Transcript AP Review Part 3:

AP Review Part 3:
• AP Review Part 3:
– Evolution
• Natural Selection
• Speciation
– Plants
• Reproduction in Flowering Plants
• Plant Tropisms and Hormones (esp. auxins)
AP Review
• Evolution
– Natural Selection (Darwin’s “survival of that fittest”)
• Some individuals possess alleles (genotypes) that
generate traits (phenotypes) that enable them to
cope more successfully with their environment.
These individuals survive to produce more
offspring.
– If environment favors a trait, that trait is considered
adaptive
– If environment is unfavorable for that trait, it is
maladaptive
AP Review
• Darwin’s arguments (postulates) for Natural Selection:
–
–
–
–
–
–
–
–
Populations have enormous reproductive potential
Population sizes remain stable
Resources are limited
Individuals compete for survival
There is variation among individuals in a population
Much variation is heritable
Only the most fit will survive
Evolution occurs as advantageous traits accumulate
AP Review
• Types of natural selection
–
–
–
–
–
Stabilizing selection
Directional selection
Disruptive selection
Sexual selection
Artificial selection
AP Review
• Stabilizing selection
– Eliminates individuals with extreme or unusual traits
AP Review
• Directional selection
– Favors extremes that are at one end of the spectrum
and selects against the ones at the opposite end.
AP Review
• Disruptive selection
– Environment favors extreme or unusual traits and
selects against the common traits.
AP Review
• Sexual selection
– Male competition
• Antlers, horns, heavy musculature selected for
– Female choice
• Chooses male she finds attractive
– Colorful feathers etc
AP Review
• Artificial selection
– Form of directional selection carried out by
humans on plants and animals
The BEST
Breed!
AP Review
• Genetic equilibrium
– is when allele frequency in a population remains
constant, also called Hardy-Weinberg equilibrium
– At equilibrium no evolution is occurring, so can use
HW formula to show evolution has occurred.
– In order for equilibrium to occur, the following must be
true:
•
•
•
•
•
All traits are selectively neutral
Mutations do not occur
Isolated population – no gene flow
Large population
Random mating
AP Review
• Hardy Weinberg Equation
AP Review
– Hardy Weinberg Equation
• States that an equilibrium of allele frequencies in a gene pool will
remain in effect each successive generation of a sexually
reproducing population, as long as these five conditions are met:
– 1. No mutations: allelic changes do not occur, or changes in one
direction balanced by changes in the opposite direction.
– 2.. No gene flow: migration of alleles into or out of the population does
not occur. No immigration of emigration.
– 3. Random mating: pair by chance.
– 4. No genetic drift: the population is very large, and changes in allele
frequency due to chance alone are insignificant.
– 5. No selection: no selective agent favors one genotype over another.
• Are these conditions likely to be met?
• So what good is this formula?
– Tells us what factors cause evolution (opposites of the five listed
conditions)
– Use equation as a baseline to measure whether evolution has
occurred.
AP Review
• Speciation
– Species = a group of individuals capable of interbreeding
– Speciation = splitting of one species into two or more species, or
the transformation of one species into another over time.
Speciation is the final result of change in gene pool allele and
genotype frequencies.
– Processes by which speciation can occur:
• Allopatric speciation
• Sympatric speciation
• Adaptive radiation
AP Review
– Allopatric speciation
• Populations geographically isolated from each other
(mountains, rivers etc) – gene flow stops.
• Gene frequencies of the 2 populations can diverge due to
– Natural selection of different environments
– Mutations
– Genetic drift
AP Review
– Sympatric speciation
• Population develops into two or more species
without prior geographic isolation. Often occurs in
plants
– Plants often polyploid – leads to reproductive isolation
– Balanced polymorphism
» Reproductive isolation due to some trait within the
species, such as color
– Hybridization
» Hybrid may possess greater genetic variations
than either parent
AP Review
– Adaptive radiation
• Several different species develop rapidly from one
ancestor due to diverse geographical or
environmental conditions
– Marsupials of Australia all from common ancestor
– 14 species of finches on Galapagos Island all evolved
from one mainland species
AP Review
• Plants – Reproduction in Flowering Plants
Mosses (not Club mosses),
Liverworts, Hornworts
Plant divisions
Tracheophyta - vascular
Bryophyta - nonvascular
Coniferophyta –
Gymnosperms (seeds)
Conifers
Anthophyta -Angiosperms –
Flowering Plants (seeds)
Monocots
Docots
In all but Bryophytes, the diploid sporophyte
generation is dominant.
Lycophyta
Club mosses
Sphenophyta
Horsetails
Pterophyta
Ferns
AP Review
• Reproduction in Flowering Plants
– Life Cycle of flowering Plant
• Alternation of generations
– Sporophyte
» dominant in flowering plants
– plant we recognize
» Diploid – produces haploid
spore by meiosis
– Gametophyte
» Haploid- produces diploid
zygote
» Small and not
independently living (is
independent in mosses and
ferns)
» (Dominant in mosses)
AP Review
• Flower parts
– “Female”-ovary and egg
• Pistil (some texts call a carpel)
– Stigma
– Style
– Ovary
– “Male” – produces pollen
grain
• staMEN
– Anther (MANther)
– filaMENt
– Petals
– Sepals
AP Review
• Pollination and Fertilization
– Pollen (microgametophyte) usually wind
blown (in flowering plants). One pollen grain
contains 2 haploid cells.
