Biodiversity and Evolution

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Key Definitions

Species- a group of organisms that are very similar in appearance, anatomy, physiology, biochemistry and genetics. They are able to interbreed freely to produce fertile offspring.

Habitat- the place where an organism lives

Biodiversity- the variety of life, the range of living organisms to be found.

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Biodiversity at Different levels

Habitiat- the range of habitats in which different species live. In the local park there may be a variety of habitats in which a range of organisms live.

Species- all species are different from one another.These can be obvious structural differences or functional differences.

Genetic variation between individuals belonging to the same species is biodiversity at a genetic level.

Current Estimates of Biodiversity

-there are estimates for the number of known species on Earth and we are not sure how accurate they are because we are not sure if we have found all the species on earth, new species are being found all the time, evolution and speciation are occuring, many species are endangered and becoming extinct.

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Sampling- Importance

-Human activites affect the environment in a number of ways

-Unless we study how our activites affect the environment we cannot assess the impact we have. EIA is very important in planning processes.

-EIA is used to estimate the effects if a planned development on the environment.

-Sampling is representative of a whole area.

-We need to know how mnay organisms there are to maintain an area's biodiversity.

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Sampling Plants

-Choose randomly the sample sites inside the habitat by estimating the size of the habitat.Take samples at regular distances across the habitat.Use random numbers to generate co-ordiants to plot in the habitat.

-The number of samples you take depends on the size of the habitat and the time available as well as the diversity of the area. If you are comparing two areas there needs to be the same amount of samples in each area. Before sampling a table should be made to record your results.

-You can count large plants individually but smaller ons it is better to measure percentage cover. You can do this by using a Quadrat placing them on random co-ordinates and use the

  • ACFOR scale (Abundant, Common, Frequent, Obvious, Rare)
  • Calculate percentage cover using a point frame (each needle is 1%)
  • Use a transect line to use quadrats at set intervals (interrupted belt transect) or a continuous belt transect to study an area in detail.
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Sampling Animals

-Animals move so any attempt to sample animals will disturb the habitat. Larger animals can be observed so dont need to be trapped. You can also see signs that animals have left behind (burrows, droppings etc.)

-Sweep Netting: you sweep the net through the vegetation in wide arcs. Any small animals like insects will get caught in the net. Empty the contents of the net on a white sheet to identify them. This method is good for low vegetation.

-Collecting from trees: tapping branches dislodges animals so can be caught and identified.

-Pitfall trap: set in soil to catch small animals in a container just below the surface of the soil. Light trap traps flying insects at night through the use of a UV light.

-Tullgren Funnel: device for catching small animals from a leaf litter. You place the leaf litter in the funnel. A light above the litter drives the animals downwards. They fall through the mesh screen to be collected in a jar beneath the funnel

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Measuring Biodiversity

-Species richness is the number of different species in a sample or area. Species eveness is the abundance of individuals in each species. Species richness can be measured by observation (sampling methods) but species eveness is measured through surveys. First measure percentage cover or use other sampling methods, then you can measure densit or Simpson's diversity index.

-Density is how many animals there are per unit area. For large animals you observe the individuals present. For smaller animals use MARK, RELEASE, RECAPTURE to estimate population sizes. The number captured is recorded and they are marked and released. Once they are recaptured the number of marked ones are counted and the number captured. Total population is 1st number captured x 2nd number captured divided by those that were marked. This method doesnt work for tiny animals,

Simpson's index of Diversity D=1-[sum of (n/N)2)

-A high value of Simpson's index indicates a diverse habitat. A low value suggests the habitat is dominated by only a few species so small effects could damage or destroy the habitat.

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Classification- Defintions

-Classification: process of sorting living things into groups. Natural classification does this by grouping things according to how closely related they are.

-Phylogeny: the study of evolutionary relationships

-Taxonomy: the study of the principles behind classification.

Relationship between Classification and Phylogeny

-Classification places different species into groups depending on how closely related they are. Modern classificaton reflects the evolutionary distance between species. Any two species living toay had a common ancestor in the past. The later the two species branched from that ancestor, the more closely related they are. Phylogeny is used as a basis for natural classification.

