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Contents 1 Water 2 Mineral ions 2.1 Plants 2.2 Animals 2.3 Role of micro-organisms in C and N cycles 2.4 Nitrogen 2.4.1 Other sources of nitrates 3 Comments

Water

• Has important metabolic role photosynthesis, hydrolysis, osmosis.

• Acts as solvent for transport, waste removal, secretions.

• Lubricant.

• Supporting role (turgidity in plant cells).

• Temperature control.

Mineral ions

Plants

• Nitrate component of amino acids, needed for PROTEINS. If deficient causes yellow leaves and stunted growth.

• Phosphate component of nucleic acids ( DNA, RNA)and some proteins. Part of phospholipids in cell membrane. If deficient stunted growth especially of roots.

• Magnesium constituent of chlorophyll. If deficient causes yellow leaves (chlorosis ).

Animals

• Calcium main constituent of bones teeth and shells. Needed for blood clotting and muscle contraction.

• Iron needed for haemoglobin formation. Deficiency leads to anaemia.

Role of micro-organisms in C and N cycles

• Decomposers - bacteria and fungi ( saprophytes ) break down dead and decaying material (detritus, humus and waste materials). Feed by extracellular digestion - secrete enzymes onto material and products are absorbed.

Dead and decaying material contains:

• Carbon - found in all organic material. Carbon is released as carbon dioxide as a result of microbial respiration. Carbon not decomposed may form fossil fuels over time, the carbon dioxide may then be released via combustion.

Nitrogen

As proteins ( amino acids ). Also excretory products urea.

Nitrogen containing material is broken down by bacteria.

• Putrefying bacteria break down proteins and urea into ammonium compounds
• Nitrifying bacteria ( eg Nitrosomonas ) convert ammonia to nitrite.
• Nitrifying bacteria ( eg Nitrobacter ) convert nitrite to nitrate.

Denitrifying bacteria - anaerobic bacteria ( eg Pseudomonas ) found in water logged soils . Convert nitrates back into nitrogen ( released into air ).

Nitrogen fixation - Nitrogen fixing bacteria convert nitrogen in the air into ammonia. Many found free in soils. Others associated with legumes ( peas, beans, clover ) have a mutualistic relationship ( both gain from the relationship) with bacteria ( Rhizobium) found in root nodules.

Bacteria gain carbon from carbohydrates formed by plant during photosynthesis. Plants gain nitrogen from the ammonia formed by bacteria which can be used to make amino acids.

Other sources of nitrates

• Volcanic activity
• Nitrates from weathering
• Fixed by lightning
• Industrial fixation ( Haber process ) to produce inorganic fertilizers

Comments