In addition proteins give us a certain amount of energy, but they are not as important in this respect as fats or carbohydrates.
A lack of protein causes a disease, which makes the human body weak and listless. This disease is called, ‘Kwashiorkor.’
Meat is the best source of protein. However, there are substitutes for the vegetarians i.e. Soya beans which is also very high in protein.
The energy value for protein is: 1g of protein contains 39 kJ
Part of protein molecule showing how it is made up of a chain of amino acids. The different shapes represent different types of amino acids.
Fat:
The main function of fats is to give us energy so – like carbohydrates – they are energy foods. In man and other animals fat is stored under the skin: this helps to keep the body warm, as well as serving as an energy store. There are many different kinds of fats. Each contains particular fatty acids. Fat is like a carbohydrate in that it contains carbon, hydrogen relative to oxygen. Some fats are liquids. We call them oils.
A fat molecule consists of two parts. The main part is glycerol. Attached to the glycerol are chains called fatty acids. The fat can be split into its glycerol and fatty acid parts by adding water. And these parts can be linked together by taking water away. Different kinds of fat contain different fatty acids.
Now some fatty acids are described as saturated, others as unsaturated. A saturated fatty acid cannot possess any more hydrogen atoms: the molecule is ‘full up’, like a saturated sponge full of water. An unsaturated fatty acid, on the other hand, has room for more atoms.
The energy value for fat is: 1g of fat contains 17kJ
A typical fat or oil consists of a molecule of glycerol linked with three molecules of fatty acid:
The peanuts are not completely made up of fat and protein other substances such as starch, vitamins and minerals. From this I predict that there will be about 15kJ/g for the amount of energy contained.
I predict that that a peanut with more mass should give off more energy when the peanut is burned. I predict this because the peanuts with the higher mass have more chemical bonds thus, more energy will be contained within the bonds. The energy will be given off as the peanut is being burned. I predict that mass is directly proportional to energy released.
Method:
Apparatus: Bunsen burner,
Wood Splints,
Stand and Clamp,
Boiling Tubes,
Mounted Needles,
Thermometer,
Measuring Cylinder
Randomly picked peanuts,
Weighing balance.
- Put 20 cm³ of water into a boiling tube. Fix the tube in a clamp so that it is held at an angle of 45º.
- Weigh a peanut very carefully, in grams using the chemical balance and record the result.
- Fix the peanut onto a mounted needle, taking care that no bits drop off.
- Measure the temperature of the water in the boiling tube and note the result.
- Ignite the peanut in a Bunsen flame. Quickly place the burning peanut under the boiling tube. The idea is to use as much heat as possible from the burning nut to heat the water in the tube.
If the nut goes out, relight it quickly and put it back under the tube,
When the peanut has completely burnt. Measure the temperature of water in the boiling tube.
When the peanut has completely burnt/ measure the temperature of the boiling tube again and note the result.
Results:
Averages: 45.25ºC 26ºC 2835.75J 2.196kJ/g
I worked out the total energy released by a certain formula, which is:
MASS OF WATER X RISE IN TEMPERATURE X 4.2
(In Grams) (ºC)
MASS OF THE PEANUT
I worked out the energy released in kJ/G by dividing the energy released by the mass of the peanut from the energy released and I divided the answer again by one thousand to gain my answer.
Conclusion:
I have come to the conclusion that the average energy released from the peanut to be 2.196kJ/g, which is no where near to the prediction I gave in the hypothesis. This shows that there were many errors in the experiment.
I also found that the mass of the peanut was not much on an issue in the experiment as the minimum mass released the highest amount of energy. Obviously the experiments were unfair and the degree of accuracy was not good.
When the peanut was burned heat was released from the peanut. The heat was released because the reaction is exothermic and that the bonds were being broken to give off heat. Chemical energy inside the peanut was being changed into heat energy as the bonds were being heated are broken. When we eat peanuts the same experiment takes place in our bodies and from this experiment I have come to the conclusion that the whole process is not efficient.
Graph: The graph shows that there is absolutely no relation between mass and energy released. I predicted in my hypothesis that mass was directly proportional to energy released. Unfortunately, errors have occurred in the experiment, which should not have happened.
Evaluation:
The experiments were very important to the investigation as I would be getting my results from them and because they were carried out with the most possible degree of care and accuracy. However, sources of error were inevitable. The following are precautions taken whist doing the experiments to decrease the level on inaccuracy: -
The equipment was well washed so that any impurities could be washed off and therefore not contaminate the water and alter the boiling point of the water and change my results. I did not hold the thermometer as I would conduct heat into the thermometer and alter the readings so therefore a rubber bung held it.
The following sources of errors, in my opinion, have affected my results, they are: - The rounding up of temperatures and measurements.
Obviously from my results that there were many errors in the experiment. And that many improvements should be made to make the experiment more efficient so that we can get better results.
A lot of the heat was being lost to the surroundings and thus did not heat up the boiling tube with all the water. One fact is that the person doing the experiment should be very attentive because his hand when holding the mounted needle that he jerks around and more heat can be lost.
There should be a covering of some sort over the boiling tube and the mounted needle to prevent any heat loss. Aluminium foil would be ideal as heat is reflected back because of its shiny surface. Also a direct supply of oxygen should be provided so that the flame on the peanut is kept going.
The peanut took a while to ignite and when you thought you had it lit it would go straight out again. You would have to relight the peanut several times so it can continue burning.
The whole peanut would never completely burn as the flame would go out and it will be hard to ignite the peanut again. This will tell you that not all the bonds in the peanut were broken and the experiment is not complete as not all the energy is being released.
To improve the experiment maybe a I could have used a more precise thermometer to measure the temperature more accurately, instead of rounding off to the nearest temperature. The water should have been measured more accurately maybe by using a graduated pipette.
BIBLIOGRAPHY:
Textbooks: Biology For Life by M.B.V Roberts and GCSE Biology by D.G Mackean
The Internet
Teacher’s Notes
Own Knowledge.
