5.4- nutrient cycles

what are two nucleic acids?

which two other organic compounds always contain nitrogen?

why will lack of nitrogen lead to stunted growth?

DNA, RNA

amino acids, proteins, ATP/ADP

can’t produce proteins needed for growth

What are the four main stages of the nitrogen cycle?

1) Nitrogen fixation

2) Ammonification

3) Nitrification

4) Denitrification

What is nitrogen fixation?

what are the two types of bacteria?

examples of legumes?

Nitrogen fixing bacteria convert nitrogen gas in the atmosphere to ammonia (then into ammonium ions), using a reduction reaction catalysed by enzyme nitrogenase 

bacteria is either free living or soil they are symbiotic (mutualistic relationship)- living in root nodules of plants e.g legumes

peas/clover

why is there a symbiotic relationship between legumes and bacteria?

Legumes provide glucose/proteins/DNA for bacteria, whilst bacteria provides nitrogen containing compounds e.g ammonium 

mutually benefiting

what is the equation for nitrogen fixation?

N₂ → NH₃ → NH₄⁺

What is ammonification? 

Saprobionts e.g bacteria/fungi decompose dead, organic material and convert the organic nitrogen found organic compounds into ammonia, then into ammonium compounds in the soil

What are saprobiotic microrganisms and how do they cause decay? 

Bacteria that carry out extracellular digestion by secreting enzymes and digesting nitrogen containing compounds externally 

Absorbs products of digestion and use them e.g ammonia, but some are released back into the atmosphere 

what is the equation for ammonification?

Organic nitrogen → NH₃  → NH₄⁺

What is nitrification?

how do plants take up nitrogen?

1) Nitrifying bacteria convert ammonium ions into nitrites, then into nitrates (oxidation reactions)

Releases energy which they use for the synthesis of organic molecules e.g carbohydrates

Aerobic conditions

2) Plants take up nitrogen from the soil in the form of nitrates through their roots by active transport 

what is the equation for nitrification?

NH₄⁺ → NO₂^-  → NO₃^-

What are phototrophs?

Green plants use light energy to synthesise organic matter

What are chemoautotrophs? 

Some bacteria oxidise chemical compounds e.g nitrites to release energy they need to synthesise organic matter

What is denitrification?

Dentrifying bacteria convert nitrates into nitrogen gas (reduction reaction)

Anaerobic conditions

This occurs in water logged soil, so it can be aerated/drained/ploughed

what is the equation for denitrifcation?

NO₃^- → N₂

inorganic nitrogen is taken by plants from the soil in what form?

what is it used to synthesise?

nitrates

nitrogen-containing organic molecules e..g proteins or DNA

Which organisms consume nitrogen in living plant material? 

Primary consumers, herbivores and omnivores 

Which types of organisms consume nitrogen in dead plant and animal material? 

Saprobionts 

Which types of organisms consume nitrogen in living animals? 

Secondary/tertiary consumers, carnivores and omnivores 

Why do crops grown with mycorrhizhae have more growth? 

Due to their hypnae which increase surface area- more water uptake and absorption of nutrients needed for growth 

Why are fertilisers used? 

To replace the lost mineral ions and maintain crop productivity

What are the most important inorganic ions found in fertilisers, and which biological molecules are they needed for?

Nitrates (needed for proteins and nucleic acids)

Phosphates (needed for phospholipids, nucleic acids and ATP)

Potassium 

What are the advantages of natural fertilisers?

Useful, cheap means of disposal of farm waste

Adds humus to soil- improve structure and drainage

Nutrients not readily leeched

What are the advantages of artificial fertilisers?

Nutrients concentrated form- can be applied in smaller amounts- makes it more cost effective

Nutrients readily released into soil 

Clean chemicals that lack odour 

What are the disadvantages of natural fertilisers?

Minerals may be released quickly

May be difficult/require heavy machinery to spread 

Unknown quantities/concentration of nutrients 

What are the disadvantages of artificial fertilisers?

Readily leeched from soil,can damage ecosystems of ponds/lakes

Risk of fertiliser spray spreading to other areas 

Expensive to buy/manufacture 

Why will there be reduced species diversity?

what do they compete for?

why would this lead to fewer species of animals?

Fertilisers increase growth of species e.g nettles. These rapidly growing species outcompete many other species, which die as a result 

They compete for light, mineral ions and water 

There will be a reduced variety of food and animals

What is leaching? 

Rainwater will dissolve any soluble nutrients e.g nitrates and wash them out of the soil 

The leached nitrates find their away into watercourses, e.g streams and rivers 

This then causes eutrophication 

What is eutrophication? 

In most rivers and lakes, there is naturally very little nitrates- limiting factor for plant and algal growth 

Rapid algal growth 

Absorbs light and prevents it from reaching the plants below the surface- cannot photosynthesise and die 

When the plants die, they are decomposed by saprobionts, which use the oxygen in water to respire aerobically

This decreases oxygen concentration in water, therefore organisms aren’t able to respire and die