Which of the following pairs is mismatched?

Which of the following levels is not considered a biological level of organization in terms of size?

The organisms should try to maintain the constancy of its internal environment is a process called .......

Tiny free-living animals on the surface of water constitute:

Read the given statements and determine how many of them are incorrect.
$(1)$ Regional and local variations in habitats create a wide variety of biomes.
$(2)$ Temperature,light,and soil are the key elements for the physical and chemical variations in an ecosystem.
$(3)$ Tuna fish are found in the ocean and are classified as warm-blooded and homeothermic animals.
$(4)$ Red algae are found in the deep-sea regions.

What are the various possibilities seen in different organisms to achieve homeostasis? Discuss.