How did life arise? Cells to Organisms Flashcards
Topic 1: Week 1 and 2
What are the characteristics/traits of a virus in terms of the characteristics of an organism?
Against:
- cannot carry out physiological functions
- not made up of independent cells and are dependent on the host cell
For:
- contain genetic information
- evolve over time
What did viruses evolve from?
Even though viruses are not cellular organisms, it is highly likely they evolved from cellular life forms because of their dependence on them
Many biologists also use this to categorise them as living organisms
How did life arise?
- arose from non-life by chemical evolution
- the earth was formed 4.5-4.6 billion years ago, and life emerged 600 million years ago
- random physical and chemical interactions of atoms produced large variety of molecules, further interactions led to the evolution of life
- the development of an internal and external environment due to the enclosure of complex biological molecules through lipid membranes caused the first cells with the ability to self replicate to arise
- photosynthesis occured, producing oxygen and allowing the o-zone to be created. This then could protect organisms to be protected against radiation which the allowed for life outside of water, and generally more complex organisms to occur
Describe the evolution of cell structure and its importance
enclosure of complex proteins and other biological molecules by membranes that contained them in a compact internal environment that seperated them from the surrounding (external) environment
fatty acid molecules, due to their insolubility, played a large role in the development of cellular membranes
this lead to the development of an internal and external environment, concentrated reactants and products, and led to the first cells with the ability to replicate themselves; the evolution of the first cellular organisms
The characteristics of cells
- All cells come from, pre-existing cells
- The molecular structure and properties of cells define their functions
- Cells are bounded by a membrane and maintain internal environments that differ from their external environments
- Cells communicate with each other
- Cells can form organised units capable of more complex function
What is the fundamental cell theory
- Cells are the fundamental units of life
- All living organisms are comprised of cells
- All cells come from pre-existing cells
- Modern cells evolved from a common ancestor
What are the two key theories of how life arose on Earth?
- Life formed spontaneously on earth (a reducing environment facilitated the organic molecule formation such as DNA bases
- Extraterrestrial origin. e.g. comets/meteorites carrying the essential molecules for life (amino acids, DNA etc.) to our planet and then life stemmed from this
What was the cambrian explosion?
A rapid diversification of life took place approximately 541 million years ago, which is commonly referred to as the cambrian explosion
Most of the major animal groups living today appeared during the cambrian period
What are stromatolites and why are they important?
Stromatolites
a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment, found in Precambrian rocks as the earliest known fossils.
They thrive in hyper-saline water.
As the layers form they trap water and other debris and lock it away, including cyanobacteria, and therefore allowed for the fossilisation of bacteria, allowing us to see what early life looked like
And this also provides a strong timeframe as to when life first arose .
When did water arise?
Water is very common both most of it is in the form of ice
Water has been found on earth for at least 383.8 billion years
Pillow basalt- a type of rock- proved the existence of water as it trapped and stored it, suggesting there was water at that date
Properties of water
- High melting point and boiling point in comparison to smaller molecules
- High heat of vaporisation
- High Cohesion (hydrogen bonding between h20 molecules)
- High Adhesion (attraction of water to other molecules)
Features common to all lifeforms
- Composed of a common set of chemical compounds: mainly Carbohydrates, fatty acids, nucleic acids and amino acids
- Made up of cells
- Use molecules obtained from the environment to synthesise new Biological molecules
- Extract energy from the environment and use it to do work
- Regulate their internal environments
- Contain genetic information, genomes, that enables them to develop, Maintain themselves, function and reproduce
- Use a universal molecular code to build proteins from their genetic information
- Exist in a population that evolves over time
Benefits and costs of viruses
Pros:
- Contain nucleic acids (as small s 2-3 kbp
- Viruses can replicate
- Evolve and adapt to the environment
Cons:
- Not capable of independent replication
- Do not contain required metabolic processes to be considered alive
- Are not comprised of cells or organelles
- Cannot extract energy
What evidence does DNA provide to explain evolution?
All living organisms use the same genetic code,
Which leads scientists to believe that living organisms all evolved from the same source, rather than from separate sources.
Suggests a common origin about 4 billion years ago
All organisms arose from earlier more primitive forms the past 4 billion years through the processes of evolution
Because all organisms are related they share the same genetic code, chemical composition, and cellular structure
Biochemical unit of life
When did life arise on earth? 9 key events with times
- formulation of earth (start of Hadean period)
- first oceans (end of Hadean period)
- Origins of life (start of Archean period)
- Origins of Photosynthesis (end of Archean/start of Proterozoic period)
- first colonial cyanobacteria (start of proterozoic period)
- first eukaryotes (middle of proterozoic period)
- first photosynthetic eukaryotes (middle of proterozoic period)
- first multicellular eukaryotes (middle/end of proterozoic period)
- first fossils of multicellular animals (early phanerozoic period)
