Question

energy & matter in ecosystems
in an ecosystem, only 10% of the energy in one trophic level is transferred to the level above it. the rest of the energy is lost to
the environment.
if the first trophic level (green plants) contains about 200,000 kcal of energy, how much energy is transferred from frogs to
snakes?
a. 1,800 kcal
b. 20,000 kcal
c. 2,000 kcal
d. 200 kcal

Explanation:

Step1: Determine energy transfer to insects

Green plants (1st level) have 200,000 kcal. Energy to insects (2nd level) is 10% of 200,000: $0.10 \times 200000 = 20000$ kcal.

Step2: Determine energy transfer to frogs

Insects (2nd level) have 20,000 kcal. Energy to frogs (3rd level) is 10% of 20,000: $0.10 \times 20000 = 2000$ kcal.

Step3: Determine energy transfer to snakes

Frogs (3rd level) have 2,000 kcal. Energy to snakes (4th level) is 10% of 2,000: $0.10 \times 2000 = 200$ kcal? Wait, no—wait, the question is frogs to snakes. Wait, maybe trophic levels: green plants (1), insects (2), frogs (3), snakes (4). So from frogs (3) to snakes (4): 10% of frogs' energy. Wait, but maybe I miscalculated. Wait, green plants (1): 200,000. Insects (2): 20,000. Frogs (3): 2,000. Snakes (4): 200? But option A is 1800? Wait, no, maybe the trophic levels are green plants (1), insects (2), frogs (3), snakes (4). Wait, the problem says "from frogs to snakes". So frogs are 3rd, snakes 4th. So energy in frogs: 10% of insects. Insects: 10% of plants (200,000 0.1 = 20,000). Frogs: 20,000 0.1 = 2,000. Then snakes: 2,000 * 0.1 = 200? But option D is 200? Wait, but the options: A.1800, B.20,000, C.2,000, D.200. Wait, maybe I made a mistake. Wait, maybe the trophic levels are green plants (1), insects (2), frogs (3), snakes (4). Wait, but maybe the question has a typo, or maybe I misread. Wait, no—wait, the initial graph shows insects and green plants, but maybe frogs are a level above insects. Wait, the problem states: first trophic level (green plants) 200,000 kcal. Then insects (2nd), frogs (3rd), snakes (4th). So:

1st: 200,000

2nd (insects): 200,000 * 0.1 = 20,000

3rd (frogs): 20,000 * 0.1 = 2,000

4th (snakes): 2,000 * 0.1 = 200. So the energy transferred from frogs (3rd) to snakes (4th) is 200 kcal? But option D is 200. Wait, but maybe the trophic levels are different. Wait, maybe green plants (1), insects (2), frogs (3), snakes (4). So from frogs to snakes: 10% of frogs' energy. Frogs have 2,000 kcal, so 200. So answer is D? Wait, but let's check again.

Wait, the problem says "only 10% of the energy in one trophic level is transferred to the level above it". So each level gets 10% of the level below. So:

• Level 1 (green plants): 200,000 kcal

• Level 2 (insects, eat plants): 10% of 200,000 = 20,000 kcal

• Level 3 (frogs, eat insects): 10% of 20,000 = 2,000 kcal

• Level 4 (snakes, eat frogs): 10% of 2,000 = 200 kcal

So the energy transferred from frogs (level 3) to snakes (level 4) is 200 kcal. So the correct option is D. 200 kcal.

Answer:

D. 200 kcal