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Chapter 26 The Tree of Life.

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Presentation on theme: "Chapter 26 The Tree of Life."— Presentation transcript:

1 Chapter 26 The Tree of Life

2 Geological events that alter environments
1. How Life Began Geological events that alter environments Change the course of biological evolution Conversely, life changes the planet that it inhabits Figure 26.1

3 Conditions on early Earth made the origin of life possible Hypothesis:
Chemical and physical processes on early Earth produced very simple cells through a sequence of stages

4 Earth formed ~ 4.6 billion years ago Earth’s early atmosphere
Contained water vapor + many chemicals released by volcanic eruptions Little or no O2  reducing atmosphere But it did have: CO, CO2, H2, N2, H2O, S, and HCl,

5 2. SEAS First organic compounds may have formed near submerged volcanoes and deep-sea vents Figure 26.3

6 Lab simulations of early Earth atmosphere:
3. Complex Molecules Lab simulations of early Earth atmosphere: EXPERIMENT Miller and Urey set up a closed system in their laboratory to simulate conditions thought to have existed on early Earth. A warmed flask of water simulated the primeval sea. The strongly reducing “atmosphere” in the system consisted of H2, methane CH4), ammonia (NH3), and water vapor. Sparks were discharged in the synthetic atmosphere to mimic lightning. A condenser cooled the atmosphere, raining water and any dissolved compounds into the miniature sea. CH4 Electrode Water vapor RESULTS NH3 H2 As material circulated through the apparatus, Miller and Urey periodically collected samples for analysis. They identified a variety of organic molecules, including amino acids such as alanine and glutamic acid that are common in the proteins of organisms. They also found many other amino acids and complex, oily hydrocarbons. Condenser Cold water CONCLUSION Organic molecules, a first step in the origin of life, can form in a strongly reducing atmosphere. Cooled water containing organic molecules H2O Sample for chemical analysis Figure 26.2

7 Some organic cmpds. may have come from space
Carbon cmpds. have been found in some of the meteorites

8 4. Abiotic synthesis of polymers
Small organic molecules Polymerize when they are concentrated on hot sand, clay, or rock

9 5. Protobionts Aggregates of abiotically produced molecules surrounded by membrane

10 Protobionts could have formed spontaneously from abiotically produced organic cmpds
e.g., small membrane-bounded droplets called liposomes form when lipids are added to water

11 Figure 26.4a, b Glucose-phosphate 20 m Phosphorylase Starch Amylase
(a) Simple reproduction. This lipo- some is “giving birth” to smaller liposomes (LM). (b) Simple metabolism. If enzymes—in this case, phosphorylase and amylase—are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products. Glucose-phosphate Phosphorylase Starch Amylase Maltose Phosphate Figure 26.4a, b

12 Complementary RNA copy
RNA molecules (ribozymes) catalyze many different reactions, including Self-splicing Making copies of short stretches of their own sequence Figure 26.5 Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 3 5

13 Early protobionts with self-replicating, catalytic RNA
used resources and increased in number through natural selection

14 As prokaryotes evolved, they exploited and changed young Earth
6. Heterotrophs As prokaryotes evolved, they exploited and changed young Earth Oldest known fossils are stromatolites Rocklike structures w/ many layers of bacteria and sediment 3.5 billion years old

15 Lynn Margulis (top right), of the University of Massachussetts, and Kenneth Nealson, of the University of Southern California, are shown collecting bacterial mats in a Baja California lagoon. The mats are produced by colonies of bacteria that live in environments inhospitable to most other life. A section through a mat (inset) shows layers of sediment that adhere to the sticky bacteria as the bacteria migrate upward. Some bacterial mats form rocklike structures called stromatolites, such as these in Shark Bay, Western Australia. The Shark Bay stromatolites began forming about 3,000 years ago. The inset shows a section through a fossilized stromatolite that is about 3.5 billion years old. (a) (b) Figure 26.11a, b

16 Prokaryotes were Earth’s sole inhabitants
From 3.5 to about 2 billion years ago

17 Electron transport systems of a variety of types
Essential to early life Some aspects that possibly precede life itself

18 Earliest types of photosynthesis
Did not produce O2 Cyanobacteria are autotrophic prokaryotes that obtain their energy and manufacture organic compounds by photosynthesis

19 Oxygenic photosynthesis
8. Oxygen Revolution Oxygenic photosynthesis Evolved ~ 3.5 bya in cyanobacteria Figure 26.12

20 O2 began to accumulate in the atmosphere ~ 2.7 bya
Challenge for life Opportunity to gain energy from light Allowed organisms to exploit new ecosystems

21 As the ozone formed the UV light was absorbed by the atmosphere disrupting the energy available for abiotic synthesis of organic compounds.

22 9. Eukaryotes Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes

23 Oldest fossils of eukaryotic cells
2.1 billion years

24 Endosymbiosis Mitochondria and plastids were formerly small prokaryotes living within larger host cells

25 Probably undigested prey or internal parasites
Figure 26.13 Cytoplasm DNA Plasma membrane Ancestral prokaryote Infolding of plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic heterotrophic Cell with nucleus and endomembrane system Mitochondrion eukaryote Plastid Engulfing of photosynthetic prokaryote in some cells Photosynthetic

26 Eventually host and endosymbionts would have become a single organism

27 Supporting evidence: Similar inner membrane structures and functions
Both have their own circular DNA (genes) Own ribosomes

28 Chinese paleontologists recently described 570-million-year-old fossils
probably animal embryos Figure 26.15a, b 150 m 200 m (a) Two-cell stage (b) Later stage

29 The first multicellular organisms were colonies
Collections of autonomously replicating cells 10 m Figure 26.16

30 Some cells in the colonies
Became specialized for different functions The first cellular specializations Had already appeared in the prokaryotic world

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