productivity

Question 1

outline nitrogen cycle

Answer 1

nitrogen fixation
ammonification
nitrification
denitrification

Question 2

nitrogen fixation

Answer 2

nitrogen converted to ammonia
by nitrogen fixing bacteria

nitrogen from atmosphere

bacteria found in root nodules of legumes
- mutualistic relationship
- provide plant with compounds, get carbohydrates from plant

Question 3

ammonification

Answer 3

nitrogen compounds converted to ammonia
by saprobionts (decomposers)

nitrogen compounds from anima waste or dead organisms

Question 4

nitrification

Answer 4

ammonium ions -> nitrites -> nitrates
by nitrifying bacteria

ammonium from soil

Question 5

denitrification

Answer 5

nitrates converted to nitrogen gas
by denitrifying bacteria

happens in anaerobic conditions
by respiration of the bacteria

Question 6

role of saprobionts

Answer 6

decomposers
break down remains of dead plants and animals and waste
allows chemical elements in the remains to be recycled

secrete enzymes and digest matter externally
then absorbs nutrients they need - extracellular digestion

organic molecules broken down into inorganic ions

Question 7

what is saprobiontic nutrition?

Answer 7

obtaining nutrients from dead organic matter using extra cellular digestion

Question 8

role of mycorrhizae

Answer 8

a symbiotic relation between fungi and roots of plants

• fungi made of long thin strands, hyphae, which connect to plants roots
• increase surface area of plants roots
• helps plant absorb ions from soil
  eg phosphorus
• increase uptake of water for plant
• fungi get organic compounds from the plant
  eg glucose

Question 9

outline phosphorus cycle

Answer 9

1. phosphate ions in rocks released by weathering
2. phosphate ions taken into plants through roots (rate increased by mycorrhizae)
3. transferred through food chain
4. phosphate ions lost from animals in waste products
5. saprobionts release phosphate ions into soil by breaking down dead plants, animals and waste
6. weathering also releases phosphate ions into water
7. taken up by aquatic producers, eg algae
8. passed along food chain to sea birds
9. phosphate ions returned to soil through guano

Question 10

outline eutrophication

Answer 10

1. mineral ions leached from fertilised fields
2. causes rapid growth of algae
3. large amounts block sunlight
4. plants die as they cant photosynthesise
5. bacteria feed on bead plant matter
6. increase in bacteria means less oxygen in water (respire aerobically)
7. fish and species die as not enough oxygen

Question 11

how does farming reduce nutrients in soil?

Answer 11

lost when plants harvested
- removed from area
- don’t die and decompose
- mineral ions not returned to soil

animals taken in phosphates and nitrites eating grass
- animals removed
- nutrients not returned in waste

Question 12

why are fertilisers used?

Answer 12

to replace nutrients lost from soil

by harvesting and removing livestock
loses phosphates and nitrates

Question 13

artificial fertilisers

Answer 13

inorganic
pure chemicals - ammonium nitrate

Question 14

environmental impacts of fertilisers

Answer 14

leaching
eutrophication

Question 15

natural fertilisers

Answer 15

organic matter
eg manure, composted vegetables, sewage
guano

Question 16

outline leaching

Answer 16

water soluble compounds in soil washed away

happens when more fertiliser applied than a plant can use
more likely after heavy rainfall

inorganic ions in artificial more soluble - more likely to be leached

Question 17

what is biomass

Answer 17

the mass of living material
amount of chemical energy stored in a plant

made up of biological molecules made from photosynthesis
(synthesised from CO2)

estimated using calorimetry

Question 18

gross primary production

Answer 18

chemical energy store in plant biomass in a given area

Question 19

respiratory loss

Answer 19

GPP lost as heat energy when plants respire

Question 20

net primary production

Answer 20

chemical energy store in plant biomass after respiratory losses

NPP = GPP - R

remaining chemical energy
available for:
- plant growth
- reproduction
- other trophic levels in ecosystem eg decomposers

primary productivity

Question 21

what is net production

Answer 21

energy stored in the biomass of consumers

get energy by digesting plants or animals that have eaten plants
not all energy transferred, lost by:
- respiration
- urine and faeces
- not all food eaten or digestible, eg bones

secondary productivity

Question 22

how is net production calculated?

Answer 22

N = I - (F + R)

N = net production
I = chemical energy in ingested food
F = chemical energy lost in faeces and urine
R = respiratory loss

Question 23

what is primary and secondary productivity measured in?

Answer 23

biomass in a given area in a given time

kJ ha-1 year-1

Question 24

how do farming practises increase efficiency of energy transfer (2)

Answer 24

simplifying food webs
- reduces energy lost

reducing respiratory losses
- reduces energy lost

both increase energy available for human consumption

Question 25

simplifying food webs

Answer 25

reduces energy lost to other organisms

getting rid of food chains not involving humans

• increases NPP of plants
• less energy lost to pests

done by pesticides + herbicides
kills weeds and pests to reduce competition

Question 26

how are respiratory losses reduced?

Answer 26

controlling conditions livestock live in
more energy abatable for there growth

reduce movement
keep indoors - less energy wasted maintaining temperature

more energy maintained - more energy available for humans

but unethical for livestock to reduce movement

Question 27

ways nitrogen is introduced into soils

Answer 27

animal waste
nitrogen fixation (by nitrogen fixing bacteria)
artificial fertilisers
decay of organic matter by saprobionts (ammonification)

Question 28

ways phosphorus is introduced into soils/water

Answer 28

weathering of sedimentary rock
minerals in fertilisers
decomposition of animal waste