Origins of Cell Flashcards
Define abiogenesis & Spontaneous generation & Distinguish the two
Abiogenesis — The theory that living cells arose from non-living matter
Spontaneous Generation — process by which living organisms develop from nonliving matter
The difference between abiogenesis and spontaneous generation
1) abiogenesis — the theory that states all life started from inorganic molecules
2) spontaneous generation – the theory that states life arises spontaneously and continually from nonliving matter.
List the 4 stage regarding the theory of abiogenesis
1) There was non-living synthesis of simple organic molecules
2) These simple organic molecules became assembled into more complex polymers
3) Certain polymers formed the capacity to self-replicate (enabling inheritance)
4) These molecules became packaged into membranes with an internal chemistry different from their surroundings (protobionts)
What Experiment Falsified the theory of Spontaneous Generation
Through Pasteur’s experiment involving the use pf swan-necked flasks.
Why is Spontaneous generation false?
There is no evidence that living cells can be formed on Earth today except by division of pre-existing cells. Spontaneous generation of cells is not
currently possible
What Experiment supports the theory of Abiogenesis?
Miller-Urey Experiment
Describe Pasteur’s experiment involving the use pf swan-necked flasks & state its significance
He placed samples of broth in flasks with long necks and then melted the glass of the necks and bent it into a variety of shapes. Pasteur then boiled the broth in some of the flasks to kill any organisms present but left others unboiled as controls. Fungi and other organisms soon appeared in the unboiled flasks but not in the boiled ones, even after long periods of time. The broth in the flasks was in contact with air, which it had been suggested was needed for spontaneous generation, yet no spontaneous generation occurred. Pasteur snapped the necks of some of the flasks to leave a shorter vertical neck. Organisms were soon apparent in these flasks and decomposed the broth
He concluded that the swan necks prevented organisms from the air getting into the flasks and that no organisms appeared spontaneously (disproving the theory of spontaneous generation)
What was the objective of Miller-Urey’s Experiment, describe the 4 steps, the outcome and highlight its significance
Stanley Miller and Harold Urey (1953) wanted to investigate how simple organic molecules might have arisen from the ingredients present on Earth before there was life
They recreated the postulated conditions of pre-biotic Earth using a closed system of flasks and tubes
1) Water was boiled to vapour to reflect the high temperatures common to Earth’s original conditions
2) The vapour was mixed with a variety of gases (including H2, CH4, NH3) to create a reducing atmosphere (no oxygen)
3) This mixture was then exposed to an electrical discharge (simulating the effects of lightning as an energy source for reactions)
4) The mixture was then allowed to cool (concentrating components) and left for a period of ~1 week
Outcome:
They discovered that amino acids (some known components of cell proteins)
were formed naturally, as well as other compounds
Significance:
how it is possible that a wide range of organic compounds could have formed on the pre-biotic Earth
With regards to the origin of the first cell, what is one of the biggest challenges in biology
One of the great challenges in biology is to understand how the first living cells evolved from non-living matter and why spontaneous generation could take place then but not now.
Define Symbiosis
Symbiosis is two organisms living together
Describe Endosymbiotic theory
A larger cell takes in a smaller cell by endocytosis, so the smaller cell is inside a vesicle in the cytoplasm of the larger cell. Instead of the smaller cell being
digested, it is kept alive and performs a useful function for the larger cell.
What do fossil records suggest about the origin of the first cells
The fossil record tells us the first cells were prokaryotes
How did eukaryotic cells arise?
Through endosymbiosis. Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis. Is presumed that a cell that respired anaerobically took in a bacterium that respired aerobically, supplying both itself and the larger cell with energy in the form of ATP. The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis). Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle. Gradually the aerobic bacterium evolved into mitochondria and
the larger cell evolved into heterotrophic eukaryotes alive today such as animals.
Define an endosymbiont
a cell which lives inside another cell with mutual benefit
Given evidence for endosymbiosis, focusing on Mitochondria and chloroplasts
(3 points)
Endosymbiotic theory explains the characteristics of mitochondria and chloroplasts
1) They grow and divide like cells.
2) They have a naked loop of DNA, like prokaryotes
3) They have double membranes, as expected when cells are taken into a vesicle by endocytosis.
Describe the 3 types of symbiotic relationships
1) Mutualism — a mutually beneficial symbiotic relationship.
2) commensalism - a one-sided symbiotic relationship.
3) parasitism - one species lives on, in or with a host species.
