Lesson Notes By Weeks and Term v3 - Senior Secondary 2
Nutrient Cycling in Nature
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Nutrient Cycling in Nature
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Subject: Biology
Class: Senior Secondary 2
Term: 1st Term
Week: 5
Theme: The Organism And Its Environment
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Describe howcarbon circulates in nature. Draw the carboncycle in detail. State why the carbon cycle is necessary for life. Recognise the delicate balancebetween carbonand oxygen. Describe the partplayed by plantsand animals in the water cycle. Draw the water'cycle in detail. Describe With the aid of diagram the role of nitrogen. State that energy can beobtained by decomposingorganic substance Identify one of the gasses produced duringdecay.
releases O
2. Respiration by organisms (and combustion) removes O2 and releases CO
2. This continuous exchange maintains a relatively stable concentration of both gases in the atmosphere, essential for life.
Disruption: Increased combustion of fossil fuels (e.g., from industrial activities and vehicles in Nigerian cities) and deforestation (e.g., logging in rainforests) release excessive CO2, tipping the balance, leading to enhanced greenhouse effect and climate change, characterized by rising temperatures, altered rainfall patterns, and extreme weather events, which can affect agriculture and lead to desertification in the north or flooding in the south of Nigeria. B. The Water Cycle (Hydrological Cycle) The water cycle describes the continuous movement of water on, above, and below the surface of the Earth.
Parts Played by Plants and Animals: Plants: Absorption: Plants absorb water from the soil through their roots.
Transpiration: Water vapor is released into the atmosphere from plant leaves through stomata. This is a significant contributor to atmospheric moisture.
Example: A vast expanse of cassava farms in Benue state transpires huge amounts of water into the atmosphere daily.
Animals: Ingestion: Animals drink water directly or obtain it from their food.
Respiration: Animals release water vapor as a byproduct of cellular respiration into the atmosphere.
Excretion: Animals excrete water as urine, sweat, or feces, which eventually returns to the environment.
Example: A herd of cattle near a watering hole in Sokoto drinks water and later excretes urine, returning water to the soil. Detailed Water Cycle Diagram (Teacher should illustrate or use a chart): Components: Oceans, Lakes, Rivers, Groundwater, Atmosphere (Clouds), Land Surface, Plants, Animals.
Arrows/Processes:
1. Evaporation: Solar energy heats water bodies (oceans, lakes, rivers), turning liquid water into water vapor, which rises into the atmosphere.
Example: Water evaporating from the surface of the River Niger.
2. Transpiration: Water vapor released from plants into the atmosphere.
3. Condensation: As water vapor rises, it cools and changes back into tiny liquid water droplets or ice crystals, forming clouds.
4. Precipitation: When clouds become saturated, water falls back to Earth as rain, snow, sleet, or hail.
Example: Rainfall over Calabar during the rainy season.
5. Collection/Runoff: Precipitation that reaches the ground can flow over the surface as runoff into rivers, lakes, and eventually oceans.
6. Infiltration/Percolation: Some water seeps into the ground to become groundwater, which can be stored in aquifers or move slowly through the soil to replenish water bodies.
Example: Rainwater seeping into the ground to recharge boreholes in a community. C. The Nitrogen Cycle Nitrogen is an essential element for all life, forming a key component of proteins, nucleic acids (DNA and RNA), and ATP. Atmospheric nitrogen (N2) is abundant but in a form unusable by most organisms. The nitrogen cycle converts atmospheric nitrogen into usable forms and recycles it.
Role of Nitrogen: Essential for building proteins, enzymes, chlorophyll (in plants), and genetic material. Detailed Nitrogen Cycle Diagram (Teacher should illustrate or use a chart): Components: Atmospheric Nitrogen (N2), Nitrogen-fixing bacteria (in soil, root nodules of legumes), Nitrifying bacteria, Denitrifying bacteria, Plants, Animals, Decomposers (Ammonifying bacteria).
