Classification and Evolution

• Why do we classify living things?

  >for our convenience

  >to make the study of living things manageable

  >to make it easier to identify organisms

  >to help us see the relationships between species
• What is classification?

  The process if placing living things into groups.

  The existing system uses 8 taxonomic levels and organisation is based on the similarities in observable features.
• Modern classification hierarchy

  Domain: Archaea, Eubacteria and Eukaryotae

  Kingdom: Plantae, Animalia, Fungi, Protocista, Prokaryotae

  Phylum: Groups of organisms that have the same body plan (Ex. A backbone)

  Class: Group of organisms that all have the same general traits (Ex. 10 legs)

  Order: Subdivision of the class using additional information about the organisms (Ex. is a herbivore)

  Family: Group of closely related genera

  Genus: Group of closely related species

  Species: Basic unit. All members of a species within have variations but are essentially the same
• Binomial system of naming species

  Carl Linnaeus devised this system that uses Genus and species.

  > Genus starts with a capital

  > species is all lowercase

  Binomial name is written in latin as it is a universally understood language which prevents misinterpretation.
• Why is a common name not used in the Binomial system

  > the same organism may have a completely different common name in different parts of one country

  > different common names are used in different countries

  > translation of languages or dialects may give different names

  > the same common name may be used for different species in other parts of the world
• Biological definition of a species: a group of organisms that can freely interbreed to produce fertile offspring.

  • This definition does not work for organisms that reproduce asexually and is hard to apply those found in fossils

  Phylogenic definition of a species: a group of individual organisms that are similar in appearance, anatomy, physiology, biochemistry and genetics.
• Features used to classify organisms into the five kingdoms. They are based on similarities in observable features of their anatomy on a microscopic level.
• Microscopic features to classify into Kingdom Prokaryotae

  >Have no nucleus

  >have naked DNA not associated with histone proteins

  >have no membrane-bound organelles

  >have smaller ribosomes than in other groups

  >have smaller cells than those in Eurkaryotes
• Microscopic features to classify into Kingdom Protoctista

  >are eukaryotic

  >mostly single celled

  >show a wide variety of forms

  >show various plant-like or animal-like features

  >have autotrophic or heterotrophic nutrition. (Some photosynthesise, some ingest prey, some feed using extracellular enzymes and some are parasites)
• Microscopic features to classify into Kingdom Fungi

  >are eukaryotic

  >cant exist as single cells

  >have walls made of chitin

  >have cytoplasm that is multinucleate

  >mostly saprophytic (so can cause decay of organic matter)
• Microscopic features to classify into Kingdom Plantae

  >are eukaryotic and multicellular

  >cells surrounded by cellulose cell wall

  >contain chlorophyll

  >are autotrophic (absorb simple molecules and build into larger organic molecules)

  >contain chlorophyll
• Microscopic features to classify into Kingdom Animalia

  >are eukaryotic and multicellular

  >usually able to move around

  >heterotrophic (digest large organic molecules to form smaller molecules for absorption)
• Biological molecules and genetic evidence used in classification Pt.1

  All living organisms that respire must have cytochrome c. The protein is not identical in all species. If we compare the sequence of amino acids in samples of cytochrome c from 2 different species we can infer:

  >if the sequences are the same, the 2 species are closely related

  >if the sequences are different, the 2 species are not closely related

  The more differences found between the sequences the less related the species.
• Biological molecules and genetic evidence used in classification Pt.2

  >DNA provides the genetic code for producing proteins. This is universal and codes for the same sequence of amino acids in any organisms. However, mutations, changes to the sequence of bases in DNA, occur at random producing different sequences and proteins. The more similar the sequence in a part of DNA, the more closely related the species.

  >Certain biological molecules may not be identical in every species. Differences seen today in these molecules are a result of evolution.
• 3 Domain classification Pt.1

  Carl Woese made a new system by dividing the Kingdom Prokaryotae into 2 groups: Eubacteria and Archaea. This was because bacteria are more different from the Archaea and Eukaryotae. Some structural differences include that bacteria have:

  >a different cell membrane structure

  >flagella with a different internal structure

  >different enzymes and mechanisms for synthesising RNA and DNA replication

  >no proteins bound to their genetic material
• 3 Domain classification Pt.2

  Whereas Archaea share some features with Eukaryotes:

  >similar enzymes and mechanisms for synthesising RNA and DNA replication

  >production of some proteins that bind to their DNA

  As RNA and DNA translate genes into visible characteristics, Woese suggested that the differences between Eubacteria and the Archaea are more different from each other than the Archaea from the Eukaryotae.
• Artificial classification

  Ex: a book guide may have all the plants with yellow flowers and all the blue flowers on separate pages to help users turn to the section containing all the flowers of a particular colour.

