Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: Second Term
Week: 10
Age: 15 years
Duration: 45 minutes
Subject: Biology
Curriculum Theme: Biology
Previous Lesson: Functioning Ecosystem.
Topic: TROPHIC LEVELS
Subject Matter: Food chain and food web definitions, non-cyclic nature of energy transfer, nutrient movement and energy flow in aquatic and terrestrial habitats, pyramid of numbers and pyramid of energy, nature of energy flow in chains and webs

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define food chain and food web.
Identify different trophic levels in a food chain and food web.
Explain the non-cyclic nature of energy transfer in an ecosystem.
Describe nutrient movement and energy flow in aquatic and terrestrial habitats.
Differentiate between a pyramid of numbers and a pyramid of energy.

Affective Domain:

Appreciate the interconnectedness of organisms within an ecosystem.
Value the importance of energy flow for the sustenance of life.

Psychomotor Domain:

Draw examples of food chains and food webs.
Construct simple pyramids of numbers and energy from given data.
Develop examples of food chains and webs from local habitats.

Collaborate with peers to identify trophic levels in various ecosystems.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Biology.
State Unified Scheme of Work for Biology SSS 1.
Modern Biology for Senior Secondary Schools by S.T. Ramalingam.
Biology for Senior Secondary Schools by P.B. Gambari.

Instructional Materials

The teacher will teach this lesson with the aid of:

Charts showing different food chains and food webs.
Pictures of various organisms from aquatic and terrestrial habitats.
Card cut-outs of organisms for building food chains.
Markers and a whiteboard/chalkboard.
Sample habitat list (e.g., pond, forest, grassland).

Rationale for the Lesson

This lesson helps pupils understand how living organisms get their food and energy within an ecosystem. It explains how energy moves from one organism to another, which is important for understanding the balance of nature and how human activities can affect it.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of different types of living organisms, their habitats, and the concept of feeding relationships.

Lesson Content/Board Summary

TROPHIC LEVELS

Definition of Food Chain

A food chain shows the feeding relationship between different organisms in an ecosystem, indicating how energy is transferred from one organism to another. It starts with a producer and ends with a top consumer.

Example: Grass → Grasshopper → Frog → Snake → Eagle

Definition of Food Web

A food web consists of several interconnected food chains in an ecosystem. It shows more complex feeding relationships where organisms can feed on or be fed upon by multiple species, providing a more realistic representation of energy flow.

Trophic Levels

Trophic levels are the different positions organisms occupy in a food chain or food web, based on their feeding relationships. The main trophic levels are:

Producers (Autotrophs): Organisms that produce their own food, mainly through photosynthesis (e.g., plants, algae). They form the base of the food chain.
Primary Consumers (Herbivores): Organisms that feed directly on producers (e.g., grasshoppers, rabbits, cows).
Secondary Consumers (Carnivores/Omnivores): Organisms that feed on primary consumers (e.g., frogs, small birds, humans).
Tertiary Consumers (Carnivores/Omnivores): Organisms that feed on secondary consumers (e.g., snakes, eagles, lions).
Decomposers: Organisms (like bacteria and fungi) that break down dead organic matter from all trophic levels, returning nutrients to the soil.

Energy Flow in Ecosystems

Energy flow in an ecosystem is non-cyclic and unidirectional. Energy enters the ecosystem from the sun, is captured by producers, and then transferred to consumers. At each transfer, a significant amount of energy is lost as heat to the environment.

The following points describe energy flow:

Only about 10% of the energy from one trophic level is transferred to the next trophic level.
The remaining 90% is lost as heat during metabolic activities or remains unconsumed.
Therefore, the amount of available energy decreases at successively higher trophic levels.

Nutrient Movement

Unlike energy, nutrients (e.g., carbon, nitrogen, phosphorus) move in a cyclic manner within an ecosystem. Decomposers play a key role in recycling nutrients from dead organisms back into the environment for use by producers.

Pyramid of Numbers

A pyramid of numbers represents the number of individual organisms at each trophic level in an ecosystem. It usually shows a decrease in the number of individuals at higher trophic levels, but can sometimes be inverted (e.g., a single large tree supporting many insects).

