Find the relationship between amount of fat and amount of energy produced in different foods.
July 2001
Biology Coursework Year 10
Aim
Find the relationship between amount of fat and amount of energy produced in different foods.
Planning
I am going to ignite different foods and see how much heat energy they give out. The food that causes the biggest amount of change in temperature will have the most amount of energy. However, calculations have to be carried out to create an average energy output per gram.
Variables
Independent Variables: This will change from food to food, thus giving me a range of different results. In this experiment it will be type of food.
Dependant Variable: This is the amount of Energy per gram which can be calculated
Controlled Variables: These are the things that will keep the same, in order to sustain a fair test. These are;
* Apparatus
* Type of boiling tube
* Distance of boiling tube from Bunsen burner
* Distance of food from boiling tube
* Amount of time taken to move ignited food to boiling tube
Fair Test
It is essential that I keep it a fair test in order to sustain accurate results for comparison at the end. To ensure a fair test, I must keep the controlled variables for every test I do.
The apparatus must all be kept the same because there may be some minor differences in insulation properties, or measure of accuracy between them. If this were to happen, it would prevent me from sustaining accurate results.
The same type of boiling tube must be kept constant because, every boiling tube may have different conducting properties. If it were not as dense as a previous test tube, it would heat up more quickly, and if it were denser, I would get the opposite affect. This is why it is essential that all the boiling tubes are identical as it could lead to totally false results.
The boiling tube must be changed for each test though, because a previous boiling tube may have retained heat from a previous experiment. This would cause a false rise in temperature.
The distance of the boiling tube from the Bunsen burner must be kept constant. The Bunsen burner provides heat and different distances from it would be at different temperatures. This could cause the temperature of the water to rise falsely, and would again produce anomalies.
The distance of food from the boiling tube must also be kept constant. There is a different temperature at different points of a flame. The tip of a flame is the hottest part. If the distance were altered, it would apply different amounts of heat to the boiling tube. Again, this would lead to inaccurate results.
The amount of time taken to move ignited food to the boiling tube must be as quick as possible. If there were a delay, the heat energy produced by the food would be wasted. All of the energy produced must be used to heat up the water.
Accuracy
The two types of errors usually made in an experiment are either variable or constant. Variable errors are just general mistakes by the scientist. These can be avoided by making sure that all of the above procedures to ensure a fair test are followed accurately. Constant errors cannot be controlled.
To ensure accurate results, I must make sure that I carry out all of the procedures to ensure a fair test.
The only other measures of accuracy are letting the thermometer stabilise before the next experiment is carried out. Also, when using electronic scales, you must let them stabilise, before the food is taken off of them to ensure an accurate measure of weight.
It is essential that every experiment is repeated at least twice. This way, if there are anomalous results, they will be exposed and shan't affect my overall result.
Safety
Safety is extremely important in every experiment and is mandatory. In this experiment, as we will be in contact with hot foods and naked burning flames, it is essential that I carry out all of the safety features.
As we will be using a Bunsen burner, it is essential that goggles are worn at all times. The excessive heat can cause water or other substances to spit. This is why eye protection must be worn at all times.
Also, because of the naked flame, all hair must be tied back, and all loose clothing must be tucked away. If nail polish is being worn, it may be a good idea to wear gloves, as all solvents are flammable, including hairspray and deodorant. All loose clothing must be tucked as they too can catch fire but can also knock over dangerous equipment off of benches.
When and experiment has been carried out, the boiling tube will be very hot from the bottom. Therefore, it must be carried from the top to avoid scalding. Gloves may be appropriate for extra safety.
The benches are made of wood, and therefore are flammable. It is essential that two asbestos mats are used. One should be under the Bunsen burner, the other, under the boiling tube. This is because if ignited food were to fall, it would not cause any hazards to the benches.
When the food is being burnt, it is held on a needle. It is very important that the needle is held from the wooden handle and that it's wrapped slightly in foil. The foil is there to stop the wood from catching fire. It must be held from the wooden handle, as wood is a good insulator of heat, and will not cause scalding.
