Component 2.2 1. All organisms are related through their evolutionary history Flashcards
Classification
Classification is the organisation of every living thing into groups. It aims to group organisms to reflect how closely they are related in terms of their evolutionary relationships. Classification is hierarchical, meaning that large groups are split into groups of decreasing size. It is also phylogenetic, meaning that organisms in the same group are more closely related. The groups are discrete so an organism cannot belong to more than one group at the same taxonomic level. Each group is called a taxon.
The three domains are:
Eubacteria – these are the ‘true’ bacteria (remember from unit 1.2 that bacteria are prokaryotic).
Archaea – these are also prokaryotic but are extremophiles.
Eukarya - these are all the eukaryotic organisms.
Extremophiles
Extremophiles live where environmental conditions are harsh, e.g. in very high or low temperatures (thermophiles or psychrophiles), acidic or very alkaline environments, and areas with high salinity (halophiles) or high pressures.
classification
Phylogeny
Phylogeny is the study of the evolutionary relationships between organisms.
5 kingdoms
Prokaryotae, Animalia, Plantae, Fungi and Protoctista
Prokaryotae
Prokaryotae have cells without a membrane-bound nucleus or membrane-bound organelles.
They have 70S ribosomes and a cell wall of peptidoglycan (murein).
They are unicellular.
Some are heterotrophic while others are autotrophic.
Animalia
Animalia are multicellular eukaryotic organisms.
Their cells do not have cell walls.
They are all heterotrophic and have holozoic nutrition, digesting food internally.
They have nervous co-ordination.
Plantae
Plantae are multicellular eukaryotic organisms.
They have cell walls made of cellulose.
They are autotrophs, using sunlight as a source of energy to make organic molecules by photosynthesis.
Fungi
Fungi can be multicellular or unicellular, but they are all eukaryotes.
They have cell walls made of chitin.
They are all heterotrophic and feed saprophytically by secreting enzymes extracellularly onto food.
Multicellular fungi grow in long threads called hyphae (all the hyphae together are a mycelium).
All fungi reproduce by spores.
Protoctista
Protoctista are unicellular eukaryotic organisms. The cells may gather to form a functioning unit like a seaweed but there is no tissue differentiation.
Protoctists may be heterotrophic, autotrophic or both.
It is a very diverse grouping.
Species
A species is a group of organisms with similar characteristics that can interbreed to produce fertile offspring.
organism
a living thing that has an organized structure, can react to stimuli, reproduce, grow, adapt, and maintain homeostasis.
some similar organisms can interbreed to produce offspring – but if the offspring are sterile then the organisms are not the same species. This applies to plants as well as animals. Fertility in plants can be assessed by seed production.
sterile - why does it occur
Sometimes it is because the gametes of the two species have different chromosome numbers, so the chromosomes cannot pair up at the start of meiosis, therefore the hybrid cannot make gametes.
naming
The first name is capitalised and gives the genus of the organism – this is the generic name. The second, in lower case, is the species name.
relationship between organisms in the same vs different species
organisms in the same genus are more closely related to each other than to organisms in a different genus. Conventionally, the binomial of an organism is italicized.
phylogenetic tree
is a diagram that represents the evolutionary pathways leading to different species.
The axis is time, the tree branches as time moves forward.
clade.
A group of branches from one common ancestor is called a clade.
Each junction represents
the common ancestor of the organisms that branch from it.
The more recent the common ancestor
The more recent the common ancestor, the more closely related the organisms are.
Remember that you don’t need to know any specific organisms, and every living thing o
Biological polymers that have different subunits, such as DNA, RNA or protein can be used to establish relatedness.
The sequences of subunits can be compared and the number of differences counted. The more differences there are in sequence, the less closely related two organisms are.
Why are there differences in the amino acid sequence
Mutations in DNA can lead to differences in the amino acid sequence of proteins. Depending on the organism type and reproduction rate, it is possible to use these differences to construct a “molecular clock” which shows how long ago that mutation occurred, and means that a timeline can be drawn as to when a species or group diverged.
gel electrophoresis
Fragments of DNA and proteins can be separated by gel electrophoresis. The gel allows small fragments to move further and the electrical charge causes movement of the negatively charged DNA fragments to the positive electrode. A banding pattern is produced, called a DNA fingerprint, which can be used for comparison. Alternatively, sequences of DNA and amino acids can be established.
