21. Organisms and their Environment (Self-Study) (1)
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REPUBLIC POLYTECHNIC
Applied Science
Organisms and their Environment
Self-study Notes
PFP Applied Science Semester 2
Copyright © 2025
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Ecology: Environmental Factors
Definition: Ecology is the study of interactions between organisms and their environments.
Environmental Factors:
Biotic Factors: Living things affecting an organism.
Abiotic Factors: Non-living elements affecting an organism (e.g., wind, rain, sunlight, temperature).
Example:
Temperature of water (abiotic factor) is crucial for fish in a stream.
Number of food organisms (biotic factor) also impacts fish life.
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Levels of Organization in Ecology
Population: Groups of organisms of the same species.
Community: Interacting populations of different species.
Ecosystem: Interaction between organisms and their abiotic surroundings.
Habitat: Specific part of a community occupied by an organism.
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Exercise 1
Identify examples in the context of a grizzly bear catching salmon in an Alaskan river:
Population: Salmon population in the river.
Community: Interaction between bears and salmon.
Ecosystem: Forest and river.
Habitat: Physical area such as air and water.
Biotic Environment: Living elements like bears, salmon, and birds.
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Energy and Nutrients in Ecosystems
Ecosystems utilize energy and inorganic nutrients.
Sun's Role: Supplies heat and light energy essential for ecosystems.
Energy Flow: Light energy converted into chemical energy, lost as heat.
Continuous energy supply is necessary.
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Movement of Inorganic Nutrients
Sources: Inorganic nutrients are obtained from the abiotic environment, flowing through ecosystems in cycles.
Examples: Phosphorus, nitrogen, iron.
Nutrients come from a nutrient pool, often found in soil or water.
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Flow of Energy and Nutrients
All living organisms require energy from food.
Photosynthesis: Sunlight is converted to energy stored as glucose in plants.
Animals obtain energy by consuming plants or other animals.
Nutrients are also absorbed by plants and transferred through the food chain.
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Food Chains and Decomposition
Upon death, organisms recycle nutrients through decomposition.
Food Chain: Sequence of energy and nutrient transfer among organisms.
Food Web: Interlinked food chains within an ecosystem.
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Exercise 2: Food Web Understanding
Food Chain Example: Grass → Rabbit → Hawk.
Energy Distribution: Most energy is found in grass, least in the hawk due to energy loss along the chain.
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Trophic Levels and Producers
Trophic Levels: Stages in the energy flow within ecosystems.
Producers:
Organisms capable of photosynthesis.
Contain chlorophyll to trap light energy.
Occupy the first trophic level.
Examples: Trees, algae.
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Consumers in Ecosystems
Consumers: Organisms that cannot produce their food.
Types of Consumers:
Primary Consumers: Herbivores (Second Trophic Level; e.g., Rabbit).
Secondary Consumers: Carnivores (Third Trophic Level; e.g., Snake).
Tertiary Consumers: Higher-level carnivores (Fourth Trophic Level).
Omnivores: Organisms that can be herbivores and carnivores depending on their diet (e.g., Rat).
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Decomposers
Definition: Special category breaking down organic matter from all trophic levels.
Examples: Bacteria, fungi.
Not assigned to specific trophic levels as they interact with all levels.
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Exercise 3: Food Web Analysis
Identify organisms:
Primary Consumers: Rabbit, grasshopper, mouse.
Omnivore: Mouse.
Trophic Levels: Food chain Grass → Rabbit → Hawk has 3 levels.
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Ecological Pyramids
Definition: Visual representation of trophic levels in a food chain.
Types:
Pyramid of Energy: Total energy comparison across levels.
Pyramid of Numbers: Organism comparison at each level.
Pyramid of Biomass: Comparison of biomass present at each level.
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Energy Transfer Efficiency
Generally, only 10% of energy is transferred to the next trophic level; the rest is lost as heat.
Reduction of energy limits the number of viable trophic levels.
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Example of Energy Transfer
Example of energy efficacy in a food chain:
Grass (100 kJ) → Rabbit (10 kJ) → Hawk (1 kJ).
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Pyramid of Numbers
Typical shape decreases organisms from lowest to highest trophic levels; exceptions exist.
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Pyramid of Biomass
Biomass is the total living material, measured by dry weight.
Exceptions seen in aquatic ecosystems due to producer-consumer dynamics.
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Energy Availability in Human Diets
Higher energy consumption from producers (e.g., plants) compared to consumers (e.g., meat).
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Exercise 4: Construct Pyramids
Assignment to create pyramids of numbers and energy for given food chains.
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Knowledge Check: Energy Transfer
Energy utilization diminishes along the food chain; producers are more abundant.
Fewer consumers as energy diminishes limits the number of trophic levels.
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Nutrient Cycles
Essential elements (carbon, nitrogen, phosphorus) are involved in forming crucial organic compounds.
Nutrient movement referred to as the nutrient cycle; storage locations are called sinks or reservoirs.
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Carbon Cycle
Critical recycling process involving photosynthesis, feeding, respiration, decomposition, and combustion.
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Interaction in the Carbon Cycle
Plants absorb CO2 for photosynthesis.
Animals obtain carbon by feeding and release CO2 through respiration.
Microbial activity in decomposition also releases CO2.
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Exercise 6: Carbon Cycle Diagrams
Match organisms to carbon cycle diagram and identify processes.
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Carbon Sinks
Oceans: Largest carbon sinks, absorbing 1/3 of CO2 from human actions.
Forests: Large carbon storage through plant photosynthesis.
Carbon Reservoirs: Areas that store more carbon than they release.
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Greenhouse Effect and Global Warming
Importance of CO2 for maintaining Earth’s temperature.
Human activities increasing CO2 emissions lead to global warming.
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Maintenance of Biodiversity
Species functionality within ecosystems; diverse ecosystems better withstand stress.
Loss of species impacts ecosystem stability.
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Learning Outcomes
Differentiate between food chains and webs.
Understand roles of producers, consumers, decomposers.
Interpret energy, number, and biomass pyramids.
Explain the carbon cycle's importance.
Discuss species conservation for biodiversity.
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Self-Study Reminder
Lesson 26 is self-study; go through the slides for understanding.
Post queries on MS Teams/email for lecturer response in the next lesson.