6.2 variation and evolution, 6.3 development of understanding of genetics and evolution, 6.4 classification of living organisms

define variation

the observable difference (e.g physical features) and non-observable differences (e.g genetics) between different living organisms

this could be between organisms of the same species (intraspecies) or between organisms of different species (interspecies) variation

define continuous variation

always numerical data - can be described using any value, there are intermediate values

displayed through scatter/line graphs or histograms

define discontinuous variation

usually grouped into named categories, there are no intermediates

displayed through bar or pie charts

what environmental factors cause variation in animals?

can have accidents or operations causing scars/injuries, lifestyle - exercise and diet, the climate - hot, cold etc

what environmental factors cause variation in plants?

conditions such as deprivation of light, mineral ions or carbon dioxide make them smaller and weaker as they don’t get as much food

what inherited factors cause variation?

-Sexual reproduction: organisms show variation because of differences in the genes they inherit that arise through meiosis and sexual reproduction

-Mutations: can take place whenever cells divide. Those that take place when the gametes are formed may effect the phenotype of the offspring and introduce new variants into the genes of a species - many mutations have no effect on the phenotype of an organism but some are so harmful that the organism doesn’t survive

-Alleles: cause differences such as eye colour, nose shape etc.

what environmental and inherited factors cause variation?

-an organism’s appearance is affected by both genes and environment e.g genetically identical plants grown in different conditions can look different

-rarely a mutation produces an adaptation that makes an organism better suited to its environment, or it gives it an advantage if there’s an environmental change

how do scientists investigate variety in plants?

put genetically identical plants in different situations to see how the environment affects their appearance

define mutation

when the DNA of an organism is changed. This means they have a new form of that gene

what can cause a mutation?

-change in chemical structure of a gene

-change in the arrangement of genes on a chromosome

-change in the number of chromosomes found in the cell

what are the possible effects of mutations?

-some are bad and could kill the organism

-many have no effect on the organism’s phenotype (called neutral or silent mutations)

-rarely a mutation means the organism has a better characteristic and therefore puts it at an advantage over other organisms of that species

define genetic engineering

transferring genetic material (DNA) from one organism into a different organism

define transgenic organism

an organism that has been genetically modified with DNA from a different species

define plasmid

a small, circular piece of DNA found in bacteria

how can bacteria be modified to produce human insulin?

-cut out insulin gene from human DNA using a restriction enzyme

-cut bacterial plasmid with restriction enzyme

-insulin gene inserted into the plasmid and the DNA joined back together with a ligase enzyme

-plasmid inserted into bacteria

-bacteria reproduce

-bacteria will produce insulin which is extracted

what are the advantages of using insulin produced by genetically modified bacteria?

produces large quantities of insulin that is pure

will cause no side effects as it is pure

what are some examples of genetic engineering in animals?

-production of human insulin

-human growth hormone

-complex human proteins added to formula milk

-modify mice to have a human disease and then allow the disease to be studied, ‘modelling human disease’ e.g progression of Alzheimer’s or to see if a new drug is effective on a particular type of cancer

why do genes need to be transferred into cells at an early stage of development?

as animals differentiate permanently, if the gene isn’t transferred very early, it may not then be found in all types of cells because they have specialised and won’t have a copy of that transferred gene or have been told to express it

what are the advantages of genetic engineering in medicine?

-produce human proteins in large amounts

-produce human proteins that are pure - so no side effects from using non human proteins

-model human disease using animals - gain a better understanding

what are the disadvantages of genetic engineering in medicine?

-expensive

-causes suffering to animals

what are the economic advantages of GM crops?

bigger crop yield - more profit

what are the economic disadvantages of GM croops?

-expensive to produce

-have to buy new seeds each year as crops are deliberately engineered to be infertile

what are the social advantages to GM crops?

-more food to reduce famine

-better nutrition so fewer cases of deficiency disease

what are the social disadvantages of GM crops?

may be unknown or long term health effects of eating GM foods

what are the environmental advantages of GM crops?

none

what are the environmental disadvantages of GM crops?

-GM crops could breed with wild plants - could cause problems

-use of herbicides reduces biodiversity

-using plants that produce pesticides reduced biodiversity

what are the aims of selective breeding?

speeding up evolution, taking beneficial characteristics and making them more common in offspring and thus population through enabling breeding that could happen naturally but would be slower

what are the stages of selective breeding?

