23.3 Recycling within ecosystems

Why do nutrients constantly have to be recycled throughout ecosystems in order for plants and animals to grow?

they are used up by living organisms and there is no large external source constantly replenishing nutrients in the way the sun supplies energy

Decomposition?

a chemical process in which a compound is broken down into smaller molecules, or its constituent elements

What must happen to essential elements, such as nitrogen or carbon, which cannot be used directly by an organism in the organic form it is in, in dead or waste matter?

this organic material must be processed into inorganic elements and compounds, which are a more usable form, and returned to the environment

A decomposer?

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

What organisms are decomposers usually?

microscopic fungi and bacteria (but can also include larger fungi)

What do decomposers obtain their energy from?

dead or waste organic material

How do decomposers digest their food?

externally by secreting enzymes onto dead organisms or organic waste matter - the enzymes break down complex organic molecules into simpler molecules and the decomposers then absorb these molecules

What do decomposers release through their process of external digestion?

decomposers release stored inorganic compounds and elements back into the environment

What type of feeders are decomposers due to feeding on dead matter, externally using enzymes?

saprotrophs (same as a saprophyte)

Saprobiotic nutrition?

a form of heterotrophic nutrition where organisms feed on dead, decaying matter by secreting extracellular enzymes to break down complex molecules into simpler ones before absorbing them

Detritivores?

another class of organism involved in decomposition - help to speed uo the decay process by feeding on detritus

Detritus?

dead and decaying material

What do detritivores break down detritus into?

smaller pieces of organic material, which increases the surface area for the decomposers to work on

What type of digestion do detritivores perform?

internal digestion

2 examples of detritivores?

woodlice that break down wood, and, and earthworms that help break down dead leaves

What is nitrogen an essential element for making (2)?

amino acids (and therefore proteins) and nucleic acids in both plants and animals

What do animals obtain nitrogen from?

the food they eat

How do plants get nitrogen?

take in nitrogen from their environment

Nitrogen is abundant in the atmosphere - what percentage of the air is nitrogen gas?

78%

Chemical formula for nitrogen gas?

N₂

How many covalent bonds does Nitrogen form?

3

Due to forming 3 covalent bond, what is nitrogen’s structure like?

very stable so very unreactive

What has to happen to nitrogen in the air in order to be able to be taken up by plants and be used by living organisms?

nitrogen needs to be combines with other elements such as oxygen or hydrogen

What do bacteria play a very important role in?

converting nitrogen into a form useable by plants

Without bacteria, what would nitrogen become in ecosystems?

would quickly become a limiting factor in ecosystems

Nitrogen fixation: 2 examples of nitrogen fixing bacteria?

Azotobacter and Rhizobium

Nitrogen fixation: what enzyme does nitrogen-fixing bacteria contain?

nitrogenase

Nitrogen fixation: what does the enzyme nitrogenase combine?

atmospheric nitrogen (N₂) with hydrogen (H₂)

Nitrogen fixation: what does combining atmospheric nitrogen (N₂) with hydrogen (H₂) produce?

ammonia (NH₃) - a form of nitrogen that can be absorbed

Nitrogen fixation: where does Azotobacter live?

free-living soil bacterium

Nitrogen fixation: where does Rhizobium live?

root nodules

Nitrogen fixation: Root nodules?

growths on the roots of leguminous plants such as peas, beans and clove

Nitrogen fixation: what type of relationship does the bacteria that lives in root nodules (e.g. Rhizobium) have with the plant?

a symbiotic mutualistic relationship with the plant, as both organisms benefit

Nitrogen fixation: What does the plant gain from Rhizobium?

amino acids - which are produced by fixing nitrogen gas in the air into ammonia in the bacteria

Nitrogen fixation: what does the bacteria gain from the plant?

carbohydrates produced by the plant during photosynthesis - which the bacteria uses as an energy source

What do other bacteria then convert the ammonia that is produced by nitrogen fixation into?

other organic compounds that can be absorbed by plants

Nitrification?

the process by which ammonium compounds in the soil are converted into nitrogen-containing molecules that can be used by plants

Nitrification: what bacteria is involved?

free living bacteria in the soil called nitrifying bacteria

Nitrification: an example of nitrifying bacteria?

Nitrosomonas

Nitrification: why does it only occur in well-aerated (thoroughly supplied with oxygen) soil?

