In an Antarctic ecosystem, phytoplankton are the main producers. A
species of zooplankton, called krill, are the primary consumers. To some
extent, fish, penguins, seals, whales, and other animals of the ecosystem
depend on krill to survive. Which of these is a biotic factor in this
ecosystem?
A. the amount of ice at any given time
B. che amount of salt in the ocean water
C. the temperature of the air and water
D. the size of the krill population

Which statements best describe the differences or similarities between a comparative investigation and an experimental investigation? check all that apply. experimental investigations are best for showing cause-and-effect relationships, while comparative investigations do not necessarily show this type of relationship. comparative investigations are often impractical and unrealistic, while experimental investigations are the most practical and realistic kinds of investigations. comparative investigations allow for the use of a wide range of variables but do not have a control group, while experimental investigations involve variables that can be controlled. both experimental investigations and comparative investigations are designed to answer scientific questions. both experimental investigations and comparative investigations focus on making observations rather than collecting new data.