Nutrient cycles：练习题

• a.

  They are specialized plant cells that carry out the process of denitrification in waterlogged soils.

• b.

  They are saprobionts that break down DNA and RNA into phosphate ions via extracellular digestion.

• c.

  They are fungal associations that increase the surface area for the absorption of water and scarce inorganic ions like phosphate.

• d.

  They are bacteria that convert atmospheric nitrogen gas into ammonium ions within root nodules.

• a.

  Denitrifying bacteria release phosphate ions as a byproduct of converting nitrates to nitrogen gas in waterlogged soils.

• b.

  Nitrifying bacteria oxidise phosphate ions into a gaseous form that can be absorbed by the stomata of the leaves.

• c.

  Saprobionts use active transport to pump phosphate ions from sedimentary rocks directly into the phloem of living plants.

• d.

  Mycorrhizae increase the surface area for absorption through a network of hyphae, acting as a functional extension of the plant's root system.

• a.

  The fungi fix atmospheric phosphorus into a soluble form that can be easily transported into the plant's vascular system.

• b.

  The fungi perform extracellular digestion of sedimentary rocks, releasing phosphate ions directly into the plant's xylem.

• c.

  The mutualistic relationship allows the plant to bypass the need for ATP during the active transport of phosphate ions into the root hair cells.

• d.

  The fungal hyphae provide a much larger surface area for the absorption of phosphate ions, which are often in low concentration and have low mobility in the soil.

• a.Ploughing the soil to increase the oxygen concentration for aerobic nitrifying bacteria.
• b.Increasing the acidity of the soil to inhibit the activity of saprobionts.
• c.Harvesting the crop frequently to remove nitrogen-fixing bacteria from the root nodules.
• d.Adding excess water to create anaerobic conditions for denitrifying bacteria.

• a.

  Increased nitrate concentration → Increase in saprobiont activity → Increase in dissolved oxygen → Algal bloom

• b.

  Increased nitrate concentration → Nitrogen fixation by algae → Decrease in water temperature → Death of fish

• c.

  Increased nitrate concentration → Direct poisoning of fish → Bacterial growth → Oxygen depletion

• d.

  Increased nitrate concentration → Algal bloom → Competition for light → Death of plants at lower depths

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。

先自己写一遍答案，再对照解题步骤。