The food presented must not be consumed as it may have been accidentally contaminated. The labs are filled with harmful chemicals, and the food is not for consumption, but is for experimental ...
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When the food is being burnt, it is held on a needle. It is very important that the needle is held from the wooden handle and that it's wrapped slightly in foil. The foil is there to stop the wood from catching fire. It must be held from the wooden handle, as wood is a good insulator of heat, and will not cause scalding.
The food presented must not be consumed as it may have been accidentally contaminated. The labs are filled with harmful chemicals, and the food is not for consumption, but is for experimental use.
The basic laboratory rules must be abided. There should be no running, or immature behaviour (squirting of water) as this is very dangerous and could cause someone to fall and risk their own health as well as others'.
Prediction
I predict that by changing the type of food, the amount of energy per gram will change. The foods with the most fat will have the most energy. Therefore the amount of fat is proportional to the amount of energy in each food.
Scientific Knowledge
Type of Food
Sunflower Seeds
Pumpkin Seeds
Pasta
Plain Crisps
Crispbread
Dried Peas
KJ energy
in 100g
2518
2527
470
2214
2214
265
Protein
in 100g
9.8
33
2
4.3
4.3
21.6
Carbohydrate in 100g
8.6
9
72
45.2
45.2
50.0
Fat
in 100g
47.5
49
37
37
.3
Table provided to us before experiment
By looking at this table, it is clear that the food with the most Fat (Pumpkin Seeds) produces the most energy (2527 KJ per 100g). I know that 1 gram of fat produces twice as much energy as 1 gram of carbohydrate or protein. Here are the values of energy in each.
Food Group
Energy (kJ per Gram)
Carbohydrate
7
Protein
8
Fat
39
Energy is never created or destroyed. It is simply passed on.
Fat is used for energy in the body when Carbohydrate runs out. Fat produces much more energy. Animals who live in colder climates have a larger proportion of fat than those in warmer climates. This is because the fat acts as a thermal insulator and so protects them from losing heat too quickly (e.g. polar bears and walruses.)
Fats, proteins and carbohydrates are the major parts of any food. All of these can act as energy sources. These are all relatively large and complicated molecules. There is a lot of chemical energy holding the atoms together in these substances. The cells in our bodies release energy by breaking down these complicated molecules into very simple ones like carbon dioxide and water. Fats are a very good source of energy because their molecules are even bigger and more complicated than the molecules of proteins and carbohydrates. Breaking all this down releases an awful lot of energy. A gram of fat can supply more than twice as much energy as a gram of sugar. This helps explain why our bodies store energy in the form of fat.
Some foods naturally have a rich source of fat (e.g. butter, cream, oil.) However, some foods pick up higher sources of fat before they are advertised to the public. For example, crisps aren't high in fat originally, however as they are fried in oil, they have a high amount of fat. This can be said with many manufactured foods.
We naturally burn fat in our bodies when we do exercise when there is not enough Carbohydrate stored. This often happens, as Carbohydrates do not have a high source of energy, so the body uses preserve fat as an energy source. The body prefers to use carbohydrates though. When we exercise, fat is burnt and when there is excessive exercise, lactic acid is formed.
The amount of fat needed per person in their diet varies. For someone with and active lifestyle (e.g. athlete) would need more fat/carbohydrate that someone with an inactive lifestyle (e.g. office worker.) If excessive amounts of energy is digested, all of the unused energy is stored as fat. Fat is therefore harder to lose as it produces so much energy. For example, if 10grams of carbohydrate were burnt when an athlete ran 1000 meters, 10 grams of fat would be burnt when the athlete ran 2000 meters. Therefore, twice the amount of work is needed to lose the same amount of fat as carbohydrates.
In digestion, fat is broken down into fatty acidy and glycerol by enzymes called lipase.
