Topic 5 Notes - Evolution Biodiversity PDF

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Topic 5: Evolution & Biodiversity (NOTES) Topic 5.1 – Evidence for evolution Topic 5.2 – Natural selection Topic 5.3 – Classification of biodiversity Topic 5.4 – Cladistics

Topic 5.1 – Evidence for evolution Evolution  

It is the cumulative change in the heritable characteristics of a population. These traits cannot be acquired over a lifetime, they are heritable traits or alleles in an organism’s DNA

Speciation & patterns of variation     

Sometimes, populations of a species become separated in terms of geographical range, and thus are unable to breed with each other. They then can evolve differently and diverge in their characteristics more and more. The changes may be very gradual and take place over thousands of years, but eventually they are so different that they will not be able to interbreed when brought together. Thus, they now have become different species, and this is known as speciation. There is continuous variation in the amount of difference between populations from slight to very great, and this is expected if populations gradually diverge by evolution to become separate species.

Evidence for evolution

1. Fossil record     

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Fossils are the preserved remains of animals, plants, and other organisms from the past. The fossil record shows the gradual change of species over time. Rocks can be dated, allowing the age of fossils within the rocks to be deduced and the times when the organisms lived on Earth. Different kinds of organisms do not occur randomly but are found in rocks of particular ages in a consistent order The timeline in which fossils appear are what scientists would expect, with bacteria and algae being the oldest in the fossil record. Followed later by shelled animals and trilobites, then dinosaurs and early reptiles, birds and mammals (vertebrates) later still. This suggests that changes to an ancestral species was likely responsible for the appearance of subsequent species. If evolution had not occurred, the fossil record would have shown the same type of fossil in all the layers of rock.

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An illustrative diagram to show evidence of evolution by fossil record

2. Selective breeding of domesticated animals    

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Breeding plants and animals for specific genetic traits is known as selective breeding. It shows a good record of changes in genetic characteristics over a few dozens of generations that man has selected to breed. The animal breeds that are reared for human use are very much related to wild species, and in many cases can still interbreed with them. The striking difference in the heritable characteristics of domesticated breeds gives us evidence that species evolve rapidly by artificial selection, thus demonstrating evolutionary changes in a much shorter time frame than might have occurred naturally. E.g. chickens that produce more eggs or cows that produce more milk are selected to breed, in the hope of passing these traits onto next generations. The evolution of domesticated dogs has given rise to many different breeds through artificial selection (racing, herding and hunting breeds of dogs).

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3. Homologous structures      

The common internal structures that are similar in seemingly dissimilar animals that have evolved from a common ancestor are known as homologous structures. Evolution of homologous structures by adaptive radiation explains similarities in structure when there are differences in function. The best example of homologous structures is the “Pentadactyl limb” which is the five-digit limb found in the four groups of vertebrates (amphibians, reptiles, birds and mammals). E.g. In animals such as humans, dolphins, bats, dogs and moles, the pentadactyl limbs have been adapted for use in different ways like walking, swimming, flying, digging, etc. Even though the shape, size and function of this structure vary between species, the general structure and position of the bones in these limbs are the same. This suggests that the different organisms have evolved from a common ancestor, but the limbs have developed in different ways to suit their respective type of locomotion. This type of evolution is radiative evolution.

www.enviromental-adaptations.weebly.com

Melanism – An example of evolution     

Melanistic is a term given to dark varieties of typically light-coloured insects. The peppered moth was very common in England prior to Industrial revolution, with the melanistic variety of this moth being rare. But in areas where the industries developed, sulphur dioxide pollution from these industries killed lichen on tree causing them to blacken with soot/coal. Light-coloured moths died from predation as it was easily spotted by birds and other animals, whereas melanistic moths were camouflaged and survived to pass on their genes. Eventually, this caused the moth populations to evolve from being peppered to melanistic. HKEXCEL LTD.

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Topic 5.2 – Natural selection Natural selection     

Natural selection is one of the basic mechanisms of evolution, and is defined as the differential survival and reproduction of individuals due to differences in phenotype. Natural selection can only occur if there is variation among members of the same species. Within a particular species, different individuals of that species show genetic variation. Those individuals that are best suited for their environment, will survive and reproduce. If there was no variation within a species, then all individuals would be the same and no individual would be favoured over the other and natural selection would not take place.

Sources of variation As stated before, natural selection can only occur if there is variation among members of a species. There are 3 sources of variation: 1. Mutation  Genetic mutations are the source of variation within a species.  This can occur when new alleles are produced, resulting in increasing the gene pool of the population.

2. Meiosis  During the process of meiosis, 50% of the females chromosomes will end up in the egg and likewise 50% of the male’s chromosomes will end up in the sperm (haploid gametes).  During metaphase of meiosis, the chromosomes line up or assort independently of each other.  This independent assortment of chromosomes creates 2n possible variations of chromosomes in the haploid sex cells (n = haploid number of chromosomes)  Thus, during metaphase I, when the homologous chromosomes align along the equator, the paired chromosomes can randomly arrange themselves in one of two orientations (paternal left & maternal right OR paternal right & maternal left).  When the chromosomes separate in anaphase I, the final gametes will differ depending on whether they got the maternal or paternal chromosome.  Apart from this, during prophase 1, crossing over might occur in homologous chromosomes where parts of each chromosome are exchanged (exchange of genetic information between non-sister chromatids).  This crossing over greatly increases the number of potential gamete variations by creating new genetic combinations.

