The Evolution of Cells, Third Edition

Terry Smith, Kristi Lew

Description

Some 3.8 billion years ago, in an era of churning seas and murky skies, a few chemicals combined under the right conditions, and life emerged on planet Earth. From that first cell, life progressed to a myriad of one-celled organisms, to organisms capable of photosynthesis, to multicellular organisms, to simple plant and animal forms, up to the complex life-forms we know today.

The Evolution of Cells, Third Edition traces these developments and how they may have occurred, through the scientific study of fossils, relationships among organisms, biochemistry of current life-forms, genetic sequencing, and laboratory experiments. Readers will also explore the complexity of cells and the ways science is making use of internal cell mechanisms for new discoveries in sustainable energy sources, cleaning up pollution, improving the food supply, and treating disease.

Sujets

• Life Sciences
• Sciences et techniques
• Organism
• Biology
• Medicine
• Research
• Discovery
• Science

Informations

• Publié par: Infobase Publishing
• Date de parution: 01 juillet 2021
• Nombre de lectures: 0
• EAN13: 9781646937295
• Langue: English
• Poids de l'ouvrage: 1 Mo

Extrait

The Evolution of Cells, Third Edition
Copyright © 2021 by Infobase
All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:
Chelsea House An imprint of Infobase 132 West 31st Street New York NY 10001
ISBN 978-1-64693-729-5
You can find Chelsea House on the World Wide Web at http://www.infobase.com
Contents Chapters The Beginnings of Life The Chemistry of Life Prokaryotes: The Simplest Cells Eukaryotes: The Cells of Complex Life Cells in Action Genetics and Cell Evolution Plant Cells and Evolution The Diversity of Complex Cells Cells: Key to the Future Support Materials Glossary Bibliography Further Resources About the Authors Index
Chapters
The Beginnings of Life

There is something about being human that instills in us a sense of wonder. When we stop to think about it, the very idea of life seems to be such a mystery. Where did we come from? How did life begin? When we look at the sky, we wonder about the vastness of the universe and whether other life may exist there. If we look through a microscope at a drop of pond water, we are amazed at the variety of tiny creatures we see.
Since cells form the very basis of life, it is only natural that our sense of wonder also extends to the cell. Where did the first cells come from? How is it possible that cells with the same basic components can form creatures as simple as bacteria or as complex as a human being? How do brain cells allow us to think, and how do cells of the hand work together to allow us to hold a pencil? Video animations of cell interiors let us see the amazing molecular "machines" that move around inside every cell as they copy genetic molecules, shuttle nutrients, relay messages, and build or repair membranes.
The exact nature of the very first life on our planet and how it came into being may be forever unknown. Yet research into the nature of life can help us understand what is in the realm of possibility. Scientists have vastly increased our knowledge about the connectedness of all life forms through their study of contemporary organisms and their genetic structures. Further investigations into the inner workings of cells still hold great promise in the fields of evolutionary biology, medicine, and bioengineering.
The Nature of Life and its Origins
Defining Life
The existence of life might seem to be an obvious fact, but coming up with a definition of life is not so simple. Even biologists have difficulty agreeing on a description that can include all possible life forms. How can microbiologists know if they have found life on Mars if they can't first agree what defines life? Furthermore, how is it possible to look for the first signs of life on Earth without this definition? A chemist may see life as a self-sustaining chemical system that can evolve, while a physicist may see life as an ordered system, in contrast to nature's tendency toward disorder. Gerald Joyce, a prominent researcher in the origin-of-life field, was quoted in Smithsonian magazine as joking that life could be defined as "that which is squishy." 1 Some scientists have even concluded that it is not possible to agree on a definition that includes all possible life forms! Allowing for the possibility that entirely new life forms may exist elsewhere in the universe, life as we know it on Earth shares certain features: the need to take in energy; production of waste that must be eliminated; growth; replication into similar life forms; and response to the environment, both as individual organisms and through evolution across generations.
Early Beliefs
There is evidence that even very ancient people were concerned about the nature of their existence and origins of life. Paintings of animal images from 10,000-30,000 years ago have been found in caves in Altamira, Spain, and the Vézère Valley of France. They suggest that the humans who painted them were even then grappling with the nature of existence and their place in nature. Stories about the beginning of life developed in most cultures, as ancient people struggled to understand their origins. Many of these beliefs about life's origin remain alive today in the poetry and religion of various cultures around the world.

