13- Energy & Ecosystems

Question 1

Eutrophication- 4) Increase in bacteria (3)

Answer 1

1) bacteria decompose dead plants
2) As number of bacteria increase, oxygen conc in water decreases
3) Fish & other organisms die as insufficient oxygen

Question 2

Eutrophication- 3) Plant death (1)

Answer 2

• Plants underneath algae eventually die because there is insufficient light for them to photosynthesise

Question 3

Eutrophication-2) Algal overgrowth (2)

Answer 3

1) Excess nutrients cause ALGAE to rapidly grow on water surface
2) As algae accumulates, light is prevented from reaching the plants in the water beneath

Question 4

Eutrophication- 1) leaching & overflow (2)

Answer 4

• Fertilisers sprayed onto fields can LEACH through soil or flow into bodies of water (P, L, R)
• This causes a build up of nutrients in the water

Question 5

Eutrophication- stages

Answer 5

1) leaching and overflow
2) Algal overgrowth
3) Plant death
4) Increase in bacteria

Question 6

Natural vs artificial fertilisers (2)

Answer 6

natural= organic & taken from O matter 
Artificial= inorganic & produced specifically to replace nutrients

Question 7

Agricultural impacts on soil (3)

Answer 7

-leads to depleated nutrients levels (in soil)
due to:
- when crops are removed for harvest they aren’t DECOMPOSED & nutrients aren’t returned to soil for reuse
- when animals removed for slaughter, decreases nutrient levels as not DECOMPOSED

Question 8

PC- 2) Breakdown of phosphate ions (3)

Answer 8

1) As phosphate ions are transferred through food chain, they are lost as waste or organism dies
2) Saprobionts decompose waste & dead organisms through EXTRACELLULAR digestion
3) phosphate ions released into soil & can be recycled for reuse in cycle

Question 9

PC- 1) uptake of phosphate ions (2)

Answer 9

• Phosphate ions are assimilated by plants because of SYMBIOTIC relationship between plant roots and mycorrhizae
• Mycorrhizae increase SA if roots so help increase rate of uptake

Question 10

Mycorrhizae structure & importance (1+1)

Answer 10

• have hyphae (long strands extending from cell body)

- Hyphae increases the SA of plant root system: helping plants to take up inorganic ions & water at faster rate

Question 11

Stages of phosphorous cycle

Answer 11

1) uptake of phosphate ions

2) Break down of phosphate ions

Question 12

Saprobionts & nutrition (4)

Answer 12

1) Saprobionts secrete enzymes onto dead organic matter
2) The enzymes break down large insoluble molecules into smaller soluble ones
3) These absorbed by saprobiont
4) saprobiont STORES molecules or uses in respiration

Question 13

NC- 4) Denitrification (1)

Answer 13

1) Denitrifying bacteria converts NITRATES in soil back to atmospheric nitrogen (N2)

(occurs anaerobically, & requires anaerobic conditions)

Question 14

NC- 3) Nitrification

Answer 14

1) Nitrifying bacteria convert, ammonium ions > nitrites

2) Another bacteria then converts, nitrites > nitrates

Question 15

NC- 2) Ammonification (2)

Answer 15

1) when an organism DIES or excretes FAECES> Saprobionts decompose its BIOMASS by EXTRACELLULAR DIGESTION
2) inorganic ammonium ions released into the soil

Question 16

NC- 1) nitrogen fixation (3)

Answer 16

1) Atmospheric nitrogen (N2) is converted to ammonia (NH3) by nitrogen-fixing bacteria in soil
2) Bacteria form mutualistic relationship with leguminous plants by inhabiting their root nodules.
3) mutualistic as B provide ammonium ions for p and p provide sugars for B

Question 17

Stages of nitrogen cycle

Answer 17

1. nitrogen fixation
2. ammonification
3. nitrification
4. denitrification

Question 18

saprobionts=

Answer 18

microorganisms that feed on dead or decaying matter

Question 19

importance of nutrient recycling

Answer 19

nutrients allowed to be continuously reused

Question 20

Gross primary production (GPP)=

Answer 20

chemical energy store in plant biomass in given area/volume

Question 21

Net Primary Production (NPP)=

Answer 21

chemical energy store in plant biomass AFTER respiratory losses to environment

Question 22

NPP=

Answer 22

NPP= GPP-R

Question 23

Net production of consumers (equation)

Answer 23

N= I - (F+R)

I= chemical energy INGESTED
F= chemical energy lost in FAECES & urine
R= RESPIRATORY losses

Question 24

Rate of productivity units=

Answer 24

kj ha^-1 yr^-1
kj= energy unit
ha= per unit area
per year= more representational as takes in seasonal variation

Question 25

why is energy transfer between tropic levls is inefficient

sun > prdocuer) (3

Answer 25

• only certain wavelengths of light are absorbed
• light has to strike photosynthetic region
• a lot of light is reflected

Question 26

why is energy transfer between trophic levels inefficient? (producer> PC> SC) (4)

Answer 26

• respiratory losses
• energy lost as heat
• not all of the plant/animal is eaten
• some food is not digested

Question 27

Farming practices to increase energy transfer efficiency [crops] (3)

Answer 27

simplify food webs to reduce biomass/ energy loss to non-human food chain

• herbicides- kill weed (less competition)
• fungicides- reduce fungal infections (more energy to create biomass)
• pesticides- reduce loss of biomass from crops

Question 28

Farming practices to increase energy transfer efficiency [livestock]= (5)

Answer 28

reduce respiratory losses (so more energy for biomass creation)

• restrict movement
• keep warm
• slaughter animal when young (when most of the energy is used for growth)
• selective breeding (produce breeds with higher growth rates)
• treated with antibiotics (to prevent energy loss to pathogens)

Question 29

measuring biomass

Answer 29

can be measured using, either:

• mass of carbon
• dry mass of tissue/ given area.

Question 30

measuring biomass- dry mass (4)

Answer 30

1. sample dried in oven (low temp to avoid combustion)
2. Sample reweighed at intervals
3. All water removed when mass constant
4. Mass of carbon taken to be 50% of dry mass