Module 4 Section 3: Classification and Evolution Flashcards
What is classification
Classification is the act of arranging organisms into groups based on their similarities and differences
Why use classification
This makes it easier for scientists to identify them and to study them
What is taxonomy
Taxonomy is the study of classification
There are a few different classification systems in use, but they all involve placing organisms into groups in a taxonomic hierarchy
How to use the taxonomic hierarchy
There are eight levels of groups (called taxonomic groups) used in classification
Similar organisms are first sorted into one of the three very large groups called domains, e.g. animals, plants and fungi are in the Eukarya domain
Similar organisms are then sorted into smaller groups called kingdoms, e.g. all animals are in the animal kingdom
Similar organisms from that kingdom are then grouped into a phylum
Similar organisms from each phylum are then grouped into a class, and so on down the eight levels of the taxonomic hierarchy
What happens as you move down the taxonomic hierarchy and how does it end
As you move down the hierarchy, there are more groups at each level but fewer organism in each group
The hierarchy ends with species - the groups that contain only one type of organism
What are the levels of the taxonomic hierarchy
Kingdom
Phylum
Class
Order
Family
Genus
Species
General characteristics of prokaryotes
E.g. bacteria
Prokaryotic, unicellular (single-celled), no nucleus, less than 5 um
General characteristics of protoctista
E.g. Algae, Protozoa
Eukaryotic cells, usually live in water, single-celled or simple multicellular organisms
General characteristics of fungi
E.g. Moulds, yeast, mushrooms
Eukaryotic, chitin cell wall, saprotrophic (absorb substances from dead or decaying organisms), single-celled or multicellular organisms
General characteristics of plantae
E.g. Mosses, ferns flowering plants
Eukaryotic, multicellular, cell walls made of cellulose, can photosynthesise, contain chlorophyll, autotrophic (produce their own food)
General characteristics of animalia
E.g. Nematodes (roundworms), molluscs, insects, fish, reptiles, birds mammals
Eukaryotic, multicellular, no cell walls, heterotrophic (consume plants and animals)
What is phylogeny
Phylogeny is the study of the evolutionary history of groups of organisms
Tells us what organisms are related and how closely related they are
Where have all organisms evolved from
All organisms have evolved from shared common ancestors (relatives)
What is a species
A species is the smallest group that shares a common ancestor (end of a branch on a phylogenetic tree)
Similar organisms (anatomically, physiologically) that can reproduce and have fertile offspring
What does a phylogenetic tree show
Shows the relationship between different organisms
The first branch point represents a common ancestor of all the members
The ancestor is normally extinct
Each of the following branch points represents another common ancestor from which a different group diverged
What is cladistics
Where the classification system take into account phylogeny when arranging organisms into groups
What is the nomenclature used for classification
The binomial system - all organisms are given one internationally accepted scientific name in Latin that has two parts
How to name organisms using binomial system
E.g. Homo sapiens (in italics or underlined if handwritten)
The first part of the name is the genus name and has a capital letter
The second part is the species name and begins with a lower case letter
Advantage of phylogenetic classification
Produces a continuous tree whereas classification requires discrete taxonomical groups
So scientists are not forced to put organisms into a specific group that they do not quite fit
How were species classified before
Early classification systems only used observable features to place organisms into groups
E.g. whether they lay eggs, can fly etc
Problems with classification using observable features
Scientists don’t always agree on the relative importance of different features
Groups based solely on physical features may not show how related organisms are
What are classification systems now based on
Observable features and other evidence such as:
Molecular evidence
Embryological evidence
Anatomical evidence
Behavioural evidence
What is molecular evidence
The similarities in proteins and DNA
You can compare how DNA is stored and the sequence of DNA bases
More closely related organisms will have more similar molecules
Can also compare the sequence of amino acids in proteins from different organisms
The more similar the amino acid sequence of a protein in two different species, the more closely related the species are likely to be
What is embryological evidence
The similarities in the early stages of an organism’s development
What is anatomical evidence
The similarities in structure and function of different body parts
What is behavioural evidence for evolution
The similarities in behaviour and social organisation of organisms
How can technology lead to new discoveries
Technologies such as DNA techniques, better microscopes can result in new relationships between organisms being clarified
Scientists can share new discoveries in meetings and scientific journals
