3.3.5 Nutrient Cycles Flashcards
Natural ecosystem (not changed by human activity) nutrients are recycled through ___ ___
food webs
Many microorganisms (e.g. bacteria and fungi) are ________ (type of decomposer)
saprobionts
What do saprobionts do and what does this allow to happen?
- Feed on remains of dead plants & animals & on waste products = break them down
- Allows chemical elements to be recycled
How do saprobionts digest their food?
- Saprobionts secrete enzymes & digest their food externally, then absorb soluble molecules (nutrients) they need
- Known as extracellular digestion
What happens during extracellular digestion?
Organic molecules are broken down into inorganic ions
What is meant by saprobiotic nutrition?
Obtaining nutrients from dead organic matter using extracellular digestion
Some fungi form ___ relationships with roots of plants
symbiotic
Relationships between _____ and the ____ of _____ are known as mycorrhizae
Relationships between fungi and the roots of plants are known as mycorrhizae
Describe how fungi is connected to the plant’s roots
Fungi made up of long, thin strands called hyphae which connect to plant’s roots
What does the fungi’s hyphae help the plant to do?
- Hyphae increase SA of plant’s root system = helps plant to absorb ions from soil that usually are scare (e.g. phosphorus)
- Also increase uptake of water
Fungi obtain _______ _________ (e.g. glucose) from plants
organic compounds
Why do plants and animals need nitrogen?
To make proteins and nucleic acids (DNA & RNA)
Why can’t animals and plants use nitrogen from the air?
It’s inert
What does the nitrogen cycle show?
Shows how nitrogen is converted into usable form & then passed between different living + non-living organisms
Name the 4 stages in the nitrogen cycle
- Nitrogen Fixation
- Ammonification
- Nitrification
- Denitrification
What is occuring in nitrogen fixation?
Nitrogen gas → ammonia
Nitrogen Fixation
State the equation of nitrogen gas turning into ammonia
N2 + 6H → 2NH3
Nitrogen Fixation
Describe how nitrogen gas is converted into ammonia
Bacteria e.g. Rhizobium turns nitrogen into ammonia
Where are Rhizobium are found?
Inside root nodules (growths on roots) of leguminous plants (e.g. peas, beans)
Explain how Rhizobium forms a mutualistic relationship with plants
They provide the plant with nitrogen compounds & plant provides them with carbohydrates
Nitrogen Fixation
Name & describe 2 ways other than via bacteria that nitrogen gets into an ecosystem
- Lightining
- Fixes atmospheric nitrogen
- Artificial fertilisers
- Produced from atmospheric nitrogen on industrial scale in Haber process
Describe what occurs in ammonification
Nitrogen compounds from dead organisms + animal waste are turned into ammonia by saprobionts via decay, which then forms ammonium ions
Ammonification
How can ammonium ions (NH4+) also be produced?
Ammonia can also dissolve in water to produce ammonium ions
Describe what occurs in nitrification
Ammonium ions in soil are changed into nitrogen compounds which can be used by plants (nitrates)
- ammonium ions → nitrites
- nitrites → nitrates
Nitrification
Describe how first ammonium ions are turned into nitrites
Nitrifying bacteria (Nitrosomonas) change ammonium ions → nitrites
Nitrification
Describe how then nitrites are turned into nitrates
Other nitrifying bacteria (Nitrobacter) change nitrites → nitrates
Nitrification
State the equation for: ammonium ions → nitrites
NH4+ → NO2-
Nitrification
State the equation for: nitrites → nitrates
NO2- → NO3-
Nitrifying bacteria is known as chemoautotrophs. What is meant by this?
Called chemoautotrophs ∵ use chemical energy released from these reactions (nitrification) to live
What happens during denitrification?
When nitrates in soil → nitrogen gas by denitrifying bacteria
Why does denitrifying bacteria use nitrates?
To carry out respiration (use NO as source of O) & produce nitrogen gas
What kind of conditions does denitrification occur in?
Happens under anaerobic conditions e.g. in waterlogged soils
(Bacteria use NO as source of O ∵ of anaerobic conditions)
Why are fertilisers used?
