Nutrient Cycles

Nutrient Cycles

Nutrient Cycles - The Carbon Cycle

• the flow of energy through an ecosystem is in one direction only (it is linear)
• this is because energy enters an ecosystem as sunlight and is lost as heat, which cannot be recycled
• the sun continues to supply this energy to Earth so it is not a problem
• the flow of nutrients through an ecosystem is cyclic
• nurtients do not have an extraterrestrial source
• there is only a certain quantity of nutrients on Earth, meaning it is essential that they are re-cycled
• generic sequence for all nutrient cycles:

      * nutrient is taken up by producers as simple ionrganic molecules

      * producer incorporates the nutrient into complex organic molecules

      * nutrient passes into consumers when the producer is eaten

      * nutrient then passes along the food chin as animals are eaten by other consumers

      * saprobiotic microorganisms break down complex molecules when producers and

        consumers die, releasing the nutrient back into the soil in its original simple inorganic form

• carbon is a component of all the major macromolecules in living organisms
• the main source of carbon for living organisms is carbon dioxide in the atmospehere, yet it only makes up 0.04% of the air around us
• photosynthetic organisms remove carbon dioxide from the air for use in photosynthesis and build it up into macromolecules like carbohydrates, fats and proteins
• all living organisms return carbon dioxide to the air through respiration
• short-term fluctuations in the proportions of carbon dioxide and oxygen in the air arise due to variation in respiratory and photosynthetic rates
• carbon dioxide is present in a higher concentration at night than in the day because the absence of light at night means no photosynthesis can take place yet repiration is still occuring (at a slightly lower rate due to the drop in temperature at night)
• carbon dioxide concentrations are lower on a summer's day than on a winter's day because more light intensity in summer means photosynthesis is happening at a faster rate and so more carbon dioxide is being removed from the atmosphere
• globally, the level of atmospheric carbon dioxide has increased over the past few hundred years mainly due to these human activities:

     * combustion of fossil fuels - like coal, oil and peat. This releases carbon dioxide that was

       previously locked up within these fuels

     * deforestation - particularly of rainforests. This has removed huge amounts of

       photosynthesising biomass, meaning less carbon dioxide is being removed from the

       atmosphere

• these human activities threaten to upset the delicate balance of the carbon cycle, as they are

     causing additional production of carbon dioxide

• global warming is an additional consequence because carbon dioxide is a greenhouse gas
• the oceans contain a massive reserve of carbon dioxide. the store of carbon dioxide in the oceans is 50 times greater than in the atmosphere
• excess atmospheric carbon dioxide in the atmosphere dissolves in the waters of the oceans, helping to keep the atmospheric level more or less…