Chapter 10 - Classification and Evolution

Define classification

The process by which living organisms are sorted into groups based on their similarities and differences

What are the seven taxonomic groups

Kingdom

Phylum

Class

Order

Family

Genus

Species

Why are organisms classified

• To identify species

• To predict characteristics

• To find evolutionary links

What are the three domains of classification

• Archaea

• Bacteria

• Eukarya

What happens as you move down the classification system

• Organisms in each group become more similar and share more characteristics

• System ends with organisms being classified as an individual species

Define species

A group of organisms that have similar physiological and behavioural characteristics that are able to reproduce to give fertile offspring

Why was the previous system for naming organisms not useful

• Organisms were given names according to their characteristics, behaviour, habitat

• This was not useful as organisms can have more than one common name and different names in different languages

• Common names do not provide information about relationships between organisms

What did Carl Linnaeus come up with

A system for naming organisms known as binomial nomenclature

How are binomial names made

• The first word is the organism’s genus, generic name

• Second word is the organism’s species, specific name

• The scientific name should always be in italics

• It is difficult to write in italics so in handwritten documents the name is underlined

• Name should be lowercase except for first letter of genus which should be capitalised

Five-kingdom system

• Prokaryotae

• Protoctista

• Fungi

• Plantae

• Animalia

Three-domain system

• Bacteria

• Archaea

• Eukarya

Six-kingdom system

• Eubacteria

• Archaebacteria

• Protoctista

• Fungi

• Plantae

• Animalia

Features of prokaryotae

• Unicellular

• No nucleus / membrane-bound organelles

• No visible feeding mechanism

• Heterotrophic and autotrophic

Features of protoctista

• Mainly unicellular

• Have a nucleus / membrane-bound organelles

• Some have chloroplasts

• Some are sessile (don’t move) while others move by cilia, flagella

• Nutrients acquired by photosynthesis (autotrophic feeders), ingestion of other organisms (heterotrophic feeders), some are parasitic

Features of fungi

• Unicellular or multicellular

• Have a nucleus / membranes-bound organelles / cell wall (chitin)

• No chloroplasts

• No mechanism for movement

• Most have a body/mycelium made of threads/hyphae

• Nutrients acquired by absorption (saprophytic feeders), some are parasitic, heterotrophic

• Most store food as glycogen

Features of plantae

• Multicellular

• Have a nucleus / membrane-bound organelles / cell wall (cellulose)

• All contain chlorophyll

• Most don’t move

• Nutrients acquired by photosynthesis (autotrophic feeders)

• Store food as starch

Features of animalia

• Multicellular

• Have a nucleus / membrane-bound organelles

• No chloroplasts

• Move with aid of cilia, flagella

• Nutrients acquired by ingestion (heterotrophic feeders)

• Food stored as glycogen

Why do classification systems change

• Scientists learn more about organisms, so classification systems change

• Originally, classification systems were based on observable features

• Now because of the study of genetics and other biological molecules scientists are able to study evolutionary relationships

What did Carl Woese propose

Three Domain System - Archaea, Bacteria, Eukarya

How id the three domain system grouped

• Organisms grouped by differences in sequences of rRNA

• Also grouped by cells’ membrane lipid structure and sensitivity to antibiotics

What are the differences between organisms in different domains

• Unique form of rRNA

• Different ribososmes

Eukarya domain

• RNA polymerase contains 12 proteins

• 80s ribosomes

Archaea domain

• RNA polymerase contains 8-10 proteins

• 70s ribosomes

Bacteria domain

• RNA polymerase contains 5 proteins

• 70s ribosomes

Describe archaebacteria

• Live in extreme environments; hot thermal vents, anaerobic conditions, highly acidic environments

Describe eubacteria

• Found in all environments

• Different to archaebacteria as they have different chemical makeup

• Eubacteria contain peptidoglycan in cell wall whereas archaebacteria do not

Define phylogeny

The evolutionary relationships between organisms. Study of evolutionary history of groups is known as phylogenetics.

Phylogenetic trees are used to represent these relationships, with earliest species at base and most recent species at the tips of the branches.

Phylogenetic trees are produced by looking at similarities and differences in species’ physical characteristics and genetic makeup, e.g. from fossils

Advantages of phylogenetic classification

• Phylogeny can be done without reference to Linnaean classification

• Phylogeny produces a continuous tree whereas classification requires discrete taxonomical groups

• Hierarchal nature of Linnaean classification can be misleading as it implies different groups within the same rank are equivalent e.g. cats and orchids are both families but cats have approximately 35 species whilst orchids have about 20,000

How was the theory of evolution developed

• Charles Darwin made observations on finches in the Galápagos Islands and studied how the shapes and sizes of their beaks and claws varied depending on which island they were on and what foods were available

• He found that birds born with a beak more suited to the type of food available on the island were more likely to survive ad have more offspring, therefore passing on its characteristic beak until eventually the population of finches on the island all shared the same beak

• Darwin spent years developing his ideas and also shared ideas with Alfred Wallace who was working on his own theory of evolution. Eventually they came up with the theory of evolution by natural selection which was initially very controversial but eventually accepted.

