1. The primary source of energy in most ecosystems is/are A. autotrophs

B. the sun

C. heterotrophs

D. glucose

2. Which would be an autotroph in a grassland ecosystem?
A. mallard duck

B. prairie cordgrass

C. monarch butterfly

D. muskrat

3. Which of the following best explains why there are fewer secondary consumers than producers?
A. Around 10% of the energy is transferred to support the next trophic level.

B. Heat energy given off from producers kills off primary and secondary consumers.

C. Secondary consumers have less cell processes that need energy.

D. More secondary consumers can absorb radiant energy from the sun.

4. Which tropic level ingests the most biomass in order to receive the energy they need?
A. primary consumers

B. producers

C. tertiary consumers

D. secondary consumers

5. Wolves were reintroduced to Yellowstone National Park in 1995. They began to hunt the abundant elk population, so elk numbers decreased. The elk carcasses provided food for other predators, like foxes, coyotes, and bears, so all of their populations increased. Elk used to overgraze on willow plants; now that willows are growing back, beaver numbers are increasing, because they prefer the slow-moving water that willows cause.
Which of these species is a keystone species?
A. willows

B. elk

C. bears

D. wolves