Option D

Ecology

Spontaneous Origin of Life

• Spontaneous generation of life from inorganic matter can not take place; cells can only come from other cells

• To form the first cells:– Chemical reactions to produce organic

molecules– These molecules would have to form

polymers– Polymers would have to be able to self

replicate–Membranes would have to be able to

develop

Origin of Organic Compounds

• Possible locations for synthesis of organic compounds:–Miller and Urey: atmosphere and water

on the surface of the Earth– Unusual chemical conditions around

hydrothermal vents deep in the oceans– Extraterrestrial origin: formed in space

and brought to earth via meteorites, comets, etc

Miller and Urey

• Stanley Miller and Harold Urey 1953• Recreated Earth conditions–Mixed gases ammonia, methane, and

hydrogen

• After one week the water was murky brown with many organic compounds (including fifteen amino acids)

• Could have spontaneous formation of organic compounds on Earth

The Role of RNA in the Origin of Life

• RNA could have been used instead of both DNA and enzymes

• RNA catalyses a broad range of chemical reactions; could have carried out enzyme activity

• RNA can self-replicate; can synthesize and use templates with complementary base pairings

• RNA was superseded by DNA as the genetic material and by proteins as the catalysts of life

Membranes and Protobionts

• Phospholipids naturally form bilayers that form spherical structures to enclose a droplet of fluid (microspheres)

• Coacervate: water that contains these membrane-bound microspheres

• Protobionts: These phospholipid microspheres with different internal conditions from the external conditions

The Endosymbiotic Theory

• Endosymbiotic Theory: both mitochondria and chloroplasts have evolved from independent prokaryotic cells, which were taken into a larger heterotrophic cell by endocytosis. They were kept alive and continued to carry out aerobic respiration and photosynthesis

• The characteristics of mitochondria and chloroplasts support this: they grow/divide, naked loop of DNA, synthesize some of their own, double membranes

Explosion of Life on Earth

• Once eukaryotic chromosomes, meiosis, and sexual reproduction evolved, evolution could take place at a much more rapid pace

Prokaryotes and the Atmosphere

• Prokaryotes were the first organisms on Earth to use photosynthesis; oxygen released as a waste when water was its source of hydrogen

• Concentrations of oxygen built up• Other prokaryotic organisms could

use aerobic cell respiration once the atmosphere contained oxygen

Gene Pools and Allele Frequencies

• Gene Pool: All the genes in an interbreeding population

• Allele frequency: the frequency of an allele, as a proportion of all alleles of the gene in the population

• Allele frequency can range from 0.0 to 1.0

• Evolution always involves a change in allele frequency in the gene pool over several generations

What is a species?

• Morphological definition: type of living organism with fixed characteristics– Species can usually be distinguished by characteristics– Does not recognize the fact that species evolve

• Species: group of actually or potentially interbreeding populations, with a common gene pool, which are reproductively isolated from other such groups (must be able to interbreed)– Conflicts with species definition: sibling species

difficult to identify, some species with clearly different characteristics will interbreed, some are asexual, fossils can’t be classified

Speciation

• Speciation: formation of new species when a pre-existing species splits

• Allopatric speciation: members of a species migrate to a new area and interbreeding becomes impossible due to geographical isolation

• Sympatric speciation: two varieties of a species live in the same geographical area, but do not interbreed

Adaptive Radiation

• Divergent evolution: speciation repeats so each new species evolves in different ways from one ancestral species

• Adaptive radiation: rapid group diverging

Convergent Evolution

• Convergent Evolution: natural selection acts in the same way so in different parts of the world species become remarkably similar though are not closely related

Rates of Evolution

• Gradualism: evolution proceeds very slowly, but large changes can gradually take place– Not supported by fossils which show

periods of stability and periods of major change

• Punctuated equilibrium: when new adaptations are made to cope with changed environmental conditions

Transient Polymorphism

• Polymorphic: a population in which there are two alleles of a gene in a gene pool

• Transient Polymorphism: One allele is gradually replacing the other allele

Balanced Polymorphisms

• Balanced polymorphism: two alleles of a gene persist indefinitely in the gene pool– For example: sickle cell anemia

Humans as Primates

• Humas are classified as primates because they have the characteristic anatomical features– Grasping limbs, opposable thumb–Mobile arms that can transfer weight– Stereoscopic vision (forward facing eyes

on a flattened face with overlapping fields of view)

– Skull modified for upright posture

Trends in Hominid Fossils

• Hominid family includes humans– Bipedalism: walking on two legs

• Evolutionary trends of hominids:– Increasing adaptation to bipedalism– Increasing brain size in relation to body

size

Tracing Human Evolution

• Trace evolution mainly through fossils– Can be incomplete as only a tiny

proportion of animal bodies become fossilized

• Hominid fossils consist only of bones and teeth

Hominid Diets and Brain Size

• Change to a diet that included meat corresponds with the start of an increase in brain size– Eating meat increases supply of protein,

fat and energy– Catching and killing prey is more difficult

than gathering plant foods, so natural selection will favor those with larger brains

Genetic and Cultural Evolution

• Cultural Evolution: new methods, inventions or customs can be incorporated into what is passed on to later generations– Different from genetic evolution

because:• Does not involve changes in allele frequency

in a gene pool• Changes can occur in one lifetime, not over

generations• Nurture characteristics rather than nature

Dating Fossils

• Fossils can be dated using radioisotopes (radioactive isotopes of chemical elements)

• Half-life: times taken for the radioactivity to fall to half its original level