Bio

• Decay

  1. Caused by decomposers (a type of microorganism found in soil)

  2. Decomposers break down dead plant and animal matter by secreting enzymes into the environment (e.g. amylase, protease, lipase)

  3. Decay happens faster when warm, moisture is present, and oxygen is present (needed for aerobic respiration)
• Decay


  • Release of minerals that plants can take up by their roots
  • Release of heat and carbon dioxide as decomposers respire
• Reasons for maintaining biodiversity

  • Organisms make substances useful to humans
  • Duty to future generations
  • Can affect other organisms in the food chain
• Reasons for reducing biodiversity

  • Deforestation
  • Land use
  • Global warming
  • Waste management
• Human activities causing global warming

  • Burning fossil fuels
  • Farming cows
• Deforestation


  Leads to less habitats/food sources for animals, less CO2 being taken out of the atmosphere by plants, and releases more CO2
• Waste management


  Making more waste and using more resources due to a bigger human population and increases in the standard of living, pollution kills plants and animals reducing biodiversity
• Land use


  Humans are reducing land for animals by using it to build, quarry, farm, and dump waste
• Global warming


  Caused by increasing CO2 and methane levels, leading to changes in climate, rise in sea levels, habitat loss, changes in animal migration patterns, extinction
• Evidence for global warming is based on systematic reviews of thousands of peer-reviewed journals
• Ways to maintain biodiversity

  1. Breeding programmes for endangered species

  2. Protection and regeneration of rare habitats

  3. Reintroduction of field margins and hedgerows in farming areas

  4. Reducing deforestation and CO2 emissions

  5. Recycling (rather than dumping in landfills)

  6. Carbon sequestration (removing CO2 from the air)
• Environmental reasons for species numbers going down

  • Global warming
  • Pollutants in water
  • New competitors
  • New pathogens
  • New predators
• Environmental changes affect the distribution of species in an ecosystem

  Changes include temperature, availability of water, composition of atmospheric gases
• Temperature


  • Low temperatures slow decay
  • High temperatures denature enzymes and proteins, killing the organisms responsible for decay
  • Low temperatures slow the rate of reaction of enzymes and prevent growth and reproduction
• Oxygen


  • Lack of oxygen will slow or prevent most forms of decay
  • Decomposers need oxygen for respiration
  • Anaerobic decay produces methane, a greenhouse gas
• Water


  • Lack of water will slow or prevent decay
  • Water is needed for transport and to support reactions inside organisms
  • Decay organisms need water to digest their food
• Gardeners and farmers providing optimum conditions for rapid decay of waste biological material

  The compost produced is used as a natural fertiliser for growing garden plants or crops
• Biogas generators can be used to produce methane gas as a fuel
• Methane gas is a greenhouse gas, causing global warming
• Required practical: Investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change


  Label two sterilised test tubes: one ‘lipase’ /one ‘milk’ 2. In the ‘lipase’ test tube put 10 cm3 of lipase solution. 3. In the ‘milk’ test tube add 10 cm3 of milk 4. Put both test tubes into the water bath. Wait about 5 minutes. 5. Use another syringe to transfer 2 cm3 of lipase into the ‘milk’ test tube. Immediately start timing. 6. Stir the contents of the ‘milk’ test tube with the pH probe. 7. Record the time taken for the pH to reach its lowest pH (make a written note of the time every time the pH falls), this way you will know the time when it has reached its lowest. 8. Repeat steps 1-7 for different temperatures of water bath
• Fats broken down by lipase


  Break down into glycerol and fatty acids
• pH probes


  More accurate and precise than an indicator strip
• Water bath


  Used to control temperature
• Sterilised test tubes


  Heated to over 100⁰C to ensure all bacteria is killed
• Independent variable


  Thing purposefully changed in an experiment (e.g. temperature)
• Dependent variable


  Thing measured (pH)
• Rates of reaction


  How quickly reactions happen
• Change in Y axis ÷ change in X axis to calculate rates of reaction
• Control variable


  Thing kept the same to make it a fair test
• If not on a graph, divide what is made by the time
• Repeating results makes them more repeatable
• Testing smaller intervals and more precise intervals is recommended
• Accuracy


  How close values are to the true value
• Environmental changes affect the distribution of species in an ecosystem
• Environmental changes affecting species distribution

  • Temperature
  • Availability of water
  • Composition of atmospheric gases
• Changes may be seasonal, geographic, or caused by human interaction
• Evolution


  A change in the inherited features of a population over time
• Evolution


  • Happens by natural selection
• Present day organisms have evolved from simpler organisms – over 3 billion years ago
• Natural Selection


  1. There is variation in a species -caused by a random mutation

  2. Gives some individuals a survival advantage (say how)

  3. They can then reproduce and pass on their genes

  4. The amount of individuals with this feature gradually increases