Stages/Processes:
1. Nitrogen Fixation: Conversion of atmospheric N2 into ammonia (NH3) or ammonium (NH4+).
Biological Fixation: Carried out by nitrogen-fixing bacteria (e.g., Rhizobium in legume root nodules like groundnut or cowpea, and free-living bacteria like Azotobacter in soil).
Atmospheric Fixation: Lightning provides energy to convert N2 and O2 into nitrogen oxides, which dissolve in rain to form nitrates.
Industrial Fixation: Human activities (Haber-Bosch process) produce synthetic fertilizers.
2. Nitrification: Conversion of ammonia/ammonium to nitrites (NO2-) by nitrifying bacteria (Nitrosomonas). Conversion of nitrites to nitrates (NO3-) by other nitrifying bacteria (Nitrobacter). Nitrates are the primary form of nitrogen absorbed by plants.
3. Assimilation: Plants absorb nitrates (and sometimes ammonium) from the soil through their roots and incorporate them into organic molecules (proteins, nucleic acids). Animals obtain nitrogen by eating plants or other animals.
4. Ammonification (Decomposition): When plants and animals die, or animals excrete waste, decomposers (bacteria and fungi) break down organic nitrogen compounds into ammonia (NH3) and ammonium of ammonia/ammonium to nitrites (NO2-) by nitrifying bacteria (Nitrosomonas). Conversion of nitrites to nitrates (NO3-) by other nitrifying bacteria (Nitrobacter). Nitrates are the primary form of nitrogen absorbed by plants.
3. Assimilation: Plants absorb nitrates (and sometimes ammonium) from the soil through their roots and incorporate them into organic molecules (proteins, nucleic acids). Animals obtain nitrogen by eating plants or other animals.
4. Ammonification (Decomposition): When plants and animals die, or animals excrete waste, decomposers (bacteria and fungi) break down organic nitrogen compounds into ammonia (NH3) and ammonium (NH4+).
5. Denitrification: Conversion of nitrates (NO3-) back into gaseous atmospheric nitrogen (N2) by denitrifying bacteria (Pseudomonas) under anaerobic conditions (e.g., waterlogged soils). This returns nitrogen to the atmosphere, completing the cycle. Importance of Nitrogen to Plants and Animals: Plants: Essential for healthy growth, production of chlorophyll (for photosynthesis), and synthesis of proteins and nucleic acids. Lack of nitrogen leads to stunted growth and yellowing leaves.
Animals: Required for building muscle, enzymes, hormones, and genetic material. Animals cannot fix atmospheric nitrogen; they must obtain it from their diet.
D. Decomposition and Gas Production Energy from Decomposing Organic Substances: Decomposition is the process by which dead organic matter is broken down into simpler inorganic substances. Decomposers (bacteria, fungi, detritivores like earthworms) release chemical energy stored in the organic molecules as they break them down. This energy is utilized by the decomposers for their metabolic activities. In anaerobic decomposition (e.g., in waterlogged soils, refuse dumps, biogas digesters), energy can be captured in the form of methane gas, which can be burned as fuel.
Example: Biogas plants in rural communities use cow dung (organic waste) to produce methane for cooking and lighting.
Gases Produced During Decay: During aerobic decomposition (with oxygen), the primary gas produced is carbon dioxide (CO2). During anaerobic decomposition (without oxygen), several gases can be produced, including: Methane (CH4): A potent greenhouse gas, often called swamp gas.
Hydrogen sulphide (H2S): Causes the foul smell of rotten eggs, often found in anaerobic environments.
Ammonia (NH3): Produced during protein decomposition (ammonification). Other nitrogen oxides.
Introduction to Nutrient Cycling: Nutrient cycling (also known as biogeochemical cycling) refers to the continuous movement of essential chemical elements (like carbon, water, nitrogen, phosphorus) from the non-living (abiotic) components of the environment (atmosphere, hydrosphere, lithosphere) to the living (biotic) components (organisms) and back. These cycles ensure that vital elements are never truly lost but are constantly reused, making them available for new generations of organisms. A. The Carbon Cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is a fundamental building block of all organic molecules and is essential for life.
