Cycles and human influence

• Nitrification is the process by which ammonia is converted into nitrites and then into nitrates by nitrifying bacteria.
• What happens to carbon during respiration?

  Carbon in the form of glucose is incorporated into carbon dioxide in all living organisms.
• What happens to carbon during photosynthesis?

  Carbon in the form of carbon dioxide is incorporated into glucose in all plants and algae.
• What happens to carbon during decomposition?

  Carbon in the form of glucose is incorporated into carbon dioxide in all decomposers
• What happens to carbon during combustion?

  Carbon in the form of fossil fuels is incorporated into carbon dioxide by chemical reaction burning.
• How does carbon move from the inorganic to organic form in the carbon cycle?

  Photosynthesis
• Carbon cycle diagram

  Carbohydrates is needed by all living things to make carbohydrates, proteins and lipids.

  
• What can be done to reduce acid rain?

  Use more renewable sources of energy

  Use public transport

  Save energy by switching off lights when not in use.

  Removing sulphur compounds from petrol and diesel fuels.
• Impact of acid rain

  Can cause lakes to become more acidic

  Damages delicate tissue(e.g. the lining of the lungs)

  Kills aquatic life as it causes the water to become toxic.

  Damages leaves of plants

  Disrupts food webs due to loss of aquatic species

  Erodes limestone causing damage to buildings.
• What is acid rain?

  Rain that contains higher than normal concentrations of dissolved acidic gases, causing it to have a lower pH than normal rain.
• Respiration

  Carbon from complex carbon compounds is

  returned back to the atmosphere as carbon

  dioxide.
• Photosynthesis

  Carbon dioxide from the atmosphere is

  converted into complex carbon compounds in

  plants, such as glucose, as a result of

  photosynthesis. The carbon is ‘fixed’
• Decomposition


  Complex carbon compounds, acquired from the

  decay of dead organisms, are taken into the

  bodies of decomposers, where some are

  converted to carbon dioxide during respiration.
• Combustion

  Carbon from complex carbon compounds found

  in fossil fuels is released into the atmosphere

  as carbon dioxide when they are burned.
• Nitrification


  Conversion of ammonium ions in soil into nitrites and nitrates in soil.

  Carried out by nitrifying bacteria in soil.
• Nitrogen Fixation

  Conversion of atmospheric nitrogen gas into ammonia, which in then

  used to manufacture nitrogen compounds (protein and nucleic acids)

  within plants and bacteria. Carried out by nitrogen fixing bacteria

  in root nodules of legumes and soil
• Denitrification


  Conversion of nitrates in soil back to atmospheric nitrogen gas.

  Carried out by denitrying bacteria in water logged soil
• Assimilation

  Active uptake of nitrates, by root hair cells, to form nitrogen

  compounds (proteins and nucleic acids) in plants. Ingestion and

  digestion of plants by animals to form nitrogen compounds (proteins

  and nucleic acids) in animals.
• Decomposition


  Nitrogen compounds (protein, nucleic acids and urea) in faeces,

  urine and dead organisms are converted into ammonium ions in soil.

  Carried out by decomposers (bacteria and fungi).
• Carbon monoxide


  Fossil fuels also release carbon monoxide during combustion.

  Carbon monoxide is a colourless, odourless gas and is formed when carbon based fuels are

  burned in limited oxygen.

  Carbon monoxide can cause serious health problems since it binds to haemoglobin in red

  blood cells therefore reduces the supply of oxygen to tissues and organs.

  Reduced oxygen supply can be particularly damaging to the brain and heart.
• Consequences of global warming:

  Flooding / increased rainfall / rising sea levels

  ● Extreme weather - Increasingly strong storms / droughts / hurricanes

  ● Habitat destruction / food chain disruption / extinction

  ● Migration
• Eutrophication


  Sewage enters streams and rivers. Nitrate levels build up. Increased algal growth. Algae block light from aquatic plants and aquatic plants die due to lack of photosynthesis. Bacteria start to decompose the dead plants. Bacteria use up oxygen as they respire. Oxygen levels in the water fall and other aquatic organisms die due to a lack of oxygen preventing respiration. The decay of dead organisms provide more nutrients so more bacteria grow, respire and take more oxygen from the water.
• Leaching


  The loss of dissolved mineral nutrients in soil water as it soaks deep

  into the ground beyond the reach of plant roots. This loss of mineral

  nutrients from the soil is permanent and makes it very difficult for

  forest trees to regrow in the area.
• Soil erosion


  The washing away of soil as a result of rainfall. A result of the removal of

  the protective cover of vegetation from the soil The top layer of the soil is the layer that contains the most nutrients.
• Disturbance of evapotranspiration


  Trees draw ground water up through their roots and release it into

  the atmosphere by transpiration. As forest trees are removed the

  amount of water that can be hold in an area decreases, which in turn

  can cause either increasing or decreasing rainfall in the area.
• Balance in atmospheric oxygen and carbon dioxide.


  Forests are a major carbon store because carbon dioxide is taken up

  from the atmosphere during photosynthesis and used to produce the

  chemical compounds that makes up trees. When forest are cleared,

  the trees are either burned or left to rot causing this carbon to be

  released quickly as carbon dioxide.
• What are the two main cycles covered in IGCSE Biology?

  The carbon cycle and the nitrogen cycle
• What are the key processes in the carbon cycle?

  • Photosynthesis
  • Respiration
  • Feeding and Digestion
  • Decomposition
  • Combustion
• What do plants absorb during photosynthesis?

  Carbon dioxide (CO₂) and water
• What is produced during photosynthesis?

  Glucose (C₆H₁₂O₆)
• What happens to CO₂ during respiration?

  It is released back into the atmosphere
• When do plants generally absorb more CO₂?

  During the day
• How do animals obtain carbon?

  By consuming plants or other animals
• What do decomposers do to organic material?

  They break it down and release CO₂
• What releases stored carbon back into the atmosphere?

  Combustion of fossil fuels and biomass
• What does the nitrogen cycle describe?

  How nitrogen moves between organisms and the atmosphere
• What percentage of the atmosphere is nitrogen gas (N₂)?

  About 78%
• What do nitrogen-fixing bacteria convert nitrogen gas into?

  Ammonia (NH₃) or nitrates (NO₃⁻)
• What is nitrification?

  Conversion of ammonia into nitrites and nitrates
• How do plants assimilate nitrogen?

  By taking up nitrates from the soil