Origin of Cells

  • Created by: Lotto65
  • Created on: 14-01-17 13:30
What is spontaneous generation?
The theory that life could appear from non-living matter
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When did scientists believe in spontaneous generation?
Until the 19th century
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Is spontaneous generation possible?
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Is there any evidence that living cells can be formed on Earth today from non-living matter?
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How do living cells occur?
Division of pre-existing cells
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Has life always existed on Earth?
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What are the questions scientists are confused about today regarding the origin of life?
How could spontaneous generation occur then but not now? How did the first cells evolve from non-living matter?
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What suggests that all life evolved from the same original cells?
The 64 codons in the genetic code all have the same meaning in cells of all living organisms, apart from minor variations - universality of genetic code
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How did minor differences in genetic code come about?
Since the common origin of life on Earth
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What did Louis Pasteur prove?
The principle that cells can only arise from pre-existing cells
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What was Louis Pasteur's experiment?
He placed nutrient broth in swan-neck flasks and then melting the necks to bend them into shapes. Boiled the broth in some and left others as controls
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What were the results of Louis Pasteur's experiment?
Fungi and other organisms appeared in the unboiled broth but not in the boiled one; even after a long time
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What did people suggest was needed for spontaneous generation to occur in Louis Pasteur's experiment?
The broth should be in contact with the air
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What did Pasteur do after his first experiment?
Snapped the necks of some of the swan-neck flasks so they had short vertical necks
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What were the results of Pasteur's second experiment?
Fungi and organisms appeared in the flasks with snapped necks and decomposed the broth
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What did Pasteur conclude from his experiments?
The swan necks prevented organisms from the air getting into the flasks and no organisms appeared spontaneously - there would have been organisms in the ones they couldn't reach
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What is symbiosis?
Two organisms living together
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How does endosymbiosis work?
The larger cell takes in a smaller cell by endocytosis so it is in a vesicle in the cytoplasm of the larger cell
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What happens to the smaller cell in endosymbiosis instead of being digested?
It performs a useful function for the larger cell
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How many times does the smaller cell divide in relation to the larger cell?
At least as many times as the larger cell divides so every cell produced has at least one or more smaller cells in its cytoplasm
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How many times did the endosymbiosis happen according to theory?
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What happened the first time endosymbiosis happened?
A cell respiring anaerobically took in a bacterium respiring aerobically. The bacterium supplied itself and the large cell with more energy as ATP, giving the large cell a competitive advantage. The bacterium evolved into mitochondria
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What did the large cell evolve into after the bacterium evolved into mitochondria?
Heterotrophic eukaryote
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Why did the bacterium give the large cell a competitive advantage?
Aerobic respiration is more efficient than anaerobic respiration and the bacterium was supplying the large cell with large amounts of energy as ATP
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Give an example of a heterotrophic eukaryote
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What happened in the second time of endosymbiosis?
A heterotrophic cell took in a photosynthetic bacterium which provided the cell with organic compounds and autotrophic propertie. The photosynthetic bacterium evolved into chloroplasts and the heterotrophic cell evolved into an autotrophic eukaryote
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What is an autotrophic property?
The way that an organism can have self-nourishment using inorganic substances and using photosynthesis
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Give an example of an autotrophic eukaryote
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What characteristics does the endosymbiosis theory explain about mitochondria and chloroplasts?
Grow and divide like cells; synthesise some of own proteins using 70S ribosomes and mRNA; Naked loop of DNA; Double membrane; own genes; division of pre-existing organelles
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How did scientists make the first 'artificial cell'?
Made the base sequence of DNA of the bacterium 'mycoplasma mycoides' with some deliberate changes; Transferred it to 'mycoplasma capricolum' to make 'Mycoplasma mycoides'
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What is the story of silphium?
Silphium was a plant known for medicinal uses like birth control in Libya. It was so widely collected that it became extinct. It never arose again spontaneously and remained extinct
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What did Francesco Redi show?
Maggots can only develop on meat if flies were allowed to come into contact with it
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What did Lazzaro Spallanzani show?
When you boiled soup in eight containers, left four open and four closed, organisms grew only in the ones left open
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What other three principles suggest cells arise from pre-existing cells?
A cell is complex and no natural mechanism suggested producing cells from smaller units; No example of increasing cell population with cell division; Viruses produced from simple units but are not cells - they can only be produced inside host cells
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What was in Louis Pasteur's nutrient broth?
Yeast and sugar
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What did Pasteur change when he repeated his experiment?
He did the experiment with urine and milk
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What did Miller and Urey do?
Passed steam through a mixture of methane, hydrogen and ammonia. Electrical discharges represented lightning and then amino acids and other carbon compounds for life were produced
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What was the methane, hydrogen and ammonia supposed to represent in the Miller and Urey experiment?
The atmosphere of early Earth
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How could the assembly of carbon compounds into polymers have occurred?
In deep sea vents there is gushing hot water with chemicals like iron sulphide - suggesting supplies and a source of energy for polymerisation
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How would membranes have formed?
They would have naturally assembled into bilayers. Experiments show these bilayers readily form vesicles ressembling the plasma membrane
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What is required to allow replication of DNA and passing onto offspring?
DNA and enzymes - but you need genes to make the enzymes
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How was genetic information passed on in the beginning?
By RNA that can replicate itself and act as a catalyst
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What is a mutualistic relationship?
A symbiotic relationship where both organisms benefited
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How did the small cell benefit in endosymbiosis?
Supplied with food by the larger cell
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True/false: Natural selection favours cells in an endosymbiotic relationship
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How was the nucleus formed in the beginning?
A prokaryote grows in size and develops folds in the membrane to sustain sufficient SA:V ratio. Infoldings are pinched off to form an internal membrane. Nucleoid region is closed in internal membrane
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When did scientists believe in spontaneous generation?


Until the 19th century

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Is spontaneous generation possible?


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Card 4


Is there any evidence that living cells can be formed on Earth today from non-living matter?


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Card 5


How do living cells occur?


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