IB Biology HL Y1 Quarter 1

Blue highlight = example / Green highlight = important info i think probably

Standards - D4.1, A4.1, A3.1, A3.2, C4.1, B4.1

D4.1 Natural Selection (SL Standards Only)

Lamarck (wrong!)

• individuals develop traits to better survive

• passes down these traits to their offspring

• leads to all members of a species having favorable traits

Darwin (yay!)

Studied finches in the Galapagos Islands and came to these conclusions:

• there is naturally variation in a species

• some variations give advantages over other species for survival

• those that survive with favorable traits have a higher chance to reproduce compared to those with less favorable traits, passing down those traits

• number of individuals with favorable traits increases, number of individuals with less favorable traits decreases

• eventually favorable trait is the most common

• over generations (millions of years), differences can accumulate to a new species

Paradigm shift - fundamental change in approach or assumptions

• Lamarckism to Darwinism

Natural selection - mechanism driving evolutionary change

• Competition - overproduction of offspring and limited resources lead to a struggle to survive, leading to natural selection

• Abiotic factors - nonliving factors affecting survival (temperature, natural disasters, water amount, salt tolerance, etc.)

• Variation - must be variation in a population; caused by mutation, sexual reproduction, meiosis

• Fitness - different individuals have different adaptations which could increase survival chance and therefore increase reproduction (survival and reproduction of the fittest!)

• Traits must be heritable to be passed down for evolution

• Sexual selection - type of selection pressure focused on differences in physical and behavioral traits, affect success in finding a mate, can cause evolution

Endler and Guppies

Stronger predator = natural selection over sexual selection

Weaker/no predator = sexual selection over natural selection

A4.1 Evolution and Speciation

Evolution - change in the heritable characteristics of a population over time

Divergent evolution - one species split into two and then was modified over time by natural selection, embryos develop similarly

Homologous structures - same position and structure but not necessarily the same function from a common ancestor

• Vestigial limbs - leftover traits from common ancestor

• Pentadactyl limb - “five digits” most animals have some version of this

  

Convergent evolution - similar environment so species evolved to look similar (not genetically related!)

Analogous structures - same function, NOT ancestrally related, determined by looking at development

• example: Shark body vs. dolphin body

DNA and RNA evidence - can compare DNA and RNA sequences for similarities as the more similar they are the more likely they evolved from common ancestor (very strong evidence of evolution)

• stronger evidence than amino acids as one amino acid is 3 DNA/RNA bases

Selective breeding (artificial selection) - caused by humans, rapid changes

• examples: cows, chickens, tomatoes, bananas

Speciation - splitting of pre-existing species into two or more new species, only method for new species, must come from an ancestor that split

Reproductive isolation - population must be separated

Differential selection - shift in one population from another due to different selective pressures

Chimpanzees and Bonobos - geographically separated by Congo River (different habitats = different selection pressures)

• Chimpanzees had more competition for resources in the savanna and an overlapping habitat with gorillas, so they evolved to be more aggressive

• Bonobos had less competition for resources in the forest so they evolved to be less aggressive

Polyploidy - plants can hybridize and gain different chromosome numbers (very rapid speciation as they self fertilize)

• example: Knotweed

Hybridization - when two different species have an offspring, most animals have behavior that prevent cross breeding

• example: Mule (sterile hybrid)

Barriers to Hybridization

Adaptive radiation - one species rapidly diversifies into many species that are closely related due to vacant roles in an ecosystem (no competition)

• Examples: Hawaiian honeycreepers, Darwin’s finches

A3.1 Diversity of Organisms

Variation - no two individuals are alike, there are patterns of variation between organisms that are used to name them, there is more variation between species than within a species

Binomial naming system - Genus species (Genus first letter is capitalized, species is lowercase), species in a genus have similar traits (Linnaeus)

Morphological species concept - created by Linnaeus, species are groups of organisms with shared traits, sorted by morphology, no longer used as organisms that look similar could be separate species

Biological species concept - group of organisms that can breed and produce fertile offspring, only works for sexually reproducing species, some species produce hybrids, bacteria can transfer genes through horizontal gene transfer

Phylogenetic species concept - smallest set of organisms that share a common ancestor using DNA

Recognition species concept - species that recognize each other as mates

Difficulties distinguishing species and populations - genetically different enough? arbitrary distinctions, can they reproduce if brought back together?

Chromosome numbers - different species have different chromosome numbers, same species have the same chromosome numbers

• Diploid cells - even number of chromosomes

• Horse - 64, Donkey - 62 —> Mule - 63 (infertile)

Karyogram - full set of chromosomes

Karyotype - banding pattern and length of chromosome

Fusion of chromosome 2 in humans - by comparing karyotypes of chimpanzees, gorillas, orangutans, and humans, it can be seen that chromosome 12 and 13 fused to form our chromosome 2

Genome - all the genetic information of an organism

• organisms of the same species have almost the exact same DNA

• changes are caused by single-nucleotide polymorphisms (single base changes)

• vary greatly in length between species, very little difference in a species

• in 2004, next-generation sequencing (NGS) was created to speed up gene sequencing, lowered costs from $1 million in 2007 to $1000 in 2014 ($600 today)

Dichotomous keys - “two parts” use of morphology to quickly identify organisms 

DNA Barcoding - species can be identified using DNA barcodes (short known sections of DNA), often used on feces (poop) or water samples

A3.2 Classification and Cladistics

Why do we classify organisms?