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Meoisis: Crossing-over 3. Sexual reproduction  Sexual reproduction can result in variation among individuals of a species via fertilization and meiosis.  Sexual reproduction happens when two different members of a species create offspring that possess a combination of genetic material contributed from both parents.  Fertilization results from the fusion of gametes from different parents, resulting in offspring that have a combination of paternal and maternal traits.  Random fertilization through sexual reproduction allows millions of sperms a chance at fertilizing the egg.  This enables mutations that have occurred in different individuals to come together in their offspring.  As fertilization is random phenomenon, offspring will receive different combinations of alleles every time, resulting in near infinite genetic variability.

Theory of natural selection       

Species tend to produce more offspring than the environment can support. Within a population, there is genetic variation between the individuals in the population. Adaptations are characteristics that make an individual suited to its environment and way of life. Individuals that are better adapted tend to survive and produce more offspring while the less well adapted tend to die or produce fewer offspring. The organisms with the advantageous characteristics will be able to out-compete the other individuals having less beneficial or harmful genetic traits, for mates and limited food resources. Therefore, these individuals will survive and reproduce and pass these genetic traits onto the next generation of offspring. The organisms with less desirable traits will die or produce less offspring. HKEXCEL LTD.

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Individuals that reproduce pass on characteristics to their offspring. Natural selection increases the frequency of characteristics that make individuals better adapted and decreases the frequency of other characteristics leading to changes within the species. Natural selection tends to decrease the variation in a population.

Antibiotic resistance in bacteria         

Antibiotics are used to control diseases caused by bacteria, and they work by blocking certain metabolic pathways associated with the cell walls of bacteria. They can either kill bacteria directly or weaken the bacteria so that the immune system can fight and destroy the invading pathogen. If a patient having a bacterial infection is given antibiotics to fight the infection, the majority of the original population of bacteria will be destroyed. However, some of these bacteria might not die because they possess genes that give them resistance to the antibiotic. This is an example of natural selection. These changes could be caused by mutations within their genome or the transfer of an antibiotic resistant gene by means of a plasmid from another bacterium. These resistant bacteria will survive and reproduce, forming more identical resistant bacteria. These bacteria will no longer be destroyed, when treated with the same antibiotic. The resistance can be passed on to other disease-causing bacteria, creating more species of resistant strains. Resistance is more likely to occur if a patient doesn’t finish the antibiotic prescription. HKEXCEL LTD.

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Beaks of finches on Daphne Major       

Daphne Major is a small island inhabited by populations of G. fortis (medium ground finch). These finches feed on seeds with a wide range of sizes, from small to large, among which the large seeds are found to be harder and more difficult to crack. There is variation in the size of beaks among the population, with some of the individuals having large beaks than others. The climate on this island is variable with warm temperatures bringing heavy rains and cold temperatures bringing droughts. During the drought period, fewer small soft seeds are available, but the larger seeds are still found throughout the island. The severe drought period from 1974-1977 favoured finches with the large beaks. As a result of natural selection, after the period of drought the mean beak size increased for successive generation of finch offspring.

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Topic 5.3 – Classification of biodiversity Binomial system of nomenclature       

The binomial system of naming is relevant for identification of known species, and also when new species are discovered. It is the formal two naming system of classifying species. Originally developed by Swedish naturalist Carolus Linnaeus. The first name in the binomial naming system is called the genus and is given an upper case first letter (capitalized). The second name starts with a lower case first letter and is called the species. The binomial name is written in italics font. E.g. humans (Homo sapiens), Lion (Panthera leo).

Dichotomous key  

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A dichotomous key is a key constructed from a series of statements arranged into pairs. Dichotomous keys have the following features:  It consists of a series of numbered stages/steps  Each step consists of a pair of alternative characteristics  Some alternatives depict the number of the next stage in the key  The species can be identified by reaching the appropriate step. e.g. four bird species have been classified according to the dichotomous key provided below.

Dichotomous Key to Representative Birds 1. a. b. 2. a. b. 3. a. b.

The beak is relatively long and slender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Certhidea The beak is relatively stout and slender . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . go to 2 The bottom surface of the lower beak is flat and straight . . . . . . . . . . . . . . . . . . . . . Geospiza The bottom surface of the lower beak is curved . . . . . . . . . . . . . . . . . . . . . . . . . . . . go to 3 The lower edge of the upper beak has a distinct bend . . . . . . . . . . . . . . . . . . . . . . . Camarhynchus The lower edge of the upper beak is mostly flat . . . . . . . . . . . . . . . . . . . . . . . . . . . . Platyspiza Bird W: Geospiza

Bird X: Platyspiza

Bird Y: Certhidea

Bird Z: Camarhynchus

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Q: Given below are the following 6 animals. They are all related (same genus), but each is a separate species. Use the dichotomous key provided below to determine the species of each.

