Nutrient cycles and decomposers Flashcards
What are the three types of nutrient cycle?
● Carbon cycle
● Water cycle
● Nitrogen cycle
Why are the nutrient cycles important?
● Carbon, water and nitrogen are essential to life
● There is a fixed amount of nutrients on Earth
which must be constantly recycled
Describe how materials cycle through the living and
non-living components of an ecosystem
● Organisms take in elements from their surroundings e.g. soil, air
● Elements converted to complex molecules which become biomass
● Elements transferred along food chains
● Elements returned to environment during excretion and
decomposition of dead organisms
Describe the stages of the carbon cycle
- Photosynthesis
- Eating
- Respiration
- Death and Decomposition
- Combustion
- Photosynthesising plants remove CO2
from the atmosphere - Eating passes carbon compounds along a food chain
- Respiration in plants and animals returns CO2
to the atmosphere - Organisms die and decompose. Decomposers (bacteria and fungi)
break down dead material and release CO2
via respiration - Combustion of materials (e.g. wood, fossil fuels) releases CO2
Describe the stages of the water cycle
Water Vapour Stage
- Evaporation
- Transpiration
Water liqufying
3. Condensation
Rain
4. Precipitation
Uses of rain
- Absorption
- Photosynthesis, plants or food chain
How water returns
- Excretion
- Surface runoff
- Energy from the sun evaporates water from sources such as lakes and
oceans. - Transpiration also releases water vapour.
- Water vapour rises, cools and condenses forming clouds
- Precipitation occurs
- Water is absorbed by the soil and taken up by roots.
- Some is used in photosynthesis or becomes part of the plant, entering the food chain.
- Excretion returns water to the soil
- Surface runoff returns to streams, rivers and eventually the sea
What is potable water?
Drinking water
How can potable water be prepared?
Desalination
What is desalination?
A process that removes salts from saline
water
Name two methods of desalination
● Thermal desalination
● Reverse osmosis
Describe thermal desalination
Salt water is boiled. Water evaporates,
rises and condenses down a pipe. This
separates pure water from salts.
Describe reverse osmosis
● Saline water pumped into a vessel containing a partially permeable
membrane at high pressure
● High pressure forces water molecules to move from an area of low
water concentration (high salt concentration) to an area of high water
concentration (low salt concentration)
● Pure water separated from salts
What do plants use to make proteins?
Nitrates
Why can’t nitrogen be used directly by plants to form
proteins?
Nitrogen is unreactive
Name the four types of bacteria involved in the
nitrogen cycle
● Decomposers
● Nitrogen-fixing bacteria
● Nitrifying bacteria
● Denitrifying bacteria
What is the role of decomposers in the nitrogen
cycle?
● Break down proteins and urea into ammonia
● Ammonia dissolves in solution forming
ammonium ions
What is the role of nitrogen-fixing bacteria in the
nitrogen cycle?
● Convert nitrogen gas into ammonia
● Ammonia dissolves in solution forming
ammonium ions
Where are nitrogen-fixing bacteria found?
● Soil
● Root nodules of legumes
What type of relationship is exhibited between
nitrogen-fixing bacteria and legumes?
● Mutualistic relationship
● Plants receive ammonium ions from bacteria
● Bacteria gain sugars from the plant
What is the role of nitrifying bacteria in the nitrogen
cycle?
● Convert ammonium ions into nitrites
● Convert nitrites into nitrates
What is the role of denitrifying bacteria in the
nitrogen cycle?
Convert nitrates into nitrogen gas
Where are denitrifying bacteria commonly found?
Waterlogged soils
Describe the stages of the nitrogen cycle
- Formation of ammonium ions from dissolving of ammonia from nitrogen gas: Lightning and Nitrogen-Fixing Bacteria
- Ammonium ions to nitrites to nitrate ions to proteins: Nitrifying bacteria
- Feeding
- Decomposers
- Denitrification
- Lighting and nitrogen-fixing bacteria convert nitrogen gas to ammonia
which dissolves to form ammonium ions - Nitrifying bacteria convert ammonium ions to nitrate ions which are taken up
by plants and used to build proteins - Feeding passes nitrogen through the food chain
- Organisms die and decompose. Decomposers break down proteins and urea
to form ammonia which dissolves to form ammonium ions - Denitrifying bacteria convert nitrates in the soil back to nitrogen gas
How can the amount of nitrates in the soil be
increased?
● Using fertilisers e.g. animal manure, compost, artificial
fertilisers
● Crop rotation replenishes nitrates that may have been
depleted by the previous crop e.g. planting a
nitrogen-fixing crop
What is meant by decomposition?
The breakdown of dead materials into
simpler organic matter
How do decomposers break down dead matter?
Decomposers release enzymes which
catalyse the breakdown of dead material
into smaller molecules
What factors affect the rate of decomposition?
● Oxygen availability
● Temperature
● Water content
Why is oxygen required for decomposition?
Most decomposers require oxygen for
aerobic respiration
How does the availability of oxygen affect the rate of
decomposition?
● As oxygen levels increase, the rate of
decomposition increases
● As oxygen levels decrease, the rate of
decomposition decreases
Why can decomposition still occur in the absence of
oxygen?
Some decomposers respire anaerobically
*However, the rate of decomposition is slower as
anaerobic respiration produces less energy
How does temperature affect the rate of
decomposition?
Decomposers release enzymes:
● Rate highest at 50°C (optimum temperature for enzymes)
● Lower temperatures, enzymes work too slowly, rate decreases
● High temperatures, enzymes denature, decomposition stops
How does soil water content affect the rate of
decomposition?
Decomposers require water to survive:
● In moist conditions the rate of decomposition is high
● In waterlogged soils there is little oxygen for
respiration so the rate of decomposition decreases
What conditions are required to make compost?
Conditions that give a high rate of decomposition:
plentiful supply of oxygen, warm, moist etc.
Describe the methods of food storage used to slow
down the rate of decomposition
Fridge/Freezer Airtight cans Temperature- high Salt and Sugar Dry
● Stored in a fridge/freezer to slow down the activity of microbes
● Stored in airtight cans to prevent the entry of microorganisms
● High temperatures sterilise cans, destroying any bacteria
● Adding salt or sugar kills microbes (lose water by osmosis)
● Food kept dry to reduce the ability of microorganisms to survive
What is an indicator species?
A species whose presence or absence in an
environment provides indication of
environmental conditions e.g. pollution levels
What indicator species can be used to identify
polluted water?
● Bloodworms
● Sludgeworms
(adapted to live in polluted water)
What indicator species can be used to identify clean
water?
● Freshwater shrimps
● Stonefly
(sensitive to oxygen concentrations so can only
survive in clean water)
What indicator species can be used to identify clean
air?
Blackspot fungus found on rose leaves
(sensitive to sulfur dioxide concentrations so can
only survive in clean air)
What are lichens used for?
Used to monitor air pollution
How can lichens indicate air pollution?
● Sensitive to the concentration of sulfur dioxide
● Different types of lichens grow in different levels of air pollution
e.g. bushy lichens grow in cleaner air than crusty lichens
● Abundance and distribution of lichens indicate levels of
pollution
Evaluate the use of indicator species as a measure of pollution
Advantages:
● Cheaper and simpler
● Used to monitor pollution levels over long periods of time
Disadvantages:
● Less accurate than non-living indicators e.g. electronic meters
● Do not provide a definitive figure for pollution levels