- To replace lost minerals = more energy from ecosystem can used for growth
- = increases efficiency of energy transfer
Describe artificial fertilisers
- Inorganic
- Contain pure chemicals (e.g ammonium nitrate) as powders or pellets
Describe natural fertilisers
- Organic matter
- Include manure, compost vegetables, crop residues & sewage sludge
Explain how nutrients are lost when crops are harvested
- Crops take in minerals from soil as they grow
- When crops are harvested, they’re removed from field & ∴ don’t decompose there
- ∴ minerals ions they contain (e.g. phosphates and nitrates) = not returned to soil by decomposers in nitrogen or phosphorous cycles
Explain how nutrients are lost when animals or animal produces are removed from land
- Animal eat plants = take in their nutrients
- ∴ when removed = nutrients aren’t replaced though their remains or waste products
Name an environmental issue that occurs when too much fertiliser is used (more than the plant needs)
Leads to fertilisers leaching into water ways & thus eutrophication
What is leaching?
When water-soluble compounds in soil are washed way (e.g. by rain or irrigation systems) into nearby ponds/rivers
Explain why using artifical fertilisers are more likely to result in leaching than natural fertilisers
- Inorganic ions in chemical fertiliser = relatively soluble
- Excess minerals = not used immediately are more likely to leach into waterways
- VS natural fertilisers = nitrogen and phosphorus are contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants
- ∴ their release into soil = more controlled & leaching is less likely
Why is the leaching of phosphates less likely than the leaching of nitrates?
∵ phosphates less soluble in water
Using fertilisers also changes the balance of nutrients in the soil and can result in crops dying due to….
having too much of one nutrient
Describe how eutrophication occurs (6x)
- Mineral ions leached from fertilised fields stimulate rapid growth of algae in ponds + rivers
- Large amounts of algae block light from reaching plants below
- Eventually plants die ∵ unable to photosynthesise enough
- Bacteria feed on dead plant matter
- Increased no. of bacteria reduce oxygen concentration in water by carrying out aerobic respiration
- Fish & other aquatic organisms die ∵ not enough dissolved oxygen
What causes the short-term fluctuations in the proportions of oxygen and carbon dioxide in the atmosphere?
Variations in rates of respiration and photosynthesis
e.g. concentration of CO2 at night is greater than during the day ∵ no photosynthesis occurs, but respiration occurs
Excess CO2 in atmosphere dissolves in ____
ocean
Give an example of parts of organisms that don’t decompose. State what they form and how the carbon is returned to the atmosphere.
- Shells and bones sink to bottom of ocean and form rock such as chalk and limestone
- Carbon returns to atmosphere as rocks weather
Describe the greenhouse effect
- Sun’s radiation reaches Earth
- Some of it is reflected back & some radiated back to Earth by clouds + greenhouse gases that form part of the atmosphere
- Greenhouse gases absorb heat
- Gases trap this heat close to Earth’s surface keeping it warm
Carbon dioxide remains in the atmosphere for… ________ …other greenhouse gases
so much longer than
When is methane produced?
When micro-organisms break down organic molecules which organisms are made of:
- Decomposers break down dead remains of organisms
- Micro-organism in intestines of primary consumers (e.g. cattle) digest food that’s been eaten
Describe how the consequences of global warming could lead to loss of native species
- It’ll affect niches that are available in a community
- ∴ distribution of species will change
- Species may be able to migrate & compete for niches
- Leads to loss of native species that occupy those niches
Describe the effect of global warming on vectors/pests
Life cycles and populations of insect pests would change to adapt to changed conditions ∴ tropical diseases could spread towards poles (as they carry pathogens)
Explain how the growth of a forest results in a decrease in the carbon content of the atmosphere (2)
- Carbon dioxide taken in as a result of photosynthesis
- Carbon is incorporated into compounds in the trees
Explain why the mass of crop produced stays the same in both fields when more than 40 kg of fertiliser is added. (2)
Fertiliser added is sodium nitrate.
- Plants already have enough nitrate / nitrate no longer limiting
- Another named factor is limiting growth e.g. light intensity
Explain how the change in global mean temperature could decrease the yield of crop plants. Name 4 reasons. (4)
- Increased temperature could decrease yield ∵ not optimum for enzyme action
- Increase rate of transpiration
- Increased prediation by insect pests
- Unpredicated effects on rainfall
It is estimated that, each year, a total of 3 × 109tonnes of ammonia are converted to nitrate. Only 2 × 108 tonnes of ammonia are produced from nitrogen gas. Explain the difference in these figures. (2)
- Ammonia formed by decay
- On nitrogenous waste / nitrogenous compounds
