Do simple organisms have to have one cell and do complex organisms have to have more than one cell

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

For a to be healthy, it has to have lots of different kinds of plants and animals. all of the different types of plants and animals in an ecosystem. name four types of ecosystems from those listed in the video. b) c) d) most living things live here. all living things depend on how an ecosystem like a game of sticks? why should we build new buildings on existing land? name four extinct species from those listed in the video. b) c) d) the best way to wipe out a species is to the largest ecosystem in the world is this percent of the world is covered by water. how many of all species in the world live in the ocean? list five things you can do to increase biodiversity. b) c) d) e) how many species are we losing per hour?

How many chromosomes does each human cell contain? a. 23 chromosomes b. 26 chromosomes c. 43 chromosomes d. 46 chromosomes