A: ______________________________________

B: _____________________________________

C: ______________________________________

D: _____________________________________

E: ______________________________________

F: _____________________________________

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Hierarchy of taxa   

The taxonomists classify species using a hierarchy of taxa. A taxon refers to a group of something. When classifying living organisms, they are grouped according to a series of hierarchical taxa based on similar characteristics - the more similar their characteristics, the closer the grouping.

Three Domains 

All organisms are classified into three domains.

Archaea

Bacteria

Eukarya

Prokaryotes that do not have a membrane bound nucleus and DNA is not associated with proteins.

Prokaryotes that do not have a membrane bound nucleus and DNA is not associated with proteins.

Tiny tough prokaryotes, which are mostly extremophiles.

True bacteria includes heterotrophic bacteria and cyanobacteria.

These includes eukaryotes, or organisms that have a membrane bound nucleus. Complex organisms including protista, fungi, plants and animals.

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 Classification of one plant and one animal species from domain to species level.

Taxa

Human

Buttercup

Kingdom Phylum Class Order Family Genus Species

Animalia Chordata Mammalia Primate Hominidae Homo sapiens

Plantae Angiospermaphyta Magnoliopsida Ranunculales Ranunculaceae Ranunculus acris

 Recognition features of the following plant phyla: bryophyta, filicinophyta, coniferophyta and angiospermophyta.

Plant Phyla

Bryophyta

Characteristics

Examples

1. True roots absent, anchored by rhizoids 2. Small soft non-vascular plants 3. Spores produced in capsule at the end of stalk 4. e.g. Mosses, liverworts.

Filicinophyta

1. Possess leaves and roots 2. Have short non-woody stems 3. Spores produced in sporangia on the underside of the leaf 4. e.g. ferns

Coniferophyta

1. Have roots, leaves and woody stems 2. Produces seeds in cones 3. Leaves are usually narrow, needlelike or scale-like with a thick waxy cuticle 4. e.g. Conifers and pines

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Angiospermophyta

1. Vascular plants having leaf, roots and stems (usually woody) 2. Have flowers 3. Seeds are produced in fruits 4. e.g. Mango tree

 Recognition features of Animal phyla: porifera, cnidaria, platylhelmintha, annelida, mollusca, arthropoda and chordata.

Animal Phyla

Characteristics

Porifera

1. Asymmetrical body 2. No mouth and no anus 3. Pores present on the surface of the body 4. e.g. Sea sponges

Cnidaria

1. Radially symmetrical 2. Mouth, but no anus 3. Generally soft bodies with tentacles containing stinging cells 4. e.g. Jellyfish

Platyhelminthes

Examples

1. Bilaterally symmetrical 2. Mouth, but no anus 3. Flat bodies 4. e.g. Flatworms

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Annelida

1. Bilaterally symmetrical 2. Have mouth and anus 3. Ring-like segmented body 4. e.g. Earthworm

Mollusca

1. Bilaterally symmetrical 2. Have mouth and anus 3. Soft body with a muscular foot, may also have a protective shell 4. e.g. Snail, octopus

Arthropoda

1. Bilaterally symmetrical 2. Have mouth and anus 3. Hard exoskeleton made of chitin, jointed appendages present 4. e.g. Cockroach, scorpion

Chordata

1. Bilaterally symmetrical 2. Have mouth and anus 3. Possess a nerve chord 4. e.g. All vertebrates like mammals

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 Recognition features of Class: birds, mammals, reptiles, amphibians and fishes.

Class

Birds

Characteristics

1. Skin covered in feathers made of keratin 2. Two wings and two legs 3. Beak and no teeth 4. e.g. Eagle, ostrich

Mammals

1. Presence of mammary glands for feeding young ones 2. Four-legged, with some having 2 arms & 2 legs 3. Body usually covered in hair 4. e.g. Bear, human

Reptiles

1. Skin covered in scales made of keratin 2. Usually 4 limbed, but some have none 3. Lay eggs with soft shells 4. e.g. Snake, crocodile

Amphibians

1. Moist skin 2. Can breathe in land as well as under water 3. Lay eggs which are coated in a protective jelly 4. e.g. Frogs, newt

Fishes

Examples

1. Have scales made of bony plates 2. Possess gills for breathing under water 3. Fins present which aid in swimming 4. e.g. Salmon, shark

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Topic 5.4 – Cladistics Clades      

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A clade is a group of organisms that have evolved from a common ancestor. Over the course of time, species evolve and split to form new species. This process can occur repeatedly with some highly successful species leading to a large group of organisms that share a common ancestor. These groups of species evolved from a common ancestor, that have shared characteristics is termed a clade. Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein. Sequence differences accumulate gradually, and so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. Differences in the base sequence of DNA are caused by mutations, and these gradually accumulate over time. By sequencing nuclear DNA and mitochondrial DNA, it is possible to establish a biochemical phylogeny between species to show common ancestry The difference in the sequences can be used to deduce when a certain species spl...