Nutrient Cycle

• What happens at stage one of the phosphorus cycle?

  Phosphate ions in rocks are released into the soil by weathering

  
• What happens at stage two of the phosphorus cycle?

  Phosphate ions are taken into the plants through the roots. Mycorrhizae greatly increase the rate at which phosphorus can be assimilated.

  
• What happens at stage three of the phosphorus cycle?

  Phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.

  
• What happens at stage four of the phosphorus cycle?

  Phosphate ions are lost from the animals in waste products.

  
• What happens at stage five of the phosphorus cycle?

  When plants and animals die, saprobionts are involved in breaking down the organic compounds, releasing phosphate ions into the soil for assimilation by plants. These microorganisms also release the phosphate ions from urine and faeces.

  
• What happens at stage six of the phosphorus cycle?


  Weathering of rocks also releases phosphate ions into seas, lakes and rivers. This is taken up by aquatic producers, such as algae, and passed along the food chain to birds.

  
• What happens at stage seven of the phosphorus cycle?

  The waste produced by sea birds is known as guano and contains a high proportion of phosphate ions. Guano returns a significant amount of phosphate ions to soils (particularly in coastal areas). It is often used as a natural fertiliser.

  
• Mycorrhizae is a fungus that grows in and around the roots of plants. The fungus absorbs water and mineral ions from the soil and acts like extensions of the plants own root system.
• How does Mycorrhizae increase the rate of absorption?

  The fungus holds water and mineral ions near the roots of the plant to provide nutrients in dry conditions and when mineral ions are scarce. The fungus benefits too, as it receives sugars and amino acids from the plant.
• What do we call the relationship between plants and mycorrhizae?

  We call this a mutualistic relationship.
• Give some pros of organic fertilisers.

  Organic fertilisers improve the soil quality by adding organic matter which supports microbial activity and enhances soil structure.

  Additionally they improve the water holding capacity of soil by increasing organic matter which enhances soil structure and reduces the risk of nutrient leaching.

  Finally it is readily available and does not use more resources to produce it.
• Give some cons of organic fertilisers.

  Organic fertilisers release nutrients slowly, they are messier to apply and the amount of fertiliser to be applied cannot be controlled.
• Give some pros of inorganic fertilisers.

  Inorganic fertilisers are cleaner to apply, they are fast acting as nutrients are available immediately and finally the amount of fertiliser to be applied can be controlled.
• Give some cons of inorganic fertilisers.

  Inorganic fertilisers are not readily available and use more resources to produce the fertiliser, they don't use inorganic matter resulting in reduced microbial activity and poor soil structure. Finally they can easily run off into nearby water bodies and cause water pollution, e.g. eutrophication.
• What is leaching?

  Leaching is when water-soluble compounds in the soil are washed away usually by rain or irrigation systems into nearby ponds and rivers.
• What can leaching lead to if it runs off into ponds/lakes?

  This can lead to eutrophication
• What is eutrophication?


  Fertilisers are applied to crops and leach into ponds/lakes, leading to an increase in algal growth at the surface of the water which blocks light. As a result submerged plants cannot photosynthesise and die, saprobiotic bacteria start breaking down dead plant matter; as their population increases more oxygen is used by this bacteria for aerobic respiration. Less oxygen is available for fish to respire and so they die.
• How does the incorrect use of fertiliser reduce biodiversity?

  nitrogen rich soil favours specific species and so other species cannot compete.
• What is assimilation?

  This is the process at which ions are absorbed and then used to make more complex molecules.