Chapter 24, Problem 8STP

Summary Introduction

Introduction:

Animals are multicellular eukaryotes that have evolved to live in different habitats. Biologists have created an evolutionary tree to organize the great diversity of living organisms. The ancestral animals at the start of the evolutionary tree are eukaryotic and multicellular.

Correct answer :

The correct answer is option A. similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms

Explanation/justification for the correct answer:

Option A. similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms − Scientists believe that all present- day animals have evolved from colonial unicellular organisms such as choanoflagellates. These are protists that formed colonies in sea about 570 million years ago. Choanoflagellates are considered to be first true animals. The similarities in DNA or RNA of early multicellular organisms such as sponges and colonial unicellular organisms such as Zoothamnium suggest that colonial organisms were an early step in the evolution of multicellularity. Hence this is the correct option.

Explanation for incorrect answer:

Option B. differences in DNA or RNA of early multicellular organisms and colonial unicellular organisms − The evolutionary tree was created by convergence of data from phylogenetic and molecular analysis. The similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms suggest that multicellularity has originated from unicellular organisms that formed colonies. Differences in DNA or RNA of early multicellular organisms and colonial unicellular organisms would mean they do not have common ancestor. Hence this is not the correct option.

Option C. similarities of early multicellular organisms and present- day multicellular organisms - This does not suggest that early multicellular organisms and colonial unicellular organisms have common ancestor. Hence this is not the correct option.

Option D. differences between early multicellular organisms and present- day multicellular organisms − This does not indicate that early multicellular organisms and colonial unicellular organisms have common origins. Hence this is not the correct option.

Answer to Problem 8STP

Correct answer :

The correct answer is option A. similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms

Explanation of Solution

Explanation/justification for the correct answer:

Option A. similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms − Scientists believe that all present- day animals have evolved from colonial unicellular organisms such as choanoflagellates. These are protists that formed colonies in sea about 570 million years ago. Choanoflagellates are considered to be first true animals. The similarities in DNA or RNA of early multicellular organisms such as sponges and colonial unicellular organisms such as Zoothamnium suggest that colonial organisms were an early step in the evolution of multicellularity. Hence this is the correct option.

Explanation for incorrect answer:

Option B. differences in DNA or RNA of early multicellular organisms and colonial unicellular organisms − The evolutionary tree was created by convergence of data from phylogenetic and molecular analysis. The similarities in DNA or RNA of early multicellular organisms and colonial unicellular organisms suggest that multicellularity has originated from unicellular organisms that formed colonies. Differences in DNA or RNA of early multicellular organisms and colonial unicellular organisms would mean they do not have common ancestor. Hence this is not the correct option.

Option C. similarities of early multicellular organisms and present- day multicellular organisms - This does not suggest that early multicellular organisms and colonial unicellular organisms have common ancestor. Hence this is not the correct option.

Option D. differences between early multicellular organisms and present- day multicellular organisms − This does not indicate that early multicellular organisms and colonial unicellular organisms have common origins. Hence this is not the correct option.