Disclaimer: Due to unforeseen difficulties, we have had to take down the images on this notes page. They will be replaced shortly. We apologise for the inconvenience, but hope that the new images will provide you with an even better learning experience.
- List the chemical elements that make up:
- Carbohydrates
- Fats
- Proteins
All three biomolecules contain Carbon, Hydrogen and Oxygen.
Proteins also contain Nitrogen, and sometimes Sulfur and Phosphorus too.
- Define nutrition:
The taking in of nutrients which are organic substances and mineral ions, containing raw materials or energy for growth and tissue repair, absorbing and assimilating them.
- Describe the structure of large molecules made from smaller basic units, ie.
- Simple sugars to starch and glycogen
- Amino acids to proteins
- Fatty acids and glycerol to fats and oils
Polymers are large molecules made from small, similar molecules (often referred to as sub units)
In the case of carbohydrates; starch
and glycogen are large polymer molecules made of glucose.
Note: the simplest sugar is a glucose molecule (C6H1206).
In the case of proteins, amino acids are the monomers.
Different amino acids bond together, to form chains known as peptides. These peptides come together to form proteins such as enzymes.
As for fats and oils; the most common type of fats are triglycerides – this means three fatty acid molecules are bonded to each glycerol molecule. Because the subunits aren’t all similiar, fats and oils aren’t polymers – they are not made of similar s
ubunits (fatty acids and glycerol are rather different, actually).
- Describe the tests for:
- Starch (iodine solution)
This is probably the easiest test of the three! All that needs to be done, is adding a few drops of iodine to the test solution. If it contains starch, the solution will turn blue-black, if not, it’ll remain an orangey/ brown colour (the colour of iodine).
- Reducing sugars (Benedict’s solution)
To a known volume of test solution, you add the equal volume of Benedict’s reagent/ solution. Give it a stir and look for any colour changes. If none, try heating it in a warm water bath (about 80oC), and look for any colour changes. If there are no changes, there are no reducing sugars present in the solution.
Benedict’s reagent is blue in colour. If there are any sugars present, it’ll change from blue, to green, to yellow, to orange, to red (the fire colours). Green means that there are only traces of reducing sugars and red means that the solution has a high concentration of reducing sugars.
Note: sucrose is not a reducing sugar.
- Fats (ethanol):
This one’s pretty simple too! You add the test sample to concentrated ethanol solution. You put that ethanol-sample solution into a test tube of distilled water, close it and shake it around. If a cloudy emulsion forms, fats are present; if not, there are no fats.
- List the principle sources of, and describe the importance of:
- Carbohydrates
Carbohydrates can be found in staple foods such as rice, potatoes, wheat, cereal, bread, etc.
They are essential for respiration – they are broken down to release energy in respiration.
- Fats
Fats are found in oil, butter, margarine, it’s the white stuff on animal meat, etc.
Fats insulate the body, and serve as a store of energy (when we don’t have enough carbohydrates, fats can be respired instead).
- Proteins
Proteins are found in meats, such as chicken, beef, fish, etc. It is also found in vegetables such as lentils and beans.
Proteins form our muscles, our enzymes, our skin, our hair, etc.
- Vitamins (C and D only)
Vitamin C is found in many fresh fruit, especially citrus fruits e.g. oranges, lemons, peppers, etc. It is also found in dark leafy greens.
Vitamin C is required for the development and maintenance of scar tissue, blood vessels and cartilage. It’s needed to make ATP (your source of energy), too. Vitamin C contributes to healthy teeth and gums as well.
Most of the vitamin D in our body is formed under our skin as a reaction to sunlight. Food sources include oily fish (e.g. salmon, sardines and mackerel), eggs, fortified fat spreads, fortified breakfast cereals, and some powdered milks.
Vitamin D is equally important to the maintenance of bone health as Calcium, because it regulates the flow of calcium into the blood stream. This is done by promoting the absorption of calcium from food.
- Mineral salts (calcium and iron only)
Calcium is found in so many foods! Dairy foods such as milk cheese and yoghurt contain it; greens like kale, broccoli and chinese cabbage are good vegetable sources; fish with bones soft enough to eat, such as sardines and salmon; most grainy food, like bread or rice; etc.
Almost all calcium is stored in bones and teeth, where it supports their structure and hardness. Calcium is also required for certain muscles to move and for nerves to carry messages between the brain and every body part. It’s also used to help blood vessels move blood through the body and to help release hormones and enzymes (almost every function in the body is controlled by hormones and enzymes).
Iron can be found in liver, meat, beans, nuts, dried fruit, wholegrains (e.g brown rice), fortified breakfast cereals, sorbean flour and dark-green leafy vegetables.
Iron is primarily needed to form the haemoglobin in RBCs. It also plays an essential role in the process of respiration (the actual complete process of respiration is much more complicated than the simple equation you have to learn about in iGCSE…. not to worry, you can suffer through that in A levels :p)
- Fibre (roughage)
There are two types of fibre: soluble and insoluble. In iGCSE, you should only have to learn about insoluble fibres. These fibres can not be digested. It basically adds bulk to your food so that your intestines can push it along your alimentary canal. Insoluble fibres keeps your bowels healthy and helps prevent digestive problems.
Insoluble fibre sources include wholemeal bread, bran, cereals, nuts and seeds (other than golden linseeds).
Water is usually present in varying amounts in food, but that’s not nearly enough for our body. Water can be drawn from wells, taken from springs, rivers (sea water isn’t very good drinking water), but hopefully, you live in a house with running tap water.
Every cell in our body is surrounded by water (unless they’re dead. Then maybe not.) and every reaction (respiration, digestion, growth, etc.) occurs in water. Hormones and other substances are dissolved in water; most of your blood is made of plasma (which is 92% water), gas exchange is possible because the gas exchange surface are moistened using water, etc. Basically, water, to us, is the ‘Elixir of Life.’
- Describe the deficiency symptoms for:
- Vitamins (C and D only)
Chronic pains in the limbs or joints; bruising easily; dental disease (mostly the deterioration of gums) (one example is ‘scurvy’, experienced by sailors who had no access to nutrients (or even fresh water) on long trips at sea; dry hair and skin, infections (because the body’s immune system may become compromised).
Vitamin D deficiency symptoms include bone pain and muscle weakness and rickets (a disease where the bone tissue doesn’t properly mineralize, leading to soft bones and skeletal deformities.)
- Mineral salts (calcium and iron only).
Early stage calcium deficiency may not cause any symptoms; however, as the condition progresses, the symptoms become worse. Severe symptoms include memory loss, musle spasms, numbness and tingling in the hands, feet and face, depression, hallucinations and organ failure.
Signs of Iron deficiency include fatigue, decreased work and school performance, slow cognitive and social development in childhood, difficulty in regulating body temperature, decreased immune function and glossitis (an inflamed tongue). It is also the leading cause of anaemia (a condition where there is a deficiency in RBCs or haemoglobin in the blood, resulting in fatigue).
- Describe the use of microorganisms in the manufacture of yoghurt.
The type of microbe used in yoghurt production is bacteria. This bacteria is added to milk. It respires to produce lactic acid, which acts on milk protein to give yoghurt its texture and characteristic tang.
Notes Submitted by Sarah.
Click here to go to the next topic.
Click here to go to the previous topic.
Click here to go back to the Science menu.
IGCSE AID 