-natural variation occurs in wild populations

-adults displaying the desired traits are chosen

-seeds/gametes are collected from these adults and combined with seeds/gametes of other adults displaying the characteristics

-repeat this process with the offspring that best show the desired the traits (collect/breed/assess/collect/breed over and over)

-over time the population will show the trait more commonly, perhaps even all individuals

what are the advantages of selective breeding?

-increased frequency of alleles coding for desirable traits

-allows humans to manipulate genetic inheritance to suit their needs

what are the disadvantages of selective breeding?

-reduces genetic variation by decreasing the number of alleles

-reduces adaptability of a breed if environmental conditions change

-risk of inbreeding, which causes health problems

define evolution

the process of slow change in living organisms over long periods of time as those best suited to survive can breed successfully

define natural selection

the process by which evolution takes place

organisms produce more offspring than the environment can support so only those which are most suited to the environment survive - the ‘‘fittest’’ will survive to breed and pass on their useful genes/alleles

what are the requirements for natural selection?

-variation of characteristics: caused by mutations to create new alleles and sexual reproduction

-overproduction of offspring

-competition for resources

what are the stages of natural selection?

-sexual reproduction and/or mutations over many generations would have created variety amongst the individuals in the population

-some of this variety would give the individual an advantage

-overproduction of offspring results in more competition and pressure on resources which begin to lack

-these individuals with an advantage are more likely to survive long enough to mate and raise offspring

-the offspring would most probably possess the same genes as their parents so would also have an advantage and be more likely to survive

-this is repeated over successive generations, meaning the species would slowly evolve with characteristics favourable to their environment

define classification

organisation of living things into groups according to their similarities

define species

a group of organisms with many features in common that can breed successfully to produce fertile offspring

why do scientists use the binomial naming system?

in some places animals have different names or the same language may not be understood but the Binomial naming definitively says what the organism actually is and is the same in all languages

what are the rules for writing scientific names using the binomial system?

-the first name is the name of the genus to which the organism belongs, written with a capital letter

-the second name is the name of a species to which the organism belongs, written with lowercase

-the two names are underlined when handwritten or in italics when printed

if two organisms share the same genus, what does this tell you?

they are closely related (but not closely enough to interbreed to have viable offspring)

why do biologists classify organisms?

-easier to study organisms having some linkable knowledge about them

-allows us to make sense of the living world and recognise all the biodiversity

who was Carl Linnaeus?

an 18th century scientist who came up with the binomial system for naming organisms and the Linnaean classification system for classifying living organisms

what are kingdoms?

a kingdom contains many organisms

there can be many differences in appearances

all the organisms in that kingdom have a key similarity

what is the Linnaean classification system?

Linnaeus classified living things into kingdom, phylum, class, order, family, genus and species

what features are now used to help classify organisms?

1. biochemistry

2. structure (internal) of cells

3. genome comparisons

what is a domain?

a new, higher level of classification, this shows which kingdoms are more alike and which ones are more different to each other

Who was Carl Woese?

Carl Woese was a 20th century scientist who used microscopes and modern technology to develop the three domain system to classify organisms

what is the evidence for the three domain system?

-biochemistry of the ribosomes in cells

-how the cells reproduce

what are the features of eukaryota?

contain a nucleus enclosing the genetic material

the 4 kingdoms within this domain are all much more closely re;ated to each other than they are to any kingdom in another domain

what are the features of bacteria (prokaryota)?

-’true’ bacteria and the cyanobacteria (bacteria-like organisms that photosynthesise like algae)

-they do not have membrane bound organelles

-they have a cell wall (so can some eukarytoa) but it will always be made of peptidoglycan

what are the features of archae (prokaryota)?

-primitive bacteria - includes extremophiles

-have a cell wall but not made of peptidoglycan but a simple protein coat

define evolutionary relationship

how closely related two species are, for example how long ago the tow species diverged from a common ancestor

define evolutionary tree

models used to explain the evolutionary links between groups of organisms

what are evolutionary trees useful for?

-how long ago a species first evolved

-whether a species is still alive today

-how closely related two species are - the further back in time they share a common ancestor, the less closely related they are

how can evolutionary trees help our understanding of the process of evolution?

