Cell as the Basis of Life (Origin of the Cell) (HL) Flashcards
Explain how the Earth was formed?
accretion
- basically gravity pulled swirling dust leftovers from the sun’s creation and compressed the proto-Earth to in increase in temperature.
Then the proto-Earth cooled, to stratified according to density leading to a layered composition (aka the crust, upper mantle…)
Outline how water was created in Earth.
It is likely it came from extra planetary objects
- objects outside the Earth’s orbit.
Describe the Pre-Biotic Earth
In the Hadean Eon - frequent volcanic eruptions, meterorites, lightning and high temperatures; penetration of high UV radiation.
Describe the First Prebiotic Atmospheres (ADD PHOTO)
Atmosphere 1:
- Earth likely began as a region of escaping hydrogen and helium.
- Due to these being the main gases in the dusty disk from which the planets were formed.
- Molecules of hydrogen and helium move fast when warm. BECAUSE OF THAT, they eventually all escaped Earth’s gravity and drifted off into space
- THAT’S HOW THEY COOLED
Describe the Second Pre-Biotic Atmosphere
-It came from Earth itself
- Generally thought that ammonia (NH3), methane (CH4), Carbon Dioxide (CO2) and water vapour (H2O) were present sometime after the crust cooled due to volcanic outgassing.
-> Amy (ammonia nh3) Meant (methane) Carl Doesn’t (Carbon Dioxide) Wet Vipers (water vapour)
Explain the first step of Oparin and Haldane’s framework origin of life.
Inorganic “precursors” > Organic Molecules
Compare and contrast inorganic and organic molecules. (ADD PHOTO)
- Inorganic Molecules
- Do not have carbon and hydrogen within the same molecule.
- Usually have a small number of atoms
- (look like balls and half balls together)
- associated with non-living matter
- Organic molecules
- contain **carbon and hydrogen*
- can be large molecules with many atoms
-(in the pictures they look like multiple balls with tubular branches) - associated with living organism.
According to Oparin and Holdane, there was life, how did organic molecules such as carbon form from inorganic precursors?
“The early earth provided the needed conditions to form carbon compounds”
- which are again needed for organic molecules
- These conditions do not exist on Earth today
-> How was carbon formed?: The molecules in *early Earth atmos. were chemically reducing* (electron of an atom or atoms increased) in nature, meaning they are reactive gasses that transfer electrons when they react
- Due to reducing atmos, energy from volcanic reactions and lightning catalyze the basic small molecules of life (e.g. amino acids) and then they form polymers, self-replicate then form the cell (see specific card)
Outline the evidences that small organic molecules could form polymers.
Amino acids linked together form proteins (building blocks = biomolecules?)
Fatty acids (carboxylics) could assemble cell membranes.
RNA nucleotides can link together when exposed to catalysts found in clay or water
- Notice how all of these are “building blocks” discussed by Sir Calix.
Outline the process of how a cell may have been formed by an inorganic compound.
ADD IMAGE
Inorganic compounds -> Organic monomers (aka building blocks so: carboxylic/fatty acids, amino acids, carbohydrates/simple sugars, nucleotides…) -> (via anabolic reactions aka biosynthesis) polymers -> self-replication -> formation of cell.
When’s the chemical evidence of life?
3.8 billion years ago
When’s the fossil evidence of life?
3.5 billion years ago
Describe the “Great Oxygenation Event”.
- Due to early photosynthesis, it released oxygen to atmosphere.
- The oxygen concentration in the atmosphere increased from 0% to around 20%
- The increasing oxygen level eventually depleted the reducing capacity of ferrous compounds, hydrogen sulfide and atmospheric methane, and compounded by a global glaciation, devastated the microbial mats around the Earth’s surface
- caused by phototroph prokaryotes which gave oxygen as a byproduct (cyanobacteria),
Define Panspermia
a philosophical thought that life migrates naturally through space
Define Chemical Evolution
simple chemicals assembled into more complex molecular systems, from which, eventually came the first functioning cell(s).
Define Spontaneous Generation
AKA Abiogenesis. The belief that life came from non-living things
(e.g. trash can spawn a rat.)
Define life.
There are multiple definitions of life. But, there is consensus that life on earth is composed of cells.
Explain why is the cell the basic unit of life.