Pyramid of Energy

A pyramid of energy represents the total amount of energy available at each trophic level. This pyramid is always upright, as energy decreases at successive trophic levels due to energy loss at each transfer. It is the most accurate representation of energy flow.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them to recall what they know about how living things get food. The teacher then introduces the topic “Trophic Levels” by explaining that organisms get food from other organisms, forming feeding relationships.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils are prepared for the lesson and connect new information to prior knowledge.

Step 2: Food Chain and Food Web

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines food chain and food web, using charts and card cut-outs to demonstrate simple food chains (e.g., grass-goat-man) and then combines them to form a food web. The teacher also helps pupils identify non-cyclic energy flow and nutrient movement.
Pupils’ Activity: Pupils observe the charts and demonstrations, participate in forming simple food chains, and ask questions for clarification.
Learning Point: Pupils understand the definitions and basic structure of food chains and food webs.

Step 3: Trophic Levels

Time: 7 minutes
Teaching Skill: Explanation/Questioning
Teacher’s Activity: The teacher explains the concept of trophic levels, listing and defining producers, primary consumers, secondary consumers, tertiary consumers, and decomposers. The teacher gives examples for each level from both aquatic and terrestrial habitats.
Pupils’ Activity: Pupils listen, take notes, and identify different organisms as belonging to specific trophic levels when prompted.
Learning Point: Pupils can identify and classify organisms into their respective trophic levels.

Step 4: Energy Flow in Ecosystems

Time: 7 minutes
Teaching Skill: Explanation/Discussion
Teacher’s Activity: The teacher explains that energy flow is non-cyclic and unidirectional, using the “10% rule” to illustrate how energy decreases at higher trophic levels. The teacher discusses how energy is lost as heat.
Pupils’ Activity: Pupils listen, ask questions about energy loss, and discuss why higher trophic levels have less energy.
Learning Point: Pupils understand the pattern of energy transfer and loss in an ecosystem.

Step 5: Nutrient Movement

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains that unlike energy, nutrients move in a cyclic manner. The role of decomposers in recycling nutrients is emphasized.
Pupils’ Activity: Pupils listen and differentiate between energy flow and nutrient movement.
Learning Point: Pupils understand the cyclic nature of nutrient movement in ecosystems.

Step 6: Pyramids of Numbers and Energy

Time: 8 minutes
Teaching Skill: Explanation/Visualisation
Teacher’s Activity: The teacher defines and explains the pyramid of numbers and the pyramid of energy. The teacher uses diagrams to show why the pyramid of energy is always upright, while the pyramid of numbers can sometimes be inverted. Examples are provided.
Pupils’ Activity: Pupils observe the diagrams, compare the two types of pyramids, and ask questions about their shapes.
Learning Point: Pupils can differentiate between the pyramid of numbers and the pyramid of energy and understand their significance.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define a food chain and a food web.
List the five main trophic levels in an ecosystem.
Explain why energy flow is non-cyclic.
State one difference between a pyramid of numbers and a pyramid of energy.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization/Consolidation
Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, reiterating the importance of trophic levels, energy flow, and nutrient cycling. The teacher assigns homework: “Draw a food web found in a local pond or forest habitat and identify at least three trophic levels within it.”
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their learning and prepare for independent practice.

Lesson Keywords

Food Chain – A linear sequence showing how energy is transferred from one organism to another by feeding.
Food Web – A network of interconnected food chains in an ecosystem.
Trophic Levels – The position an organism occupies in a food chain.
Producers – Organisms that make their own food (e.g., plants).
Consumers – Organisms that obtain energy by feeding on other organisms.
Decomposers – Organisms that break down dead organic matter.
Energy Flow – The movement of energy through an ecosystem, typically in one direction.
Pyramid of Numbers – A diagram showing the number of individual organisms at each trophic level.
Pyramid of Energy – A diagram showing the amount of energy available at each trophic level.

Differentiation

For visual learners, extensive use of charts, diagrams, and card cut-outs will be employed. Kinesthetic learners will benefit from arranging the card cut-outs to form food chains and webs. For advanced learners, additional research questions on specific ecosystem examples or the impact of human activities on trophic levels will be provided. Struggling learners will receive simplified explanations and more direct guidance during activities.

Note for teachers using this lesson plan

Teachers should ensure that the examples used for food chains and food webs are relevant to the pupils’ local environment to make the lesson more relatable. Encourage pupils to think critically about the consequences of removing organisms from different trophic levels. Practical activities, such as drawing and constructing, should be emphasized to reinforce learning.