3.5.4 Nutrient cycles Flashcards
What are saprobionts?
A type of decomposer that feeds on the remains of dead plants and animals as well as their waste products.
How do mycorrhizae benefit plants?
- Mycorrhizae connect to the plant’s roots.
- This greatly increases the surface area of the plant’s root system, helping the plant to absorb ions from the soil.
- It also increases the uptake of water by the plant.
Why do plants and animals need nitrogen?
Plants and animals need nitrogen to make proteins and nucleic acids (DNA and RNA).
Briefly describe the process of nitrification.
- Ammonium ions in the soil are changed into nitrogen compounds that can be used by plants.
- Nitrifying bacteria (Nitrosomonas) change ammonium ions into nitrites.
- Then other nitrifying bacteria (Nitrobacter) change nitrites into nitrates.
How do animals obtain phosphate ions?
Phosphate ions are transferred through the food chain as animals eat the plants and are in turn eaten by other animals.
How are phosphate ions transferred from the sea to the land?
- Phosphate ions in the sea is taken up ny aquatic producers,…
- …and passed along the food chain to birds.
- The waste (guano) produced by seabirds contains a high proportion of phosphate ions.
- Guano returns a significant amount of phosphate ions to soils.
Describe the role of saprobionts in ammonification.
[2 marks]
- Saprobionts convert nitrogen compounds in dead organisms, faeces and urine…
- …into ammonia.
Describe how saprobionts obtain their nutrients.
[2 marks]
- They secrete enzymes and digest their food externally,…
- …then absorb the nutrients they need.
Heavy rain combined with poor drainage can lead to soils becoming waterlogged. Suggest and explain what might happen to the amount of nitrogen assimilated by a plant in waterlogged soil.
- It might decrease because waterlogged soils create anaerobic conditions.
- This means that denitrifying bacteria convert nitrates in the soil back into nitrogen gas, which the plants can’t assimilate without nitrogen fixation.
