a2.3: viruses (hl only)
The unit is planned for
- 2 hrs
Guiding questions
- How can viruses exist with so few genes?
- In what ways do viruses vary?
Understandings:
1.5.U.1 Cells can only be formed by division of pre-existing cells. (Oxford Biology Course Companion page 45).
- Discuss two implications of all cells being formed from preexisting cells.
image from askabiologist.asu.edu
Remember the Cell Theory?
Prokaryotic cells are formed during a process called binary fission.
Eukaryotic cells form new identical cells by the process called mitosis (genetically identical) and form sex cells through meiosis (haploid cells which not genetically identical to the parent cell and contain half the genetic material). Cell division forms the new cells from pre-existing cells replaced the concept of spontaneous generation, where cells were formed from inanimate matter.
The chemical processes that contributed to the initial formation of biological life required specific conditions to proceed. This included a reducing atmosphere and high temperatures (>100ºC) or electrical discharges to catalyse chemical reactions. These conditions do not commonly exist on modern Earth and hence living cells cannot arise independently by abiogenesis. Instead, cells can only be formed by the division of pre-existing cells (biogenesis)
- all living things are composed of cells or cell parts
- the cell is the smallest unit of life
- cells only arise from pre-existing cells
Prokaryotic cells are formed during a process called binary fission.
Eukaryotic cells form new identical cells by the process called mitosis (genetically identical) and form sex cells through meiosis (haploid cells which not genetically identical to the parent cell and contain half the genetic material). Cell division forms the new cells from pre-existing cells replaced the concept of spontaneous generation, where cells were formed from inanimate matter.
The chemical processes that contributed to the initial formation of biological life required specific conditions to proceed. This included a reducing atmosphere and high temperatures (>100ºC) or electrical discharges to catalyse chemical reactions. These conditions do not commonly exist on modern Earth and hence living cells cannot arise independently by abiogenesis. Instead, cells can only be formed by the division of pre-existing cells (biogenesis)
1.5.U.2 The first cells must have arisen from non-living material. (Oxford Biology Course Companion page 48).
- Outline the four processes needed for the spontaneous origin of cells on Earth.
- Outline the experiments of Miller and Urey into the origin of organic compounds.
- Define polymerization, monomer and polymer.
- Outline two properties of RNA that would have allowed it to play a role in the origin of life.
Abiogenesis is the natural process of life arising from non-living matter such as simple organic compounds.
If we go back to how the very first living cells were created, we have to conclude they either originated from non-living material, came from somewhere else in the universe or were created by some other unknown entity
These are the hypothesized steps of how living cells possibly developed from non-living material over millions of years
If we go back to how the very first living cells were created, we have to conclude they either originated from non-living material, came from somewhere else in the universe or were created by some other unknown entity
These are the hypothesized steps of how living cells possibly developed from non-living material over millions of years
- Production of carbon compounds such amino acids and sugars. Miler and Urey’s experiment showed how this could happen by passing water vapour through Ammonia, methane and hydrogen (early earth atmosphere). They added electricity to simulate lightening discharge. They found they could create amino acids and carbon compounds
- Assembly of carbon compounds into polymers might have occurred at the deep sea hydrothermal vents, which could have supplied the inorganic compounds such as iron sulphide and thermal energy for the assembly
- Formation of membranes would be possible if phospholipids were some of the first polymers created. These phospholipids would naturally form vesicles allowing for a different environment to exist inside compared to the surrounding water
- Development of a mechanism for inheritance would be needed in order for the organism to replicate and pass its DNA on to the next generation. Current organisms need enzymes to replicate DNA; however, enzymes are created by the genes on the DNA. A possible solution to this would be RNA being the first nucleic acid formed because it is self-replicating and can also act as a catalyst.
image from KaiserScience
The non-living synthesis of simple organic molecules has been demonstrated by the Miller-Urey experiment. Stanley Miller and Harold Urey recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes. Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions). The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules.
The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions). The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
After this time, the condensed mixture was analysed and found to contain traces of simple organic molecules.
1.5.U.3 The origin of eukaryotic cells can be explained by the endosymbiotic theory. (Oxford Biology Course Companion page 49).
- State the endosymbiosis theory.
- Outline the major events in the origin of eukaryotic cells.
- Describe the evidence for the endosymbiotic theory
There is compelling evidence that mitochondria and chloroplasts were once primitive free-living bacterial cells.
Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and the bacteria ingested through endocytosis, could easily become dependent on one another for survival, resulting in a permanent relationship. As long as the smaller mitochondria living inside the cytoplasm of the larger cell divided at the same rate, they could persist indefinitely inside those cells.
The smaller cell was provided food and protection by the larger cell and the smaller mitochondria would supply energy through aerobic respiration for the larger cell. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.
Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and the bacteria ingested through endocytosis, could easily become dependent on one another for survival, resulting in a permanent relationship. As long as the smaller mitochondria living inside the cytoplasm of the larger cell divided at the same rate, they could persist indefinitely inside those cells.
The smaller cell was provided food and protection by the larger cell and the smaller mitochondria would supply energy through aerobic respiration for the larger cell. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.
Application:
1.5.A.1 Evidence from Pasteur’s experiments that spontaneous generation of cells and organisms does not now occur on Earth. (Oxford Biology Course Companion page 47).
- Define spontaneous generation.
- Describe Pasteur’s experiments about spontaneous generation.