-evolutionary trees model evolutionary relationships between organisms

-can be used to determine how long ago they divided away from a common ancestor

-help to understand evolutionary pathways

-help to understand relationships between species that look very similar but are not related, or are related but do not look similar

what does the phrase antibiotic resistance mean?

bacteria that have developed resistance to one or multiple antibiotics so that the antibiotic no longer effectively kills them

what is an antibiotic?

natural or synthetic substances that kill bacteria

how do antibiotics become resistant?

-add antibiotic to a location with bacteria e.g patient or environment that needs clearing

-the antibiotics start killing the susceptible bacteria

-the resistant bacteria can reproduce more rapidly, as they have less competition for food

-most of the susceptible bacteria are killed by the antibiotics, natural selection of an antibiotic resistant strain that naturally existed by chance in the population begins, these bacteria survive and reproduce

-the resistant bacteria are now present in larger numbers, so eventually the whole population will be resistant

what ways can the development of antibiotic resistant bacteria be reduced?

-don’t use antibiotics unnecessarily (e.g if you have a viral infection or a mild bacterial infection)

-patients should finish the entire course of antibiotics

what ways can the spread of antibiotic resistant bacteria be reduced?

-isolate patients with severe bacterial infections

-wear masks to prevent airborne droplets

-wash hands

-vaccinations in some cases

-kill vectors for bacteria if spread by animals

-sanitise hospital bedding etc.

define fossil

fossils are the preserved remains or impressions of organisms, often from millions of years ago

when do rock (or mineralised fossils) occur?

-Rocks (or mineralised fossils) e.g shells, imprints of feet, calcified replacement of skeletons

-Occur when animals or plants die and sink to the bottom of a lake or swamp, the harder parts of the organisms (e.g bones, shells, bark) are replaced by minerals over millions of years

when do other fossils (not rock) occur?

when an organism doesn’t decay after it dies, the fossilised remains can often be very well preserved and have soft tissue still remaining as well as the harder parts

when do ice fossils occur?

too cold for decay to occur (e.g bodies on mountains or in caves or mammoths in tundra)

when do fossils in peat bogs occur?

little to no oxygen is available in peat bogs and without oxygen bacteria or microorganisms that cause decay can’t survive or if they can, poisonous gases can build up and kill the bacteria that cause decay

when do amber fossils occur?

hardened tree resin also seals an organism from oxygen and thus preserves the tissue almost as it died, if the resin dries quickly and remains undisturbed

how do rock fossils form?

-animal dies and falls to the ground

-soft tissue like flesh rots and leaves harder tissue (e.g skeleton) revealed, the harder tissue is covered in sand or soil or clay before it gets too damaged by external factors

-if the skeleton remains covered for a long time (millions of years), the skeleton becomes mineralised and turns to rock, the rocks shift in the earth due to the movement of tectonic plates and the fossilised remains stay trapped inside them

-eventually the fossil emerges as the rocks move and erosion takes place and can come close enough to the surface they are accidentally dug up or in particular hotspots (regions where we know ancient rock layers have moved up towards the surface and could yield fossils if the conditions were right)

why are fossils used as evidence for evolution?

demonstrates how plants and animals have changed over time and how different organisms have developed, it provides proof that some species have become extinct

Why are there not many fossils from the earliest organisms on earth?

-many of the earliest life on earth was soft-bodied (e.g jellyfish or worms) so few fossils were left

-geological activity (mountain formation, erosion events, volcanic activity and earthquakes) will destroy fossils

-most organisms that have lived do not die in locations where fossils are likely to form and even then the conditions needed are rare

-so never fossilised

define extinction

permanent loss of all members of a species

what are causes of extinction?

-new predator

- hunting by humans

-new disease

-competition from another species (often a non-native species introduced by mistake by humans)

-lack of resources/food

-loss of habitat

-climate change

-pollution

-catastrophic natural disaster

what is a mass extinction event and what might cause them?

-often linked to catastrophic natural disasters that are widespread/global

-they cause a rapid change on too large of a scale that most organisms can’t adapt

why is it important to prevent extinction?

preventing acceleration/human extinction is important because the natural world is so interlinked that a smalll change in one are ripples to many areas

e.g if one species was prey for others, they become forced to eat more of other species, reducing their numbers or themselves going extinct through lack of food and this domino effect can be unstoppable once it starts

why is extinction an important part of evolution?

the planet can only provide and support a certain amount of life - extinction has to happen for the best adapted organisms to thrive and exist

this process is ever changing, and it is difficult for organisms to stay on top and there will forever be an eternal struggle to survive