3.2.1B - Functioning Ecosystems Cycles

Question 1

define hydrosphere

Answer 1

the total amount of water on the Earth’s surface, whether this be in a liquid, frozen or gas (water vapor) form

Question 2

recall the water cycle

Answer 2

1. it rains. some water is immediately evaporated from ground surface
2. it rains. water is taken in by plants and then transpired back to the atmosphere
3. some water runs off, on the surface of the ground, reaching streams and rivers. These link to the ocean, and this water is evaporated back to the atmosphere
4. some water infiltrates the soil, is sent through the groundwater, reaches the oceans and is then evaporated back to the atmosphere

Question 3

recall the processes involved in the carbon cycle

Answer 3

1. photosynthesis - plants absorb carbon dioxide from the atmosphere and form it into sugar, starch and other organic compounds. This is the only process in the cycle that decreases the level of carbon dioxide in the atmosphere.
2. feeding - moves carbon in the form of biological molecules along the food chain
3. respiration - when living organisms (plants, animals and decomposers) respire they release carbon dioxide into the atmosphere (form of excretion)
4. fossilisation - if conditions are not favorable for the process of decomposition, dead organisms decay slowly or not at all. These organisms build and, if compressed over millions of years, can form fossil fuels or carbon stores such as limestone
5. weathering - dissolving of limestone deposits by rain returns carbon atoms to atmospheric carbon dioxide
6. combustion - the burning of fossil fuels releases stored carbon dioxide into the atmosphere
7. excretion - when waste is removed from the body (urine). This excreted material can be broken down during the process of decomposition
8. Egestion - the removal of faeces from an animal that will contain carbon. This egested material can be broken down during the process of decomposition
9. Decomposition - when complex, carbon compounds in dead organisms, urine and faeces are broken down into simpler carbon compounds by bacteria and fungi

Question 4

what is the name of the only process that remobed CO2?

Answer 4

photosynthesis

Question 5

what are the things you must include when drawing the carbon cycle?

Answer 5

• living plants (photosynthesis, respiration)
• living animals (feeding, respiration)
• dead plants and animals (decomposition, respiration)
• factory and cars (combustion)
• volcano
• ocean (exposed limestone)

Question 6

what is the role of decomposers in the carbon cycle?

Answer 6

1. break down/ decay carbon based life forms
2. store carbon as organic matter
3. respire, releasing carbon dioxide to the atmosphere

Question 7

what is nitrogen useful for?

Answer 7

• nitrogen is essential for the formation of amino acids in proteins or for use in necessary biomolecules such as nucleic acids

Question 8

why does the nitrogen cycle need to occur?

Answer 8

• 78% of the air is nitrogen
• nitrogen is unreactive so it cannot be used directly by plants to make protein
• only nitrates are useful to plants, so other processes are needed to convert free nitrogen (N2) to useable forms
• plants must secure their nitrogen in ‘fixed’ form, ie, incorporated in compounds such as:
  
  • nitrate ions (NO3-)/ammonium (NH4+) which is directly used
  • ammonia (NH3)/nitrite ions (NO2-) which is converted to the above

Question 9

what are the 4 processes in the nitrogen cycle?

Answer 9

1. nitrogen fixation
   - turning nitrogen into nitrates
2. decomposition
   - converting organic material into ammonia and ammonium
3. nitrification
   - turning ammonia into nitrites and nitrates
4. denitrification
   - converting nitrates into nitrogen

Question 10

what are the 4 types of bacteria in the nitrogen cycle?

Answer 10

1. saprophytic bacteria
   - (also fungi). Undertake ammonification by converting organic material into ammonia/ammonium
2. nitrifying
   - live in the soil and turn ammonia/ammonium into nitrates
3. nitrogen-fixing
   - either free-living in the soil, or in root nodules. convert nitrogen gas into nitrates
4. denitrifying
   - undertake denitrification by converting nitrates into nitrogen. Usually in waterlogged soils

Question 11

explain nitrogen fixation

Answer 11

1. lightning converts nitrogen gas in the air (N2) to nitrates (NO3-) by bonding it with oxygen and then dissolving in rain
2. Nitrogen gas (N2) is also converted to ammonia (NH3) or ammonium (NH4+) by nitrogen-fixing bacteria in soil or root nodules

Question 12

explain assimilation

Answer 12

• plants absorb nitrates (NO3-) from the soil and use these to build up proteins
• the plant may be eaten by the animal, and its biomass used to produce animal protein

Question 13

explain ammonification/nitrification

Answer 13

• urea and egested material is broken down by decomposers
• this results in nitrogen being returned to the soil as ammonia (NH3) or ammonium (NH4+).
• ammonia (NH3) and ammonium (NH4+) are converted to nitrites (NO2-) and then nitrates (NO3-) by nitrifying bacteria in the soil
• decomposers also break down the bodies of dead organisms resulting in nitrogen being returned to the soil as ammonia (NH3) and ammonium (NH4+).
• ammonia (NH3) and ammonium (NH4+) are converted to nitrites (NO2-) and then to nitrates (NO3-) by nitrifying bacteria

Question 14

explain denitrification

Answer 14

• in some conditions denitrifying bacteria in the soil break down nitrates (NO3-) by liberating oxygen and returning nitrogen to the air (N2). This is usually in anaerobic or waterlogged soil