Endosymbiont Hypothesis and Membrane Invagination Hypothesis

Concept of Evolution

In a bid to discuss the cause of the diversity of life and the correlation amongst living organisms, two schools of thought emerged in the early 19th century.

Creationists believed in the Theory of special creation, whereas evolutionists believed in the Theory of Natural Selection.

According to the theory of special creation, all living things originated in their present forms and were specifically created by Nature.

Amongst the scientists who believed in divine creation was Carolus Linnaeus (1707-1778).

The concept that organisms might develop through time, with one kind of organism causing another kind of organism, is an ancient one, existing from the days of Aristotle.

Aristotle recognized that organisms varied from relatively basic to really complicated structures. However, the present-day principle of evolution is based on known history.

Let us now talk about some details of the work done by these scientists.

As you know, Carolus Linnaeus in the eighteenth-century classified organisms. He grouped similar species in the same genus and similar genera in one family.

But as a natural theologian, he thought that species were permanent creations. A century later, the taxonomic system of Linnaeus ended up being a centerpiece in Darwin’s arguments for evolution.

Evolution from Prokaryotes to Eukaryotes

Among the speculations attempting to explain the origin of life is that it might have begun deep in the oceans, in undersea warm springs called hydrothermal vents. These vents could have provided the energy and basic materials (for the origin and survival of early life kinds. A group of bacteria, called archaebacteria-that tolerate temperatures as much as 120 ° C and appear to have actually undergone less evolutionary change than any other living species supports this vent hypothesis.

The nutrients produced in the primitive environment would have limited early life. If life were to continue, another source of nutrients as needed. Photosynthesis, probably released living organisms from a diminishing supply of nutrients.

The first photosynthetic organisms most likely used hydrogen sulfide as a source of hydrogen for reducing CO2 to sugars. Later, water served this same function, and oxygen freed by photosynthetic responses started to accumulate in the environment. Earth and its atmosphere slowly started to alter.

Ozone in the upper atmosphere started to filter ultraviolet radiation from the sun, the reducing atmosphere slowly ended up being an oxidizing atmosphere, and a minimum of some living organisms started to utilize oxygen. About 420 million years ago, enough protective ozone had actually developed to make life on land possible. Ironically, the modification from a reducing environment to an oxidizing environment also implied that life could no longer occur abiotically.

The first cells were more than likely really simple prokaryotic forms. The prokaryotes might have developed more than 3.5 billion years back. Eukaryotes are believed to have first appeared about 1.5 billion years ago.

Endosymbiont Hypothesis

The eukaryotic cell may have developed when a large anaerobic (living without oxygen) amoeboid prokaryote ingested small aerobic (living with oxygen) bacteria and stabilized them instead of absorbing or digesting them. This concept is referred to as the endosymbiont hypothesis and was first proposed by Lynn Margulis.

According to this hypothesis, the aerobic bacteria turned into mitochondria, which are the sites of aerobic respiration and many energy conversions in eukaryotic cells. The belongings of these mitochondria like endosymbionts brought the advantage of aerobic respiration to the host.

Endosymbiont-Hypothes

Flagella (whiplike structures) might have arisen through the consumption of prokaryotes similar to spiral-shaped bacteria called spirochetes. Intake of prokaryotes that looked like present-day cyanobacteria might have caused the endosymbiotic development of chloroplasts in plants.

Further Reading:  Glycolysis, Pyruvic Oxidation, Krebs cycle, and Respiratory Chain
Membrane Invagination Hypothesis

Another hypothesis for the evolution of eukaryotic cells proposes that the prokaryotic cell membrane invaginated (folded inward) to confine copies of its hereditary product. This invagination led to the formation of a number of double membranes bound entities (organelles) in a single cell. These entities might then have actually evolved into the eukaryotic mitochondrion, nucleus, chloroplast, and so on.

Membrane-Invagination

Whatever the exact mechanism for the advancement of the eukaryotic cell might be, the formation of the eukaryotic cell led to a significant boost in the intricacy and diversity of life-forms on the earth. At first, these newly formed eukaryotic cells existed only on their own.

Later, nevertheless, some most likely developed into multicellular organisms in which different cells became specialized into tissues, which, in turn, formed organs for many different functions. These multicellular kinds then adjusted themselves to live in a huge range of environments.

