor areas,  sources of proteins like meat are unaffordable, mycoprotein is used.
The process takes place in a sterilised container called fermenter. The micro-organisms are grown in the fermenter and supplied with air which  contains oxygen for aerobic respiration, ammonia as a source of nitrogen to be  used by the micro-organisms to make proteins, and methanol which contains  carbon for the formation of carbohydrates.
Advantages of mycoproteins are that it is cheaper than any  source of protein but equal in value, and that it contains much less fats and more roughages and carbohydrates
 Production Of Yoghurt:
  • Milk is sterilised by boiling
  • Certain types Bacteria are added to the milk
  • The milk is kept warm to provide best conditions for  bacteria growing
  • Bacteria respire producing lactic acid, thickening the milk  and giving it the pleasant flavour
  • Yoghurt is cooled and flavours or fruits could be added.
   Food Tests:  Starch Test:
  • Put sample in a test tube
  • Add water to make it a solution
  • Add iodine solution
  • Is starch is present the solution changes colour from  yellowish brown to Blue Black.
  • If starch is not present the solution remains yellowish  brown.
Reducing sugars (carbohydrates) test:  Note: This test is only applicable on all sugars  (monosaccharide and disaccharide) EXCEPT FOR SUCROSE.
  • Add sample to a test tube
  • Add Benedict’s Reagent
  • Put test tube in water bath for heating
  • If reducing sugars are present the solution turns from  blue to yellow,orange,red (fire colours)
  • If reducing sugars are not present the solution remains  blue.
Proteins Test:
  • Put sample in a test tube
  • Add water to make a solution
  • Add Buiret Reagent
  • If proteins are present in the solution turns Purple
  • If proteins are not present the solution remains blue.
Note: Biuret Reagent is blue in colour and made of copper  sulphate and a small amount of sodium hydroxide.
 Fats Test:
  • Add sample to a test tube
  • Add ethanol
  • Add water and shake well
  • If fats are present the solution becomes unclear
  • If fats are not present the solution remains clear
General Table:
Iodine sol.
Yellow / Brown
Blue / Black
Yellow / Brown
Red (fire)
Biuret reagent



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