Nitrification is an oxidation reaction

Nitrification: first step - what does nitrifying bacteria oxidise?

oxidises ammonium compounds into nitrites (NO₂^-)

Nitrification: what is Nitrobacter?

another genus of nitrifying bacteria

Nitrification: second step - what does nitrobacter oxidise?

oxidises nitrites into nitrates (NO₃^-)

Nitrification: why are nitrate ions the form in which most nitrogen enters a plant?

they are highly soluble

Denitrification?

in the absence of oxygen, for example, in waterlogged soils denitrifying bacteria convert nitrates in the soil back to nitrogen gas

Denitrification: an example of where it takes place (somewhere with no oxygen)?

in waterlogged soils

Denitrification: what conditions does is only happen under?

anaerobic conditions

Denitrification: what does the bacteria use as a source of energy for respiration?

uses the nitrates as a source of energy for respiration - releasing nitrogen gas

Ammonification?

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

What is carbon a component of?

all major organic molecules present in living organisms such as fats, carbohydrates, and proteins

What is the main source of carbon for land-living organisms?

the atmosphere

What percentage of the atmosphere does carbon dioxide (CO₂) make up?

0.04%

Carbon cycle: what provides the major source of inorganic carbon for plants?

carbon dioxide in the atmosphere and dissolved in the seas and oceans

Carbon cycle: how is carbon dioxide converted into small carbon-containing organic molecules?

photosynthesis in plants and other photosynthetic organisms

Carbon cycle: through photosynthesis what is carbon dioxide in the atmosphere transferred to?

carbon-containing compounds in producers

Carbon cycle: what is the carbon-containing compounds in producers used in?

the production of macromolecules such as carbohydrates, proteins, and lipids in producers

Carbon cycle: how are carbon macromolecules passed from producers into primary consumers?

feeding - when producers are eaten

Carbon cycle: what is carbon transferred to through feeding?

carbon-containing compounds in consumers

Carbon cycle: When are these carbon macromolecules subsequently passed up the food chain?

when a consumer itself is consumed

Carbon cycle: when living organisms die, how are the carbon compounds in their bodies released?

through decomposition

Carbon cycle: when producers or consumers die what is the carbon transfered to?

carbon-containing compounds in decomposers

Carbon cycle: how is the carbon then released into atmosphere through decomposition?

the carbon is released into the atmosphere as carbon dioxide when decomposers respire

Carbon cycle: when do fossil fuels form?

if dead organic matter accumulates in areas where decomposers are not present, decomposition is prevented, and the carbon it contains may become ‘trapped’ - over millions of years these remains form fossil fuels

Carbon cycle: 2 examples of where decomposers are not present?

the bottom of oceans and bogs

Carbon cycle: what causes fossil fuels to become carbon dioxide in the atmosphere again?

combustion reactions

How do carbon dioxide levels fluctuate throughout the day?

atmospheric carbon dioxide levels are higher at night than during the day

Why are atmospheric carbon dioxide levels are higher at night than during the day?

carbon dioxide is only removed from the atmosphere during the daytime, but carbon dioxide is released at a relatively constant rate throughout the whole day

Why is carbon dioxide only removed from the atmosphere during the daytime, but carbon dioxide is released at a relatively constant rate throughout the whole day?

photosynthesis only takes place in the light (daytime), however respiration is carried out by all living organisms throughout the day and night

Localised carbon dioxide levels also fluctuate seasonally - why are carbon dioxide levels lower on a summer’s day than a winter’s day?

photosynthesis rates are higher during summer

The two main reasons for why global atmospheric carbon dioxide levels have increased significantly over the past 200 years?

the combustion of fossil fuels and deforestation

What has the combustion of fossil fuels released?

carbon dioxide back into the atmosphere from carbon that had previously been trapped for millions of years below the earth’s surface

What has deforestation removed?

significant quantities of photosynthesising biomass from Earth, resulting in less carbon dioxide being removed from the atmosphere

How does deforestation release even more carbon dioxide into the atmosphere?

in many cases the cleared forest is burnt

What does increased levels of atmospheric carbon dioxide trap more of?

thermal energy (heat) in the atmosphere

Therefore, what is the production of carbon dioxide through human activity contributing to?

global warming

What is the amount of carbon dioxide dissolved in the sea and oceans affected by?

the temperature of the water - the higher the temperature, the less gas dissolved

Due to the higher the temperature, the less gas dissolved into the oceans, what does global warming reduce?

the carbon bank in the oceans and releases more carbon dioxide into the atmosphere - further contributing to the process in a positive feedback group

To gain information how carbon dioxide atmospheric levels have varied significantly over time where are samples taken from?

deep within a glacier - when the ice formed air bubbles were trapped

Why do you take samples from deep within a glacier to learn about how the atmosphere has changed over time?

when the ice formed air bubbles were trapped within the ice - these bubbles reflect the composition of the atmosphere at this point in time and analysis of the gases present in the bubbles therefore reveals the composition of the atmosphere at this point in history

How old is the ice at a depth of 3.6km in the Antarctic glacier?

420,000 years old

What is directly related to the level of carbon dioxide present?

the temperature of the atmosphere