Nutrient cycles

Question 1

What are producers and consumers broken down by?

Answer 1

Saprobionts

Question 2

What is the greenhouse effect?

Answer 2

• Some reaches the earth’s surface
• This is then reflected back to the earth by clouds
• The gases trap heat close to the earths surface to keep it warm

Question 3

What are the consequences of global warming?

Answer 3

• Changes the temperature, precipitation, timing of seasons, and causes extreme events
• Sea levels will rise
• Flooding
• Crop failure
• Greater rainfall and storms
• Spread of tropical diseases

Question 4

What are the four main stages in the nitrogen cycle?

Answer 4

• Ammonification
• Nitrification
• Nitrogen fixation
• Denitrification

Question 5

What occurs during ammonification?

Answer 5

• Production of ammonia from organic ammonium containing compounds
• Saprobionts feed on these materials, releasing ammonia

Question 6

What occurs during nitrification?

Answer 6

• Ammonia is oxidated into nitrite ions (NO₂⁻)
• These nitrite ions are then oxidated into nitrate ions (NO₃⁻)
• Nitrifying bacteria require oxygen to carry out this, so need soil with many air spaces

Question 7

What occurs during nitrogen fixation?

Answer 7

• Nitrogen gas is converted into nitrogen-containing compounds
• Carried out by free-living bacteria
• These reduce nitrogen gases to ammonia which is used to make amino acids
• Nitrogen-fixing bacteria live in root nodules and convert nitrogen gases to ammonia

Question 8

What occurs during denitrification?

Answer 8

• When soil is water-logged, becomes short of oxygen
• Increase of anaerobic denitrifying bacteria which convert soil nitrates into nitrogen gas
• Soil is well aerated to prevent this

Question 9

What are natural / organic fertilisers?

Answer 9

• Dead and decaying remains of plants and animals
• Also can contain animal waste such as manure and bone meal

Question 10

What are artificial / inorganic fertilisers?

Answer 10

• Mined from rocks and deposits
• Converted into different forms and blended together
• Gives the appropriate balance of minerals for a particular crop

Question 11

Why is nitrogen so important?

Answer 11

It is a necessary component of proteins and is needed for growth

Question 12

Why are nitrogen-containing fertilisers bad for the environment?

Answer 12

• Reduces species diversity as it favours certain plants and therefore reduces competition
• Leeching, leading to pollution of water bodies
• Eutrophication, caused by leeching of fertiliser into water bodies

Question 13

What is leeching?

Answer 13

• Process by which nutrients are removed from the soil
• Rain water will dissolve soluble nutrients such as nitrates and carry them into the soil
• These nitrates find their ways into water bodies and may have harmful effects on organisms drinking this water

Question 14

What is the process of eutrophication?

Answer 14

1. Nitrate conc. increases due to leeching causing plants and algae to grow
2. Algae grows on upper layer of water
3. Algae layer absorbs light, preventing it from reaching lower depths
4. Light becomes limiting factor so plants die
5. Saprobionts feed on dead plants, population grows
6. Saprobionts use up oxygen for respiration
7. Conc. oxygen in water reduced and nitrates released from decaying organisms
8. Oxygen limiting factor so other organisms begin to die
9. Less competition for saprobionts
10. Saprobionts continue to decompose dead material, releasing toxic waste