Morphology
Morphology means looking at the shape and form of an organism. Before biochemical analysis was possible, this was the main evidence that naturalists had to classify organisms and construct phylogenetic diagrams.
convergent evolution
Some organisms have similar morphology but are unrelated in evolutionary terms.
There are many examples of convergent evolution, where the selection pressures are similar and mutations giving rise to similar features provide an advantage.
Homologous structures
are similar structures that have different functions.
The structure is the same even though evolution has resulted in adaptations for particular functions. Homologous structures indicate that organisms are related.
Analogous structures
arise through convergent evolution; the function is the same, however the origin of the structure is different.
Biodiversity
Biodiversity describes the number of species (species richness) and number of individuals of each species (species evenness) in a given area. The more biodiverse an area is, the more types of species and individuals there are.
How and why does biodiversity vary across the world
Biodiversity on the planet varies spatially; it increases going from the poles towards the equator.
There are several reasons for this trend.
More UV light causes a higher rate of mutation and therefore more rapid evolution.
More species types means there are more habitats (places to live) and niches (food types).
A more stable temperature range and water availability means conditions are more favourable for survival.
With more species and individuals, competition is high, leading to more specialized and narrower exploitation of niches, making it more difficult to move out of the area.
Why does biodiversity vary over time
Biodiversity varies over time; throughout evolutionary history there have been mass extinctions caused by climate change. These have been followed by rapid expansion and diversification of species. A good example of this is the extinction event for dinosaurs followed by the rapid expansion and diversification of mammals. It is feared that human activities are currently driving a sixth mass extinction event with a massive loss of biodiversity.
To investigate biodiversity in a habitat
what needs to be measured
the number of different species (species richness) and the numbers of individuals of each species (species evenness) must be counted.
process of investigating biodiversity
The area is sampled, either by gridding or by sampling along a line (transect). Gridding is used where two areas are to be compared, for example a mown and unmown area of grassland. Transects are used where there is a gradual change in the environment, for example moving from under a tree into the open.
Random sampling is important as it avoids unconscious sampler bias, increasing the reliability of the data. Random number tables are used to generate random co-ordinates for a gridded area and the quadrats placed at those co-ordinates only. Sampling along a transect is often done at a fixed distance, e.g. every 2 metres.
In terrestrial ecosystems a quadrat is placed; this is a grid of known area inside which plants can be counted. Many samples are taken to improve reliability. In aquatic ecosystems the method of collection in each area is standardised. This could include time for collection or mesh size of net. Kick sampling is also used in aquatic ecosystems.
The main hazards in field work
Biting and stinging insects and stinging or thorny plants - the risk is scratches or allergic reaction, and these are controlled by wearing insect repellent and protective clothing.
Different ecosystems have different hazards, e.g. the tide is a hazard on a seashore. The risk is being cut off, and the control would be to utilise tide tables and choose an appropriate time for the work.
Slippery surfaces can be a hazard causing risks of strains and sprains - appropriate footwear with grip should be worn.
What is Simpsons Biodiversity Index
Simpson’s Diversity Index is a calculation that reduces the data about numbers of species and individuals of each species to a single number. This number can be used to compare biodiversity in two different areas or ecosystems.
As the calculation is “1-…” the number is always between 0 and 1. A higher value indicates that the biodiversity is higher.
Simpson’s Biodiversity Index Equation
N is the total number of individuals counted of all species.
n is the number of individuals of each individual species.
∑ means “sum of” so add up the numbers in the column.
Other explanations for differences in SDI
n order to draw conclusions about differences in Simpson’s Diversity Index, it may be necessary to measure physical aspects of the areas or ecosystems. These factors are termed abiotic factors and may include, temperature, pH, nitrate concentration, oxygen concentration (in aquatic systems) or light intensity.
