1.10 - ENERGY FLOW AND THE 10% RULE

Question 1

Which of the following BEST explains the 10% transfer of energy between trophic levels?

a) The first law of thermodynamics.
b) The second law of thermodynamics.
c) The law of conservation of matter.
d) Newton’s first law.

Answer 1

Choice B is correct because the second law of thermodnamics states that all energy in a system moves toward entropy, the fact that not all of the energy consumed through feeding gets transferred is evidence that the energy is moving toward entropy. According to the 10% law, only 10% of the energy is stored as flesh. The remaining 90% is lost or used to maintain homeostasis.

Question 2

The percent growth rate of a country with a doubling time of 7.

a) 10%
b) 20%
c) 40%
d) 70%

Answer 2

Choice A is correct.

To determine growth rate when provided the doubling time of a country, use the Rule of 70:

Doubling Time = 70/r

… where r is the growth rate.

Therefore, for this question:

7 = 70/r

r = 10

… making the growth rate 10%

Question 3

Methylmercury was found in a primary consumer population in a concentration of 15 mg/L.

What would be the concentration of a secondary consumer who eats those fish?

a) 1.5 mg/L
b) 15 mg/L
c) 150 mg/L
d) 30 mg/L

Answer 3

Choice C is the correct answer.

Methylmercury is a toxic pollutant that is most likely found in aquatic systems. It is known to bioaccumulate in fish species and cause disorders of the nervous system.

Pollutants and energy are magnified by a factor of 10 as you move up each trophic level. If the concentration at the primary producer level is 15 mg/L then the secondary consumer would need to consume approximately ten organisms at the lower level for enough energy to survive. Thus, the secondary consumer would uptake ten times the pollutant or 150 mg.L of methylmercury.