3 pieces of evidence for evolution

• Palaeontology

• Comparative anatomy

• Comparative biochemistry

Palaeontology

• Fossils are formed over time as sediment is deposited on earth to form layers (strata) of rock. Fossils found in different rock strata are quite different, forming a sequence showing the gradual change over time which is known as the fossil record

Evidence provided by the fossil record:

• Fossils of simple organisms are found in oldest rocks whilst more complex organisms are found in recent rocks. This suggests simple life forms evolved into more complex ones gradually over time

• Sequence in which organisms are found matches their ecological links. E.g. plant fossils appear before animals showing that animals require plants to survive

• Studying similarities in anatomy of fossil organisms shows how closely related organisms have evolved from the same ancestor

• Fossils allow relationships between extinct and living organisms to be investigated

Why is the fossil record incomplete

• Many organisms are soft bodied so decompose before they have a chance to fossilise

• Conditions needed for fossilisation are often not present

• Many fossils destroyed by Earth’s movements or are still undiscovered

Comparative anatomy

This is the study of similarities and differences in the anatomy of different living species.

Homologous stuctures

• A structure that appears superficially different but has the same underlying structure

• Vertebrate limbs are used for different functions such as running, jumping, flying so you would expect their bone structure to be very different from that in a walking or swimming vertebrate.

• However, basic structured of all vertebrate limbs are very similar, the same bones are adapted to carry out the whole range of different functions

• An explanation is that all vertebrates have evolved from a common ancestor

Divergent evolution

Describes that from a common ancestor, different species have evolved, each with a different set of adaptive features.

This evolution occurs when a closely related species diversify to adapt to new habitats as a result of migration or loss of habitat

Convergent evolution

When unrelated species begin to share similar traits.

These similarities evolve because the organisms adapt to similar environments or selection pressures

Comparative biochemistry

The study of similarities and differences in the proteins and other molecules that control life processes.

• Some important molecules are highly conserved among species. Slight changes in these molecules can help identify evolutionary links.

• 2 molecules most commonly studied are: cytochrome c and ribosomal RNA

• Neutral evolution - Most of the variability in the structure of a molecule does not affect its function. Changes that do not affect a molecule’s functional regions are called neutral as they don’t change the function. Neutral changes are not affected by natural selection so occur at a fairly regular rate.

• To observe how closely related two species are, scientists look at the order of DNA bases or the order of amino acids in a protein

• Number of differences are plotted against the rate of neutral base pair substitutions to estimate the point at which two species last shared a common ancestor

• Closely related species have more similar DNA and proteins whilst distantly related species have fewer similarities

• Ribosomal RNA has a slow rate of substitution so is used with fossil information to determine relationships between ancient species

Define variation

The differences in characteristics between organisms

Interspecific variation

Widest type of variation which is differences between members of different species, e.g. mouse has fur, teeth, four legs whilst bird has wings, beak, two legs

Intraspecific variation

Differences between organisms within a species, e.g. people have different height, hair colour, intelligence

Two factors causing variation

• Genetic variation

• Environmental variation

Causes of genetic variation

• Alleles - Genes have different alleles so different alleles can produce different effects

• Mutations - Changes to the DNA sequence lead to changes in the proteins coded for. If mutation occurs in body cells then just the individual is affected but if it occurs in the gametes then the mutation is passed to offspring, both result in variation

• Meiosis - Each gamete receives half genetic content of a parent cell. Genetic material inherited from two parents is mixed up by independent assortment and crossing over leading to variation

• Sexual reproduction - Offspring is produced from two individuals inherits genes from each parent so is genetically different from both parents

• Chance - Many different gametes are produces so it is a result of chance as to which two will combine (random fertilisation)

The last 3 points are all aspects of sexual reproduction therefore there is more variation in sexual than asexual reproduction. Variation in organisms produced asexually can only occur as a result of mutation

Causes of environmental variation

• All organisms are affected by environment however plants may be affected more than animals due to lack of mobility

• E.g. a rose bush planted in the sun will grow larger than one in the shade

• Plant is more affected because an animal can simply move to another area to look for things it needs such as food or shelter

