Sources:
1. Solar
2. Chemical
Energy
Types of organisms:
Heterotrophs = get chemical energy by
consuming other organisms
Sources:
1. Solar
2. Chemical
Energy
Types of organisms:
Heterotrophs = get chemical energy by
consuming other organisms
Autotrophs = can make chemical energy by
converting energy from the sun (photosynthesis) or
inorganic chemical compounds (chemosynthesis)
Photosynthesis
Process that captures and converts solar energy and stores it as
chemical energy.
H20 + CO2 + light
C6H12O6 + O2
CO2 from air
O2
H2O from roots
C6H12O6 (sugar)
stored
Photosynthesis
Chlorophyll
C6H12O6
Photosynthesis
H20 + CO2 + light
C6H12O6 + O2
Light
Light response curve
Light saturation
Rate of photosynthesis
Light limitation
Photosynthesis increases only
slightly as light increases.
0
Incident light
Full sun
Photosynthesis limited by
light availability
Adaptation  increase efficiency
Efficiency = the proportion of light that is converted into chemical energy
Rate of photosynthesis
Light
Bright sun plant
Shade plant
Efficiency = slope of line
Steeper slope  more efficient
0
Incident light
Full sun
Adaptation  increase efficiency
• increase leaf surface area
• increase amount of chlorophyll in leaves
Water
1. Necessary for the light reactions.
2. Can limit CO2 uptake.
Chlorophyll
C6H12O6
Water
Adaptation  use an alternative photosynthetic pathway
CAM photosynthesis
• stoma open only at night  cooler temperatures and higher humidity
decrease water loss by transpiration
• CO2 taken in at night and stored until needed for Calvin cycle
• thick, succulent leaves
Evolution
A change in the genetic structure of a population over time. The
accumulation of many genetic changes (allele frequency changes)
results in differences from their ancestors (descent with modification).
Genetic structure = genes and alleles present in the population and
at what frequency
Gene Pool = The total collection of genes in a population at any one
time.
Evolution
Gene Pool = The total collection of
genes in a population at any one time.
Green allele = 0.80 (80%)
Blue allele =
0.13 (13%)
Red allele =
0.07 (7%)
Factors that cause evolution
1. Mutation
• creates new alleles
• ultimate source of new genetic variation
Factors that cause evolution
2. Gene flow
Before:
After:
Freq. green = 1.0
Freq. green = 0.86
Freq. brown = 0.14
Freq. brown = 1.0
Factors that cause evolution
3. Genetic drift
Freq. green = 0.33
Freq. brown = 0.67
Freq. green = 0.14
Freq. brown = 0.86
Genetic Drift - Greatest effects in small populations
0.2 orange; 0.2 red; 0.2 yellow; 0.2 green; 0.2 blue
Genetic Drift - Greatest effects in small populations
0.4 orange; 0.2 red; 0.0 yellow;
0.18 orange; 0.18 red; 0.2 yellow;
0.4 green; 0.0 blue
0.24 green; 0.2 blue
Factors that cause evolution
4. Selection
• only mechanism that brings about adaptive evolution
Charles Darwin & Alfred Russell Wallace
Definition of Natural Selection:
The theory that evolution occurs by natural selection asserts that, of the
range of different individuals which make up the population of a given
species, those individuals having certain characteristics contribute
more offspring to the succeeding generation than those having other
characteristics; and if such characteristics have an inherited basis, the
composition of the population is thereby changed in the next generation.
Conditions:
1. Variation
2. Inherited basis
3. Differential survival and reproductive success
= Darwinian fitness differences
Patterns of Selection:
1. Directional selection
# individuals
E.g. fur color in mice
disfavored
favored
Light fur
Dark fur
X
X
Patterns of Selection:
2. Stabilizing selection
# individuals
E.g. birth weight in humans
disfavored
favored
Low
disfavored
high
X
Birth weight
Patterns of Selection:
3. Disruptive selection
# individuals
E.g. reproductive success in Coho Salmon
favored
disfavored
Size of mature male
favored
# individuals
X
Dark
fur
X
Low
high
X
# individuals
Light
fur
Small
Large
X
Important points:
1. Selection acts on individuals but individuals do NOT evolve.
2. There is no intent in evolution.
Adaptation
Any feature of an organism that helps it to better survive and
reproduce
• all adaptations are the result of natural selection
• natural selection brings about adaptive evolution
• adaptations are not perfect
Why not?
1. Lack of genetic variation
2. Evolutionary history
3. Ecological trade-offs