Let's look at all the statements:Which of the following statements is true?
Parts of an ecosystem only include biotic factors such as plants and animals. - this is not true, it also includes abiotic factors, such as stones
If a common plant in an ecosystem becomes diseased, the ecosystem may become unbalanced. - this is the true statement! it could be a source of food for other animals, and thus it could influence the population of other species
Abiotic factors include decomposers such as fungi and bacteria. - this is false, those are biotic factors.
Tundras have a high diversity of species. - this is not true - compared to the rain forest, for example, tundras are not very diverse
