Energy Transfers - Nutrient Cycles

Question 1

Whyh is nitrogen needed in organisms

Answer 1

• To make amino acids and proteins
• For use in nitrogen containing bases to make DNA nucleotides
• To make ATP and ADP
• To make chlorophyll
• To make NADP for photosynthesis
• To make NAD for resporation

Question 2

Describe the process of nitrification

Answer 2

• Saprobiotic bacteria secrete enzymes onto dead organisms, faeces and urine
• They hydrolyse nitrogen compounds such as proteins by extracellular digestion and absorb the products
• Ammonium ions are released into the soil

Question 3

Describe the process of nitrification

Answer 3

• Aerobic nitrifying bacteria oxidise ammonium ions in 2 stages:
  1. Ammonium to nitrite ions (NO2-)
  2. Nitrite to Nitrate (NO3-)
• Plants absorb nitrate ions via active transport and use them to make proteins, DNA etc

Question 4

Describe the process of nitrogen fixation

Answer 4

• Nitrogen gas is rduced to ammonium ions by nitrigen fixing bacteria in the soil and nitrogen fixing bacteria in the root nodules of legumes

Question 5

Describe the process of denitrification

Answer 5

• Denitrifying bacteria reduce nitrate ions to nitrogen gas
• This happens in anaerobic conditions such as waterlogged soil

Question 6

How do saprobionts carry out decomposition

Answer 6

Saprobionts secrete extracellular enzymes which ydrolyse proteins

Question 7

Why is phosphorus needed in organisms

Answer 7

• To make ATP and ADP
• To make phospholipids to make new cell membranes
• For us ein the sugar phosphate backbone to make DNA and RNA nucleotides
• To make NADP for photosynthesis and NAD in respiration

Question 8

How do mycorrhizae facilitate plant growth

Answer 8

• The hyphae of the fungi increase the surface area for the absorption of water and nutrients

Question 9

Describe the process of the phosphorus cycle

Answer 9

• Phosphate ions present in rocks are released through weathering and erosion
• The phosphate ions dissolve into lakes and soil
• Plants absorb the phosphate ions into their roots via active trabsport. Mycorrhizae increase the surface area for this as the concentration of phosphate ions in the soil is low
• Plants use the phosphate ions to make molecules such as ATP, DNA and phospholipids which are incorporated into their biomass
• The phosphates are then transferred to consumers when they digest and absorb molecules. The animals then assimilate the phosphate into their own molecules
• When animals and plants die they are decompposed by saprobiotic organisms which digest the phosphate containing molecules such as DNA by extracellular digestion. This returns phosphate ions to the soil
• Phosphate ions are also excreted from animals in their urine and via guano in birds
• The phosphate in the soil can return to rocks via deposition

Question 10

Why are fertilisers neccesary to ise in agricultural systems

Answer 10

• Fertilisers add nitrates and phosphates to the soil to replace those lost after harvesting crops or if livestock are removed
• Productivity is increased since nitrates are used for making proteins and phosphates are used for making ATP for growth

Question 11

What is a natural fertiliser

Answer 11

Compost and manure

Question 12

What is an artificial fertiliser

Answer 12

Chemichal compounds that have been added to the soil

Question 13

What is leaching

Answer 13

Leaching is the removal of nitrates and phosphates from the soil by rainwater into rivers and lakes

Question 14

Explain how eutrification causes the death of fish in a pond

Answer 14

• Nitrates and phosphates from the leaching of fertilisers enter streams and rivers
• Nitrates and phosphetes increases the growth of algae on the surface of the rivers
• This reduces light available to plants in the water so these plants stop phososynthesising and die
• Saprobiotic bacteria reproduce rapidly and decompose the dead plant matter, using oxygen for aerobic respiration
• This reduces oxygen available for fish in the river so they cannot aerobically respire and die