Definitions may include, but are not limited to,

What is the difference between renewable and non-renewable natural resources? What are examples of each?
What factors affect the water cycle?
What is the difference between sustainability and viability?
Why is biodiversity important?
What role do recycling, reusing, and reducing play in our daily lives, and what is the effect of these life choices?
What are the major differences between preservation and conservation, and what influence do they have on our lives today and in the future?
What role does carrying capacity play in the environment and in agriculture production?
What effect does an invasive species have on a native species? Immediately? In the long term?
What are the components of a food web?
How does population density play a role in an ecosystem?
What is the implication of natality and mortality on an ecosystem?
What is the difference between abiotic and biotic?