GCSE Biology B3 (Incomplete)


Human Genome Project

The main aims of the Human Genome Project are-

  • Identify all the 20,000-25,000 genes in the human DNA.
  • To find where each gene is located
  • Determine the sequence of the 3 billion chemical base pairs that make up human DNA.
  • Store this in a database

Estimated time - 15 years         Estimated cost $3 billion.

Possible disadvantages - 

  • May be under pressure to not have/ abort pregnancies
  • Increases pressure for germ line therapy to prevent children inheriting diseases
  • Embryo has no choice/say in the matter
  • May lead to discrimination with jobs and tougher times getting insurances (life, health)
  • May lead to designer babies with a selection of fashionable genes.
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A species is a group of organisms that are capable of interbreeding to produce fertile offspring.

We have fonud 290,000 species of plants, 1,250,000 species of animals and 5,000,000 species of bacteria.

Carl Linnaeus developed the classification system in the 18th centure, where the first part of an arganisms name is its genus and the second is its species, e.g. Tyrannosaurus Rex.

The five kingdoms are-

  • Animals - No cell walls, cells have nuclei, multicellular
  • Plants - Cells have nuclei and chloroplasts, Cellulose cell walls, multicellular
  • Fungi - Chitin cell walls, Feed of dead matter, Multicellular (except yeast), cells have nuclei
  • Protists - Mostly unicellular, Cells have nuclei, some have cell walls (not chitin)
  • Prokaryotes - Unicellular, no nucleus, flexible cell wall

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

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Selective Breeding

Selective breeding is done intentionally to pass on desired genetic traits in both plants and animals, e.g. cattle for beef, large cow, healthy / sheep for wool, long, fluffy.

Farmers that want to grow a type of  fruti that is tasty and resistent to disease could cross a fruit that is tasty and another that is resistent to disease.

It is done by selecting parents that have the best qualities that you want to produce so the chances of offspring with both these qualities is high.

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Gene Modification

These are the steps for gene modification -

  • Human gene of interest is cut out using an enzyme
  • The plasmid is taken out of the bacteria
  • The gene of interest in bacteria is cut out using the same enzyme
  • Using ligase, the enzymes are stuck back into the plasmid
  • The plasmid is put back in the bacteria

Use the same restriction enzyme because it will cut the chromosomes exactly in the same place and they will fit perfectly.

By using the same restriction enzyme, you will get complementary base pairs.

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Protein Synthesis

The first steps in protin synthesis happen in the nucleus. This is called transcription.

  • The gene is exposed when helicase unwinds the DNA. 
  • mRNA will break the hydrogen bonds and copy the DNA needed.
  • It will then leave the nucleus through nuclear pores.
  • The DNA will then rezip using an enzyme called ligase.
  • In mRNA, the base T  gets replaced with U.

The second stage of protein synthesis happens in the cytoplasm. This is called translation.

  • mRNA moves to the ribosomes active sites.
  • Every 3 base pairs code for an amino acid. This is called a codon.
  • The codons will link together with anticodons, which carry amino acids.
  • As the codons and anti-codons match up, the amino acids will connect, detatching from the anti codons.
  • This forms a polypeptide chain of amino acids which folds up to make globular proteins.
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Inheritance & Mendel's Laws

Mendel thought of three laws about inheritance - 

  • Each gamete only recieves one factor for a characteristic.
  • The version of a factor a gamete recieves is random and does not depend on other factors in the gamete.
  • Some versions of the factor are more powerful than others and always have an effect in the offspring.

TT- homozygous dominant          tt- homozygous recessive        Tt- heterozygous

A phenotype is what is physically seen in the offspring and a genotype is its coding.

The X chromosome is larger than the Y chromosome, so genes in the X chromosome where there is no backup from the Y chromosome are at risk of malfunctioning but are always expressed in the phenotype.

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Darwin's Theory

1835- Darwin visited the Galapagos Islands where he noticed differences between mockingbirds. He wondered whether a species could change if it moved to a new place. He collected birds and brought them back to the UK.

1838- Darwin read an essay by Thomas Malthus which argued that if people hd too many children, there would not be enough food. In the resulting struggle, some children would die. This gave Darwin the idea that most organisms produced more offspring than could survive. Only those est suited to its environment would survive.

He spent 20 years gathering evidence and writing a book. 

1858- Darwin recieved a letter from Alfred Russel allace, who had also read Malthus's essay and had come to the same conclusion. Darwin wrote a sum,mary of his ideas, which he later published along with Wallace's letter.

1859- Darwin finished his book , which was a bestseller. The theory was slowly accepted but his ideas challenged the church's and Drwin's theory had masive jumps due to the lack of fossil doscoveries.

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Tissue Culture

Tissue culture is the growing of cells and tissue in a liquid containing nutrients of a solid medium. This is a useful way to grow identical cells. These may form a callus (an unspecified group of cells), which can then be treated to differentiate. 

  • Plant is placed in bleach solution to sterilise it.
  • Sometimes a small piece of plant is cut off and placed on a sterile nutrient medium to grow.
  • The piece of plant is treated with hormones so it grows roots and shoots.

Everything must be kept sterile to prevent growth of micro organisms.

Sugar is a source of energy so is put of the growth medium.

Plant tissues in order to grow will need to use photosynthesis. The bright light will act as the sun.

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Fertiliser and Biological Control

Farmers can make plants resistent to pests by using chemicals like Bt gene, which makes plants resistent to caterpillars.

Fertilisers are used to help crops grow faster.

Producer organisms take food from sunlight. They are autotrophes that make thier own food.

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Evidence for Human Evolution

We can see that human have evolved throughout many years because of fossil discoveries and carbon dating.

Examples of these skeletons are

Fossil Ardi,


H0mo habilis & H0mo erectus.

H0mo erectus was discovered in 1944 by Richard Peaky. Its translation is upright man. It is believed to be around 1.9 million to 43,000 years old and shows the most similarities to modern humans.

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