Ch. 25 - The History of Life on Earth

Campbell - Campbell Biology 11th Edition

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Urry 11th Edition

Ch. 25 - The History of Life on Earth

Problem 5

Chapter 25, Problem 5

Which of the following steps has not yet been accomplished by scientists studying the origin of life?
a. Synthesis of small RNA polymers by ribozymes
b. Formation of molecular aggregates with selectively permeable membranes
c. Formation of protocells that use DNA to direct the polymerization of amino acids
d. Abiotic synthesis of organic molecules

Verified step by step guidance

Step 1: Begin by understanding the context of the question, which is about the origin of life and the scientific progress made in studying it. Scientists have explored various steps that could have led to the emergence of life on Earth.

Step 2: Review the listed options and identify the processes described. For example: (a) Synthesis of small RNA polymers by ribozymes refers to the ability of RNA molecules to catalyze reactions, (b) Formation of molecular aggregates with selectively permeable membranes refers to the creation of structures resembling cell membranes, (c) Formation of protocells that use DNA to direct the polymerization of amino acids refers to a more advanced step involving genetic material and protein synthesis, and (d) Abiotic synthesis of organic molecules refers to the creation of organic compounds without biological intervention.

Step 3: Recall the scientific advancements in each area. Scientists have successfully demonstrated abiotic synthesis of organic molecules in experiments like the Miller-Urey experiment. They have also observed the formation of molecular aggregates with selectively permeable membranes and the catalytic activity of ribozymes in synthesizing RNA polymers.

Step 4: Consider the complexity of the processes described. The formation of protocells that use DNA to direct the polymerization of amino acids is a highly advanced step requiring the integration of genetic material and protein synthesis, which has not yet been fully accomplished in laboratory settings.

Step 5: Conclude that the step not yet accomplished by scientists studying the origin of life is the formation of protocells that use DNA to direct the polymerization of amino acids, as this represents a significant leap in complexity compared to the other steps.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ribozymes and RNA Synthesis

Ribozymes are RNA molecules that can catalyze chemical reactions, including the synthesis of RNA polymers. This concept is crucial in understanding the RNA world hypothesis, which posits that self-replicating RNA molecules were precursors to current life forms. The ability of ribozymes to catalyze their own synthesis suggests a potential pathway for the origin of life.

Protocells and Membrane Formation

Protocells are simple, cell-like structures that are thought to be precursors to true cells. They typically consist of lipid membranes that can encapsulate biochemical reactions. The formation of protocells with selectively permeable membranes is significant because it represents a step towards cellular organization and the compartmentalization of biochemical processes necessary for life.

Abiotic Synthesis of Organic Molecules

Abiotic synthesis refers to the formation of organic compounds from inorganic precursors without the involvement of living organisms. This process is believed to have occurred on early Earth, leading to the creation of essential biomolecules like amino acids and nucleotides. Understanding abiotic synthesis is fundamental to exploring how life could have originated from non-living chemical systems.

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Related Practice

Textbook Question

The oxygen revolution changed Earth's environment dramatically. Which of the following took advantage of the presence of free oxygen in the oceans and atmosphere?

a. The evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules

b. The persistence of some animal groups in anaerobic habitats

c. The evolution of photosynthetic pigments that protected early algae from the corrosive effects of oxygen

d. The evolution of chloroplasts after early protists incorporated photosynthetic cyanobacteria

Textbook Question

Which factor most likely caused animals and plants in India to differ greatly from species in nearby Southeast Asia?

a. The species became separated by convergent evolution.

b. The climates of the two regions are similar.

c. India is in the process of separating from the rest of Asia.

d. India was a separate continent until 45 million years ago.

Textbook Question

Adaptive radiations can be a direct consequence of three of the following four factors. Select the exception:

a. Vacant ecological niches

b. Genetic drift

c. Colonization of an isolated region that contains suitable habitat and few competitor species

d. Evolutionary innovation

Textbook Question

A genetic change that caused a certain Hox gene to be expressed along the tip of a vertebrate limb bud instead of farther back helped make possible the evolution of the tetrapod limb. This type of change is illustrative of

a. The influence of environment on development.

b. Paedomorphosis.

c. A change in a developmental gene or in its regulation that altered the spatial organization of body parts.

d. Heterochrony.

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