Graph on data above.
By looking at this data, it seems as though pumpkin seeds have the most fat in them. However, in my experiment, I will not be testing pumpkin seeds, as I tested them in my preliminary experiment. In my experiment I will be testing sunflower seeds, plain crisps, dried peas and pasta. Out of these four, sunflower seeds contain the most amount of fat.
Prediction
I predict that sunflower seeds will create the most amount of energy because they have the most amount of fat. Pasta will release the least as they have the least fat.
Apparatus
* One beaker of tap water
* Eight boiling tubes of the same type
* One Bunsen burner
* Two asbestos mats
* A syringe
* Electronic scales
* Thermometer
* Retort stand with a clamp
* One mounted needle with top wrapped in foil
* Two dried peas
* Two pieces of pasta
* Two crisps
* Two sunflower seeds
Method
* Put on safety goggles (and gloves if necessary)
* Place out equipment
* Put Bunsen burner on one mat, put retort stand with clamp on other mat.
* Ensure that the Bunsen burner is a considerable distance away from beaker so that it won't interfere with the thermometer reading.
* Using a pipette, place 20cm3 of water in the boiling tube.
* Attach boiling tube to clamp.
* Place thermometer in boiling tube. Record temperature.
* Collect and weigh food. Wait for the scale to stabilise. Record the weight.
* Light the Bunsen. Make sure goggles and/or gloves are worn.
* Carefully place food on mounted needle.
* Ignite the food and place under boiling tube immediately.
* Hold approximately 2cm under boiling tube.
* Hold until food extinguishes.
* Attempt to re-ignite.
* If it doesn't, record the temperature again.
* Repeat with all foods, changing the boiling tube each time. All of the other apparatus must be the same.
* Record results and do the calculations.
OBTAINING EVIDENCE
Results from Preliminary Experiment
FOOD
WEIGHT
OF FOOD
START TEMPERATURE
END TEMPERATURE
TEMPERATURE DIFFERENCE
WEIGHT OF WATER
ENERGY (J)
ENERGY
(J/g)
PUMPKIN
SEEDS
0.1g
6?C
35?C
9?C
20g
596
5960
0.1g
8?C
48?C
30?C
20g
2520
25200
0.1g
26?C
29?C
3?C
20g
260
2600
CRISPBREAD
.1g
5?C
25?C
0?C
20g
840
764
.2g
6?C
32?C
32?C
20g
344
120
.1g
7?C
29?C
2?C
20g
008
916
.1g
9?C
37?C
8?C
20g
512
375
Calculations
Energy (Joules) = 4.2 x temperature difference x weight of water
Energy (Joules/g) = Energy (J)
Weight of food
Crispbread
. Energy (J) = 4.2 x 10?C x 20g = 840J
Energy (J/g) = 840J / 1.1g = 764J/g
2. Energy (J) = 4.2 x 32?C x 20g = 1344J
Energy (J/g) = 1344J / 1.2g = 1120J/g
3. Energy (J) = 4.2 x 12?C x 20g = 1008J
Energy (J/g) = 1008 / 1.2g = 916J/g
4. Energy (J) = 4.2 x 18?C x 20g = 1512J
Energy (J/g) = 1512 / 1.1 = 1375
Pumpkin Seeds
. Energy (J) = 4.2 x 19?C x 20g = 1596J
Energy (J/g) = 432J / 0.1g = 15960J/g
2. Energy (J) = 4.2 x 30?C x 20g = 2520J
Energy (J/g) = 480 / 0.1g = 25200J/g
3. Energy (J) = 4.2 x 20?C x 20g = 1680J
Energy (J/g) = 432J / 0.2g = 840J/g