How Carbon Circulates in Nature:
1. Atmospheric Carbon Dioxide: Carbon exists primarily in the atmosphere as carbon dioxide (CO2).
2. Photosynthesis (Carbon Fixation): Green plants (producers) absorb atmospheric CO2 during photosynthesis. They use solar energy to convert CO2 and water into glucose (organic compounds) and oxygen. This process removes carbon from the atmosphere and incorporates it into biomass.
Example: A farmer's maize plants in Kano take in CO2 from the air to grow, converting it into starch in the grains.
3. Respiration: All living organisms (plants, animals, microorganisms) release CO2 back into the atmosphere through cellular respiration. They break down organic compounds to obtain energy, producing CO2 as a byproduct.
Example: A goat grazing on grass in Kaduna breathes out CO2 as it digests its food.
4. Consumption: Animals (consumers) obtain carbon by eating plants or other animals. The carbon then becomes part of their tissues.
Example: A cattle egret feeding on insects in a ranch in Ibadan acquires carbon from the insects.
5. Decomposition: When plants and animals die, decomposers (bacteria and fungi) break down their organic matter. This process releases carbon (as CO2) back into the atmosphere and soil.
Example: Rotting leaves in a forest floor in Cross River are broken down by microbes, releasing CO2.
6. Combustion: The burning of fossil fuels (coal, petroleum, natural gas), wood, and other organic matter releases large amounts of CO2 into the atmosphere. Fossil fuels are formed from the remains of ancient organisms over millions of years, storing carbon underground. Bush burning (as observed in some parts of rural Nigeria) also releases stored carbon.
7. Oceanic Exchange: Oceans absorb CO2 from the atmosphere and release it back. Marine organisms (e.g., shellfish) use dissolved carbon to form shells (calcium carbonate). When these organisms die, their shells can form sedimentary rocks (limestone), storing carbon for long periods. Detailed Carbon Cycle Diagram (Teacher should illustrate on the board or use a chart): Components: Atmosphere (CO2), Plants (Producers), Animals (Consumers), Decomposers (Bacteria, Fungi), Oceans (Dissolved CO2, marine life), Fossil fuels (Coal, Oil, Gas).
Arrows: Atmosphere → Plants (Photosynthesis) Plants → Atmosphere (Respiration) Plants → Animals (Feeding) Animals → Atmosphere (Respiration) Plants, Animals → Soil/Decomposers (Death/Excretion) Decomposers → Atmosphere (Respiration/Decomposition) Fossil Fuels → Atmosphere (Combustion) Atmosphere ⇌ Oceans (Dissolution/Release) Oceans → Marine organisms (Shell formation) Marine organisms → Sedimentary rocks (Long-term storage)
Necessity for Life: Building Block: Carbon is the backbone of all organic molecules (carbohydrates, proteins, lipids, nucleic acids) that make up living organisms. Without carbon, life as we know it cannot exist.
Energy Source: Organic compounds containing carbon serve as primary energy sources for most living things.
Climate Regulation: Atmospheric CO2 traps heat, contributing to the greenhouse effect, which keeps the Earth warm enough to support life. Delicate Balance between Carbon and Oxygen: Photosynthesis by plants removes CO2 from the atmosphere and releases O
2. Respiration by organisms (and combustion) removes O2 and releases CO
2. This continuous exchange maintains a relatively stable concentration of both gases in the atmosphere, essential for life. * Disruption: Increased combustion of fossil fuels (e.g., from industrial activities and vehicles in Nigerian cities) and deforestation (e.g., logging in rainforests) release excessive CO2, tipping the balance, leading to enhanced greenhouse effect and climate change, characterized by rising temperatures, altered rainfall patterns, and extreme weather events, which can affect agriculture and lead to desertification in the north or flooding in Introduction (10 minutes)
Teacher Activity: Begins by asking students to recall what happens to dead leaves or animals. Guides discussion to the concept of recycling in nature. Introduces the topic of "Nutrient Cycling" and its importance for sustainable ecosystems.
