Chapter 14, Problem 18A

Summary Introduction

To replace:

The underlined words with a correct vocabulary term from the Study Guide page

Introduction: Evidence indicates that a sequence of chemical events preceded the origin of life on Earth and that life has evolved continuously over time. There are many theories that attempted to explain the origin of life from spontaneous generation to theory of biogenesis to the endosymbiont theory.

Answer to Problem 18A

The endosymbiont theory was proposed by Lynn Margulis

Explanation of Solution

Eukaryotic fossils first appeared in record about 1.8 billion years ago, around two billion years after life first originated on Earth. Eukaryotic cells are more complex than prokaryotic cells. This led the scientists speculate that prokaryotes were involved in evolution of eukaryotes.

The endosymbiont theory which states that bacteria might have lived inside prokaryotes and eventually became organelles was proposed by Lynn Margulis. In 1966, Margulis proposed that the ancestors of eukaryotic cells lived in association with prokaryotic cells. In some cases prokaryotes might have lived inside eukaryotes. Prokaryotes might have entered as undigested prey or could have been internal parasites. Eventually the relationship became mutually beneficial and prokaryotic symbionts became organelles in eukaryotic cells.