nitrogen and carbon cycle

Question 1

decomposition

Answer 1

chemical process in which a compound is broken down into smaller molecules or its constituent elements e.g. nitrogen and carbon

Question 2

decomposers

Answer 2

organism that feeds on and breaks down dead plant or animal matter, thus returning organic compounds into inorganic ones (nutrients) available to photosynthetic producers in the ecosystem

Question 3

saprobiotic nutrition

Answer 3

saprotrophs feeding on dead organic matter

Question 4

how does saprobiotic nutrition work

Answer 4

• decomposers digest their food externally by secreting enzymes onto dead organisms/organic waste matter
• enzymes break down complex organic molecules into simpler soluble molecules
• decomposers absorb these molecules
• so decomposers release stored inorganic compounds and elements back into the environment

Question 5

detritivores

Answer 5

• class of organism involved in decomposition
• help speed up decay process by feeding on detritus (dead/decaying material)
• they break it down into smaller pieces of organic material which increases SA for the decomposers to work on
• e.g. woodlice, earthworms

Question 6

how much of the air is nitrogen gas

Answer 6

78%

Question 7

why does nitrogen have to be combined with other elements in the nitrogen cycle

Answer 7

nitrogen cannot be taken up by plants in its gaseous (N2) form so has to be combined with oxygen and hydrogen for example

Question 8

what is nitrogen fixation

Answer 8

when nitrogen gas in the atmosphere is converted to ammonia by nitrogen-fixing bacteria such as Rhizobium and Azotobacter

Question 9

ammonia symbol

Answer 9

NH3

Question 10

how do Azotobacter and Rhizobium work

Answer 10

they contain nitrogenase enzyme which combines atmospheric nitrogen (N2) with hydrogen (H2) to produce ammonia (NH3) which can be absorbed and used by plants

Question 11

where is Rhizobium found

Answer 11

• inside root nodules of leguminous plants
• they have a symbiotic/ mutualistic relationship with the plant where both organisms benefit
• plant gains amino acids from Rhizobium which are produced by fixing nitrogen gas into ammonia in the bacteria
• bacteria gains carbohydrates produced by the plant during photosynthesis which they use as an energy source

Question 12

ammonium ions

Answer 12

NH4,+

Question 13

nitrites

Answer 13

NO2,-

Question 14

nitrates

Answer 14

NO3,-

Question 15

what is nitrification

Answer 15

the process by which ammonium compounds in soil are converted to nitrogen-containing molecules that can be used by plants. This involves nitrifying bacteria

Question 16

how does nitrification work

Answer 16

• nitrifying bacteria (nitrosomonas) in soil oxidise ammonium compounds into nitrites (NO2,-)
• nitrobacter (genus of nitrifying bacteria) oxidise nitrites into nitrates (NO3,-)
• nitrate ions are highly soluble

Question 17

denitrification

Answer 17

• in the absence of oxygen (e.g. waterlogged soils), denitrifying bacteria convert nitrates in the soil back into nitrogen gas
• bacteria use the nitrates as a source of energy for respiration and nitrogen gas is released

Question 18

ammonification

Answer 18

the process by which decomposers convert nitrogen-containing molecules in dead organisms, faeces and urine into ammonium compounds

Question 19

other ways that nitrogen enters the nitrogen cycle

Answer 19

• lightning (also fixes atmospheric nitrogen)
• artificial fertilisers (Haber process)

Question 20

where is Azotobacter found

Answer 20

free living in the soil

Question 21

how much of the atmosphere does carbon dioxide make up

Answer 21

0.04%

Question 22

main processes in the carbon cycle

Answer 22

• photosynthesis
• decomposition
• respiration
• combustion
• release from volcanoes
• weathering
• release from and absorption into ocean

Question 23

photosynthesis

Answer 23

• CO2 is absorbed by plants
• becomes carbon compounds in plant tissues like macromolecules
• passed onto primary consumers when they eat plants and so on up the food chain

Question 24

decomposition carbon cycle

Answer 24

• decomposers secrete enzymes which break down carbon compounds e.g. starch in dead organic material
• they absorb the products of digestion e.g. maltose for respiration

Question 25

respiration

Answer 25

CO2 is returned to air as all living organisms including decomposers respire

Question 26

combustion

Answer 26

- if dead organic material ends up in places with no decomposers e.g. oceans or bogs, its carbon compounds can be turned into fossil fuels over millions of years - the carbon is then released when they're burnt e.g. coal and oil

Question 27

main processes involved in the nitrogen cycle

Answer 27

- nitrogen fixation - ammonification - nitrification - denitrification

Question 28

release of carbon from volcanoes

Answer 28

- types of rock can be formed from dead organic material deposited on the sea floor - e.g. limestone and chalk are mainly composed of calcium carbonate (CaCO3) which comes from marine organisms like crab, mussels, sea urchins and coral - when rocks are drawn deep under the earth's crust by tectonic plate movement, they undergo chemical changes and release carbon dioxide, which is returned to the atmosphere via volcanoes

Question 29

weathering

Answer 29

- rocks are weathered chemically by exposure to rainwater which is slightly acidic and physically by plant roots and animals - chemical weathering causes mineral ions and bicarbonate ions to be released into solution and transported into rivers and oceans - they combine to form carbon containing compounds such as CaCO3

Question 30

release from and absorption into the ocean

Answer 30

- CO2 can dissolve directly into the oceans from the atmosphere and be transported in the ocean by currents - CO2 can remain in these slow moving currents for hundreds of years before returning to the surface and being released into the atmosphere