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Classifying things

  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

-Classified by observable features down to molecular evidence and relationships.

-The binominal sytem for naming species uses Latin because common names are not universal. Each species has two names (binominal) : the genus name and the species name. The binominal name is written in italics or in handwritten text underlined.

-Organisms can be identified using a dichotomous key by providing a series of question which lead to the right species (based on observable features.)

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The 5 Kingdoms


  • Have no nucleus but a loop of DNA in the form of linear chromosomes
  • No membrane bound organelles
  • Smaller ribosomes than eukaryotes
  • Carry out respiration on mesosomes not mitochondria
  • Free living or parasitic, can cause disease.


  • Are eukaryotes and mostly single celled
  • Show a wide variety of forms (both plant-like and animal-like)
  • Feed autotrophically or heterotrophically and mostly free-living
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  • Are eukaryotes
  • Gain their nutrition from photosytnthesis so are autotrophs
  • Are multicelluar, have a cellulose cell wall and produce embryos.


  • Are eukaryotes
  • Are multicellular
  • Have heterotrophic nutrition
  • Fertilised eggs develop into blastula and are able to move around


  • Are eukaryotes with cell walls made of chitin, saprophytic, freeliving and have mycelium which contains hyphae
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Modern Classification

Classification systems were originally based on observable features, but more modern approaches draw on a wider range of evidence to clarify relationships between organisms.

  • Technological advances such as microscopes help to identify differences between species
  • Dicovery of DNA led to molecular evidence.

-Biochemistry can determine how closely related one species is to another as certain large biochemical molecules are found in all living things but they may not be identical in all individuals.

-Cytochrome C is used in respiration but are not identical in all organisms so the amino acid sequence is identified to compare species. The more similar the sequence the more closely related they are.

-DNA: all organisms have DNA or RNA. DNA always provides a genetic code for the proteins. Sequences of DNA can be compared to demonstrate evolutionary relationships.

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The Three Domains

-Introduced in 1990 by Carl Woese based on the study of RNA

-The kingdom Prokaryote was divided into two groups: Bacteria and Archaeae. The division is based on the fact that Bacteria are fundementally different from Archae and Eukaryotae.

-Archaea share certain features with Eukaryotae:

  • Similar enzymes for building RNA
  • similar mechanisms for repliacting DNA
  • Production of some proteins that bind to their DNA

The differences between Archaeae and Bacteria need to be reflected in the classification system so it was put as a group on the hierachy as Domain.

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-Variation is the differences between individuals.Variation occurs within as well as between species.

-Continuous Variation: is when there are two extremes and a full range of intermediate phenotypes between those extremes. Examples of this type of variation include height, weight, length of leaves.

-Discontinuous Variation: is when there are two or more distinct categories with no intermediate phenotypes in between. Examples of this type of variation include sex, blood groups, eye colour, flagella.

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-Inherited or Genetic Variation: the genes we inherit from our parents provide information that determine our characteristics. The combination of alleles we inherit are not the same as other living things, the chance of two individuals having the same combination of alleles is remote so the characteristics we possess are unique.

-Environmental Variataion: characteristics that are affected by the environment eg. obesity.

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-Varitation that helps an organism to survive is called an adaptation. The process of evolution works by selecting particular adaptations to survive from one generation to the next. An individual with a chartacteristic that helps it survive is more likely to live longer and reproduce than an individual without that characteristic.

Behavioural: an aspect of behaviour that helps the organism to survive for example earthworms quickly contract and burrow into the ground when they are touched. It is a way of them preventing predation.

Physiological/ Biochemical: ensures the correct functioning of cell processes, for example some yeast can respire anaerobically and aerobically depending on how much oxygen is in the air.

Anatomical: means structural, so any structural adaptation for example bacteria have flagella that help them move independantly.

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Adaptations of Xerophytes

Behavioural Adaptations: response to the envrionment

  • Close stomata when little water is available.
  • Some only open their stomata at night
  • Some fold or roll their leaves when there is little water.

