Investigation by David Masterman
In this Investigation, you calculate the amount of land required to produce the food eaten by an individual for one year and compare the amount of land required to produce animal versus plant products.
Humans require energy and their energy is obtained from food. Energy moves from its source in the sun through the photosynthetic organisms that make that energy available to living things (producers) and then through organisms that eat other organisms (consumers). Land therefore yields fewer kilo calories per square meter per year in animal products than in plant products. Energy is lost in the transition from producers to consumers. (respiration, heat loss, animal waste)
Plants can be divided into two groups, C-3 and C-4, based on the photosynthetic and respiratory pathways they utilize. Under the right conditions C-4 plants such as sugarcane and corn photosynthesize two to three times as fast as C-3 plants. C-4 plants are also more efficient because they don’t lose energy due to photorespiration which frequently occurs in C-3 plants. C-3 and C-4 plants are separated on the Analysis Sheet because the C-3 plants are less energy efficient.
A final point to remember in dealing with food energy, a food Calorie used by nutritionists is equivalent to a kilocalorie (kcal) used by chemists and physicists.Investigation: How Much Land Does It Take? (continued)
calorie counters — Mac Diet computer program or calorie counter
Note: All calculations must be clearly displayed.
Show all you steps, and be sure to include units in every calculation.
- Record the types and amount of food eaten during a 24-hour period. Be sure to count everything, not just what is eaten at meals – snacks, candy, etc. too. If you record your food intake for more than one day, just average your results in step 2 to get the amount consumed in a single day.
- Using calorie counter references, determine the total number of calories taken in during those 24 hours. Multiply this amount by 365 to determine the total number of calories taken in during a year.
- Create an Analysis Sheet for Trophic Ecology of Humans (sample on page 60) and students’ calorie data to determine the square meters of land required to support the individual. Do this by determining the number of calories that fall into each food category and divide each of these values by the “yield”.
Add all the values in the “square meters of land” column to arrive at the total land required to support the individual.
Add the values in each subgroup, C-3 plants, C-4 plants, and animal products, to compare plant and animal land requirements.
- Calculate a class average for the square meters of land required to support an individual.
- Assuming a football field/soccer field is 5000 square meters, how many fields do you need to support an average member of your class for one year?
- Calculate the amount of land (in m2) required to support the world’s population for one year.
- Examine a world atlas to determine the total surface area of the arable land on earth (the land that can be farmed). Convert this number into square meters, if it is not already in those units.
Hint: 1 km2 = 106 m2, 1 mile2 = 2.56(106) m2
(One source gives this value as approximately 1.3732(1013) m2)
- If everyone on earth ate as the average member of your class did, what percent of the earth would be needed to produce that amount of food?
To calculate this, divide the amount of land needed to support the world’s population for one year by the total surface area of the land on earth, and multiply by 100.
- Is there sufficient land to meet the needs of today’s people? Explain.
- Assume that you have a great grandchild and your great grandchild will die of old age. Estimate the year s/he might die. What assumptions are you making?
- What is the doubling time for the earth’s population of humans?
- Complete a table like the one shown on this page. To do so, enter the year in the first empty row of the first column (e.g., 1997).
a. Enter the world’s population of human beings in the first empty row of the second column.
b. Enter the percent of land needed to grow the world’s food in the first empty row of the third column.
c. Add the doubling time to today’s date and enter the result below today’s date.
d. Double the population of earth and enter the result below today’s population.
e. Double the percent of land needed to grow the world’s food and enter the result below today’s percent.
f. Continue this until you have reached or passed the year that you estimate your great grandchild might die of old age.
|Human Population (billions)
|Percent of Land Needed to Grow the World’s Food?
- At what year do you estimate that the biodiversity of the world will collapse to zero? Explain.
- Are these predictions possible? Explain.
- What assumptions were made in determining these values? How might each be modified in the future to change the predictions you made?
- Comparing land required to produce an equal amount of plant versus animal calories:
Choose one plant product (e.g., rice) and one animal product (e.g., beef)
from the Analysis Sheet for Trophic Ecology of Humans.
Any foods from the Analysis Sheet could be used.
Assume that an individual takes in 200 calories of each product in one meal.
Divide the 200 calories by the yield from the Analysis Sheet.
Discuss the implications of vegetarian versus non-vegetarian diets.
How would this affect the results in the table of “Land Needed for Food?”
Most of the people in the world live primarily on varieties of grain and other plant products. More affluent people bring meat into their diets. In addition, cattle and poultry are often fattened up by feeding them grain, which could be used for human consumption
By eating less meat and relying more on plant products for food, the energy transfer would be 10 times more efficient. Americans would not put on so much weight if their diet consisted of more vegetables and less red meat. If we did, we certainly would be adding to the world’s food supply. It has been estimated that if Americans decreased their meat consumption by only 10%, enough grain could be released to feed 60 million people.
Source: Source: Brewer, Richard and M. T. McCann, Laboratory and Field Manual of Ecology, Saunders College Publishing, Philadelphia, 1982. Modified from materials presented by Janis Lariviere at the Woodrow Wilson NFF Biology Institute, 1991. Modified by David Masterman, 1996