A2 – Assignment (20 points) essay

Chapters 23-24

1. Briefly describe the following cycles:

  • Carbon cycle

Carbon is the main constitute of living things. Carbon is also foundplentifully in air, dissolved in water and in soil and rocks. Carboncycle refers to transformation and circulation of carbon in thebiosphere. Carbon is found abundantly in the air in the form ofcarbon dioxide. By using sunlight energy, plants convert carbondioxide into plant tissues through photosynthesis. Some of theseplants are eaten by animals, converting the plant carbon into animaltissues. When plant and animals die, their remained are buried andconverted into fossil fuels. Carbon dioxide is released back into theatmosphere through burning of fossil fuels. Carbon dioxide is alsoproduced by animals and plants through respiration (Weathers, 2012).

  • Nitrogen cycle

Nitrogen exists in the atmosphere in the form of nitrogen gas. Italso exists in the biosphere in the form of nitrates or ammonia.Nitrogen is a major constitute of proteins in living systems. Throughthe process of fixation, both industrial and biotic, nitrogen gas isconverted into nitrates which are absorbed by plants and microbes.Nitrogen can also be converted into nitrates through the action oflightning. The plant protein is converted into animal proteins. Whenplants and animals die, the proteins are converted into ammoniathrough the process of decay. The ammonia is converted into nitratesand back to nitrogen gas by nitrifying bacteria and denitrifyingbacteria respectively (Weathers, 2012).

  • Phosphorus cycle

Phosphorus is an important nutrient in both plants and animals. Itexists in the biosphere in the form of organic phosphates in livingtissues and inorganic phosphates on rocks. Inorganic phosphates areabsorbed from the soil by plants and converted into organicphosphates. The plant phosphates are converted into animalphosphates. The organic phosphates are later converted into inorganicphosphates in soils and oceanic sediments after the death of livingsystems. Inorganic phosphates are also released from rocks through aprocess called weathering or industrial processes in the manufactureof phosphate fertilizers (Weathers, 2012).

  • Water Cycle

Water exists everywhere in the biosphere,and therefore, the watercycle has no starting point. Water is found abundantly in oceans andother water bodies. Due to solar energy, water in the oceansevaporates into the atmosphere. Water also reaches the atmospherethrough evaporation from the earth surface and evapotranspiration.After condensation, water vapor reaches the earth surface throughprecipitation. Water from precipitation is converted into groundwaterthrough infiltration. Groundwater is stored, reaches the earthsurface through seepage and springs or uptake by plants. Stream fromsurface runoffs, springs, seepage and snow melt flows back to theoceans and other large water bodies (Weathers, 2012).

2. Describe the greenhouse effect.

It is a process through whichradiations from the earth surface warms the earth’s atmosphere. Asthe earth surface receive heat energy from the sun, some of the heatenergy is absorbed by the earth surface while the rest is reflectedback into space. Greenhouse gases keep the earth surface warm bytrapping some of the energy released into space (Weathers, 2012).

3. Define or otherwise explain the following terms:

  • Ecological footprint: refers to the impacts of human activity on the ecosystems or biosphere.

  • Global hectares: represents the average productivity of an ecosystem and is used to measure biocapacity and ecological footprint.

  • Biocapacity refers to the ability of a ‘biologically productive’ area to supply enough natural resources and absorb the excess supplies such as carbon dioxide.

  • Sustainability: refers to the ability of a system to endure and remain productive and diverse for an indefinite period of time (Weathers, 2012).

4. List and describe five different steps you can take to live moresustainably.

  1. Use of renewable sources of energy to reduce carbon footprint.

  2. Recycling of waste.

  3. Protection of endangered species.

  4. Sustainable agricultural activities.

  5. Preservation of biological diversity.


Weathers, K. (2013). Fundamentalsof ecosystem science.Boston: Academic Press/Elsevier.

Yadav, M. (2003). Ecology.New Delhi: Discovery Publishing.