energy transfers and nutrient cycles

Question 1

why are plants always producers in a food web?

Answer 1

plants synthesise organic compounds from atmospheric/aquatic carbon dioxide

Question 2

biomass =

Answer 2

the mass of living material/the chemical energy stored within the plant

Question 3

suggest why most light isn’t used by producers

Answer 3

1. the light may be reflected
2. the light may be the wrong wavelength
3. the light misses the chlorophyll
4. temperature is a limiting factor

Question 4

explain how to determine plant respiratory rate

(rate so known length of time)

Answer 4

1. put plant by itself
2. in dark so no photosynthesis
3. for known length of time

Question 5

net productivity =

Answer 5

gross productivity - respiratory loss

Question 6

gross productivity units

Answer 6

unit of energy per area per year

Question 7

explain why net productivity may level off

Answer 7

1. net productivity = gross productivity - respiratory loss
2. decrease in gross productivity/increase in respiration

Question 8

explain features of a calorimeter

Answer 8

1. thermometer –> measure temp
2. stirrer –> distributes heat energy

Question 9

why is dry mass used for comparisons instead of fresh biomass?

Answer 9

1. dry mass measures organic material
2. water content varies
3. so the fresh mass is affected

Question 10

how to ensure all water is removed from a sample

Answer 10

1. heat at high temp. to drive off water
2. weigh samples at intervals & reheat
3. until mass is constant

Question 11

eutrophication process

Answer 11

1. fertiliser leaks into lake
2. increased nitrate causes algal bloom
3. as more proteins for cell division
4. growth of algae blocks light
5. so no photosynthesis & plants die
6. more food supply for saprobionts so aerobically respire
7. less oxygen for fish to respire

Question 12

why are animals reared indoors?

Answer 12

less energy lost via movement

Question 13

explain why fertilisers increase yield

Answer 13

1. replaces nutrients removed
2. provides nitrate to make protein for growth
3. provides phosphate to make DNA for growth

Question 14

describe the role of bacteria in making nitrates
(nitrification by oxidation)

Answer 14

• saprobiotic microorganisms break down dead material
• molecules like protein –> amino acids
• then into ammonia by releasing enzymes
• ammonia –> nitrite –> nitrate
• by nitrifying bacteria

Question 15

describe the role of nitrogen-fixing bacteria

Answer 15

1. convert nitrogen gas into ammonia
2. adds nitrogen to an ecosystem

Question 16

explain the effects of nitrogen-fixing bacteria

Answer 16

1. nitrogen-fixing bacteria in root nodules
2. forms mutualistic relationship with plant
3. makes ammonia from nitrogen gas
4. helps produce protein

Question 17

how does ploughing legumes into soil increase yield?

Answer 17

1. legumes contain nitrogen-fixing bacteria in root nodules
2. saprobionts convert protein into ammonia
3. deamination releases ammonia
4. ammonia –> nitrite –> nitrate by nitrifying bacteria
5. nitrates absorbed by roots to form protein for growth

Question 18

explain how nitrogen is removed from a field

Answer 18

1. bare soil causes soil erosion
2. uptake of nitrates by crops that are harvested

Question 19

how do farming practices increase crop yield?

Answer 19

1. fertilisers –> nitrate for protein
2. cattle grazing –> adds manure
3. ploughing –> decreases denitrification

Question 20

explain how saprobionts increase temp

Answer 20

they respire and release heat