– Pollen (male) sticks on sticky stigma (female)
– Pollen grain contains one generative cell and
one tube cell (each haploid)
– Generative cell divides by mitosis to produce
two sperm cells
– Tube cell forms a tube that grows down to
the ovule and sperm cells enter through the
micropyle. The ovule contains the egg (egg
developed from the megagmetophyte).
– One sperm joins with egg to form zygote.
– Other sperm joins with both polar nuclei to
form triploid (3n) endosperm which will
provide nutrition to the embryo.
– This double fertilization is unique to
flowering plants
Fertilization animation
..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology animations\PlantFertilization.mov
Zygote becomes sporophyte
embryo
Ovule matures into seed and seed
coat
Ovary becomes the fruit
AP Review
• Embryo Development
– Endosperm nucleus divides to become endosperm tissue
(seed development animation)
– Zygote divides into embryo (which will develop cotyledons) and
suspender which will transfer nutrients to the embryo
AP Review
• Plant tropisms and hormones
– Plant hormones
•
•
•
•
•
Auxins
Gibberellins
Cytokinins
Ethylene
Abscisic acid (ABA)
– Plant tropisms
• Phototropism
• Gravitropis/geotropism
• thigmotropism
AP Review
• Plant hormones
– Auxins
• Indolacetic acid (IAA) most common
auxin
• Promotes plant growth by facilitating
elongation of cells
• Produced at tips of roots and shoots
– Promotes adventitious roots and
apical dominance
• Promotes phototropism
– Cells on dark side grow faster
• Promotes geotropism/gravitropism
– Auxin moves to lower side of stem or
root in response to gravity
» Auxin inhibits growth of root
cells on lower side  root grows
down
» Stimulates growth of stem cells
on lower side  stem grows up
• Spraying fruits and leaves with auxins
keeps them from falling off
AP Review
• How auxins work
– Auxin (red sphere) binds to receptors on cell membrane
– Activates ATP driven proton (H+) pump
• Needs energy, process of chemiosmosis
–
–
–
–
Pumps H ions into space between cell membrane and cell wall.
H ions (acid) weaken cell wall.
Gradient set up that pulls solutes then water into cell causing it to swell
Pushes on cell wall causing cell to elongate
AP Review
• Plants hormones
– Gibberellins
• Group of over 60
hormones that also
promote cell growth
• Synthesized in young
leaves, roots and seeds,
but often transported to
other parts of plant
• Promote stem elongation
especially in dwarf plants
• Can break dormancy in
seeds and buds
AP Review
• How Gibberellins work
– Gibberellin binds to a
receptor on the cell
membrane
– Activates a second
messenger inside the cell –
Ca++
– Ca++ combines with a
protein called calmodulin
– This complex activates the
gene that codes for
amylase
– Amylase acts on starch to
release sugars
AP Review
• Plant hormones
– Cytokinins
•
•
•
•
Zeatin and synthetic kinetin
Promote cell division and differentiation
Derivatives of adenine
Prevent senescence
– Often sprayed on cut flowers to prolong
• Varying ratios of cytokinins and auxins can effect how plant
differentiates
• Stimulate growth of lateral buds, weakens apical dominance
• Produced in roots and transported
• Variety of effects depending on target organ and other hormones
AP Review
• Plant hormones
– Ethylene
•
•
•
•
Inhibits growth
CH3 - gas that promotes ripening of fruit
Involved in stimulating the production of flowers
Ethylene in combination with auxins
– Inhibits root, stem and leaf elongation
– Influences leaf abscission (aging and dropping of leaves)
– Abscisic acid
• Inhibits growth
• Maintains dormancy
• Influence on abscission is controversial
AP Review
Functions of Plant Hormones
Hormone
Function – all of these hormones work together
Auxins
Stimulate growth
Involved in stem and root cell elongation in phototropism and
gravitropism
Gibberellins
Stimulate growth especially stems, especially in dwarf plants.
Can break seed and bud dormancy
Cytokines
Stimulate growth by causing cell division
Abscisic Acid
Inhibit growth
Causes stomates to close
Maintains seed and bud dormancy
Ethylene
Inhibit growth
Causes fruit to ripen and fall
AP Review
• Plant tropisms
– Phototropism
• Response to light caused by auxin
– Auxin accumulates on shady side
causing increased growth, so
plant bends toward light
– Gravitropism
• Response to gravity by roots and
stems, involves auxins and
gibberellins
• Action depends on relative
hormone concentration and type
of tissue (root vs stem – roots
grow down, stems grow up)
– Thigmotropism
• Response to touch, such as in
vines