Variation

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Classification

Classification is organising living organisms into groups.

  • Organisms are classified based on how closely related they are to each other.
  • All living things fall under 5 Kingdoms: Plants, animals, fungi, protoctists & prokaryotes.
  • Plants contain chlorophyll and are autotrophs (Can produce their own food by photosynthesis) Their multicellular and have rigid cell walls for support.
  • Animals are hetrophs (Can't produce their own food and have to go out and find things to eat) Their multicellular but don't have cell walls or chlorophyll.
  • Fungi are saprophytes (Feed off dead organisms and decaying material) Their multicellular, have a cell wall but don't contain chlorophyll.
  • Protoctists are unicellucar (single-celled) and have a nucleus.
  • Prokaryotes are also unicellular but don't have a nucleus.
  • Organisms can be hard to classify, for instnac emost sciencists beleive viruses aren't living so can't be placed into any kingdom.
  • Kingdoms are subdivided into smaller and smaller groups of organisms that have common features: kingdom, phylum, class, order, genus, species.
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Vertebrates & Invertebrates

Vertebrates have a backbone and internal skeleton & invertebrates don't.

  • Vertebrates are split into 5 groups called clesses: fish, amphibians, reptiles, birds & mammals.
  • Vertebrates are divided based on these 3 things

1) How they absorb oxygen - through the lungs, skin or gills.

2) How they reproduce - if fertilisation occurs internally or externally, if they are oviparous (lay eggs) or viviparous (give birth to live young wich are fed milk)

3) How they regulate their internal body temperature - if they're homotherms (warm blooded kept constant by homeostasis) or if they're poikilotherms (Cold blooded with temperatures changing with external temperature)

  • The rules of classification were made using animals that were known at the time meaning that newly discovered speicies don't fit into any of the catagories.
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More Classification

Organisms are the same spiecies if they can interbreed to produce fertile offspring.

Organisms can't always be put into neat boxes called species, this is why:

  • Not all organisms interbreed like they're supposed to, some reproduce asexually but are still the same species.
  • If the male from one species breeds with a female from another you'll get a hybrid and these can be fertile.
  • There can be many different variations of a species when it comes down to looks.
  • A ring species is a group of related populations that live in neighbouring areas. The populations can breed to produce fertile offspring but populations living further away can't.
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Binomial System & keys

The Binomial system gives everything a 2 part latin name. The 1st part refers to the genus that the organism beongs to and the 2nd to the species.

The system helps scientists to:

  • Identify a species, to avoid consusion.
  • Study species, by naming a species scientists can share information on them.
  • Conserve species, especially endangered ones. (Offten 2 species can look idential when in reality they're different and a situation where one is protected and the other is endangered could occur)
  • Target conservation efforts, to protect areas that contain a wide variety of species.

Keys are used to identify creatures.

  • A key is a series of questions that can be used to tell what an unknown organism is.
  • The answers of the questions will narrow down the options until only 1 remains.
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Variation - Differences

Differenct species look different but even organisms of the same species will tend to look a litte different from one another. These differences are called variation and have 2 causes - genes and the environment.

  • All plants and animals have characteristics that are somewhat similar to their parents.
  • This is because an organisms characteristics are determined by their inhereted genes.
  • The majority of animals and a lot of plants get a mix of genes from mother and some from the father.
  • The combination of genes casuse genetic variation,  this means no two species are genetically identical. (with the exeption of identical twins)
  • Genetic variation also occurs because of mutilations (Changes in an organisms genes) These changes can cause differences in the characteristics.
  • Some characteristics are only determined  by genes. In animals these include eye colour, blood group and inherited disorders.
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Variation - Characteristics

Characteristics are influences by the environment.

  • The environment organisms live and grow in causes differences between members of the same species. This is called environmental variation and it covers a range of differences.
  • Environmental factors that can cause variation include: diet, exercise, temperature, light level and amount of water.

Most characteristics come down to a mix of genes and the environment.

  • Most characteristics ( body weight, height, skin colour, condition of teeth, academic or athletic skills) are due to a mixture of both environmental and genetic factors.
  • E.g. The maximum height that an animal or plant could grow to is determined by it's genes, but whether it actually grows that tall depends on the environment
  • It is very difficult to say which factor is more influential.
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Continuous & Discontinuous Variation

Continuous variation is when individuals of a population differ within a range, meaning there aren't any set catagories.

  • A graph of continuous variation is a bell shaped curve and is symetrical around the mean.
  • Examples of continuous variation can include mass in animals, number of leaves within a plant & width of microorganisms.

Discontinuous variation is when there are two or more distinct catagories and each individual falls under only 1 of them. 

  • Examples of discontinuous variation can include blood group in animals, colour of plant & if bacteria are antibiotic resistant or not in microorganisms.

A way to help remeber is that continuous results could vary from 0% to 47.3% to 100% or anything inbetween however discontinuous is either true or false, yes or no.

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Extreme environments - Deep Sea

Organisms that live in extreme environments like deserts or deep oceans need to be specially adapted to help them survive,

Deep under the sea conditions are hard to live in as there is barely anysunlight meaning that plants can't grow and organisms down there live off scraps that have floated down from above. Animals have adapted to this by:

  • Being able to emit light from their own body,
  • Having huge mouths,
  • Having huge eyes adapted to the dark,
  • Having long feelers to locate prey.

