NUTRIENT CYCLING

NUTRIENT CYCLING

At the end of the lesson, students should be able to:
Describe how carbon circulates in nature.
Draw the carbon cycle in detail.
State why the carbon cycle is used necessary for life.
Recognize the delicate balance between carbon and oxygen.
Describe the role played by plants and animals in water cycle.
Draw the water cycle in detail.
Describe with the aid of diagram the role of nitrogen.
State that energy can be obtained by decomposing organic substances.
Identify one of the gases produced during decay.


Nutrient Cycling
Nutrient cycle or ecological cycle is the movement and exchange of organic and inorganic matter back into the production of living matter. It occurs within ecosystem, since energy flow is unidirectional hence, the movement of mineral nutrients should be cyclic. Mineral cycles include: nitrogen cycle, water cycle, oxygen cycle, sulphur cycle e.t.c.

Carbon Cycle
Carbon cycle involves the series of processes in which carbon is continuously being removed from and added to the carbon dioxide in the atmosphere and the ocean.
Process of carbon cycling

The processes of carbon cycling include:
Removal (or absorption) of carbon from the air and water;
Addition of carbon into the air.

Removal (or absorption) of carbon from the air and water:

Photosynthesis: carbon dioxide is removed from the air (atmosphere) by photosynthesis during which plants use it to manufacture their food.
Leaching and drainage: Carbon is lost in form of carbonates of calcium and magnesium through leaching and drainage.

2.   Addition (or returning) of carbon into the air (atmosphere) and water:

Combustion: burning of fossil fuel like coal and and other crude oil, and wood are sources of carbon into the air.
Respiration: The release of gas during exhalation and fermentation send carbon out in form of carbon dioxide.
Decomposition: The death of all organisms bring about decay, and this results in release of  locked up carbon as carbon dioxide.
Diffusion of carbon dioxide from seas and other bodies of water acting as reservoir of carbon dioxide.
The action of volcanoes (i.e. volcanic eruption)which releases carbon dioxide.

Importance of carbon cycle in nature
Plant uses carbon dioxide obtained from the air to produce their food.
It is the major block of all organic matter.
It helps to purify the atmosphere and maintain atmospheric level of carbon dioxide.
Organic matter which is made from carbon helps to replenish soil nutrient.

Oxygen Cycle
Oxygen cycle involves the circulation of oxygen between the living organism and the non living things.

Process of oxygen cycle

The process of oxygen cycling include:
Removal/ or absorption of oxygen from the air and water;
Addition of oxygen into the air.

1. Removal of oxygen from the air and water:

Respiration in both plant and animal;
Combustion of fuels;
Decay of dead organic matter.

2.    Addition of oxygen into the air and water:
Photosynthesis.
Note: Oxygen cycle is the carbon cycle in reverse!

Importance of oxygen cycle in nature

It brings about life sustenance.
It makes carbon dioxide readily available for photosynthesis.
It purifies the air by avoiding pollution.
Oxygen cycle, if not altered, ensures balance in nature.
Carbon-Oxygen Balance
Many human activities increase the level of carbon dioxide, while oxygen is left at a very low pace.

Such activities that deplete oxygen level in the atmosphere include:

Deforestation;
Combustion of fuel;
Overpopulation which increases respiration rate;
Decay of many dead animals through war, and other means;
Burning of bush indiscriminately.

 If the activities mentioned above are not checked, they result into the following:

Climate change which could affect the important food-growing areas of the world. Hence, this result in food shortage;
Death of many aquatic organisms e.g. fish.
Greenhouse effect (i.e. an increase in the retention of the sun's radiant energy)
Global warming (i.e. an average increase in the earth's temperature which in turn causes changes in climate) which may result in melting of the polar ice-caps with a related rise in sea level.

Suggested solution to maintain a balanced carbon-oxygen level.

Limiting the use of land fill sites to reduce production of greenhouse gases such as methane, carbon dioxide, sulphur dioxide etc;
Limiting deforestation and encourage afforestation;
Exhaust fumes of vehicles should be properly checked to ensure that carbon dioxide and other gases are emitted are reduced;
Education and enlightenment on the effect of man's activities that alter oxygen level;
Birth control measure should be adopted to discourage overpopulation;
Production of chlorofluorocarbons must be discouraged.