Multiple Choice Questions (MCQs) – Endosymbiont Hypothesis and Membrane Invagination Hypothesis

  1. What is the main focus of the Endosymbiont Hypothesis?
    • A) Origin of life in hydrothermal vents
    • B) Evolution from prokaryotes to eukaryotes
    • C) Membrane invagination in primitive cells
    • D) Creation of diverse life forms by natural selection
    • Answer: B
  2. Who first proposed the Endosymbiont Hypothesis?
    • A) Charles Darwin
    • B) Lynn Margulis
    • C) Carolus Linnaeus
    • D) Aristotle
    • Answer: B
  3. According to the Endosymbiont Hypothesis, what do mitochondria evolve from?
    • A) Anaerobic amoeboid prokaryotes
    • B) Aerobic bacteria
    • C) Cyanobacteria
    • D) Spiral-shaped bacteria
    • Answer: B
  4. What is the role of mitochondria in eukaryotic cells, according to the Endosymbiont Hypothesis?
    • A) Aerobic respiration
    • B) Photosynthesis
    • C) Anaerobic metabolism
    • D) Protein synthesis
    • Answer: A
  5. Which organelles might have originated through the endosymbiotic development of prokaryotes resembling cyanobacteria?
    • A) Mitochondria
    • B) Nucleus
    • C) Chloroplasts
    • D) Flagella
    • Answer: C
  6. What is the Membrane Invagination Hypothesis proposing?
    • A) Evolution from prokaryotes to eukaryotes
    • B) Formation of double-membraned organelles
    • C) Origin of life in hydrothermal vents
    • D) Special creation of species
    • Answer: B
  7. How does the Membrane Invagination Hypothesis suggest the evolution of eukaryotic cells?
    • A) Through ingestion of aerobic bacteria
    • B) Through invagination of the cell membrane
    • C) Through photosynthetic reactions
    • D) Through natural selection
    • Answer: B
  8. Which cellular structures might have formed as a result of membrane invagination?
    • A) Ribosomes
    • B) Nucleus
    • C) Chloroplasts
    • D) Flagella
    • Answer: B
  9. Who proposed the Membrane Invagination Hypothesis?
    • A) Lynn Margulis
    • B) Charles Darwin
    • C) Carolus Linnaeus
    • D) Aristotle
    • Answer: Not provided in the passage
  10. According to the passage, what did early life forms rely on for nutrients in the primitive environment?
  • A) Photosynthesis
  • B) Hydrothermal vents
  • C) Ozone
  • D) External organic sources
  • Answer: B
  1. When did eukaryotes first appear, according to the passage?
    • A) About 1.5 billion years ago
    • B) About 3.5 billion years ago
    • C) About 420 million years ago
    • D) About 120 million years ago
    • Answer: A
  2. What was the primary source of hydrogen for the first photosynthetic organisms?
    • A) Oxygen
    • B) Water
    • C) Hydrogen sulfide
    • D) Carbon dioxide
    • Answer: C
  3. According to the passage, what did the development of ozone in the upper atmosphere contribute to?
    • A) Accumulation of oxygen in the environment
    • B) Increased ultraviolet radiation from the sun
    • C) Abiotic life
    • D) Hydrothermal vent hypothesis
    • Answer: A
  4. Which scientist believed in the Theory of Special Creation and contributed to taxonomy?
    • A) Lynn Margulis
    • B) Charles Darwin
    • C) Carolus Linnaeus
    • D) Aristotle
    • Answer: C
  5. What is the main contrast between Creationists and Evolutionists, as mentioned in the passage?
    • A) Origin of life in hydrothermal vents
    • B) Cause of the diversity of life
    • C) Role of natural selection
    • D) Classification of organisms
    • Answer: B
  6. What role did hydrothermal vents play in the origin of life, according to one of the speculations mentioned in the passage?
    • A) Providing energy for aerobic respiration
    • B) Acting as sources of basic materials for life
    • C) Serving as environments for membrane invagination
    • D) Enhancing natural selection processes
    • Answer: B
  7. What is the significance of the development of protective ozone in the upper atmosphere, as per the passage?
    • A) Increased ultraviolet radiation
    • B) Abiotic life forms
    • C) Making life on land possible
    • D) Accelerating photosynthetic reactions
    • Answer: C
  8. How did the taxonomic system of Linnaeus become a centerpiece in Darwin’s arguments for evolution?
    • A) By classifying organisms based on their size
    • B) By proposing the endosymbiont hypothesis
    • C) By supporting the Theory of Special Creation
    • D) By grouping similar species and genera
    • Answer: D
  9. What might have been the source of hydrogen for the first photosynthetic organisms, as suggested in the passage?
    • A) Water
    • B) Oxygen
    • C) Hydrogen sulfide
    • D) Carbon dioxide
    • Answer: C
  10. According to the Membrane Invagination Hypothesis, what process led to the formation of double-membraned entities in eukaryotic cells?
    • A) Cellular division
    • B) Membrane digestion
    • C) Cell membrane invagination
    • D) Mitochondrial fusion
    • Answer: C
  11. Who is credited with proposing the idea that flagella might have originated through the consumption of prokaryotes?
    • A) Charles Darwin
    • B) Lynn Margulis
    • C) Aristotle
    • D) Carolus Linnaeus
    • Answer: B
Further Reading:  Xenobiotics and Mechanism of Xenobiotics

 