How organisms are classified is continually revised to take account of any new findings that scientists discover
How does the five kingdoms differ from the three domain system
In the older system the largest groups were the five kingdoms - all organisms were placed into one of these groups
The three domain system was then proposed which has three domains (large superkingdoms that are above the kingdoms in the taxonomic hierarchy)
In this system, organisms that were in the kingdom prokaryotae (containing unicellular organisms without a nucleus) are separated into two domains - the Archaea and Bacteria
All organisms that contain a nucleus are placed in the domain Eukarya (this includes 4 of the 5 kingdoms)
Lower hierarchy stays the same (kingdom, phylum, class, order, family, genus, species)
Why was the three domain system first proposed
Mainly due to molecular evidence:
The enzyme RNA polymerase is different in Bacteria and Archaea
Archaea, but not Bacteria, have similar histones to Eukarya
Also due to cell membrane evidence:
The bonds of the lipids in the cell membranes of Bacteria and Archaea are different
The development and composition of flagellae are also different
Bacteria have a cell wall made of murein whereas archeae cell walls do not contain this
This shows that Bacteria and Archaea evolved separately and that Archaea are more closely related to Eukarya than Bacteria
Comparison between bacteria and archaea
Bacteria:
Peptidoglycan
Protein
Polysaccharides
Lipids
Archaea:
No peptidoglycan
Protein
Polysaccharides
Lipids
Darwin’s observations
Organisms produce more offspring than survive
There’s variation in the characteristics of members of the same species
Some of these characteristics can be passed on from one generation to the next
Individuals that are best adapted to their environment are more likely to survive
Darwin’s theory
Individuals within a population show variation in their phenotypes (genetic variation)
These new alleles are caused by genetic mutation
Selection pressures (environmental factors such as predation, disease and competition) create a struggle for survival
Individuals with better adaptations (characteristics that give a survival advantage, e.g. being able to run faster) are more likely to survive and reproduce successfully (survival of the fittest)
They can pass on their advantageous adaptations to their offspring
Overtime, the proportion of the population possessing the advantageous adaptations increases
Over generations this leads to evolution as the favourable adaptations become more common in the population
How did Wallace contribute to the theory of evolution
Independently came up with natural selection and wrote to Darwin about it
Wallace and Darwin published their papers on evolution together and acknowledged eachother’s work
Wallace’s observations provided lots of evidence to support the theory of evolution by natural selection
E.g. warning colours can be used by species to deter predators from eating them (e.g. butterflies) and this is an example of an advantageous adaptation that had evolved from natural selection
Why is Darwin more remembered than Wallace
Darwin is better remembered than Wallace because of the book On The Origin of Species where he mentioned the examples of species he had observed during the voyage to the Galápagos Islands
This is when scientists started to pay attention to the theory
Evidence to support evolution
Fossil record evidence
DNA evidence
Molecular evidence
What is fossil record evidence
Fossils are remains of organisms preserved in rocks
By arranging fossils in chronological order, gradual changes in organisms can be observed that provide evidence of evolution
What is DNA evidence for evolution
Theory of evolution says that all organisms evolved from shared common ancestors
Closely related species diverged more recently
Evolution is caused by gradual changes in the base sequence of an organisms DNA
Organisms that diverged more recently should have more similar DNA
Because less time has passed for changes in the DNA sequences to occur
What is molecular evidence
Scientists compare the sequence of amino acids in proteins, and compare antibodies
Organisms that diverged away from each other more recently have more similar molecules
As less time has passed for changes in proteins and other molecules to occur
What are pesticides
Pesticides are chemicals which kills pests (e.g. insects that damage crops)
How can insects evolve resistance to pesticides
There is variation in a population of insects
Genetic mutations create alleles that make some insects naturally resistant to a pesticide
If the population is exposed to that pesticide only then the resistant individuals will survive and reproduce
The alleles which cause the resistance will be passed on to the next generation
The population will evolve and more individuals will carry the allele than in the previous generation
How can pesticide resistance impact humans
Infestations with insects which have resistance to lots of different pesticides will take longer to control, in that time all the crops may be destroyed
Farmers may have to use broader pesticides which can kill beneficial insects
If disease carrying insects (e.g. mosquitoes) become pesticide resistant, the spread of disease could increase