Student Activity: Students share their ideas about decomposition and recycling, contributing to a class discussion.
Lesson Development (60 minutes)
Phase 1: Carbon Cycle (20 minutes)
Teacher Activity: Explains the carbon cycle step-by-step, emphasizing photosynthesis, respiration, decomposition, and combustion. Draws a detailed, labeled diagram of the carbon cycle on the board, pointing out each component and flow. Discusses the importance of carbon for life and the delicate carbon-oxygen balance. Relates excessive CO2 to climate change, giving local examples like increased flooding in coastal areas or desertification in Northern Nigeria.
Student Activity: Students listen, ask clarifying questions, and copy the carbon cycle diagram into their notebooks. Students identify organisms involved in photosynthesis and respiration from their local environment (e.g., mango tree, human, fungi).
Phase 2: Water Cycle (15 minutes)
Teacher Activity: Explains the water cycle using terms like evaporation, condensation, precipitation, collection, runoff, and infiltration. Highlights the specific roles of plants (transpiration) and animals (respiration, excretion). Draws/projects a detailed, labeled diagram of the water cycle. Discusses local rainfall patterns and sources of water (rivers, wells, boreholes) in Nigeria.
Student Activity: Students follow along, making notes and sketching the water cycle diagram. Students describe how plants they know (e.g., cocoa, oil palm) contribute to the water cycle.
Phase 3: Nitrogen Cycle (15 minutes)
Teacher Activity: Explains the necessity of nitrogen for living organisms. Describes the stages of the nitrogen cycle: nitrogen fixation, nitrification, assimilation, ammonification, and denitrification. Emphasizes the crucial roles of various bacteria at each stage. Draws/projects a detailed, labeled diagram of the nitrogen cycle. Connects to Nigerian agriculture, discussing the use of legumes (e.g., groundnuts, cowpeas) in crop rotation to enrich soil nitrogen.
Student Activity: Students pay close attention to the microbial roles and sketch the nitrogen cycle. Students list the importance of nitrogen to plants and animals.
Phase 4: Decomposition and Gas Production (10 minutes)
Teacher Activity: Defines decomposition and explains how energy is obtained by decomposers. Identifies common gases produced during decay (CO2, methane, H2S, ammonia), differentiating between aerobic and anaerobic conditions. Uses examples like biogas production from animal waste or the smell from refuse dumps.
Student Activity: Students note down the gases produced and the conditions for their production. Students discuss local observations of decay (e.g., rotting food, refuse dumps).
Conclusion (10 minutes)
Teacher Activity: Summarizes the key learning points, emphasizing the interconnectedness of the cycles and their importance for environmental sustainability. Reviews performance objectives with students.
Student Activity: Students ask any remaining questions and prepare for guided practice.
Agriculture and Food Security: Understanding nutrient cycles (especially nitrogen and carbon) is crucial for sustainable agriculture in Nigeria. Farmers can implement practices like crop rotation (planting legumes to fix nitrogen), using organic fertilizers (compost, manure) to enrich soil carbon and nitrogen, and avoiding excessive use of synthetic fertilizers that can lead to nutrient runoff and water pollution. This directly impacts food production and soil health across diverse Nigerian farming communities. Climate Change and Environmental Management: The carbon cycle is at the heart of climate change discussions. Students can relate excessive CO2 emissions from gas flaring in the Niger Delta, vehicular emissions in congested cities like Lagos or Port Harcourt, and deforestation across the country to global warming and its local impacts (e.g., increased flooding, desertification, changes in crop yields). This knowledge fosters environmental responsibility and advocacy for sustainable energy and land use policies.
Water Resource Management and Sanitation: The water cycle helps explain rainfall patterns, groundwater recharge, and the availability of fresh water. Understanding it is vital for managing water resources, conserving water during dry seasons (common in Northern Nigeria), and addressing issues like flooding (e.g., in coastal and riverine communities) and water scarcity. The role of decomposition also links to waste management and the potential for biogas production from organic waste in communities lacking reliable electricity.