Notes: 1  When s is a string or Unicode string object the in and not in operations act like a substring test. In Python versions before 2.3, x had to be a string of length 1. 2  Values of n less than 0 are treated as 0 (which yields an empty sequence of the same type as s).
A food web describes the flow of energy and nutrients through an ecosystem, while a food chain is a linear path through a food web. Distinguish between food chains and food webs as models of energy flow in ecosystems. Organisms can be organized into trophic levels: primary producer, primary consumer, secondary consumer, and tertiary or higher-order consumer.
Types of Potential Energy. 1  Potential energy is a type of energy that is hidden in some way. It is a type of energy that can be converted to other forms and often is related to some attractive or pushing forces.  Anything that can act like a spring or a rubber band can have elastic potential energy.