Biology paper 2

• Organisms compete for


  • Food
  • Water
  • Space
  • CO2 and light for plants
  • Shelter and mates for animals
• Interdependence


  Organisms can rely on each other for resources and form a community
• Abiotic factors in an ecosystem


  • Light
  • Temperature
  • Moisture
  • Soil pH
  • CO2 levels
  • O2 levels
• Food chain


  Shows the direction that biomass and energy flow in an ecosystem
• Trophic levels


  • Producers
  • Primary consumers
  • Secondary consumers
  • Tertiary consumers
  • Apex predators
• Pyramid of biomass


  Shows how much mass enters the next trophic level relatively
• Biomass is lost at each trophic level due to organisms living before being eaten, and loss as water, urea and CO2
• Factors affecting food security

  • Increasing world population
  • Changing diets
  • Food transportation
  • Cost of farming
  • Conflicts
• Sustainable fishing


  Fishing at a rate less than the breeding rate to maintain populations
• All life is carbon-based, so carbon is recycled when organisms die
• Water cycle


  Rain falls, runs into rivers, evaporates, repeats
• Biodiversity


  The variety of different types of organisms in an ecosystem
• High biodiversity generally makes for a stable ecosystem
• Human development usually results in lower biodiversity
• Environmental problems from human development


  • Sewage
  • Fertilizers
  • Toxic chemicals
  • Atmospheric pollution
• Carbon dioxide and methane contribute to global warming
• Water vapor is responsible for 95% of the greenhouse effect
• Deforestation reduces biodiversity and releases CO2
• Sexual reproduction in plants

  1. Pollen and egg cells

  2. Variation in offspring
• Asexual reproduction in plants


  Mitosis to produce genetically identical daughter cells
• Genome


  All the genetic material in an organism
• Gene


  A section of DNA that codes for a specific protein
• The Human Genome Project mapped out what each gene codes for
• Genotype


  The genetic code stored in DNA
• Phenotype


  How the genetic code is expressed in an organism's characteristics
• Nucleotides


  • Sugar
  • Phosphate
  • A
  • T
  • C
  • G
• Protein synthesis


  1. DNA sequence copied to mRNA

  2. mRNA taken to ribosome

  3. Amino acids connected in sequence
• Harmful mutation


  Changes a gene so much it results in a non-functional protein
• Some DNA doesn't code for proteins but influences gene expression (epigenetics)
• Alleles


  Different versions of the same gene
• Dominant allele


  Expressed even if a recessive allele is also present
• Recessive allele


  Only expressed if no dominant allele is present
• Homozygous


  Having two of the same allele
• Heterozygous


  Having two different alleles
• Using a Punnett square


  To predict the probability of offspring phenotypes
• Dominant alleles can cause inherited disorders, recessive alleles can be carried without expression
• Human chromosomes


  23 pairs, one pair determines sex (XX female, XY male)
• Charles Darwin's theory of evolution

  Random variation in offspring leads to some being better suited to the environment and more likely to survive and reproduce
• Lamarck's theory of evolution asserted that adaptation is guided by DNA in response to the environment, which is now supported by epigenetics
• Bacterial resistance to antibiotics is evidence of Darwinian evolution