BIOLOGY LESSON NOTE ON ENERGY LOSS IN THE ECOSYSTEM

TOPIC: ENERGY LOSS IN THE ECOSYSTEM

TIME: 40 minutes

Content Objective: By the of the lesson, learner should be able to;

1. Explain energy loss in an ecosystem Relevance of biology to agriculture
2. Summarize the fate of solar energy utilized or lost by primary producers
3. State two laws of thermodynamics
4. Discuss the various applications of laws of thermodynamics to ecological phenomena

PREVIOUS KNOWLEDGE: The learners know about energy loss in the ecosystem from their previous lesson 

TEACHING AIDS: Research work from the internet, pictures 

PROCEDURE: The teacher presents the lesson with the following steps 

STEP ONE: Energy flow

Energy is lost in the ecosystem during energy flow. Energy flow is the movement of energy or a transfer of energy among organisms in an ecosystem, along the food chain. The flow of energy in an ecosystem is through one direction (unidirectional / non-cyclic) i.e. starting from the producer upwards to the consumers and energy always decreases along the chain. Light energy from the sun is absorbed by chlorophyll in green plants and used in photosynthesis to produce carbohydrates.

The chemical energy in the carbohydrates is passed down the food chain when the primary consumers feed on the plants/producers; the chemical energy is then passed along the food chain to the secondary consumer and the to the tertiary consumer/decomposer.

Energy Loss: Energy is lost at each trophic level. When a herbivore feeds on a plant/producer, not all parts of the plant is eaten, as a result not all energy in the plant/producer is consumed. Plants loose energy through respiration or transpiration.

Solar radiation/solar energy: Solar energy is the first form of energy that comes into the ecosystem. The green plants or the producers trap only a fraction of this solar energy (about 1%) for use in manufacturing of food.

Energy loss in the biosphere: Biosphere is the part of the earth in which life exists, comprising of lithosphere, atmosphere and hydrosphere. More than half of the solar energy that reaches the earth’s atmosphere is reflected or absorbed. 

 STEP TWO: LAWS OF THERMODYNAMICS

First law of thermodynamics: This states that energy can neither be created nor destroyed but may be transformed from one form into another. In order words, the total amount of energy resulting from any conversion is the same as the initial amount of energy. Example, transformation of solar energy to chemical energy by plants during photosynthesis.

Solar energy = Chemical + Heat energy

(Absorbed by plants) (Stored as food) (Energy of respiration)

Second Law of Thermodynamics: This states that in conversion of energy from one form to another, there is always a decrease in the amount of useful energy. Example is seen in food chain. The transfer of energy among organisms between trophic levels is not 100%. This means that successive levels have less energy and support fewer animals. The primary producers (plants) have the highest energy. When herbivores consume plants, the energy level is reduced and when carnivores consume herbivores, the energy level is further reduced, as shown;

STEP THREE: APPLICATION OF LAWS OF THERMODYNAMICS TO ECOLOGICAL PHENOMENA

The laws of thermodynamics are applied to ecological phenomena in the following processes.

Transformation of energy within organisms in an ecosystem. For instance, during photosynthesis the solar energy from sunlight is transformed to chemical energy and then heat energy that is lost during respiration

Ecological pyramids: These are graphic representations of feeding relationships. Feeding relationship (food chain) in an ecosystem can be represented graphically by plotting the number, the biomass and the energy content of organisms at each trophic level. The producer level forms the base and the successive trophic levels are stacked in ascending order.

Types of Ecological Pyramids

Pyramid of numbers

Pyramid of biomass

Pyramid of energy

Pyramid of numbers: This is a graphical representation of the number of individuals at each trophic level of a food chain at a particular time. The length of each bar in the pyramid gives an approximate measure of the number of individuals at that particular trophic level. In most ecosystems the number of individuals decreases progressively up the trophic level in the food chain while the size of the individuals increase

Pyramid of biomass: This represents the total wet or dry mass of the organisms in each trophic level. The organisms at the higher level are usually larger in size. and their numbers.

Pyramid of energy: This indicates the rate of flow of food energy through each trophic level of a food chain. Each horizontal bar represents the amount of energy (KJ or Kcal) in a given unit area (m2). There is a decrease in energy from one trophic level to another along the food chain. 

Evaluation

1. Explain energy loss in an ecosystem
2. Summarize the fate of solar energy utilized or lost by primary producers
3. State two laws of thermodynamics
4. Discuss the various applications of laws of thermodynamics to ecological phenomena

Conclusion: Energy is lost in the ecosystem during energy flow.

Assignment

1. Explain the term pyramids.
2. State two laws of thermodynamics
3. Discuss the various applications of laws of thermodynamics to ecological