Takes time and money to develop new pesticides to kill insects which are completely resistant to all current pesticides
How can drug resistant pathogens impact humans
MRSA (methicillin resistant staphylococcus aureus) has become resistant to many types of antibiotics
Other pathogens have also evolved drug resistance e.g. protoctists that cause malaria
Infections by drug resistant pathogens take longer to treat and the patient may become very ill or die by the time treatment is found
Developing new drugs to kill completely resistant pathogens takes time and money
How do bacteria evolve resistance to antibiotics
When bacteria were exposed to an antibiotics
Resistance individuals survived and reproduced (bacteria reproduce rapidly), passing the allele for resistance on to their offspring
Non-resistant individuals died
Over time the number of resistant individuals in the population increased
How do insects become resistant to pesticides
Individual insects with resistance survived exposure to the insecticide, and passed on this characteristic through their alleles, allowing a resistant population to evolve
What is variation
The differences that exist between individuals
Every organisms is unique - even identical twins show some variation
Where can variation occur
Within species
Between species
What is variation within a species
Called intraspecific
E.g. European robins weigh between 16g and 22g and show some variation in many other characteristics including length, wingspan, colour and beak size
How can variation occur between species
Called interspecific variation
E.g. the lightest species of bird is a bee hummingbird, which weighs around 1.6g
The heaviest species of bird is the ostrich, which can weigh up to 160kg
What is continuous variation
When the individuals in a population vary within a range
There are no distinct categories
E.g. humans can be any height within a range, not just tall or short
What are the two types of variation
Continuous or discontinuous
What can continuous variation occur in
Animals
Plants
Microorganisms
How can continuous variation occur in animals
Milk yield: cow can produce any volume of milk within a range
Mass: humans can be any mass within a range
How can continuous variation occur in plants
Number of leaves: a tree can have any number of leaves within a range
Mass: the mass of the seeds from a flower head varies within a range
How can continuous variation occur in microorganisms
Width: the width of E. coli bacteria within a range
Length: the length of the flagellum can vary within a range
How can variation be discontinuous
When there are two or more distinct categories
Each individual falls into only one of these categories, there are no intermediates
E.g. 4 distinct blood groups
How can variation be discontinuous in animals
Blood group: humans can be group A, B, AB or O
How can variation be discontinuous in plants
Colour: courgettes are either yellow, dark green or light green
Seed shape: some pea plants have smooth seeds and some have wrinkled seeds
How can variation be discontinuous in microorganisms
Antibiotic resistance: bacteria are either resistant or not
Pigment production: some types of bacteria can produce a coloured pigment, some can’t
How can variation be caused
Genetic factors
Environmental factors
Both
How can variation be caused by genetic factors
Different species have different genes
Individuals of the same species have the same genes but different versions of them (alleles)
The genes and alleles an organism has make up its genotype
The differences in genotype results in varied phenotypes
E.g. blood group in humans are caused by only genetic factors as well as antibiotic resistance in bacteria
Genetic variation is inherited
How is variation caused by environmental factors
Variation can be caused by differences in environments
E.g. climate, food, lifestyle
Environmental characteristics can change over an organisms life
E.g. accents and whether people have pierced ears are purely causes by environmental factors
How can variation be caused by both environmental and genetic factors
Genetic factors determine the characteristics on organism’s born with, but environmental factors can influence how some characteristics develop
E.g:
Height: genes determine how tall an organism can grow, but diet or nutrient availability affect how tall an organism actually grow
Flagellum: genes determine if a microorganism can grow a flagellum, but some will only start to grow them in certain environments e.g. if metal ions are present
How can the mean be used to look for variation between samples
The mean is the average of the values collected in a sample
Can be used to tell if there is variation between samples
Most samples will include values either side of the mean, so you end up with a bell shaped graph - this is called normal distribution
A normal distribution is symmetrical about the mean
What does the standard deviation sample tell you
Says how much the values in a single sample vary
It’s a measure of the spread of values about the mean
What does it mean when you see the mean written as 9±3
This means the mean is 9 and the standard deviation is 3
So most of the values are spread between 6 and 12