Physiological Adaptations: mechanisms by which the plant can open or close its stomata, fold leaves, or store water eg, the accordian fold structure of some cacti make the folds tighten into ridges in dry periods and when water becomes available the cells expand and become rounded so water can be stroed for years.

Anatomical Adaptations: structures

  • Roots may be shallow but spread over a wide area or very long.
  • Leaves may be reduced in size
  • Leaves may be waxy, curled, folded, hairy or have their stomata sunk in pits.
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Natural Selection

Darwin's Observations

  • Offspring generally appear similar to their parents
  • No two individuals are identical
  • Organisms have the ability to produce large numbers of offspring
  • Populations in nature tend to remain fairly stable in numbers.

-Darwin realised that variation was the key to understanding how species change. When too many young are produced there is a competition for food and resources. Some offspring may be better adapted than others Better adapted individuals live long enough to survive and reproduce passing their characteristics on to the next generation. Those who are less well adapted are less likley to survive so the population remains stable.

Darwin's Conclusions

  • There is a struggle to survive
  • Better adapted individuals survive and pass on their characteristics
  • Over time a number of changes may give rise to a new species
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Natural Selection

-Natural selection is the process in which an environmental factor determines which individuals will survive. We say they are selected from the population or that they undergo selection pressure. If the individual has benficial characterisitcs it will be at an advantage, survive and pass on its beneficial characteristics. Those who dont will struggle and die.

Selective Pressures

  • Availability of food
  • Predators
  • Diseases
  • Climate/ Chemical factors
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-The formation of a new species is called specication.

-Speciation takes a long time as the changes need to accumulate. However, bacteria and single-celled organisms can pass through several generations in several hours, sufficient enough for speciation to occur.

-Speciation occurs by reproductive barriers. This means that some organisms will not be able to breed in the group. Variations are passed on, so if changes only occur in one part of the group only that part will benefit. The groups become so different they cannot interbreed.Reproductive barriers include:

  • Geographical separation (allopatric speciation)
  • Reproductive barrier within the population (sympatric speciation) a biochemical or physical change.
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Evidence for Evolution


  • Darwin based his evidence on observations and fossil finds. Today many more fossils have been found. One of the main lines of evidence for evolution is that the general trend in the fossil record shows a trend from smaller simple organsims to more complex organisms today. Several fossil dicoveries include the evolution of the modern horse, humans and similarites between birds and reptiles.
  • The problem with fossil evidence is that there are gaps in the fossil record. Fossils only form under certain conditions and can be damaged.

Biological Molecules

  • certain molecules are found throughout the living world but there are differences in individuals. These can be compared to judge how closely related they are.
  • Evidence from Cytochrome C and other proteins can show patterns of changes.
  • DNA- the structure of DNA can be used like Cytochrome C as they can be compared by the sequencing of bases. Species that have similar sequences are likely to be more closely related.
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Evolution today

How evolution works:

  • There is variation within a population
  • The environment puts selection pressure on the population selecting those with variations that give an advantage.
  • Individuals with that advantage are more likely to survive and reproduce/
  • They pass on their beneficial characteristics to their offspring.
  • The next generation will be better adapted to its environment.

In some situations a group of individuals will evolve into another species if

  • a population migrates to a new environment
  • an environmental change effects only some of the popualiton
  • there is a reproductive barrier
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Evolution Today


  • Insects are pests and kill crops or damage them and they carry disease. Humans use pesticides to kill pests, insectisides specifically kill insects. Insecticides produce stronf selection pressures, those with resitance will survive those without will die. Resistance can quickly spread throughout the population. Malarial treatments for example have become ineffective.
  • Another problem is pesticides in the food chain. Humans may recieve large doses of insectisides as predators eat the insects and we eat the predators.

Bacteria/ Micro-organisms

  • Use of antibiotics applies a selection pressure to bacteria. Most of the bacteria are killed when using antibiotics but some may be resistant. Some people stop taking the antibiotics before the course is over allowing resistant bacteria to survive and pass on their resistance. Bacteria reproduce quickly, so producing new drugs can be difficult. MRSA is resistant to many drugs.
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