4. Energy (J) = 4.2 x 3?C x 20g = 1260J
Energy (J/g) = 480 / 0.1g = 12600J/g
Results from Main Experiment
FOOD
WEIGHT OF FOOD
START TEMPERATURE
END TEMPERATURE
TEMPERATURE DIFFERENCE
WEIGHT OF WATER
ENERGY (J)
ENERGY
(J/g)
DRIED PEAS
0.49g
22?C
29?C
7?C
20g
582
200
0.25g
23?C
26?C
3?C
20g
252
008
SUNFLOWER
SEED
0.13g
24?C
34?C
0?C
20g
840
6462
0.15g
21?C
26?C
5?C
20g
420
2800
PASTA
0.33g
22?C
24?C
2?C
20g
68
509
0.30g
24?C
26?C
2?C
20g
68
560
CRISP
.48g
20?C
33?C
3?C
20g
092
738
0.86g
24?C
37?C
3?C
20g
092
270
Calculations
Energy (Joules) = 4.2 x temperature difference x amount of water
Energy (Joules/g) = Energy (J)
Weight
Dried Peas
. Energy (J) = 4.2 x 7?C x 20g = 582J
Energy (J/g) = 582J / 0.49g = 1200J/g
2. Energy (J) = 4.2 x 3?C x 20g = 252J
Energy (J/g) = 252J / 0.25g = 1008J/g
Sunflower Seeds
. Energy (J) = 4.2 x 10?C x 20g = 840J
Energy (J/g) = 840J / 0.13g = 6462J/g
2. Energy (J) = 4.2 x 5?C x 20g = 420J
Energy (J/g) = 420J / 0.15g = 2800J/g
Pasta
. Energy (J) = 4.2 x 2?C x 20g = 168J
Energy (J/g) = 168J / 0.33g = 509J/g
2. Energy (J) = 4.2 x 2?C x 20g = 168J
Energy (J/g) = 168J / 0.30g = 560
Crisp
. Energy (J) = 4.2 x 13?C x 20g = 1092J
Energy (J/g) = 1092J / 1.48g = 738J/g
2. Energy (J) = 4.2 x 13?C x 20g = 1092J
Energy (J/g) = 1092J / 0.86g = 1270J/g
Analysing Evidence
Anomalies: an anomaly is an incorrect result, an abnormal glitch in the results. It is an incorrect result.
In order to distinguish all of the anomalies, I have plotted this graph. The result(s) that look incorrect are the anomalies.
Food
Energy difference between experiment with least energy produced and most energy produced (J)
Dried Peas
92
Sunflower Seeds
3662
Pasta
51
Crisps
532
Pumpkin Seeds
6800
Crisp bread
611
By looking at this table, it is clear that results for Sunflower seeds and for pumpkin seeds are anomalous. Therefore one of the results is incorrect and has to be eliminated.
FOOD
WEIGHT OF FOOD
START TEMPERATURE
END TEMPERATURE
TEMPERATURE DIFFERENCE
WEIGHT
OF
WATER
ENERGY (J)
ENERGY
(J/g)
SUNFLOWER
SEED
0.13g
24?C
34?C
0?C
20g
840
6462
0.15g
21?C
26?C
5?C
20g
420
2800
PUMPKIN
SEEDS
0.1g
6?C
35?C
9?C
20g
596
5960
0.1g
8?C
48?C
30?C
20g
2520
25200
0.2g
5?C
35?C
20?C
20g
680
8400
0.1g
26?C
29?C
3?C
20g
260
2600
I have four results for pumpkin seeds, so it is easy to recognise the anomalous result. 8400 is definitely an anomalous result as it is far too low. 25 200 is over 9000 Joules higher than my other results. Therefore, I suspect that 25 200 is also an anomalous result, so I will also eliminate this.
For Sunflower seeds, I only have two results and one of them is definitely anomalous, but which one? Here are the results for Sunflower Seeds for another pupil.
SUNFLOWER SEEDS
0.09g
9?C
21?C
2?C
20g
68
886.67
0.11g
9?C
21?C
2?C
20g
68
527.27
These results are going toward 2000. My result 2800 is closer to these figures than 6462. Therefore, 6462 is an anomalous result. This will be eliminated.