- Explain why Pasteur’s experiments did not support the idea of spontaneous generation.
image from http://www.brighthub.com/
For centuries people accepted the "spontaneous generation" of life from inanimate matter. When this long-standing myth was finally dispelled in the mid-1800s, it became clear that all life must arise from pre-existing life — via a process of reproduction. If cells are the fundamental units of life, they too must have a reproductive mechanism that maintains the proper chromosome number in each cell. About a decade after the publication of Mendel's paper,scientists carefully documented the behavior of chromosomes during cell division (mitosis), using dyes to make them visible. First, each chromosome copies itself, and the duplicates line up at the "equator" of the cell. Then, duplicate copies of each chromosome are pulled toward opposite poles. Finally, the cell splits at the equator, producing two new cells with identical sets of chromosomes.
Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)
"Omne vivum ex vivo” – All life (is) from life
The law of biogenesis is largely attributed to Louis Pasteur, who demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass. The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation). Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside. From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur.
Biogenesis describes the principle that living things only arise from other living things by reproduction (not spontaneous generation)
"Omne vivum ex vivo” – All life (is) from life
The law of biogenesis is largely attributed to Louis Pasteur, who demonstrated that emergent bacterial growth in nutrient broths was due to contamination by pre-existing cells Broths were stored in vessels that contained long tubings (swan neck ducts) that did not allow external dust particles to pass. The broths were boiled to kill any micro-organisms present in the growth medium (sterilisation). Growth only occurred in the broth if the flask was broken open, exposing the contents to contaminants from the outside. From this it was concluded that emergent bacterial growth came from external contaminants and did not spontaneously occur.
Key Terms:
|
cell theory
endocytosis prokaryotes chloroplasts aerobic respiration abiogenesis |
multinucleated cell
Pasteur Miller and Urey 70s ribosomes anaerobic respiration |
endosymbiotic
polymers symbiosis circular DNA linear chromosomes |
eukaryotic
monomers polymerization chromosomes inorganic |
mitochondria
inheritance mutualistic nucleus organic |
Class Materials:
Synthesis of Inorganic Molecules ppt
Polymerization ppt
Synthesis and Polymerization notes
Origin of Life article
Origin of Life worksheet
Topic 1.5 Review Notes
Topic 1.5 Kahoot Review Quiz
Synthesis of Inorganic Molecules ppt
Polymerization ppt
Synthesis and Polymerization notes
Origin of Life article
Origin of Life worksheet
Topic 1.5 Review Notes
Topic 1.5 Kahoot Review Quiz
Topic 1.5 Origin of Cells Powerpoint and Notes by Chris Payne
Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Useful Links:
Evidence against spontaneous generation
Science as a process: arriving at scientific insights by Sumanas Inc.
Rejecting spontaneous generation a simulated by PH School
Evolution of the first cells
Miller-Urey experiment from Stanley Miller
The origin of complex life: it was all about energy - Ed Yong
Endosymbiosis
The evolution of organelles - Sunamas Inc.
Endosymbiosis - McGraw and Hill
Evolution of the cell - Learn.genetics
In the News:
TOK
- Biology is the study of life, yet life is an emergent property. Under what circumstances is a systems approach productive in biology and under what circumstances is a reductionist approach more appropriate? How do scientists decide between competing approaches?
Video Clips:
Four and a half billion years ago, the young Earth was a hellish place—a seething chaos of meteorite impacts, volcanoes belching noxious gases, and lightning flashing through a thin, torrid atmosphere. Then, in a process that has puzzled scientists for decades, life emerged. But how? Mineralogist Robert Hazen as he journeys around the globe. From an ancient Moroccan market to the Australian Outback, he advances a startling and counterintuitive idea—that the rocks beneath our feet were not only essential to jump-starting life, but that microbial life helped give birth to hundreds of minerals we know and depend on today. It's a theory of the co-evolution of Earth and life that is reshaping the grand-narrative of our planet’s story.
Darwin's theory of biological evolution helps us understand how simple life forms can give rise to complex lifeforms, but how did the first reproducing creatures come about? The origin of life needs its own explanation
The Miller-Urey experiment was the first attempt to scientifically explore ideas about the origin of life. Stanley Miller simulated conditions thought be common on the ancient Earth. The purpose was to test the idea that the complex molecules of life (in this case, amino acids) could have arisen on our young planet through simple, natural chemical reactions.
RNA may have been the origin of life on Earth. Go on a whirlwind tour of RNA's evolving role through billions of years of evolutionary history.
Imagine you swallowed a small bird and suddenly gained the ability to fly … or you ate a cobra and were able to spit poisonous venom! Well, throughout the history of life (and specifically during the evolution of complex eukaryotic cells) things like this happened all the time. Adam Jacobson explains endosymbiosis, a type of symbiosis in which one symbiotic organism lives inside anothe
In his lab, Martin Hanczyc makes "protocells," experimental blobs of chemicals that behave like living cells. His work demonstrates how life might have first occurred on Earth ... and perhaps elsewhere too.
Before life existed on Earth, there was just matter, inorganic dead "stuff." How improbable is it that life arose? And -- could it use a different type of chemistry? Using an elegant definition of life (anything that can evolve), chemist Lee Cronin is exploring this question by attempting to create a fully inorganic cell using a "Lego kit" of inorganic molecules -- no carbon -- that can assemble, replicate and compete.
Paul Andersen explains how eukaryotic cells were formed through a process of endosymbiosis. He describes how aerobic bacteria became mitochondria and cyanobacteria became chloroplasts. He mentions an example of symbiosis that occurs today and mentions the importance of Dr. Lynn Margulis in the development of this modern theory.
This isn't information that we cover in class, however, it is good to know.
Scientists use “carbon dating” to determine the age of ancient artifacts and dinosaur bones. But what is the real science behind carbon dating, and how does it work?
Scientists use “carbon dating” to determine the age of ancient artifacts and dinosaur bones. But what is the real science behind carbon dating, and how does it work?
It turns out life may have gotten its start pretty early in Earth's history, and while the first couple billion years saw several important developments, the period was still dominated by very simple life forms
