origin of life on earth Flashcards
(38 cards)
for an organism to be classified as being ‘alive’ they must
exhibit ALL seven life processes
what are the seven essential life processes (MRS GREN)
Movement, Respiration, Stimuli, Growth, Respiration, Excretion, Nutrition
how long has life been around for?
evidence shows that life has existed on earth for around 3.5 billion years
exiting cells are the products of
evolution
what is evolution?
evolution is the change from simple to complex forms of life
true or false: life on earth evolved only once from pre-existing cells
true
the cell theory states
- all organisms consist of cells or products of cells
- all cells arise from pre-existing cells
- cells are the fundamental units of life
how old is earth?
4.5 billion years old
what were the early conditions of earth like?
the atmosphere contained, no oxygen, and large amounts of CO2, water vapour, methane, ammonia gas, nitrogen, volcanic activity, electrical storms
the first cells:
were formed in the sea, and were prokaryotic
what are the necessary processes for life to begin on earth?
- the synthesis of simple organic molecules (amino acids and ultimately proteins)
- the origin of molecules that can self-replicate (DNA and RNA)
- the packaging of these molecules into membranes with a homeostatic internal environment
the difference between evolution and origin of life is
evolution is the process of how life has diversified on earth, and origin of life is how life began, evidently through the process of abiogenesis
abiogenesis is
the process that life arises naturally from non-living matter
what do scientists speculate about abiogenesis?
life may arisen as a result of random chemical processes happening to self-replicating molecules. it is believed that membranes formed spontaneously and the first simple cells may have used RNA as genetic information. ribozymes may have played a role in this development
deep sea vents
evidence suggests that life originated at the bottom of the ocean in an area called ‘deep sea vents’ and hydrothermal vents
structures of RNA and DNA
RNA: Cytosine-Guanine, Adenine-Uracil
DNA: Cytosine-Guanine, Adenine-Thymine
how did the first simple cells or protocells form?
- membranes could have formed spontaneously
- RNA was used as a source of genetic information
- ribozymes had a catalytic role
what are ribozymes?
combination between ribosomes and enzymes
the spontaneous formation of membranes:
the cell membrane is composed mainly of phospholipids, these modern cells used lipid membranes to selectively control what molecules may enter and exit the cell.
earlier simple cells probably needed a membrane for the same reason as modern cells. rather than being formed from phospholipids, what may have early membranes form from?
early membranes may have formed from fatty acids which can also form vesicles in much the same way
what are the possible roles of RNA and ribozymes in the first simple cells?
- RNA was the first molecule of hereditary, and it stored and expressed genetic information before DNA
- RNA molecules can also function as ribozymes to carry out catalytic reactions i the absence of ribozymes (protein enzymes)
- single stranded RNA is unstable and easily damaged by enzymes
- the existing RNA doubled (became double stranded) and the ribose sugar was replaced with the deoxyribose sugar to produce DNA
how do scientists prove that the RNA model is not proven?
- scientists believe that it is incomparable for RNA to evolve in the first cells
- scientists suggest that ‘small molecules’ and a ‘metabolism first’ approach and these first cells were then subject to Darwinian evolution
what is Darwinian evolution?
Darwinism is a theory of biological evolution developed by the English naturalist Charles Darwin and others, stating that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual’s ability to compete, survive, and reproduce.
self replicating RNA molecules were present
in cells before the evolution of DNA and proteins
