These questions ask students to analyze data presented in the Science News article “Dreaming up tomorrow’s burger,” which describes how some scientists are trying to grow edible meat in lab dishes as well as plant ingredients that taste like meat. If they can make cultured meat and plant-based meat substitutes sufficiently inexpensive and tasty, it may benefit the environment and human health.
Farm to table
The amount of greenhouse gases released from farming, processing and transporting meats and other proteins varies between the most efficient producers (left side of bars) and the least efficient (right sides). Beef is the top emitter overall.
Read the graph:
1. What variable is graphed on the horizontal axis? Be sure to provide units, if appropriate.
Possible student response: Kilograms of climate-warming gasses, classified as carbon dioxide (CO2) equivalent, emitted during the farm-to-retail production chain.
2. What variable is graphed on the vertical axis? Be sure to provide units, if appropriate.
Possible student response: Protein-rich foods including beef, pork, poultry, cheese, peas and tofu.
3. The gray bar near the lower right is a key for how data are plotted in the graph. What is the meaning of a dot, and what is the meaning of the length of a bar?
Possible student response: A dot shows the mean, or average, amount of greenhouse gas emissions for a particular protein-rich food. The gray bar shows the range of greenhouse gas emissions for that food, from the 10th to the 90th percentile. Bars stretch from the amount of CO2 equivalent released by lower-impact producers (far left) to the higher-impact ones (far right).
4. What is the mean value of greenhouse gas emissions for 100 grams (g) of beef and what are the minimum and maximum emission values? What are the values for poultry and tofu?
Possible student response: For every 100 g of beef produced, an average of 50 kilograms (kg) of CO2 equivalent is emitted. The most efficient producers emit approximately 20 kg of CO2 equivalent per 100 g of beef and the least efficient producers emit about 105 kg of CO2 equivalent per 100 g of beef.
For every 100 g of poultry produced, an average of 6 kg of CO2 equivalent is emitted. The most efficient producers emit approximately 2 kg of CO2 equivalent per 100 g of poultry. And the least efficient producers emit about 12 kg of CO2 equivalent per 100 g of poultry.
For every 100 g of tofu produced, approximately 2 kg of CO2 equivalent is emitted. The most efficient producers emit approximately 1 kg of CO2 equivalent per 100 grams of tofu. The least efficient producers emit roughly 3 kg of CO2 equivalent per 100 g of tofu.
Manipulate the data:
5. On average, how much more greenhouse gases does beef produce than poultry for the same amount of food? How much more greenhouse gases does beef produce than tofu for the same amount of food?
Possible student response: Beef produces roughly 8 times more greenhouse gas emissions than poultry. Beef produces roughly 25 times more greenhouse gas emissions than tofu.
6. If producing 100 g of beef emits 50 kg of CO2 equivalent, what is the ratio of CO2 equivalent to mass of beef produced?
Possible student response: 500:1.
The production of 100 grams of beef, on average produces 50 kilograms or 50,000 grams of CO2 equivalent. In terms of mass, 500 times more CO2 is produced than beef.
7. “Dreaming up tomorrow’s burger” reports that Americans eat 79 g of meat per day. Assuming that this is true for 7 days of the week and that Americans eat only beef, how much CO2 equivalent, in grams and kilograms, is emitted to supply one person with beef for a week? For one month? For one year?
Possible student response: Using the mean value for beef:
8. Based on your calculations above, now estimate the amount of CO2 equivalent, in kg, emitted to supply the U.S. population with beef for one year. Assume that 325 million people live in the United States.
Possible student response: U.S. population = 325,000,000 people
9. The American Heart Association recommends people eat four to five 107-gram servings of meat per week. If Americans adhered to American Heart Association recommendations, how many grams of CO2 equivalent would be emitted per year? Make the same assumptions that you did in the previous questions.
10. According to the article, animal agriculture accounts for 14.5 percent of humankind’s total greenhouse gas emissions. Let us assume that beef is responsible for the entirety of the 14.5 percent. (In reality, it is a mix of animals, but we will make an assumption for simplicity.) Using mean values in the graph “From farm to table,” calculate the percent decrease in greenhouse gas emissions if the whole planet switched from beef to poultry, and produced the same amount of meat.
Possible student response: If all beef produces 14.5 percent, all poultry would produce approximately 1.7 percent (see calculation below). Total greenhouse gases would decrease by 12.8 percent. (See calculations below. Note: the unit CO2 equivalent represents total greenhouse gas emissions.)
11. Suppose the world switched from producing solely beef to solely tofu, by what percentage would total greenhouse gas emissions decrease?
Possible student response: If beef produces 14.5 percent, tofu would produce approximately 0.6 percent. Total greenhouse gases would decrease by 13.9 percent. (See calculations below. Note: the unit CO2 equivalent represents total greenhouse gas emissions.)
12. Does this graph effectively display the data? Can you think of a better way to show the same data?
Possible student response: This graph clearly and effectively displays the data, especially because there is such a large range of emission values for some protein-rich foods. It might be worthwhile to show both the mean and median values in the graph.
13. How does the graph provide motivation for the technologies reported in the article?
Possible student response: The graph shows that the current methods of farming, processing and transporting protein-rich food also produce a lot of greenhouse gases. Reducing greenhouse gases is one reason to develop more efficient ways to produce protein-rich food.
Analyze beyond the article:
14. Where do you think lab-grown beef might end up on the graph? How might its mean compare to beef?
Possible student response: Student answers will vary. An example is provided below.
Growing beef in a lab involves culturing animal cells in a bioreactor and using fetal serum harvested from cows. That process might resemble current industrial processes for producing cheese, which involve culturing bacterial cells in a bioreactor and using milk harvested from cows. It might be possible that the two processes produce similar amounts of greenhouse gases. In that case, the mean amount of emissions for beef would likely shift left, relative to the current mean.
15. What processes mentioned in the article might contribute to CO2 equivalent emissions from lab-grown meat? What processes might be the most intensive? Why?
Possible student response: Collecting and incubating stem cells with fetal bovine serum, building scaffolds and seeding the scaffolds with stem cells are just a few of the complex steps that could possibly make large contributions to lab-grown meat’s CO2 equivalent emissions. These steps are resource and energy intensive. If lab-grown meat producers didn’t use renewable energy throughout the growing process, the amount of CO2 equivalent emissions from lab-grown meat might exceed traditional meat production emissions.