Here are my new results without any anomalies.
FOOD
WEIGHT
OF FOOD
START TEMPERATURE
END TEMPERATURE
TEMPERATURE DIFFERENCE
WEIGHT OF WATER
ENERGY (J)
ENERGY
(J/g)
CRISPBREAD
.1g
5?C
25?C
0?C
20g
840
764
.2g
6?C
32?C
32?C
20g
344
120
.1g
7?C
29?C
2?C
20g
008
916
.1g
9?C
37?C
8?C
20g
512
375
PUMPKIN
SEEDS
0.1g
6?C
35?C
9?C
20g
596
5960
0.1g
8?C
48?C
30?C
20g
2520
25200
0.1g
26?C
29?C
3?C
20g
260
2600
DRIED PEAS
0.49g
22?C
29?C
7?C
20g
582
200
0.25g
23?C
26?C
3?C
20g
252
008
SUNFLOWER
SEED
0.15g
21?C
26?C
5?C
20g
420
2800
PASTA
0.33g
22?C
24?C
2?C
20g
68
509
0.30g
24?C
26?C
2?C
20g
68
560
CRISP
.48g
20?C
33?C
3?C
20g
092
738
0.86g
24?C
37?C
3?C
20g
092
270
Here is a table of average energy amounts for all of the foods above.
Food Type
Average Energy (J/g)
Fat per 100g
Pumpkin Seeds
7920
49
Sunflower Seeds
2800
47.5
Dried Peas
104
.3
Crisp Bread
044
37
Crisps
004
37
Pasta
535
In this table, the average energy decreases as you ascend down it. The third column represents how much fat there is in the food per 100g. Here is a graph for these results.
Analysis of Prediction and Causes for Fault
I predicted that the food with the most amount of fat would create the most amount of energy.
Here is a table of my predicted results compared to the actual results.
Actual results (energy decreases as you descend)
Actual Results (energy decreases as you descend)
Advertised nutritional values 9energy decreases as you descend
Pumpkin seeds
Pumpkin seeds
Pumpkin seeds
Sunflower Seeds
Sunflower seeds
Sunflower Seeds
Crisps
Dried Peas
Crisps
Crispbread
Crispbread
Crispbread
Dried Peas
Crisps
Pasta
Pasta
Pasta
Dried peas
Out of my prediction, I got for out of six correct, that's 66%. So why did I predict a third of them wrongly? What were the odd results?
Dried peas created more energy than Crisp and Crispbread, yet it only contains a fraction of the amount of fat. Why?
Pumpkin seeds only contain 1.5g of fat more that Sunflower Seeds, yet it produced over 6 times more energy. Why?
Only two results from the experiment matches the authentic results given to us as a reliable source. Why?
Fat is not the only source of energy in a food. It may produce the majority of energy in some foods, however others are rich in protein and carbohydrates. This is what happened with Dried Peas, although it contains hardly any fat, it is rich in protein and carbohydrates. That is why it was able to produce so much energy without having a lot of fat.
Here is a table comparing known energy values compared to experiment ones that I have done.
Food Type
Energy Values from results (J/g)
Known energy values (J/g)
Pumpkin seeds
7920
2527
Sunflower Seeds
2800
2518
Crisps
104
2214
Crispbread
044
2214
Dried Peas
004
265
Pasta
535
470
For every food, the known value is greater than my results, apart from Pumpkin Seeds. Therefore, my results for pumpkin seeds were wrong. Why are all of the other values smaller? When the heat energy is transferred, it does not give you the full amount as it takes some energy to heat up the glass in the boiling tube. This does not register as a rise in the temperature of the water. Also, some of the food may have been left over at the end. Usually, not all of the food burns. The biggest thing by far though is that a lot of the heat of the flame simply misses the boiling tube. So it has no effect on the water. This energy is in effect "wasted". That's why if you check the Joules per gram on the table of nutritional value (Scientific Knowledge), it is a lot higher than my estimate. They get these figures using what is called a bomb calorimeter. It collects virtually all the heat and ensures that all of the food is burned.
