1 Case Study: Lunchtime!

Lunchtime!

Lunchtime is the favorite class of the day for many schoolchildren. After a long day in Mr. Kitumaini’s science class, 12-year old LaKiesha Washington and her four friends head out to the cafeteria to feast! Consider the following meals that the children are eating.

*Paneer=Indian cheese

Knowing the trophic level of the food that is being consumed is important to calculating the solar energy needed to produce that food. Please use this figure to determine the trophic level of the food source:

Figure 1. KCals of Sunlight Needed for Every Trophic Level of Animal and Plant Food Sources. While pigs are actually omnivores, we have categorized the pig as a herbivore for the sake of this exercise. Let’s pretend that all the pigs come from Happy Pig Farms where they are fed a 100% vegan diet.

1. How much sunlight energy is required for Charlotte to derive energy from the diet she is consuming?

Here are the steps we will use to solve this problem.

Total Kcal per day * 10^{# of trophic levels the food is in} * 100(fraction of sunlight energy)

Because Charlotte’s diet is both meat and plants, we need to treat those two parts separately. The meat that Charlotte eats all comes from primary consumers, which are at trophic level 2, and the plants are all primary producers which is trophic level 1.

Charlotte’s diet consists of 75% meat at the primary consumer level. To determine how much sunlight energy is required for her to derive energy from the meat that she is consuming, we must do the following calculation:

2000 kcal (0.75) * 10 * 10 * 100 = 1.5 x 107 kcal of sunlight needed

To determine how much sunlight energy is required for the plants that she is consuming, we must do the following calculation:

2000 kcal (0.25) * 10 * 100 = 5 x 105 kcal of sunlight needed

So in total, her meals require 1.505 x 107 kcal of sunlight.