  >is based on only a few characteristics

  >does not reflect any evolutionary relationships

  >provides limited information

  >is stable
• Natural Classification

  >uses many characteristics

  >reflects evolutionary relationships

  >provides useful information

  >may change with advancing knowledge
• Phylogeny is the study of the evolutionary relationships between species. Phylogenetic trees can be used to show this. The branches indicate where 2 or more species may have evolved separately from a common ancestor. The more recent the common ancestor, the more closely related the species. Species that are known to be monophyletic mean they have all evolved from the same species. Common ancestors do not survive today, any 2 species today have evolved from an ancestor in the past.
• Theory of Evolution by Natural selection

  After Darwins voyage on the HMS Beagle and Alfred Russel Wallace's study in the Amazon, they both proposed the mechanism of natural selection, which explains how features of the environment apply a selective force on the reproduction of individuals in a population.
• Darwins 4 observations for the theory of evolution

  1> Offspring generally appear similar to their parents

  2> No two individuals are the same

  3> Organisms have the ability to produce large numbers of offspring

  4> Populations in nature tend to remain fairly stable in size
• Darwins 3 conclusions for the theory of evolution

  1> there is a struggle to survive

  2> better-adapted individuals survive and pass on their characteristics

  3> over time a number of changes may give rise to a new species
• Evidence for evolution in fossils

  Fossils show that:

  >in the past the world was inhabited by species that were different from those present today

  >old species have died out and new species have arisen

  >the new species that have appeared are often similar to older ones found in the similar place
• Evidence for evolution in Biological molecules

  >If one species gives rise to another they both likely have the same biological molecule, suggesting they all arose from one original ancestor. The more identical the molecules between the 2 species, the more closely related the species and suggest they only separated recently.

  >Alike cytochrome c, the structure of DNA can be used as evidence. Genes can be compared by sequencing the bases in the DNA. The greater the number of similarities between the gene sequences, the more closely related the species and the more recent their evolution.
• Types of variation

  Intraspecific - variation within a species (ex. hair and eye colour)

  Interspecific - variation between species
• Continuous variation

  >where there are two extremes and a full range of intermediate values between them. It is often regulated by more than one gene and can be influenced by the environment that an organism lives in.

  >For example: height in humans, length of leaves in an oak tree, stalk length of a toadstool and number of flagella on bacteria

  >Most individuals are close to the mean value and few are at the extremes. The type of variation is usually quantifiable, best plotted in a histogram.
• Discontinuous variation

  >where there are two or more distinct categories with no intermediate values. It is often regulated by a single gene and is not influenced by the environment an organism lives in.

  > For example: 2 genders in mammals, 3 in plants, some bacteria have flagella others do not, variation in human blood groups.

  >Members of a species may be evenly distributed between the different forms or there may be more in one type than another. Variation is best shown on a bar chart.
• Causes of variation

  >Genetic: The combination of alleles we inherit is unique and not the same in any other living organism

  >Environmental: Many characteristics can be affected by our environment (ex. a persons skin will become lighter and darker with exposure to sunlight

  >Combined effects: changes in environment can affect which genes are active.

  A better diet has helped humans grow taller however, some many not grow very tall as they are limited by their inherited genes. Genes become expressed in puberty which results to changes in our bodies.
• Adaptation is a characteristic that enhances survival in the habitat of an organism.

  >An organism may need this adaptation to: gather enough nutrients and water, reproduce successfully, defend itself from predators, photosynthesise, survive the physical conditions of its environment such as changes in temperature, light and water availability.
• Types of adaptation

  >Anatomical: any structure that enhances an organisms chances of survival (ex. roots, waxy cuticle)

  >Behavioural: an aspect of behaviour modified to help an organism survive conditions it lives in (ex. rolling leaves in marram grass due to water scarcity)

  > Physiological: one that ensures the correct functioning of cell processes (ex. guard cells open when cells become turgid)
• Convergent evolution

  When two unrelated species evolve similar adaptations in the same place due to the same environmental pressures. This can be seen in between the Marsupial mole and Placental mole. They have evolved separately and are unrelated however share many anatomical characteristics:

  >cylindrical body

  >small eyes

  >strong front legs with large claws

  >short fur and tail
• How natural selection can affect the characteristics of a population over time

  An individual that has a characteristic which helps it survive is more likely to survive long enough to reproduce continuing process of evolution. This trait will be passed onto other generations and more individuals in the population will have that adaptive characteristic. This mean the trait has been selected.
• Natural selection process

  1> Mutation creates alternative alleles

  2> this creates genetic variation within the individuals of the species (intraspecific variation)

  3> Then environment changes, applying selection pressure. This selects the characteristics that give an advantage

  4> Individuals with the advantageous characteristic will survive and reproduce, passing on their trait for their offspring to inherit

  5> The next generation will have a higher proportion of individuals with the successful characteristics. Organism then becomes well adapted to its environment.
• Evolution of pesticide resistance in insects - implications on humans

  >Insecticides on food apply selection pressure

  >If an insect has a resistance to the pesticide, due to a mutation, it is more likely to survive and pass on its characteristic in reproduction.

  >Larger populations of resistant insects accumulate and survive being sprayed with pesticides.

  >These can then be eaten by predators and insecticide may move all the way up the food chain, where humans may receive large doses.
• Drug resistance in microorganisms

  >Antibiotics place a high selection pressure on bacteria.

  Resistant bacteria that haven't been killed by the antibiotics can reproduce to create a resistant strain of bacteria. Overuse and incorrect use of antibiotics increases this.

  >The bacteria, MRSA has a wide range of resistance and becomes rapidly resistant to stronger drugs.
• Why do we say microorganisms have developed resistance to antibiotics and not immunity?

  Immunity implies activation of an immune system and microorganisms do not have one.