• There are millions of species

• Allows us to understand how they are related to other species

• Useful in medicine (related plants could have similar effects)

• Allows us to predict characteristics of organisms

Clades - groups of organisms with common ancestry and shared characteristics, created through base sequences/amino acids or morphology

Parsimony analysis - the fewest changes is the most likely (smallest number of sequence changes)

Cladograms - tree diagrams that show the most probable sequence of divergence in clades

• Root - initial ancestor common to all organisms within the cladogram (incoming line)

• Node - hypothetical common ancestor that speciated to two or more species

• Outgroup - most distantly related species in the cladogram (comparison/reference)

• Clades - a node and all of its connected branches

• Terminal branch - individual species included in the analysis

• Inner branches - show splitting of ancestors (typically extinct)

Molecular Clock - allows an estimate on how long species have been separated

• Mutation rate * Number of mutations = time 

• Time per mutation = (t/mutation)

• Mutation rates are affected by generation time (longer = lower rate), population size (larger = higher rate), and selective pressure (depends but usually lower)

Cladistics vs traditional taxonomy

• traditional taxonomy was rigid

• cladistics has natural clades that are unranked

• better matches patterns of divergence through evolution

Three Domain System

• Woese used rRNA sequences to create a new cladogram of life

• created three new domains (a level above kingdoms)

• Paradigm shift from 5 kingdoms to 3 domains

Changing Clades - can redo cladograms that were based on morphology or had small sample sizes with new evidence, example that theories can be falsified

• Example: Figworts went from one big family to many families (convergent evolution)

C4.1 Populations and Communities

Ecosystem - organisms and their environment (biotic and abiotic)

Habitat - the non living component

Community - all organisms living in an area

Population - Same Species, Area, Time (SAT)

Carrying capacity - max capacity of animals an ecosystem can support due to lack of resources

Positive feedback - one variable causes an increase in another variable

Negative feedback - one variable causes a decrease in another variable

Density dependent - depends on density of population size, bring towards carrying capacity

• Examples: Disease, predators, food

Density independent - does not depend on population size, fluctuating population

• Examples: Weather, natural disasters

Interspecies interactions

More mutualism examples

• Root nodules in Fabaceae - Bacteria get carbon (sugar), legumes get nitrogen

• Mycorrhizae in Orchidaceae - Mycorrhizae Fungi get carbon (sugar), orchids get nitrogen

• Zooxanthellae in hard corals - Zooxanthellae get protection, coral gets nutrients like glucose (sugar)

Lotka Volterra - predator prey graph, as predator goes up prey goes down, form of negative population control

• Time Gap - gap between changes

• Example: lynx and hare

Intraspecific competition - competition between same species for resources

• Examples: male zebras, tigers, bears, male antelopes, eagles, hawks

Intraspecific cooperation - cooperation between same species to increase survival

• Examples: wolves, humans, ants, bees

Allelopathy - plants produce toxic compounds that affect the growth of other plants, transferred by rain, as a gas, and dead leaves

• Examples: Black walnut, mustard

Antibiotics from plants - kill bacteria, bitter taste

• Examples: California bay, coffeeberry

Population control in communities

• Top down - predators limit population size

• Bottom up - nutrients in ecosystem limit population sizes

• Example: Phytoplankton (bottom up)

Population size by random sampling

• Sampling error - difference between the population total and the population estimate

• Random quadrat sampling - sample random squares from a grid to estimate the total population of sessile (nonmoving) organisms 

• How many are in the squares multiplied by total squares divided by squares sampled

• Capture-mark-release-recapture - capture animals, mark them, release them, wait, recapture them, count how many you captured and specifically how many were marked, used to estimate population of moving organisms

• Lincoln Index 

  

• Association between species - use chi squared

  

Population Growth Curves

• Most populations start exponential because there is an abundance of resources

• Starts to flatten (logistic/sigmoid) as resources become limited

• Take the log of the y axis to confirm exponential growth

Competition between species?

• Lab experiments - trying growing them together and see what happens

• Field experiments observation - use random sampling and chi squared (see if species are usually together)

• Field experiments manipulation - remove species and see what happens

• Null hypothesis - no correlation between species

• Alternative hypothesis - there is a correlation (most likely negative)

Invasive species - competes with native species, if it can outcompete native species then the native species is threatened

• Example: Western pond turtle and red eared slider (invader)

B4.1 Adaptation to Environment

Habitat - place in which a community, species, population or organism lives, geographic and physical location, type of ecosystem

Biome: Ecosystems with similar communities

• Temperature and rainfall affect distribution of biomes

Adaptation to Hot Desert and Tropical Rainforest Examples

Abiotic Factors affect species distribution

• Species can only survive in certain areas because of abiotic factors, like temperature, pH, salinity, humidity, and oxygen levels

• Example: Sugar maple - temp between -18 degrees C and 27 degrees C

• Example: Tropical fish - temp ranges from 60-85 degrees F

Range of tolerance - limiting factor of population size, outside of range means lower population

Coral reefs

• Temperature - 23-29 degrees C

• Salinity - high salt levels 32-42 parts per thousand

• Light - clear water for high levels of light 

• pH - need a stable pH above 7.7

• Water depth - most corals occur within less than 25 m of water depth

American beachgrass

• lives on sand dunes

• has a deep, strong and extensively creeping rhizome (connecting root)

• survives in sandy and salty environments

Mangroves

• lives in coastal intertidal zones

• Prop roots - stay upright with changing tide AND aerial to get oxygen

• Salt filtration - can remove salt from the roots OR through the leaves

• Pneumatophores - breathing tubes to get air