Energy Transfers in and Between Organisms- Energy and Ecosystems and Nutrient cycles ( Year 13 Content )

Question 1

How do plants use sugars from photosynthesis?

Answer 1

• primarily as respiratory substrates
• to synthesise other biological molecules ( cellulose )

Question 2

what is biomass?

Answer 2

total dry mass of tissue or mass of carbon measured over a given time in specific areas

Question 3

suggest the units for biomass

Answer 3

• when an area is being sampled: gm-2
• when a volume is being samples: gm-3

Question 4

how can the chemical energy store in dry mass be estimated?

Answer 4

using calorimetry
q= m x c x Δt

Question 5

why is bomb calorimetry preferable to simple calorimetry?

Answer 5

reduces heat loss to surroundings

Question 6

how could a student ensure that all water had been removed from a sample before weighing?

Answer 6

heat the sample and reweigh it until the mass reading is constant

Question 7

define gross primary production ( GPP )

Answer 7

total chemical energy stored in a plants biomass within a given volume or area

Question 8

define net primary productivity ( NPP )

Answer 8

total chemical energy available for plant growth, plant reproduction and energy transfer to other trophic levels after respiratory losses

Question 9

what equation is used to calculate NPP?

Answer 9

NPP = GPP - R

where R represents respiratory losses

Question 10

why is most of the sun’s energy not converted to organic matter?

Answer 10

• most solar energy is absorbed by the atmosphere ( ozone layer ) or reflected by clouds
• the chlorophyll cant absorb some wavelengths of light
• some of the light might miss the chlorophyll molecule
• energy lost as heat during respiration/ photosynthesis

Question 11

how can the net production of consumers be calculated?

Answer 11

N = I - ( F + R )
l: chemical energy from ingested food
F: energy lost as faeces and urine
R: respiratory losses

Question 12

why does biomass decrease along a food chain?

Answer 12

• energy lost in nitrogenous waste ( urine ) and faeces
• some parts of the organism are not consumed ( cellulose and bones )
• energy lost to the surroundings as heat

Question 13

outline some common farming practices used to increase efficiency of energy transfer

Answer 13

• exclusion of predators: no energy lost to other organisms in food web
• artificial heating: reduce energy lost to maintain constant body temperature
• restriction of movement
• feeding is controlled at the optimum

Question 14

give the equation for efficiency

Answer 14

useful energy / total energy x100

Question 15

explain why the length of food chains is limited

Answer 15

energy lost at each trophic level
so there is insufficient energy to support a higher trophic level

Question 16

what is a pyramid of biomass?

Answer 16

diagram that shows the biomass at each trophic level

Question 17

name the general stages in the phosphorus cycle

Answer 17

• weathering
• run off
• assimilation
• decomposition
• uplift

Question 18

why is the phosphorus cycle a slow process?

Answer 18

• phosphorus has no gas phase, so there is no atmospheric cycle
• most of the phosphorus is stored as PO4 3− in rock s

Question 19

what happens during weathering and run off?

Answer 19

phosphate compounds from sedimentary rocks leach into surface water and soil

Question 20

explain the significance of phosphorus to living organism

Answer 20

plants convert inorganic phosphate into biological molecules e.g. DNA,ATP,NADP

Question 21

what happens during uplift?

Answer 21

sedimentary layers from oceans ( formed from
the bodies of aquatic organisms) are brought up to land over many years

Question 22

how does mining affect the phosphorus cycle?

Answer 22

speeds up uplift

Question 23

name the 4 main stages of the nitrogen cycle

Answer 23

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

Question 24

why cant organisms directly use nitrogen from the atmosphere?

Answer 24

nitrogen is very stable due to the strong covalent triple bond

Question 25

what happens during atmospheric fixation of nitrogen?

Answer 25

1) high energy of lighting breaks N2 to N
2) N reacts with oxygen to form NO2 - ( nitrite )
3) NO2 - dissolves in water to form NO3 - ( nitrate )

Question 26

outline the role of bacteria in nitrogen fixation

Answer 26

nitrogen-fixing bacteria in the nodules of legumes use enzyme nitrogenase to reduce gaseous nitrogen into ammonia

Question 27

outline the role of bacteria in ammonification

Answer 27

1) saprobionts feed on and decompose organic waste containing nitrogen
2) NH3 is released
3) NH3 dissolves in water in soil to form NH4+

Question 28

outline the role of bacteria in nitrification

Answer 28

2-step oxidation process carried out by saprobionts in aerobic conditions
2NH4+ + 3O2 —> 2NO2- + 2H2O + 4H
2NO2- + O2 —> 2NO3-

Question 29

outline the role of bacteria in denitrification

Answer 29

anaerobic denitrifying bacteria convert nitrates in soil back into gaseous nitrogen

Question 30

explain the significance of nitrogen to living organism

Answer 30

plant roots uptake nitrates via active transport and use them to make biological compounds
- amino acids
- nucleic acid
- NAD/NADP

Question 31

outline the role of mycorrhizae

Answer 31

symbiotic relationship between plant and fungus increases surface area of root system = increases uptake of water and mineral ions

Question 32

give 3 benefits of planting a different crop on the same field each year

Answer 32

• nitrogen-fixing bacteria make soil more fertile by increasing soil nitrate content
• different crops have different pathogens
• different crops use different proportions of certain ions

Question 33

name the 2 types of fertilisers and the use of fertilisers

Answer 33

-Organic: decaying organic matter and animal waste
-Artificial/Inorganic: minerals from rocks usually containing nitrogen,phosphorus and potassium
-fertilisers are used to increase crop yield

Question 34

at a certain point, using more fertiliser no longer increases crop yield. why?

Answer 34

another factor affects the rate of photosynthesis so the rate of growth cannot increase any furher

Question 35

outline 2 environmental issues caused by the use of fertilisers

Answer 35

1) Leaching: nitrates dissolve in rainwater and runoff into water sources
2) Eutrophication: water sources become putrid as a result of algal bloom

Question 36

outline the stages of eutrophication

Answer 36

1) aquatic plants grow rapidly due to the high nitrate levels
2) algal bloom on the surface prevents light from reaching the bottom and the plants die
3) oxygen level start to decrease because the number of saprobionts respiring aerobically increases so the fish die

Question 37

how can the risk of eutrophication be reduced?

Answer 37

• sewage treatment marshes on farms
• pumping nutrient-enriched sediment out of the water