TEKS 7.12A : Energy Flow & Trophic Levels

  1. What is the primary source of energy for nearly all food chains on Earth?

    • Answer: The Sun (Radiant Energy).

  2. True or False: Energy is recycled in an ecosystem just like matter.

    • Answer: False. Energy flows in one direction and is eventually lost as heat; it does not cycle back to the sun.

  3. What is the "10% Rule" in an energy pyramid?

    • Answer: Only about 10% of the energy from one trophic level is passed on to the next level.

  4. If a producer level has 5,000 Joules of energy, how much is available to the primary consumers?

    • Answer: 500 Joules.

  5. Where does the other 90% of the energy go if it isn't passed to the next level?

    • Answer: It is used for metabolic processes (moving, growing, reproducing) and lost to the environment as heat.

  6. Which trophic level always contains the most available energy?

    • Answer: Producers (Autotrophs).

  7. Define "Autotroph."

    • Answer: An organism that can produce its own food using light or chemical energy.

  8. Define "Heterotroph."

    • Answer: An organism that must consume other organisms for energy.

  9. In a food web, what do the arrows represent?

    • Answer: The direction of energy flow (from the organism being eaten to the one doing the eating).

  10. Tricky: If a hawk eats a mouse that ate a grasshopper, what trophic level is the hawk?

    • Answer: Tertiary consumer (3rd level consumer). Don't confuse this with the 3rd trophic level—it's actually the 4th trophic level.

  11. Why are there rarely more than 4 or 5 trophic levels in an ecosystem?

    • Answer: Because energy decreases by 90% at each level, there isn't enough energy left to support a higher level of predators.

  12. Which organism is the "Apex Predator"?

    • Answer: The organism at the very top of the food web with no natural predators.

  13. What happens to the population of secondary consumers if the producer population significantly decreases?

    • Answer: Their population will likely decrease because there is less energy available at the base of the web.

  14. Tricky: Does a decomposer belong to a specific trophic level?

    • Answer: No, they can break down organisms from any trophic level, recycling nutrients back into the soil.

  15. What is the chemical equation for Photosynthesis?

    • Answer: 6CO_{2} + 6H_{2}O + \text{light} \rightarrow C_{6}H_{12}O_{6} + 6O_{2}

  1. If a secondary consumer has 20 units of energy, how much did the producers originally have?

    • Answer: 2,000 units (20 × 10 × 10)

  2. Explain the difference between a food chain and a food web.

    • Answer: A food chain shows one linear path of energy; a food web shows many interconnected paths within an ecosystem.

  3. What role do herbivores play in an energy pyramid?

    • Answer: They are primary consumers.

  4. Can an organism be both a secondary and tertiary consumer in the same food web?

    • Answer: Yes, depending on which path the energy takes to reach them.

  5. Tricky: A student says, "The 90% of energy is 'destroyed' during digestion." Why is this scientifically incorrect?

    • Answer: The Law of Conservation of Energy states energy cannot be destroyed; it is transformed into heat energy.

  6. Identify the producer in this chain: Sun—→Grass——>Zebra—→ Lion.

    • Answer: Grass.

  7. What is "Radiant Energy"?

    • Answer: Energy coming from the sun.

  8. Why is the bottom of an energy pyramid the widest?

    • Answer: It represents the largest amount of available energy and biomass.

  9. What would happen if 100% of energy was transferred between levels?

    • Answer: Food chains could be infinitely long, and predators would not need to eat as much.