Name a characteristic that is determined purely by genetic and purely by environmental variation

Genetic variation: Blood type, as genes passed from your parents will determine your blood type

Environmental variation: Scars, they occur from an accident or disease, no genetic origin as these can’t be inherited from a parent

Causes of both environmental and genetic variation

• Most variation is caused by a combination of environmental and genetic factors

• E.g. if you have tall parents you will inherit genes for a tall height, however, if you have a poor diet or disease you may not grow as tall

• E.g. skin colour is determined at birth by genetic, however, if you are exposed to sunlight then your body produces more melanin to protect from UV resulting in darker skin

Discontinuous variation

A characteristic that can only result in certain values shows discontinuous variation, e.g. sex, blood group, bacteria shape

Usually purely determined by genetic factors

Represented using a bar chart but pie chart may also be used

Continuous variation

A characteristic that can take any value within a range is said to show continuous variation, e.g. height, mass

Often also influenced by environmental factors

Represented using a histogram with a curve drawn on to show trend.

Define adaptation

A characteristic which increases an organism’s chance of survival and reproduction in its environment

3 types of adaptations

• Anatomical

• Behavioural

• Physiological

Examples of anatomical adaptations

• Body covering - hair, scales, feathers, shells - These can provide a variety of different functions such as: warmth, protection, prevent water loss, deter herbivores, protect from sun damage

• Camouflage - colour allows animal to blend into environment preventing a predator from spotting it

• Teeth - shape and type of teeth in animal’s jaw are related to diet - Herbivores have molars for chewing tough grass, carnivores have sharp canines to kill prey and tear meat

• Mimicry - copying of another animal’s appearance or sound allows harmless organism to fool predators into thinking it’s dangerous

Describe Marram grass

It is adapted to live in an environment with little water by reducing rate of transpiration

It has:

• Curled leaves to minimise surface area of moist tissue exposed to air

• Hairs on inside surface to trap moist air close to leaf

• Stomata sunk into pits making them less likely to lose water

• Thick waxy cuticle reducing water loss via evaporation

Examples of behavioural adaptations

• Survival behaviours - play dead or freeze to escape predator’s detection

• Courtship - exhibit behaviours to attract a partner - scorpions dance to attract partner

• Seasonal behaviours - migration (animals move one region to another then back when conditions are favourable), hibernation (period of inactivity where animal’s body temp, heart rate, breathing rate slow down to conserve energy)

2 categories of behavioural adaptations

• Innate - Ability to do this is inherited through genes

• Learned behaviour - Ability is learnt from experience or observing other animals

Examples of physiological adaptations

• Poison production - produce venom to kill prey

• Antibiotic production - bacteria produce antibiotics to kill other bacteria in surrounding area

• Water holding - water is stored in body

What are analogous structures

They have adapted to perform the same function but have a different genetic origin

Define selection pressures

Factors that affect the organism’s chance of survival or reproductive success

Steps of natural selection

• Organisms within a species show variation in characteristics caused by differences in genes

• Organisms whose characteristics are best adapted to a selection pressures have increased chance of survival and successful reproduction (survival of the fittest)

• Successful organisms pass allele coding for advantageous characteristic to their offspring

• Process is repeated for every generation. Over time proportion of individuals with advantageous adaptation increases

• Over long periods of time, this process can lead to evolution of a new species

Antibiotic-resistant bacteria

MRSA has developed resistance to many antibiotics. Bacteria reproduce rapidly so evolve in a relatively short time. When exposed to antibiotic, resistant individuals survive and reproduce, passing down allele whilst non-resistant individuals die.

Peppered moths

• Before industrial revolution, most peppered moths were pale coloured. This provided camouflage against light-coloured tree bark, increasing chance of survival

• During industrial revolution, trees became darker due to soot and loss of lichen. Dark moths were better adapted so more survived and reproduced so increased population of dark peppered moths

Sheep blowflies

• Lay eggs in faecal matter around sheep’s tail, the larvae hatch and cause sores which can be fatal if untreated

• Pesticide diazinon was used to kill blow flies

• Few years later, blowflies developed resistance to diazinon

• Insects with resistance survived and passed on this characteristic through their alleles

What is pre-adaptation

When an organism’s existing trait is advantageous for a new situation

Flavobacterium

• Flavobacterium lives in waste water from factories that produce Nylon 6

• This strain of bacteria has evolved to digest nylon so is beneficial to humans as they help to clear up factory waste

• These bacteria use enzymes to digest nylon known as nylonases

• This is useful to the bacteria as it provides them with another source of nutrients

• Scientists believe the gene mutation occurred or produce these enzymes as a result of gene duplication combined with frameshift mutation