There are volcanic vents in some parts of the sea bed that send out minerals and hot water out into the cold ocean. Organisms have adapted to them by:

  • Bacteria that make their own food using chemical energy, 
  • Animals that feed on those bacteria,
  • They all have to be adapted to cope with the high temperature and pressure.
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Extreme environments - Polar Regions

The polar regions are the Arctic and the Antarctic. Some animals living there have adapted to live in the extreme cold such as:

  • Polar bears have a compact (round) shape that gives them a small surface area compared to volume which reduces heat loss.
  • They have a layer of thick blubber for insulation which doubbles up as an energy store for when food is scarce.
  • Polar bears have a thick hiary coat that traps a layer of warm air next to the skin and their greasy fur sheds water to prevent cooling from evaporation.
  • Their big feet help to spread their weight and this stops them sinking into the snow or breaking thin ice.
  • They have a white fur to camouflage them in the snow.

Penguins also have adaptations like the polar bears such as the thick layer of fat to insulate and oily feathers to shed water. They also:

  • Huddle together in the cold to conserve heat.
  • Have streamlined bodies to reduce water resistance and this helps them swim fast to catch fish.
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Natural Selection

Natural selection means survival of the fittest. There are always more organisms born than can survive and so must compete for things like food. Only the fittest survive and they pass on their characteristics to any offspring. Evolution is the slow, continuous change of of organisms from one generation to the next. Here is how it works:

  • Individuals are all different (Variation) and they tend to give birth to more young than can survive to adulthood.
  • Populations don't generally increase quickly in size because individuals have to compete for resources that are in limited supply.
  • The individuals with characteristics that make them better adapted to the environment are the ones that have better chance of survival and are more likely to breed and pass on the useful characteristics.
  • However some unlucky individuals will be less adapted and may be less able to compete, making them less likely to survive and reproduce.
  • Over time there will be a higher number of individuals with beneficial characteristicas compared to those with poorly adapted characteristics which will eventually die out.
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Evidence Of Evolution

Evolution is the change of organisms from one generation to the next. Here is the evidence to support this idea:

DNA Research - 

  • The theory of evolution suggests how all organisms have evolved from shared common ancestors.
  • Closely related species diverged more recently, (evolved to create a new species)
  • Evolution happens because of gradual changes in DNA.
  • Organisms recently diverged from one another sholud have more similar DNA.

Resistant Organisms - 

  • The poson warfarin was used to kill rats.
  • But a certain gene gives rats the abiltiy to resist warfarin and these rats are more likely to survive and breed.
  • Now there are rat populations that are totally warfarin resistant. 
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Scientific Community - Evolution

The scientific community are all the scientist around the world.

Scientsist within this community accept the theory of evolution becaue they've shared and talked through evidence to make sure it's all valid and reliable. There are 3 main ways to do this:

  • Scientists publishing their work in scientific journals or academic magazines. If other scientists can repeat the experiment using the same methods and get the same results, the scientific community can be sure that it's reliable.
  • Before scientists can post thier reveiws however, it must nudergo peer reveiw. This is when other scientists read the work to check it's valid and has been carried out to the highest standard. 
  • Scientific conferences are meetings that scientists attend to present and talk about their work. They're an easy way for the latest theories and evidence to be shared and discussed.
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Speciation

Specification is where evolution leads to a new species.

Specification happens when populations of the same species become so different that they can no longer breed to produce fertile offspring.

  • Isolation is where populations of a species are seperated and this can happen becuase of a physical barrier.
  • Conditions on either side of the barrier will be slightly different and this means that due to the different environments, different characteristics will become more common in each population. (natural selection)
  • Eventually individuals from the different populations will have changed so much that they won't be compatable to breed and produce firtile offspring. The two groups will now be different species.
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Genes

There can be different versions of the same gene that can give different versions of characteristics like eye colour. The different versions of the same gene are called alleles. Becuase there are 2 copies of each chromosone, there are 2 copies of each gene so you might have 2 alleles the same or 2 different alleles. 

  • Most cells in your body will have a nucleus.
  • The human cell nucleus has 23 pairs of chromosomes.
  • Chromosones are long lenghts of DNA coiled up.
  • Genes are a short section of DNA. 
  • Chromosones carry genes.
  • Different genes control the development of characteristics.
  • All genes come in pairs.
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Genetic Diagrams

  • In genetic diagrams letters are normally used to represent alleles.
  • If an organism has two alleles for a certain gene that's the same, then it's homozygous.
  • If the 2 alleles are different, only 1 can decide what characteristic is there. The allele for the characteristic that's shown is called the dominant allele (Use capital letter). The other is recessive. (Use lowercase)
  • For an organism to display a recessive characteristic, both its alleles must be recessive. But to display a dominant characteristic the organism can be either CC or Cc because the dominant allele over powers the recessive one if the plant/animal/organism is heterozygous.

(See page 17 of core science book for more detail)

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Genetic Diagrams & Disorders

We normally don't notice our genes, but a faulty allele (Creates a faulty protein) can cause genetic disorder.

Cystic fibrosis is a genetic disorder of the cell membranes. It causes the body to produce lots of thick mucus in the air passages, gut and pancreas. It can create difficulty breathing, lung infection, malnutrition & fertility problems.

  • The allele that creates cystic fibrosis is a recessive allele 'f' carried by 1 in 30 people.
  • Because it's recessive, people with only 1 copy of the allele won't have the disorder, both parents have to be carriers or sufferers
  • There is a 1 in 4 chance of a child having the disorder if both parents are carriers. 

Sickle cell anemia is a genetic disorder charicterised by strance shaped red blood cells that can get stuck in the capillaries and can deprive the body of oxygen. it can cause fever, amemia, painful joints & muscles.

  • It's caused by inheriting two recessive alleles 'a'. If two people who carry the sickle cell anemia allele have children the probability of each shild suffering is 1 in 4.
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