Nutrient Cycles

Note by , created over 5 years ago

IGCSE Biology (B3 Energy Flow in Ecosystems and Human Influences) Note on Nutrient Cycles, created by ShreyaDas on 03/26/2014.

Created by ShreyaDas over 5 years ago
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Page 1

Minerals that plants need from the soil = mostly released from decayed remains of animals + plants + their waste^example of natural recyclingthere is only a limited amount of the elements that living things need and useFour of the most important things: carbon, hydrogen, oxygen, nitrogenCarbohydrates, fats and proteins are made up of carbon, hydrogen and oxygenProteins also contain nitrogen

Only way that animals and plants can continue to take in and use substances containing these elements = substances are constantly cycled around the ecosystem for reuse. 

Plants take in carbon dioxide for photosynthesisWhen animals eat plants they use some of the carbon-containing conpounds to grow and respirewaste product = breathing carbon dioxidePlants can use it Carbon Dioxide is also released:- when animal and plant remains decay (decomposition)- when wood, peat or fossil fuels are burnt (combustion)

In the past 200 years, CO2 levels have been increasing because:- burning fossil fuels (coal, oil and natural gas) which release CO2- burning peat for fuel- making concrete and cement from limestone- deforestation of tropical rain forests

There is a big reduction in soil fertility because: 90% of the nutrients in a forest ecosystem are lost as deciduous trees contain that percentage of nutrients and after those trees are cut down the nutrients are lost. soil erosion is rapid because wind and direct rain (which wasn’t possible before as the trees prevented direct and damaging rain) remove soil. It also becomes easier as the soil structure is no longer stabilised by tree root systems.  This means that it will take an even longer time for the trees to grow back, and the forest will have lost much of its vegetation and food source for the animals living in it.

The forest also goes through many climatic changes after deforestation because: a drier atmosphere and slower transpiration affects the water cycle therefore causing less rainfall rapid heat absorption by bare soil raises the temperature of the lower atmosphere in some areas which results in frequent and intense winds, which causes more soil erosion.

After deforestation, there is a higher probability of flooding and landslips because when there are lots of trees: 25% of rainfall is absorbed and/or evaporated by the foliage 50% is absorbed by the root systems Now that there aren’t enough trees to absorb all of the water there is accumulation in river valleys causing landslips and flooding.

There are changes in the recycling of materials because: the atmospheric concentration of CO2 rises as less CO2 is removed by photosynthesis. There is less O2 because less is produced by photosynthesis. O2 is vital in aerobic respiration and lower amounts of O2 results in a negative impact on the ecosystem. The atmosphere becomes drier and the soil becomes wetter because transpiration is faster than evaporation. This means that there won’t be enough oxygen for the living organisms in the forests and the increase in CO2 concentration will lead to more global warming. 

Soils do not always have enough nitrates to allow enough food to be grown to feed everybodyfertilisers are used to increase food productionproblems can occur if:- the farmer uses too much fertiliser- the fertiliser is added before a period of heavy rain

1. Leaching - fertilizers are washed into rivers and streams through the soil2. Causes weeds and algae to grow3. These plants die and rot on the river bed4. Decomposers thrive with all the dead vegetation5. Multiply rapidly and use up a lot of oxygen6. River becomes so low in oxygen that fish and invertebrates die


Carbon Cycle

CO2 Levels and Deforestation