14.3 the first life forms
Learning objectives I will be able to: List 3 inferred characteristics that describe the first life forms of cellular life on Earth Compare the two types of autotrophy used by early cells Relate the development of photosynthesis to the development of aerobic respiration in early cells
Role of RNA in early life Ribozymes developed Type of RNA that acts as a catalyst Can catalyze its own replication
The first cells No direct evidence of what first cells were like Scientists made inferences
inferences Little or no oxygen gas existed on Earth Oldest fossilized cells resemble modern prokaryotes First cells developed in environment filled with organic molecules for food
What do these inferences mean?
What inferences mean Little or no oxygen gas existed on Earth First organisms likely were anaerobic Anaerobic literally means “living without air”
What inferences mean First cells developed in environment filled with organic molecules for food First organisms were likely heterotrophic Heterotrophic – organism must obtain energy from another organism
Connect the dots Heterotrophs competed for food…so…
Connect the dots Heterotrophs competed for food…so… Food ran low Food ran low…so…
Connect the dots Heterotrophs competed for food…so… Food ran low Food ran low…so… Autotrophs arose that could use chemosynthesis
Photosynthesis First photosynthetic organisms arose 3 billion years ago Similar to cyanobacteria What would increase in photosynthesis result in?
Photosynthesis Increased photosynthesis produced oxygen in the atmosphere More oxygen means aerobic respiration can now take place
Ozone layer Oxygen in atmosphere hit by UV light Creates ozone Ozone layer allows life to move onto land
The first eukaryotes Arose 1.5-2 billion years ago Endosymbiosis occurred
The first eukaryotes Small aerobic prokaryote engulfed by larger anaerobic eukaryote Both began to reproduce Small prokaryote evolved into mitochondria
Endosymbiosis evidence Mitochondria have their own circular DNA Reproduce independently of cell