The only unexplainable result that I got was for Pumpkin Seeds. The numbers are simply incorrect. It is most probably a variable error that I made in reading the thermometer or the electronic scale. Another pupil got 7980J/g for pumpkin seeds. This is more accurate than mine, but is still incorrect. This means that there were problems with the experiment. What caused this?
Most of the other foods had a strong uncontrollable flame that burned aggressively for a few seconds. The Pumpkin seed however, had a small flame that lasted a long time. This meant that it was easy to control and had a longer chance to heat the water. This may have been one of reasons for the inaccurate result.
The experiment was done in pairs, so readings were shouted by one and recorded by another. This could have caused numerous errors. The experiment was also rushed, as it was a lot to do within an hour, which may have lead to carelessness.
Also, as it was done in pairs, there may have been differences in the technique of the two doing the experiment leading to further change.
The known results proved that my prediction and scientific knowledge was correct. However, my results did not. This means that my results were simply inaccurate and wrong. The experiment was not very reliable and resulted in unexplainable results and numerous anomalous results.
Conclusion
As my results were unreliable and inaccurate, I have to rely on my prediction and the known nutritional information provided to me. The bonds in fats are very complex compared to the bonds in carbohydrates. Therefore, more work is required to break down fats than carbohydrates. Carbohydrates and fats give out exothermic reactions when they are burned as you heat up when exercising. This is because the transfer of energy is greater when bonds are broken than when bonds are formed, giving it an overall energy loss.
Therefore, as more energy is required to break down fats, it is safe to say that as fat levels increase in a food, energy levels do also. Fat levels and energy levels are proportional. However, some foods defy this because they are very rich in proteins and carbohydrates. This means that they may contain more energy than a food of more fat.
In conclusion, Fats create twice-as-much energy than carbohydrates and protein. This is why as fat levels increase in foods energy levels also increase. However, food energy is not solely dependant on fat levels, and carbohydrates have the same affect as fat, just to a lesser extent.
Evaluation
The results weren't really reliable at all. I ended up with three anomalies. And after this, I realised that the four results I got for Pumpkin Seeds look preposterous when compared with the known results provided to us. This means there were seven inaccurate results. This is a very large number. I think there must have been a fixed error for the Pumpkin Seed results as I doubt that my partner and I made a variable error four times in a row. This could have been faulty equipment being used.
The time taken for the food to be put under the boiling tube once lit was not measured. Therefore I suspect that it was different for every experiment. We did not time it and it was hard to tell when the food was totally ignited. This made the test unfair.
Also there was the fact that not all of the energy was being used to heat the water. Some would have been lost. Also, the food is not completely burned. The black residue left behind proves this. Therefore, not all of the energy is used.
I don't think there are many ways of improving the accuracy of the experiment large deal. If it were repeated around 5 times for each food, it may prove better because only two comparisons is not very helpful. When an anomaly was present, I often did not know which one was the anomaly, and had to find out via comparison with other pupils' results.
Also, a larger range of foods should be tested. Therefore, there would be more means of comparison.
The main cause of inaccuracy was the lack of energy reaching the water. To increase this, maybe if the burning food was placed into a metallic container, and the rise in temperature in the atmosphere in the container was recorded, it may be more accurate.
However, one way to encourage the complete combustion is to burn the food in a higher concentration of oxygen than normal atmospheric conditions. However, oxygen is pretty explosive so it would require greater safety features and would be done in a controlled environment. That is why experimenting it in a bomb calorimeter, would be most accurate and is how official results are obtained. Bomb calorimeters burn the food in special chamber totally enclosed by the water it is heating. In these the food is burned in pure oxygen as this helps to ensure that it is totally burned and therefore all the energy is released. The experiment that we carried out is an example of a simple calorimeter.