Nutrient Cycling In Nature: Carbon cycle, Water cycle and Nitrogen cycle

CONTENT  

• Definition
• Carbon Cycle

·         Process of Cycling

·         Importance of Carbon

·         Carbon-oxygen balance

Meaning

Nutrient cycling refers to the movement of certain nutrients like nitrogen, carbon, water, oxygen and other elements from the environment into various organisms and back into the environment. The path along which the atoms or elements pass is called a cycle. The popular well known nutrients cycles are nitrogen cycle, carbon cycle, water cycle and decomposition in nature.

Carbon Cycle

Carbon Cycle is the cycle of carbon usage by which energy flows through Earth’s ecosystem. The basic cycle begins when photosynthesizing plants use carbon dioxide (CO₂) found in the atmosphere or dissolved in water.

The atmosphere gains carbon dioxide through:

1.    Combustion of organic materials such as coal, wood and petroleum

2.    The action of volcanoes which releases carbon dioxide

3.    The respiration by plant and animals

4.    The death, decay and putrefaction of plants and animals

5. Diffusion of carbon dioxide from seas and other bodies of water acting as reservoir of carbon dioxide

Evaluation

1. Define carbon cycle.
2. Mention three ways atmosphere gain carbon dioxide.

Importance of Carbon in Nature   

1. Plant uses carbon dioxide obtained from the air to manufacture their food during photosynthesis.
2. It provides carbon which is the major building block of all organic matter.
3. It helps to purify the atmosphere and maintain atmospheric level of carbon dioxide
4. Organic matter which is made from carbon helps to replenish soil nutrient.

CARBON-OXYGEN BALANCE

Oxygen constitutes 21% of the gases in the atmosphere. Respiration, decay and combustion are the processes which remove oxygen from the atmosphere while photosynthesis is the process that releases oxygen into the atmosphere. Human activities such as deforestation lead to the release of less oxygen into the atmosphere while less carbon dioxide is removed from atmosphere. Increase in the combustion of fuel, respiration and decay leads to the removal of more oxygen from the atmosphere while more carbon dioxide is added As a result of the activities mentioned above, oxygen level in the atmosphere decreases while carbon dioxide level increases. A decrease in the atmospheric oxygen level by 2-8% do not cause any significant effect but a slight increase in the atmospheric carbon dioxide may cause green house effect, i.e., increase in-the retention of the sun’s radiant (heat) energy. This result in the warming of the atmosphere of the earth. So to prevent this, there is the need to balance the carbon-oxygen level in the atmosphere.

EVALUATION

1. What is the importance of carbon?

2. Explain carbon-oxygen balance.

Water Cycle

Definition: Water cycle is the continuous movement of water from the earth to the atmosphere by evaporation, transpiration and perspiration and back from the atmosphere to the earth by precipitation.

Process of Water Cycling in Nature                               

The solar energy causes water to evaporate from the hydrosphere into the atmosphere. When the water vapour cools, it condenses. At high altitude, the condensed water form clouds. The clouds precipitate as rain returning to the hydrosphere.

Evaluation

1. Define water cycle.

2. State the major processes that bring about water cycle.

Importance of Water to plants

Water is very important to living organisms, both plants and animals, in number of ways:

• Water provides the medium for absorption of dissolved mineral salts by plants.
• Water is an essential raw material in the process of photosynthesis.
• It acts as a medium of transport for plants nutrients.
• It maintains osmotic content of body tissues.
• Water is the main component of plant protoplasm.
• Water is required for germination.

Importance of Water to animal

• It acts as a solvent for soluble food substances in digestion of food.
•  it constitutes a large portion of the blood.
• Water aids excretion-of waste products by animals.
• Water regulates body temperature.
• Water provides a natural habit for aquatic organisms.

General Evaluation

1. Mention three processes that involve carbon.

2. Mention three importance of water to animals.       

3. Explain the following terms: Hypertonic, Hypotonic and Isotonic solution.

4. Outline the process of water cycle in nature.

5. List the constituents of air in nature.

Reading Assignment

College Biology by Idodo Umeh. Chapter 23, page 553-555

WEEKEND ASSIGNMENT

1. Which of the following processes removes water from the water cycle? (a) Condensation (b) Perspiration (c) Photosynthesis (d) Transpiration.

2. What type of energy causes water to evaporate from the hydrosphere (a) mechanical  energy (b) chemical energy (c) solar energy (d) hydro-electric power.

3. Water is returned to the atmosphere from animals through the following processes except (a) excretion (b) respiration (c) condensation (d) perspiration.

4. When organisms die, water returns to the atmosphere by (a) decay (b) sweating (c) respiration (d) condensation.

5. Atmosphere gains carbon through the following processes except (a) Photosynthesis (b) Decay (c) Respiration (d) Volcano

THEORY

1. Water is essential for living organism, discuss.

2. Describe the process of carbon cycling in nature.

NITROGEN CYCLE

CONTENT

• Definition
• Process of cycling
• Importance of Nitrogen
• Decomposition in nature
• Types of decomposers (Micro and Macro decomposers)
• Roles of decomposers

Nitrogen Cycle

Nitrogen is an abundant element in the atmosphere. It is an essential constituent of proteins, a group of substances found in all living cells. About 78% of air is composed of gaseous nitrogen. Plants cannot incorporate nitrogen gas into organic compound and therefore depend on various types of bacteria to make nitrogen available for them in a global cycle called the nitrogen cycle. In nature, nitrogen is constantly being removed from the soil and returned to it via the nitrogen cycle.