It is because it is the smallest structural unit that is capable of energy to sustain itself in a highly ordered state (aka living?)
Distinguish the difference between cells and subcellular components.
Cells = alive
Subcellular components = not alive
- because they’re parts of the cell
Outline the reasons why viruses are non-living.
They are not made out of cells
◎ They can not keep themselves in a stable state
◎ They do not grow
◎ They can not replicate themselves
◎ They can not perform independent metabolism
Define the NASA definition of life
a self-sustaining chemical system capable of Darwinian evolution.
Outline the reasons why explaining the origin of cells is so challenging
It is difficult to directly test hypotheses related to the origin of cells because it happened billions of years ago
Causes:
- Conditions on Earth were very different
- It’s impossible to replicate with certainty the conditions that would have existed in early earth
- Well-preserved fossils were rare
- The methods used to estimate the dates of the first living cells have ranges of uncertainty.
Explain the reason why claims (of the origins of cells) need to be tested
Karl Popper: “Scientific claims should be falsifiable”
- can be tested and discarded (falsified) if they don’t hold up their testing.
Outline the reason why viruses are not living
They are not made of cells
On Earth today, where do cells come from.
They come from other (pre-existing) cells
Outline the different implications of cells being only formed pre-existing cells
Implication 1: We can trace the origin of all the cells in our body.
Implication 2: All cells can be traced back to LUCA (last common ancestor)
Implication 3: If you keep tracing, you would eventually reach the earliest cells to have existed. There have been a first cell that arose from non-living material
Explain hypothesized process needed for the spontaneous origin of cells on Earth. (ADD PHOTO) (Oparin and Haldane)
1.) Synthesis of simple organic molecules from inorganic compounds.
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2.) Assembly of these organic molecules into polymers
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3.) The formation of a polymer
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4.) Packaging of molecules into membranes with an internal chemistry different from the surroundings (e.g. RNA, membrane-enclosed, lipid membrane)
Give (Outline? IB command terms) the experiment used for the Origin of Carbon Compounds
The Miller-Uray experiment.
Outline the conclusion of the Miller-Uray experiment.
- A variety of carbon compounds (aka organic molecules such as amino acids) were formed from inorganic compounds.
- Implications: Carbon compounds could have spontaneously formed (aka abiogenesis) on Earth
Outline the apparatus used for Miller-Urey’s original experiment. (ADD PHOTO)
1.) Water in a flask (representing ocean) is boiled so that it evaporates and moves into a larger flask.
2.) Water combines with methane, ammonia and hydrogen gases (representative of the prebiotic atmos). Sparks are fired between electrodes to simulate lightning.
3.) A cooling condenser turns stream back into liquid water
4.) Liquid water drips down into a trap, where molecules produced in the reactions can settle for collection
Outline the reasons why scientists use models.
-Artificial rep of natural phenomena that are useful when direct observation or experimentation is difficult.
-Models simplify complex systems
- via physical rep, abstract diagrams, mathematical equations or algorithms.
Explain the reason why all models have limitations and the implications of it (?)
1.) They may be oversimplified/cannot represent all aspects of a system.
2.) They are only as accurate as the scientific knowledge they are based.
- So if the knowledge is faulty, the model would be faulty as well.
Implications: all limitations need to be considered in their application
Describe the membrane of early cells. (ADD 1 MORE PHOTO)
Membrane barrier separating the interior from its surroundings.
- Hydrophilic exteriors, hydrophobic interiors
- due to phospholipids’ hydrophilic heads and hydrophobic tails
Explain the formation of micelles (ADD GIF/PHOTO)
Fatty acids in a watery solution get attracted to one another
Explain the formation of vesicles
Fatty acid micelles at higher concentration and appropriate pH conditions can form vesicles
- captures fluids and dissolved molecules
Outline how the early cells membrane may have been formed. (ADD PHOTO)
Fatty acids coalesce into micelles -> Micelles coalesce to create phospholipids -> Phospholipids coalesce form membranes -> phospholipids arrange themselves back-to-back to form bilayers
Outline how the hydrothermal vents were formed.
1.) They are the result of seawater filtered through the fissueres (gaps) in the ocean crust in the vicinity of spreading centers or subduction zones.
2.) The cold seawater is heated by hot magma and remerges to form the vents.
Electron microscope benefits and limitations
