Why are protists considered paraphyletic? a. They include many extinct forms, including lineages that no longer have any living representatives. b. They include some but not all descendants of their most recent common ancestor. c. They represent all of the descendants of a single common ancestor. d. Not all protists have all of the synapomorphies that define the Eukarya, such as a nucleus.

Verified step by step guidance

1. Understand the term 'paraphyletic': A paraphyletic group consists of an ancestral species and some, but not all, of its descendants.
2. Review the definition of protists: Protists are a diverse group of eukaryotic organisms that are not animals, plants, or fungi. They can be unicellular or multicellular.
3. Analyze the options in relation to the definition of paraphyletic: Option b states that protists include some but not all descendants of their most recent common ancestor, which aligns with the definition of a paraphyletic group.
4. Eliminate other options: Options a, c, and d do not directly address the concept of a paraphyletic group as they do not focus on the inclusion of some but not all descendants of a common ancestor.
5. Conclude the correct answer: Based on the definition of paraphyletic and the characteristics of protists, the correct answer is b. They include some but not all descendants of their most recent common ancestor.

Key Concepts

Paraphyly

Paraphyly refers to a group of organisms that includes a common ancestor and some, but not all, of its descendants. This contrasts with monophyletic groups, which include an ancestor and all its descendants, and polyphyletic groups, which do not include the most recent common ancestor. In the context of protists, they are considered paraphyletic because they do not encompass all descendants of their most recent common ancestor, particularly the animals, plants, and fungi that evolved from them.

Eukarya

Eukarya is one of the three domains of life, characterized by organisms that possess complex cells with a nucleus and membrane-bound organelles. This domain includes animals, plants, fungi, and protists. Understanding Eukarya is essential for discussing protists, as they are a diverse group within this domain, and their classification highlights the evolutionary relationships among different life forms.

Synapomorphies

Synapomorphies are shared derived characteristics that are used to define and identify groups of organisms in phylogenetic studies. These traits are inherited from a common ancestor and help establish evolutionary relationships. In the context of protists and Eukarya, not all protists share the synapomorphies that define the Eukarya, such as the presence of a nucleus, which contributes to the paraphyletic nature of protists.