Frequently Asked Questions (FAQs) – Endosymbiont Hypothesis and Membrane Invagination Hypothesis

  1. Q: What are the two main schools of thought mentioned in the passage regarding the cause of the diversity of life?
    • A: Creationists believed in the Theory of Special Creation, while evolutionists believed in the Theory of Natural Selection.
  2. Q: Who was Carolus Linnaeus, and what was his contribution to the concept of evolution?
    • A: Carolus Linnaeus was an eighteenth-century scientist who classified organisms. His taxonomic system became a centerpiece in Darwin’s arguments for evolution.
  3. Q: How did early life forms possibly obtain nutrients in the primitive environment, according to the passage?
    • A: Nutrients might have been obtained from undersea warm springs called hydrothermal vents.
  4. Q: What role did hydrothermal vents play in the speculations about the origin of life?
    • A: Hydrothermal vents are speculated to have provided the energy and basic materials for the origin and survival of early life forms.
  5. Q: What is the significance of oxygen accumulation in the environment due to photosynthetic reactions?
    • A: Oxygen accumulation led to the alteration of Earth’s atmosphere, the development of protective ozone, and the possibility of life on land.
  6. Q: Who first proposed the Endosymbiont Hypothesis, and what does it suggest about the origin of eukaryotic cells?
    • A: Lynn Margulis proposed the Endosymbiont Hypothesis, suggesting that eukaryotic cells evolved when anaerobic prokaryotes ingested aerobic bacteria, leading to the development of mitochondria.
  7. Q: According to the Endosymbiont Hypothesis, what organelles might have originated from the consumption of prokaryotes resembling cyanobacteria?
    • A: Chloroplasts might have originated through endosymbiotic development.
  8. Q: What is the Membrane Invagination Hypothesis proposing about the evolution of eukaryotic cells?
    • A: The hypothesis proposes that the prokaryotic cell membrane invaginated to confine copies of its hereditary material, leading to the formation of double-membraned entities in a single cell.
  9. Q: How did the formation of eukaryotic cells impact the diversity of life-forms on Earth?
    • A: The formation of eukaryotic cells significantly increased the complexity and diversity of life-forms on Earth.
  10. Q: When did eukaryotes first appear, and what might have been the origin of the first cells?
    • A: Eukaryotes are believed to have first appeared about 1.5 billion years ago, and the first cells were likely very simple prokaryotic forms.
  11. Q: How did the transition from a reducing environment to an oxidizing environment impact the possibility of abiotic life?
    • A: The transition made it unlikely for life to occur abiotically.
  12. Q: What is the role of flagella in the context of the Endosymbiont Hypothesis?
    • A: Flagella might have originated through the consumption of prokaryotes, contributing to the evolution of eukaryotic cells.
  13. Q: Are there any proposed mechanisms for the evolution of eukaryotic cells besides the Endosymbiont Hypothesis?
    • A: Yes, the Membrane Invagination Hypothesis suggests that the prokaryotic cell membrane invaginated, leading to the formation of organelles.
  14. Q: What drove the adaptation of multicellular organisms, according to the passage?
    • A: Multicellular organisms adapted as different cells became specialized into tissues, forming organs for various functions.
  15. Q: Is there any recommended further reading related to the passage content?
    • A: Yes, there are references to “Conjugation in Bacteria (E. coli)” and “Basic Techniques of Genetic Engineering in Plants” for additional information.
Further Reading:  Phylum Arthropoda - Multiple Choice Questions (MCQs)

 

Wrap up

The tutorial explores the evolution of life from prokaryotes to eukaryotes, focusing on two prominent hypotheses: the Endosymbiont Hypothesis and the Membrane Invagination Hypothesis. It begins by discussing the historical context of the concept of evolution, contrasting creationist and evolutionist perspectives. Carolus Linnaeus’s taxonomic contributions become integral in later evolutionary discussions.

The evolution from prokaryotes to eukaryotes is explored through speculations about life’s origin in hydrothermal vents and the crucial role of archaebacteria. The transition from a reducing to an oxidizing environment, marked by the development of protective ozone, is highlighted. The passage details the probable emergence of eukaryotic cells around 1.5 billion years ago.

The Endosymbiont Hypothesis, proposed by Lynn Margulis, suggests that eukaryotic cells evolved as anaerobic prokaryotes ingested aerobic bacteria, leading to the development of mitochondria. The hypothesis extends to the potential endosymbiotic origin of flagella and chloroplasts.

The Membrane Invagination Hypothesis proposes that eukaryotic cells originated when prokaryotic cell membranes invaginated, forming double-membraned organelles. This mechanism significantly increased the complexity and diversity of life-forms on Earth.

The tutorial concludes by emphasizing the transition from solitary eukaryotic cells to multicellular organisms, where specialized cells form tissues and organs for diverse functions, adapting to a variety of environments. The intricacies of these evolutionary processes contribute to the rich diversity of life on Earth.