How Much Land Does It Take To Produce Your Food?
Background:
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 kilocalories 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.
Procedure:
1. Record the types and amount of food you have eaten during the past 24-hour period. Be sure
to count everything, not just what is eaten at meals – include snacks, candy, etc. too.
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2. Using http://caloriecount.about.com, determine the total number of calories taken in from
your food during those 24 hours. Record this on the Analysis Sheet for Trophic Ecology
of Humans.
3. Multiply this amount by 365 to determine the total number of calories you consume during a
typical year.
4. Determine the square meters of land required to grow the food that you eat. Do this by
determining the number of calories that fall into each food category and divide “annual
consumption” by the "yield".
5. Add the values in the "square meters of land" for all C-3 plants, C-4 plants, and animal
products to arrive at the TOTAL land required to support you for a year.
6. Determine the class average for the square meters of land required to support an individual.
Analysis Sheet for Trophic Ecology of Humans
Food
Category
Your Daily Your Annual
Consumption Consumption
(kcal / day)
(kcal / year)
Yield
(kcal / sq. m / year)
C-3 Plants
Bread
650
Wheat, cereal
810
Oranges,
grapefruit
1000
Frozen orange
juice
410
Peanut butter
920
Rice, rice
cereal
1250
Potatoes
1600
Carrots
810
Other
vegetables
200
Apples
1500
Pears, peaches
900
Vegetable oil
300
Margarine
300
C-4 Plants
Cane sugar
3500
Soft drinks
3500
Corn cereal
1600
Corn
250
Square Meters of Land
Needed to Support You
(Consumption ÷ Yield)
Animal Products
Milk
420
Cheeses
40
Eggs
200
Chicken
190
Pork
190
Beef
130
Fish
2
TOTAL =
Class average =
Analysis:
Use the class average for the following calculations.
1. Assuming a football field/soccer field is 5000 square meters, how many fields does the
average person need to support him/herself for one year? Show your work.
2. Calculate the amount of land needed to provide food for the following populations:
Sq. Meters
Sq. Kilometers
Acres
Kennedy High (pop. 2,000) =
Cedar Rapids (pop. 126,326) =
Iowa (pop. 3,046,355) =
United States (pop. 308,745,538) =
Convert the square METERS to square KILOMETERS by dividing by 1 million.
An acre is 4047 sq meters. (slightly smaller than a football field)
3. On the Iowa map below, shade the area of land needed to support the populations of
Kennedy High School, Cedar Rapids, and the State of Iowa. Use different colors to
represent the needs of each of the population groups. Include a key.
4. Why can’t we use our calculations in this activity to determine the amount of land required
to grow food for the entire world population? What other things must we consider?