Presentation on theme: "Evolution (a) define the term variation;"— Presentation transcript:
1 Evolution (a) define the term variation; (b) discuss the fact that variation occurs within as well as between species;(c) describe the differences between continuous and discontinuous variation, using examples of a range of characteristics found in plants, animals and microorganisms;(d) explain both genetic and environmental causes of variation;(e) outline the behavioural, physiological and anatomical (structural) adaptations of organisms to their environments;(f) explain the consequences of the four observations made by Darwin in proposing his theory of natural selection; (HSW1)(g) define the term speciation;(h) discuss the evidence supporting the theory of evolution, with reference to fossil, DNA and molecular evidence (HSW1, 4, 7a, 7b);(i) outline how variation, adaptation and selection are major components of evolution;(j) discuss why the evolution of pesticide resistance in insects and drug resistance in microorganisms has implications for humans (HSW6a, 7c).
2 VariationVariation is the differences between individuals- no two individuals are exactly alike even if they look similarIdentical twins start as one cell that divides and then separates into two cells, although they started with the same original DNA, the subsequent divisions have introduced changes, also environmental changes may have taken place in the womb or after birth.
3 Variation within species Members of the same species can show variationExamples are: eye, hair and skin colour, nose shape, eye shape etc
4 Variation between species Variation between species is more obvious- it is what we use to separate one species and another
5 Continuous VariationThere are usually 2 extremes and a full range of intermediate values between the extremes- most individuals are close to the mean value and the number at the extremes is lowExamples are: human height, length of leaves on an oak tree, length of stalk of a toadstool
6 Discontinuous Variation There are two or more distinct categories, with no intermediate valuesThere may be more than one type than the other or they may be distributed evenlyExamples are: sex- male or female in plants and animalsSome bacteria have flagella, some do notHuman blood groups- A, B, AB or O
7 Inherited and Genetic Variation Genes define our characteristicsThe combination of alleles that we inherit is not the same as any other living thingHuman cells have approx genes, many with different alleles, so the chance of having the same ones is extremely remote
8 Environmental Variation Characteristics affected by the environmentExamples: skin tone can become darker in the sun, hawthorn trees may grow sideways in areas with strong gales, affecting the direction of growth, lack of water can affect the height of growthEnvironmental and genetic variation can be linked e.g. humans now have a better diet, and so can grow taller, however your genes also limit final height
9 AdaptationsAdaptations can be behavioural, physiological, or anatomicalAdaptations help the organism to cope with environmental stresses and obtain the things they need e.g. to find water, gather nutrients, respond to changes, defend from predators
10 Behavioural Adaptations An aspect of the behaviour of an organism that helps it to survive the conditions it lives inExample: an earthworm has no eyes, so cannot tell if a bird is about to eat it, however on touch, earthworms rapidly contract and recoil into their burrows- this adaptation allows them to avoid being eaten
11 Physiological Adaptations A physiological or biochemical adaptation ensures the correct functioning of cell processesExample: yeast (Saccharomyces) can respire sugar either aerobically or anaerobically depending on oxygen availability- this also involves producing the correct enzymes for the type of respiration required
12 Anatomical Adaptations Anatomical means structuralAny structure that enhances the survival of an organism is an adaptationExample: bacteria like Legionella have flagella that help them move independently
13 Case Study: PlantsXerophytes grow in areas with a low water supply e.g. cactiBehavioural adaptations: open and close stomata, open stomata at night only, fold and roll leaves when lack of water, open stomata when short of water to wilt leaves and reduce surface areaPhysiological adaptations: stem with accordion-fold structure that folds more in dry periods, when water is plentiful the cells expand and the stem enlarges and becomes more roundedAnatomical: shallow roots spread out over a large area, long roots e.g. camel thorn tree (40m long), fleshy stem and leaves, waxy leaves, curled and folded leaves with sunken stomata
14 Charles Darwin The theory of evolution was not his idea He proposed a mechanism for this processHe called it natural selectionDarwin was interested in the variation between members of the same species and this underpinned his workHe studied in the Galapagos Islands and worked on a ship called the HMS Beagle
15 The Theory of Natural Selection Darwin made 4 important observations:Offspring generally appear similar to their parentsNo two individuals are identicalOrganisms have the ability to produce large numbers of offspringPopulations in nature tend to remain fairly stable in size
16 Developing the TheoryDarwin read an essay by Thomas Malthus who said that the human population would outstrip its food supply- Darwin disagreed and said that competition for food and resources would keep the population in checkDarwin saw that too many young are produced and that this leads to competition for food and resourcesAs all offspring are different, the better adapted ones will obtain all the food and survive long enough to reproduce and pass this onto their offspringThe less well adapted ones are likely to die before they reproduce, so the population does not grow indefinitely
17 Link to EvolutionOver a long period of time, small variations arise and if beneficial, will be passed on to the next generationOver many generations a species has many variations and may even change into another species that has so many changes it could never reproduce with its ancestors as the DNA has changed so much
18 Darwin’s Conclusions There is a struggle to survive Better adapted individuals survive and pass on their characteristicsOver time, a number of random changes may give rise to a new species
19 Selection PressuresIf you can survive after undergoing these selection pressures, you are more likely to pass on your random adaptationsAvailability of suitable food; adapted to eat the available foodPredators; adaptations to avoid being seen and eaten, or to escapeDiseases; survival of diseasesPhysical and chemical factors; living in cold places, shade, hot summers
20 SpeciationSpeciation means the formation of a new species from a pre-existing oneDoes not occur suddenlyLong, slow accumulation of changes meaning the species cannot interbreed freely to produce fertile (viable) offspringTakes many generationsFaster in bacteria as reproduction happens every 20 minutes
21 How does Speciation Occur? Some reproductive barrier occursSome organisms unable to breed in the groupVariations providing a benefit will be passed onA collection of small changes means the individuals become so different they cannot breed with the rest of the group
22 Reproductive barriers Geographical separation: different members of the same species living on different islands will not breed freely, speciation is likely to occur e.g. galapagos islands- this is known as allopatric speciationBiochemical change preventing fertilisation e.g. behavioural dance not recognised or sexual organs change. This is known as sympatric speciation
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