BIOLOGY PAPER 2 OCR GCSE

• Water cycle


  1. Energy from the Sun comes down

  2. Warms the surface of the water on earth

  3. Causes the water to evaporate

  4. Water becomes less dense

  5. Water rises up

  6. Water condenses when it starts to cool down

  7. Clouds form when water is accumulated

  8. Water starts to rain (precipitation)
• Water after precipitation


  1. Goes into the mountains where it percolates deep

  2. Picks up ions and salts affecting taste and chemistry

  3. Comes out as a stream and goes into a river

  4. Goes into the soil and slowly moves back to a river or lake

  5. Goes straight onto the ground if rock/mud is saturated

  6. Runs off into nearest river, stream or lake

  7. Ends up in a large collection of water like the sea, reservoir or lake

  8. Taken up by plants and used in photosynthesis

  9. Comes out of plants in transpiration and goes up into the clouds
• Organic compounds


  Any compound that has carbon in it
• Locations of carbon


  • Carbon dioxide in the air
  • Carbon dioxide in oceans
  • Organic compounds in plants
  • Organic compounds in animals
  • Organic compounds in dead plants and animals
  • Fossil fuels
• Changes in carbon locations


  1. Fossil fuels burned (combustion)

  2. Carbon dioxide taken up by plants (photosynthesis)

  3. Plants and animals die, organic compounds turn into fossil fuels or go back into the air

  4. Animals undergo respiration
• Ecosystem


  The animals, plants and everything living within a certain area
• Community


  The plants or animals that live in an ecosystem
• Abiotic factors


  • Light intensity
  • Temperature
  • Water levels
  • pH
  • Iron levels
  • Wind
  • Carbon dioxide levels
  • Oxygen levels
• Biotic factors


  • Food
  • Predators
  • Pathogens
• Changes in abiotic or biotic factors can have a dramatic impact on a community
• Gene


  A stretch of DNA that codes for a characteristic
• Genome


  All the genes in a body
• Gamete


  A sex cell (sperm or egg)
• Chromosome


  Bundled up DNA
• Allele


  Different versions of a gene
• Dominant


  Only need one gene to express a characteristic
• Recessive


  Need two identical recessive genes to express a characteristic
• Homozygous


  Having the same genes
• Heterozygous


  Having different genes
• Genotype


  The genes an organism has
• Phenotype


  The characteristics an organism has
• Identical twins have the same genotype but different phenotypes due to environmental influences
• Natural variation in a population is influenced by diet, exercise, and personal choice
• Asexual reproduction


  Reproduction where the offspring are genetically identical to the parent
• Meiosis


  1. Chromosomes line up and sort themselves down the middle

  2. Crossing over to increase genetic diversity

  3. Two cell divisions to produce four haploid daughter cells
• Mitosis is used for growth and repair, meiosis is used for sexual reproduction
• Genetic cross


  1. Write out the genotypes of the parents

  2. Determine the possible gametes of each parent

  3. Fill in a Punnett square to determine the possible genotypes and phenotypes of the offspring
• Polydactyly


  A dominant genetic condition where a person has extra fingers or toes
• Cystic fibrosis


  A recessive genetic disease
• If only one parent is a carrier for a recessive genetic disease, the offspring have a 50% chance of being a carrier
• Sex chromosomes


  Females have XX, males have XY
• Some genetic conditions are sex-linked, like haemophilia which is on the X chromosome
• Taxonomy


  The study of grouping living things together
• The three domain system divides all life into eukaryotes, bacteria, and archaea
• DNA replication and mutation


  1. Copying DNA over and over can lead to mistakes (mutations)

  2. Mutations can be passed on and contribute to evolution through natural selection
• Charles Darwin proposed the theory of evolution by natural selection
• Darwin's theory of evolution was controversial due to religious objections
• Geographical separation of a single species can lead to speciation and the formation of new species
• Bacteria can divide very rapidly, allowing mutations and antibiotic resistance to spread quickly
• Penicillin and other antibiotics have saved many lives, but the development of new antibiotics is slow and expensive