1. 14.3 the first life forms

3. 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

4. Role of RNA in early life
Ribozymes developed
Type of RNA that acts as a catalyst
Can catalyze its own replication

5. The first cells No direct evidence of what first cells were like
Scientists made inferences

6. 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

7. What do these inferences mean?

8. What inferences mean Little or no oxygen gas existed on Earth
First organisms likely were anaerobic
Anaerobic literally means “living without air”

9. 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

10. Connect the dots
Heterotrophs competed for food…so…

11. Connect the dots Heterotrophs competed for food…so… Food ran low
Food ran low…so…

12. Connect the dots Heterotrophs competed for food…so… Food ran low
Food ran low…so…
Autotrophs arose that could use chemosynthesis

13. Photosynthesis
First photosynthetic organisms arose 3 billion years ago
Similar to cyanobacteria
What would increase in photosynthesis result in?

14. Photosynthesis
Increased photosynthesis produced oxygen in the atmosphere
More oxygen means aerobic respiration can now take place

15. Ozone layer Oxygen in atmosphere hit by UV light Creates ozone
Ozone layer allows life to move onto land

16. The first eukaryotes Arose 1.5-2 billion years ago
Endosymbiosis occurred

17. The first eukaryotes
Small aerobic prokaryote engulfed by larger anaerobic eukaryote
Both began to reproduce
Small prokaryote evolved into mitochondria

18. Endosymbiosis evidence
Mitochondria have their own circular DNA
Reproduce independently of cell