Conversion of Gaseous Nitrogen into Nitrogenous Compounds

Gaseous nitrogen is converted into nitrates in the following ways

1. The action of thunderstorms
2. Nitrogen-fixing microorganisms

During thunderstorms, nitrogen reacts with oxygen to form nitric oxide. The nitric oxide is oxidized to nitrogen peroxide which dissolves in rainwater to form nitric nitrous acids.  When these acids enter the soil, they combine with mineral salts to form nitrates. The nitrates then dissolve in soil water and are absorbed by the plants. These nitrates are converted into plant proteins and become part of the plant body (assimilated). The organisms capable of splitting the nitrogen molecule and use it to form nitrites or nitrates is known as nitrogen fixation. Some microorganisms are able to change gaseous nitrogen directly into proteins.

Types of Nitrogen-fixing Microorganism

1. Free living organism.
2. Symbiotic organism.

Azotobacter and Clostridium are free living bacteria. They are able to absorb nitrogen from the atmosphere and change it into amino compounds and proteins. Energy needed for these processes is obtained from the breakdown of carbohydrates in humus. Symbiotic bacteria like the Rhizobium which are found in the root nodules of leguminous plants use gaseous nitrogen to manufacture amino compounds and proteins which they share with the host plants. These bacteria get the energy needed for nitrogen fixation from the breakdown of carbohydrates in the host’s tissues. When the host plants die, the amino compounds and proteins in the root nodules are converted to soil nitrates.

Evaluation

1. What is nitrogen cycle?

2. Explain the types of nitrogen fixation.

Putrefaction: Plants are the food producers in nature; animals feed on plants and convert plant proteins; to animal proteins. When these animals are eaten by carnivorous animals, more animal proteins are formed. Proteins are decomposed through amino acids to ammonia when an organism dies. The nitrogen that is trapped in the bodies of all these living organisms re-enter the nitrogen cycle through putrefaction or decay. When living organisms die, they decay and the excretory product also decays.

Ammonification: The putrefying bacteria and fungi are responsible for decay. These saprophytic organisms convert plant and animal materials into simple substances like carbon dioxide, water, and ammonia. This breakdown of protein into ammonia is known ammonification.

Nitrification: Animal wastes and excreta are decomposed and the chemosynthetic bacteria then oxidize ammonia to nitrites and the nitrites are converted to nitrates by nitrifying bacteria. This process is called nitrification.

Denitrification: Denitrifying bacteria in the soil convert nitrates into gaseous nitrogen which escapes into the atmosphere. This reduces the nitrogen content and fertility of the soil.

Evaluation

1. What is nitrification?

2. Explain denitrification.

Decomposition in Nature

Decomposition is the process by which organisms, mainly bacteria and saprophytes break down dead organic materials which could be of plant or animal origin.

Types of Decomposers 

1. Micro decomposers: These are small or microscopic organisms that can cause decay e.g. certain bacteria and fungi.

2. Macro decomposers: These are bigger organisms that can cause decay of dead organic materials e.g. earthworms, termites, snails, mushroom, toad stools, etc.

Process of Decomposition

The decomposers secrete enzymes onto their food source such as a decaying dead organisms. These enzymes break down complex organic compounds (food) like carbohydrates into simple soluble inorganic Compounds. A lot of the chemical energy in the compounds Is lost as unstable heat energy. The decomposers only absorb a small amount of nutrients and energy for their use. The rest is released into the soil, air and water. When decomposers die, other decomposers feed on them, the nutrient released  are used by plants to manufacture their food. Products released during decomposition are gases such as carbon dioxide, hydrogen sulphide, ammonia and water vapour. Others are heat energy and nutrients such as nitrates, sulphates, phosphate, ions, etc.

Role of Decomposers

1. They enrich the soil with nutrients required for plant growth.

2. They contribute to environmental pollution.
3. Decomposition is useful in the making of cheese and yoghurt.
4. They allow the ecosystem to function by enabling the recycling of nutrients.
5. They also prevent an unsightly accumulation of remains and wastes of living organisms on earth surface.

General Evaluation

1. Write on the two types of decomposers.

2.  State the roles of decomposers.

3. What is autotrophic nutrition?

4. List the two modes of autotrophic nutrition.

5. Differentiate between the two modes listed above.

Reading Assignment

College Biology by idodo Umeh. Chapter 23, page 556-558

WEEKEND ASSIGNMENT

1. Legumes incorporate nitrogen gas into their proteins because (a). of the presence of Azotobacter in their roots (b) they posses root nodules containing Rhizobium (c) they have a well developed root system (d) they are autotrophic.
2. Thunderstorm can be beneficial to plants because (a) it kills the pest that attacks crops (b) it destroys some of the major crops (c) it adds nitrate to the soil (d) it makes rain water available to plants.
3. Which of the following is responsible for the conversion of nitrites to nitrates?(a) Denitrifying bacteria (b) Nitrifying bacteria (c) Lightening (d) Fungi.
4. Which of the folloowing is a nitrifying bacterium? (a) Nitrobacter (b) Rhizobium (c) Azotobacter (d) Nitrosomonas.
5. Bacteria inhabiting legume root nodules and which add atmospheric nitrogen to the soil are referred to as (a) denitrifying bacteria (b) nitrifying bacteria (c) nitrogen-fixing bacteria (d) nitrogen putrefying bacteria.

     THEORY

1. Explain the types of nitrogen fixing mechanisms.
   1. Explain the following a. Nitrification b. Ammonification.