Cave paintings found in the Vézère Valley in southwestern France feature images of animals. Discovered in 1940, they are believed to be about 17,000 years old.
Source: © Alamy. Hemis.
Recorded history of medieval Europe (from about A.D. 500– A.D. 1100) tells us that humans also came to depend on their observations to form their belief systems about the origin of life. If a piece of meat was left to rot, maggots soon appeared; to a person unfamiliar with science, it was easy to conclude that the maggots had spontaneously appeared in the rotten flesh. This gave rise to the commonly held belief in "spontaneous generation" as a source of many life forms. In fact, there was even a seventeenth-century recipe for the creation of mice: store dirty underwear with grains of wheat in an open jar and after 21 days mice will spontaneously appear. Although the real source of the mice seems obvious to us today, this belief was consistent with the knowledge of that era.
Era of Science
The idea of spontaneous generation of life held sway for several centuries. Beginning in the sixteenth century, the principles of modern science were also gradually coming into existence. Early scientists began to systematically investigate their observations of the natural world. Tools such as the microscope were invented, and for the first time, it was possible to view a hidden world unavailable to the naked eye. Even if they did not understand what they were observing, these early scientists realized that plants were made of tiny partitions they called cells , for their resemblance to the tiny residential cells of monks. They also observed organisms they called animalcules , which they believed arose spontaneously in water after it sat for a few days in the laboratory.
Then, in 1859, the French Academy of Science sponsored a competition for the best experiment to prove or disprove the idea of spontaneous generation. Louis Pasteur, a prominent scientist of the time, set out to disprove the idea. His experiment has become a classic example of what we know as the scientific method, which forms the basis of all modern science.
Pasteur started with two glass flasks into each of which he poured a meat broth. One flask had a straight neck; Pasteur bent the neck of the second flask into a curved shape. The contents of both flasks were then heated to a high temperature to kill any living matter in the broth. The flasks were left at room temperature and exposed to the air for some time. Microorganisms present in the air could fall into the straight-neck flask but not into the flask with the curved neck. At the end of the experiment, the broth in the straight-neck flask was dark and cloudy, and microorganisms could be observed in the broth. No evidence of organisms was found in the curve-necked flask, thereby demonstrating that organisms were not spontaneously generated in the broth but had fallen in from the air.

Louis Pasteur’s swan-neck flask experiment designed to disprove the theory of spontaneous generation. He partly filled the body of the flask with a nutrient rich broth. He then boiled the broth killing any bacteria already present in the liquid. If the swan-neck remained intact, there was no growth in the broth. Once the broth was exposed to the air (where bacteria were present) by either breaking the neck or allowing the broth to make contact with the air by tilting the flask, bacteria grew in the once-sterile broth, thus proving that the bacteria would not spontaneously arise from the nutrient broth, but had to be introduced from the outside.
Source: Infobase Learning.

To convince the French Academy of the truth of his discovery, Pasteur first formed a hypothesis based on his previous observations of the growth of microorganisms. It stated that microorganisms would not grow in the sterilized broth if they could not fall into the flask from the air. His next step was to conduct an experiment consisting of a control case (straight-neck flask) and a test case (curved-neck flask). After observing the results of the experiment, Pasteur concluded, "Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment." Today's scientists who seek evidence of the first life forms on Earth—whether analyzing fossils or conducting experiments in chemistry or genetics—continue to adhere to the centuries old steps of the scientific method.
Early Earth
How life on Earth began is one of the most fundamental unexplained questions in modern science. No one will ever know for certain exactly how it came about. Yet, to think about how life could have begun, how that very first cell developed, it is essential to understand the physical conditions that existed on early Earth.
Our solar system is thought to have formed some 4.5-4.6 billion years ago from a giant rotating cloud of gas and dust. 2 , 3 As much of the rotating material collapsed toward the center, a new star, our planet's Sun, was formed. Other large chunks of material collided and eventually attracted additional matter until rotating planets formed. Shortly after Earth's formation, in an event known as the Giant Impact, Earth collided with another large object, resulting in the expulsion of a chunk of vaporized rock that gave rise to our moon. Earth would have been a violent place over the next billion or so years as it underwent frequent collisions with asteroids and comets, periods of extreme heat, and volcanic eruptions.
Gradually, the Earth cooled, and the oceans, a surface crust, and surrou