Unit 5 Energy,Ecosystems and Nutrient Cycle

Question 1

1Describe how plants are their own producer and how they 2synthesise sugars from photosynthesis

Answer 1

1- Plants synthesise organic compounds from the atmosphere, water & carbon dioxide
2- Sugars from photosynthesis used primarily as respiratory substrates and synthesise other biological molecules e.g biomass

Question 2

Describe how biomass can be measured

Answer 2

• Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area
• Chemical energy store in dry biomass can be estimated using calorimetry

Question 3

Define the term GPP

Answer 3

Gross primary production ( GPP) is the chemical energy store in
plant biomass, in a given area or volume, total energy resulting from photosynthesis

Question 4

Define the term NPP

Answer 4

Net primary production ( NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

NPP = GPP – R
R - respitatory losses

• Also used for herbivores and decomposers

Question 5

Define the term N

Answer 5

Net production of consumers ( N), such as animals, can be calculated as:
N = I – ( F + R)
I - chemical energy store in ingested food
F - chemical energy lost to the environment in faeces and urine and
R - respiratory losses to the environment.

Question 6

Describe the types of productivity

Answer 6

• Rates of productivity(pri & sec) are the rate of s the rate of primary or secondary production
• It is measured as biomass in a given area in a given time kJ ha–1 year–1

Question 7

Outline common farming practices used to increase the enery transfer

Answer 7

• simplifying food webs to reduce energy losses to non-human food chains
• reducing respiratory losses within a human food chain.

Question 8

Describe how nutrients are recycled

Answer 8

Within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle.

Question 9

Outline stages in the nitrogen cycle

Answer 9

1 Saprobiotic nutrition and microbes
2 Ammonification
3 Nitrification,
4 Nitrogen fixation and
5 Denitrification.

Question 10

Describe the role of bacteria in all 4 processes

Answer 10

• Nitrogen fixing bacteria convert nitrogen to ammonium NH4+ (Nitrogen fixation)
• NH4 + ions cannot be absorbed by plants therefore is converted into nitrites NO2- then NO3- by nitrifying bacteria (Nitrification)
• NO3- ions absorbed by plants to make aa/proteins and nucleotides, consumers can eat the plant to obtain the AA and nucleotides
• Organic material (dead plants, animal waste, urea proteins) are broken down by saprobiotic decomposers, this releases Ammonia ions NH4+ back into the soil (Ammonification)
• Nitrate ions can be converted back into Nitrogen gas by denitrifying bacteria – they work in anaerobic conditions (Denitrification)

Question 11

Describe the importance of nitrogen and phosphorus in plants

Answer 11

Nitrogen = make amino acids and proteins
Phosphorus = make DNA and phospholipid

Question 12

Outline the stages needed of phosphorus cycle

Answer 12

• Organic material (dead plants, dead animals, animal waste, urea, proteins) are broken down by saprobiotic decomposers, this releases Phosphate Ions PO4 3- back into the soil
• Mycorrhize are fungi which act like a sponge and hold water and mineral ions around roots and have large SA
• Support uptake of inorganic ions and water through roots by plant

Question 13

Describe the role of fertilisers and outline the 2 types

Answer 13

• Natural and artificial fertilisers replace the nitrates and phosphates lost by harvesting plants and removing livestock
  NATURAL - applying dead plants, dead animals, animal waste leading to ammonification & nitrification
  ARTIFICAL - Spraying on concentrated solutions of the exact proportions of minerals

Question 14

Evaluate the use of both fertilisers

Answer 14

cheaperNatural = Reduced risk of leaching/eutrophication but slower release of minerals
Artificial = Faster release of minerals and higher concentration but risk of
leaching/eutrophication and lowers water potential of soil

Question 15

Describe what is meant by Eutrophication and leeching

Answer 15

Leeching
- Water soluble compounds washed away into rivers or ponds
Eutrophication
- Nitrates leached from fertilised fields simulate growth of algae in pond
- Growth of algae blocks light so no photosynthesis so submerged plants die
- Saprobiotic microorganisms use oxygen in respiration;
- Less oxygen for fish to respire

Question 16

things to remember

Answer 16

• weigh and reheat for constant mass