Water Cycle
Water cycle is the continuous movement of water from the atmosphere to the earth and from the earth to the atmosphere.

Process of Water Cycling in Nature

The process of water cycling include:

Removal/ or absorption of water from the air;
Addition of water into the air.

1. Removal of water from the air/atmosphere involves all forms of processes in which land receives water. These processes include:
Rainfall or precipitation.
Infiltration and percolation.

2.   Addition of water into the air/atmosphere include all processes in which the atmosphere receives water. These processes include:
Evaporation from oceans, seas, rivers and land (e.g. from decay, excretory wastes, run off water etc)
Transpiration from plants.
Breathing or respiration by plants and animals.

Importance of water (cycle) to living organisms.

Maintains osmotic content of body.
Medium of transport of nutrient for both plant and animal.
Required for seed germination.
Provides medium for absorption of mineral salts by plants.
Aids excretion of waste products.
Provides a natural habitat for aquatic organisms.
It is an essential raw material in the process of photosynthesis.
Regulates body temperature i.e. thermoregulation.
It acts as a solvent for soluble food substances in digestion of food.

EXPERIMENT 1
Aim: To show the absorption of carbon dioxide and release of oxygen during photosynthesis.
Materials required: three beakers, test tubes, funnels, water plants, glowing splint.


Method: set up three set of apparatus as shown above. Distilled water is put in A, B, and C and then filled with water saturated with carbon dioxide.
Place C in a dark cupboard and A in bright sunlight and B in dim light until some gas has collected in one of the test tubes.
Test the gas in the test tube with a glowing splint, to find out if it is oxygen.
Observation: (tabulate your observation as shown below)


From this table, using glowing splint to test the presence of oxygen, it is observed that flask  C did not produce oxygen while flasks A and B produced oxygen.
Conclusion: The experiment simply shows that carbon dioxide and sunlight are required by plants🌿 during photosynthesis and during the process, oxygen is released to the environment.

EXPERIMENT 2
Aim: To show that water is given off during transpiration.
Materials required: Two polythene bags, two bell jars, anhydrous white copper II tetraoxosulphate VI, two potted plants (with one having its stem cut) and crucible.

Method: Place the copper II tetraoxosulphate VI (CUSO4) in a crucible along with the potted plant, covering the soils with the polythene bag. Repeat same with the control. Cover the white anhydrous copper II tetraoxosulphate VI with bell jars.
Observation: The white anhydrous copper II tetraoxosulphate VI in the main experiment turns blue while the control did not change colour.
Conclusion: The change in colour is due to the water given off during transpiration through the leaves.
Class work.
Using experiment 2 above, explain why;
the pot is enclosed in a transparent polythene bag;
the stem above the soil is smeared with a layer of vaseline.

Nitrogen Cycle                            
The nitrogen cycle is the pathway along which nitrogen moves through living and non-living components of the ecosystem to continuous uses.

Process of Nitrogen Cycling in Nature

1. Removal of atmospheric nitrogen: This is conversion of gaseous nitrogen into nitrates. This occurs in the following ways:

Nitrogen fixation by some free bacteria: Some bacteria can convert free atmospheric nitrogen in the soil to produce nitrates. Examples are  Azotobacter, Clostridium and Rhodospirillum.
Nitrogen fixation by symbiotic bacteria: Some bacteria have symbiotic association with roots of some leguminous plants ( such as groundnuts, beans, Crotalaria). They form nodules in which atmospheric nitrogen is converted to nitrates and absorbed by by the plant to form proteins. Example is Rhizobium leguminosarium.
Note: The Rhizobium bacteria are not capable of fixing nitrogen if they are free from leguminous roots.
Action of blue green algae: The blue green algae are capable of converting/fixing atmospheric nitrogen into nitrate. Examples are Anabaena and Nostoc.
Electrical discharge: During thunderstorms, the lightening produced causes the atmospheric nitrogen to combine with oxygen to form nitrogen (II) oxide i.e. N2 + O2 →2NO. The nitrogen (II) oxide reacts with oxygen to form nitrogen (IV) oxide i.e. 2NO + O2→ 2NO2. The nitrogen (IV) oxide reacts with rain water to form a weak solution of trioxonitrate (V) acid and dioxonitrate (III) acid i.e. 2NO2  + H2O → HNO3 + HNO2 . When this weak acid reaches soil, it combines with mineral salts in the soil to form nitrates which the plants absorb.
Putrefaction: The death of plants and animals releases protein into the soil. These proteins are converted by bacteria into ammonium compounds. The ammonium is therefore converted into nitrite by the genus of Nitrosomonas bacteria, then by those of the genus Nitrobacter into nitrates. The nitrates are absorbed by plants through their roots.

