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Biology > Nutrient cycles and decomposers > Flashcards

Nutrient cycles and decomposers Flashcards

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1
Q

What are the three types of nutrient cycle?

A

● Carbon cycle
● Water cycle
● Nitrogen cycle

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2
Q

Why are the nutrient cycles important?

A

● Carbon, water and nitrogen are essential to life
● There is a fixed amount of nutrients on Earth
which must be constantly recycled

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3
Q

Describe how materials cycle through the living and

non-living components of an ecosystem

A

● 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

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4
Q

Describe the stages of the carbon cycle

A
  • Photosynthesis
  • Eating
  • Respiration
  • Death and Decomposition
  • Combustion
  1. Photosynthesising plants remove CO2
    from the atmosphere
  2. Eating passes carbon compounds along a food chain
  3. Respiration in plants and animals returns CO2
    to the atmosphere
  4. Organisms die and decompose. Decomposers (bacteria and fungi)
    break down dead material and release CO2
    via respiration
  5. Combustion of materials (e.g. wood, fossil fuels) releases CO2
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5
Q

Describe the stages of the water cycle

A

Water Vapour Stage

  1. Evaporation
  2. Transpiration

Water liqufying
3. Condensation

Rain
4. Precipitation

Uses of rain

  1. Absorption
  2. Photosynthesis, plants or food chain

How water returns

  1. Excretion
  2. Surface runoff
  3. Energy from the sun evaporates water from sources such as lakes and
    oceans.
  4. Transpiration also releases water vapour.
  5. Water vapour rises, cools and condenses forming clouds
  6. Precipitation occurs
  7. Water is absorbed by the soil and taken up by roots.
  8. Some is used in photosynthesis or becomes part of the plant, entering the food chain.
  9. Excretion returns water to the soil
  10. Surface runoff returns to streams, rivers and eventually the sea
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6
Q

What is potable water?

A

Drinking water

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7
Q

How can potable water be prepared?

A

Desalination

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8
Q

What is desalination?

A

A process that removes salts from saline

water

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9
Q

Name two methods of desalination

A

● Thermal desalination

● Reverse osmosis

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10
Q

Describe thermal desalination

A

Salt water is boiled. Water evaporates,
rises and condenses down a pipe. This
separates pure water from salts.

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11
Q

Describe reverse osmosis

A

● 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

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12
Q

What do plants use to make proteins?

A

Nitrates

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13
Q

Why can’t nitrogen be used directly by plants to form

proteins?

A

Nitrogen is unreactive

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14
Q

Name the four types of bacteria involved in the

nitrogen cycle

A

● Decomposers
● Nitrogen-fixing bacteria
● Nitrifying bacteria
● Denitrifying bacteria

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15
Q

What is the role of decomposers in the nitrogen

cycle?

A

● Break down proteins and urea into ammonia
● Ammonia dissolves in solution forming
ammonium ions

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16
Q

What is the role of nitrogen-fixing bacteria in the

nitrogen cycle?

A

● Convert nitrogen gas into ammonia
● Ammonia dissolves in solution forming
ammonium ions

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17
Q

Where are nitrogen-fixing bacteria found?

A

● Soil

● Root nodules of legumes

18
Q

What type of relationship is exhibited between

nitrogen-fixing bacteria and legumes?

A

● Mutualistic relationship
● Plants receive ammonium ions from bacteria
● Bacteria gain sugars from the plant

19
Q

What is the role of nitrifying bacteria in the nitrogen

cycle?

A

● Convert ammonium ions into nitrites

● Convert nitrites into nitrates

20
Q

What is the role of denitrifying bacteria in the

nitrogen cycle?

A

Convert nitrates into nitrogen gas

21
Q

Where are denitrifying bacteria commonly found?

A

Waterlogged soils

22
Q

Describe the stages of the nitrogen cycle

A
  1. Formation of ammonium ions from dissolving of ammonia from nitrogen gas: Lightning and Nitrogen-Fixing Bacteria
  2. Ammonium ions to nitrites to nitrate ions to proteins: Nitrifying bacteria
  3. Feeding
  4. Decomposers
  5. Denitrification
  6. Lighting and nitrogen-fixing bacteria convert nitrogen gas to ammonia
    which dissolves to form ammonium ions
  7. Nitrifying bacteria convert ammonium ions to nitrate ions which are taken up
    by plants and used to build proteins
  8. Feeding passes nitrogen through the food chain
  9. Organisms die and decompose. Decomposers break down proteins and urea
    to form ammonia which dissolves to form ammonium ions
  10. Denitrifying bacteria convert nitrates in the soil back to nitrogen gas
23
Q

How can the amount of nitrates in the soil be

increased?

A

● 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

24
Q

What is meant by decomposition?

A

The breakdown of dead materials into

simpler organic matter

25
Q

How do decomposers break down dead matter?

A

Decomposers release enzymes which
catalyse the breakdown of dead material
into smaller molecules

26
Q

What factors affect the rate of decomposition?

A

● Oxygen availability
● Temperature
● Water content

27
Q

Why is oxygen required for decomposition?

A

Most decomposers require oxygen for

aerobic respiration

28
Q

How does the availability of oxygen affect the rate of

decomposition?

A

● As oxygen levels increase, the rate of
decomposition increases
● As oxygen levels decrease, the rate of
decomposition decreases

29
Q

Why can decomposition still occur in the absence of

oxygen?

A

Some decomposers respire anaerobically

*However, the rate of decomposition is slower as
anaerobic respiration produces less energy

30
Q

How does temperature affect the rate of

decomposition?

A

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

31
Q

How does soil water content affect the rate of

decomposition?

A

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

32
Q

What conditions are required to make compost?

A

Conditions that give a high rate of decomposition:

plentiful supply of oxygen, warm, moist etc.

33
Q

Describe the methods of food storage used to slow

down the rate of decomposition

A 
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

34
Q

What is an indicator species?

A

A species whose presence or absence in an
environment provides indication of
environmental conditions e.g. pollution levels

35
Q

What indicator species can be used to identify

polluted water?

A

● Bloodworms
● Sludgeworms

(adapted to live in polluted water)

36
Q

What indicator species can be used to identify clean

water?

A

● Freshwater shrimps
● Stonefly

(sensitive to oxygen concentrations so can only
survive in clean water)

37
Q

What indicator species can be used to identify clean

air?

A

Blackspot fungus found on rose leaves

(sensitive to sulfur dioxide concentrations so can
only survive in clean air)

38
Q

What are lichens used for?

A

Used to monitor air pollution

39
Q

How can lichens indicate air pollution?

A

● 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

40
Q

Evaluate the use of indicator species as a measure of pollution

A

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

Biology (36 decks)

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