What does a large and small standard deviation mean
Large: means that the values in the sample vary a lot
Small: most of the sample data is around the mean value, so varies little
What is the standard deviation equation and what do the values mean
S = √ Σ (x - x̄)^2 / n - 1
s: standard deviation
Σ: sum of these values
x: a value in the data set
x̄: the mean value
n: the number of values
Work out the standard deviation example:
Tree height in metres
A: 22
B: 27
C: 26
D: 29
- s = √ Σ (x - x̄)^2 / n - 1
- Mean height of trees: 26
- Work out (x - x̄)^2 for each value of x
- Add them all up to get Σ (x - x̄)^2
- Divide this number by the number of values minus 1 (n-1) then square root to get the answer
Answer: 2.94 - 3sf
What do adaptations do
They make an organism well suited to the environment
What does being adapted to an environment mean
An organism has features called adaptations that increase its chances of survival and reproduction and also increase the chances of its offspring reproducing successfully
Where can adaptations be found
Behavioural
Physiological
Anatomical
How are adaptations passed down a generation
The best adapted individuals in each generation are more likely to survive and reproduce
They pass their adaptations on to their offspring
Individuals that are less well adapted are more likely to die before reproducing
How can adaptations be behavioural
These are the ways an organism acts that increase its chance of survival
How can adaptations be physiological
These are processes inside an organism’s body that increase its chance of survival
Examples of behavioural adaptations
Possum ‘play dead’ if they’re being threatened by a predator they play dead to escape attack
This increases their chance of survival
Scorpions dance before mating, makes sure they attract a mate of the same species, increases the likelihood of successful mating
Examples of physiological adaptations
Brown bears hibernate which lowers their rate of metabolism over winter, conserves energy so they don’t have to look for food when it’s scarce which increases their chance of survival
Some bacteria produce antibiotics which kill other species of bacteria in the area so there’s less competition and they’re more likely to survive
How can adaptations be anatomical (structural)
Structural features of an organism’s body that increases its chance of survival
Examples of anatomical adaptations
Otters have a streamlined shape which makes it easier to glide through water, this makes it easier for them to catch prey and escape predators, increasing their chance of survival
Whales have a thick layer of blubber, this helps to keep them warm in the cold sea which increases their chance of survival in places where their food is found
Why might different taxonomic groups have similar features
Might have similar features despite not being closely related
E.g. whales and sharks
This is because they have evolved in similar environments and to fill similar ecological niches
What are the three groups of mammals
Placental
Marsupial
Egg laying monotremes
Where are marsupial mammals found and do they relate to placental mammals?
Marsupials are found mainly in Australia and the Americas
They diverged from placental mammals many millions of years ago and have been evolving separately ever since
Features of marsupial mammals
E.g. kangaroos
Short gestation period (pregnancy)
Don’t develop full placenta
Born early in development and climb into mothers pouch
They then become attached to a teat and receive milk while they continue to develop
Features of placental mammals
E.g. humans
Longer gestation period (pregnancy)
Develop placenta during pregnancy, allows for exchange of nutrients and waste products between the fetus and the mother
Born fully developed
About marsupial and placental moles
Are not closely related and evolved independently on different continents
Share anatomical features because they’ve both evolved to live in similar environments
How are marsupial and placental moles similar
Both live in tunnels and burrow to reach food supply (earthworms and insects)
Small or nonexistent eyes because they don’t need to see underground
No external ears, to keep a streamlined head for burrowing
Scoop-shaped and powerful front paws, which are good for digging
Tube shaped body and cone shaped head, makes it easier to push through sand or soil
What is the student’s t test
Used to compare the mean values of two sets of data
t = (x̄1-x̄2) / √(σ1^2/n1) + (σ2^2/n2)
x̄1, x̄2: mean of populations 1 and 2
σ1, σ2: standard deviation of populations 1 and 2
n1,n2: total number of values in sample 1 and 2
What is the spearman’s rank
Spearman’s rank correlation coefficient is used to consider the relationship of between two sets of data
rs = 1 - 6Σd^2 / n(n^2 - 1)
rs: correlation coefficient
d: difference in ranks
Σ: sum of
n: number of pairs of data
Method of spearman’s rank
Rank each value in the data set from smallest to largest
Repeat this for the other data set
Find the difference between the ranking of each row (can be negative)
Square these differences to get d^2
Add these up to get Σd^2
Plug into equation
How can scientists compare the age of extinct organisms
Compare fossils
Fossils deeper in the group are older than fossils closer to the surface