Note:
The bacteria converting protein into ammonia are called putrefying bacteria and the process is known as ammonification, while those converting/oxidizing ammonia to nitrites and nitrates are collectively called nitrifying bacteria and the process is called nitrification.
Application of farmyard manure/organic fertilizers/green manure also add nitrogen into the soil, but at the same time ammonification and nitrification end the reaction.

2. Addition of nitrogen into the atmosphere: This involves conversion of soil nitrates to gaseous nitrogen. This occurs through:
Denitrification: Some bacteria convert ammonia, nitrites or nitrates into free nitrogen which escapes into the atmosphere. This process is called denitrification. Example of denitrifying bacteria include Pseudomonas denitrificans.
Note:
Nitrogen is lost from the soil through the following:
Action of denitrifying bacteria;
Absorption by plant roots;
Action of leaching.


Decomposition in Nature
A decomposer is an organism that breaks down dead organisms or wastes of plants and animals into simpler substances and obtaining energy in the processes. Such organism is a saprophyte and feeds saprophytically i.e. undergoes saprophytic nutrition. Examples include all the fungi (e.g mushroom, Mucor) and some bacteria, others are earthworm, termite.
Classes/types of decomposer:
Micro-decomposers: They are tiny, and cannot be seen with the naked eyes. Examples are certain bacteria and some fungi
Macro-decomposer: they can be easily seen with the naked eyes. Examples are mushrooms, toadstools, mould, termite, earthworms, snails.

Process of Decomposition
The decomposer come on the dead matter/organism; secrete a lytic enzyme which breaks down the complex organic (e.g. proteins and carbohydrates) components into simpler and soluble inorganic (e.g. ammonia gas, hydrogen sulphide gas, carbon dioxide, water vapor and salts like phosphates, sulphate, nitrates, and potassium ions) components/compounds. The salts released are leached into the soil for plants use, while the carbon dioxide released is used for food manufacturing. The decomposer also make use of the nutrients and the energy released in form of heat. When the plant dies, the nutrients absorbed are returned back into the soil and the decomposer re-use it. This use and re-use is called recycling. When the decomposer dies, another decomposer feeds on it and utilize its energy as well for itself and other living organisms e.g. plants.


Roles of Decomposers in Ecosystem
They enrich the soil with nutrients which is used by plants for anabolism.
They cause nuisance and pollute environment when they are present in large numbers.
They are useful in the production of some economic products such as cheese and yoghourt.
They purify the environment through their cleaning activities.
They prevent accumulation of wastes which may be dangerous to our lives.
They maintain a steady supply of useful materials to the producers and the consumers.
Production of fuel e.g. biogas (produced from methane and carbon dioxide formed during decomposition).

EXPERIMENT 3

Aim: To show that carbon dioxide is released during decomposition.
Materials required: two test tubes, delivery tube, decaying humus, lime water.
Method: set-up two experiments; test experiment and control experiment. Label the test experiment as set-up A, while the control experiment is labeled as set-up B. In set-up A, add humus in the test tube as shown below, while in set-up up B, do not add humus. The whole experiment is allowed to stand for about 4-6 hours.
Observation: It is observed that the lime water in set-up A turns milky, while that of set-up B remains the same.
Conclusion: Since the lime water turns milky, it shows that carbon dioxide is released during decomposition.
Note: Hydrogen sulphide (a product of decomposition) can be identified by smell. It smells like a rotten egg.
Assignment.
Describe an experiment to show that heat is released during decomposition.
Construct a detritus food chain.
Discuss the statement: "The movement of energy through an ecosystem is unidirectional but the movement of nutrients is cyclic.