18 terms

Clements High School Biology Pre-ap: Chapter 12 The History of Life

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Relative Dating
-Comparative dating
-Uses index fossils
-Doesn't give specific age in years
Radiometric Dating
-measures radioactive isotopes
-dates rocks and therefore fossils it contains
MANY THINK THERE IS A FOUR-STAGE HYPOTHESIS FOR THE ORIGIN OF LIFE
1. inorganic chemicals form simple organic molecules in primitive ocean
2. formation of complex organic molecules (proteins,...)
3. formation of self-replicating molecules that make inheritance possible
4. membrane formation
OPARIN'S PRIMORDIAL SOUP MODEL (1920'S)
Inorganic compounds
------(sun, lightning)------>
organic compounds
STANLEY MILLER AND HAROLD UREY'S EXPERIMENT
-Set up flask with gases representing primitive atmosphere
-No microorganisms present
-Electric sparks represented lightning
-Several days amino acids formed
-1995 experiment done - cytosine and uracil formed
PROBLEMS WITH THE MODEL AND EXPERIMENT
1. Takes too long for molecules to form
2. No oxygen means no ozone; UV light would destroy gases needed to produce molecules needed for life
1986 - LERMAN'S BUBBLE MODEL
Chemical reactions occurred in bubbles in the ocean
Solved Problems with Primordial Soup Model
1. Reactions faster since molecules concentrated in bubbles
2. Gases protected from UV light
Hereditary information
RNA may have evolved before DNA because:
1. can act like enzymes (ribozymes)
2. can form simple proteins
3. can replicate
4. stores genetic information
5. has been found to form as water is frozen and nucleotides are pushed into spaces between water crystals
WHAT ABOUT A CELL MEMBRANE?
Several proposed ideas
1. Lipid membrane hypothesis-
liposomes - lipid molecules form spheres around other molecules
2. Protenoid microspheres- tiny bubbles formed as dilute solutions with organic compounds dropped onto hot sand, rock, clay,...
Early Cellular Evolution
Heterotroph Hypothesis
1. heterotrophic anaerobic prokaryotes
2. chemosynthesizing prokaryotic autotrophs
3. photosynthesizing autotrophic prokaryotes which produced oxygen in atmosphere (cyanobacteria)
4. Ozone formation :
A. more complex organisms evolved
B. extinction of first cells except those that found anaerobic habitat or able to survive with oxygen
Endosymbiosis
5. eukaryotes
Mitochondria and chloroplasts have the following similar to bacteria (prokaryotic cells):
1. Membranes
2. DNA (in circle)
3. Ribosomes
4. Reproduction - reproduce by fission
on their own
5. Cell size
EVOLUTION OF SEXUAL REPRODUCTION-
Advantage - Genetic diversity
First involved exchange of genetic material between two cells and later led to sex cell formation
Other Possible Explanations for Evolution of Eukaryotes
Autogenous theory - folds in membranes formed eukaryotic organelles
Horizontal gene transfer theory - transfer of genetic material between cells (happens today - conjugation) led to more complex cell organelles
EVOLUTION OF REPRODUCTION
prokaryotes reproduce by binary fussion
EVOLUTION OF MULTICELLULAR ORGANISMS
Allows for specialization and complexity

SOME ORGANISMS TODAY ARE NOT TRULY MULTICELLULAR BUT LIVE TOGETHER -
possibly led to multicellularity
OLDEST EUKARYOTES REPRODUCED
ASEXUALLY
Half Life
Period of time that it takes for 1⁄2 of the radioactive isotope to decay