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A food chain describes the sequence of events in an ecosystem where organisms consume one another, forming a flow of nutrients and energy through different trophic levels. It illustrates the feeding relationships among living organisms, with trophic levels representing stages in the chain—producers at the bottom, followed by primary, secondary, and tertiary consumers. Each stage in the food chain is referred to as a trophic level.

The food chain consists of four major parts, namely:

1. The Sun: The sun is the initial source of energy, which provides energy for everything on the planet.

2. Producers include all autotrophs such as plants. They are called autotrophs as they can produce food through the process of photosynthesis. Consequently, all other organisms higher up on the food chain rely on producers for food.

3. Consumers or heterotrophs are organisms that depend on other organisms for food. Consumers are further classified into primary consumers, secondary consumers and tertiary consumers.

a. Primary consumers are always herbivores as they rely on producers for food.

b. Secondary consumers depend on primary consumers for energy. They can either be carnivores or omnivores.

c. Tertiary consumers are organisms that depend on secondary consumers for food.  Tertiary consumers can also be carnivores or omnivores.

d. Quaternary consumers are present in some food chains. These organisms' prey on tertiary consumers for energy. Furthermore, they are usually at the top of a food chain as they have no natural predators.

4. Decomposers include saprophytes such as fungi and bacteria. They directly thrive on the dead and decaying organic matter.  Decomposers are essential for the ecosystem as they help in recycling nutrients to be reused by plants.

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At the end of the lesson, the learners will be able to:

1. Understand the basic concepts of ecology (Trophic Levels and Energy Flow)

2. Define and differentiate biotic and abiotic factors

3. Describe the interaction between each trophic levels/organisms

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1. What are the things that you see in your school garden or the pond?

2. Which of these things are living? Which of these things are nonliving?

3. What makes living things different from nonliving things?

4. How do living things interact with each other and with their environment?

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Is a community of lifeforms in concurrence with non-living components, interacting with each other.

Biotic Components

Biotic components refer to all living components in an ecosystem.  Based on nutrition, biotic components can be categorised into autotrophs, heterotrophs and saprotrophs (or decomposers).

Abiotic Components

Abiotic components are the non-living component of an ecosystem.  It includes air, water, soil, minerals, sunlight, temperature, nutrients, wind, altitude, turbidity, etc.

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Autotrophs are organisms capable of producing their own food using various sources such as light, water, carbon dioxide, or other chemicals. Commonly referred to as producers, autotrophs include not only plants, but also algae, phytoplankton, and certain bacteria. The predominant method for most autotrophs to generate food is through photosynthesis, where they utilize sunlight to convert water and carbon dioxide into glucose, a form of sugar providing energy for growth and cellular processes.

While most autotrophs rely on photosynthesis, some, particularly in extreme environments, employ chemosynthesis. This process involves utilizing energy from chemical reactions, often involving substances like hydrogen sulfide or methane, to produce food. Examples of such environments include active volcanoes, hot springs in Yellowstone National Park, and deep-sea hydrothermal vents. Bacteria thriving in these locations oxidize specific chemicals to synthesize their own food, showcasing the diverse strategies autotrophs employ to sustain themselves.

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Heterotrophs are organisms that obtain their energy and nutrients by consuming other plants or animals. Heterotrophs, including dogs, birds, fish, and humans, are consumers in a food chain and occupy the second and third trophic levels.

4 Types:

1. Herbivores – Organisms that eat only producers (plants); also called a primary or first-level consumer; Examples are the ruminants – cows, goats, carabaws.

2. Carnivores – Organisms that eat only other animals; can be a secondary / tertiary / quarternary consumer; Examples are members of Order Carnivora – Dogs, cats, bears, wolves.

3. Omnivores –Organisms that eat both plant and animal material; Example – Humans

4. Scavengers– Organisms that eat only other animals after they are already killed; Example - vultures, hyenas

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Decomposers are a crucial group of organisms in nature's recycling system. These organisms, which include microscopic entities like protozoa and bacteria, as well as visible ones such as fungi and detritivores like earthworms, termites, and millipedes, play a vital role in breaking down dead plant and animal matter. By feeding on materials like leaf litter, wood, carcasses, and feces, decomposers serve as Earth's cleanup crew, preventing the accumulation of dead organic matter.

The significance of decomposers lies in their ability to convert complex organic substances into simpler compounds, including water and carbon dioxide, along with essential nutrients like nitrogen, phosphorus, and calcium. This process replenishes the soil or water with vital nutrients, benefiting primary producers like plants and algae. Without decomposers, the world would be overwhelmed by dead leaves, insects, and animals.

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A food web comprises interconnected food chains, presenting a more extensive network than individual chains. Unlike a linear food chain, a single organism in a food web may be consumed by multiple predators or consume various organisms, creating numerous interconnections between trophic levels. Unlike food chains, food webs accurately represent the complex flow of energy in ecosystems by illustrating the diverse interactions among different organisms.

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The ecological pyramid, also known as a food or trophic pyramid, was conceptualized by Charles Elton in 1927. Later, Bodenheimer (1938) introduced the biomass pyramid, and in 1942, Hutchinson and Linderman proposed the productivity pyramid.

These pyramids, structured as a pyramid shape, represent numbers, energy, and biomass across trophic levels. They reveal the distribution of individuals, energy, or biomass at each level, with producers forming the broad base and successive levels occupied by primary, secondary, and tertiary consumers.

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Symbiosis is a relationship that exists between two organisms. There are three types of behaviours observed in symbiotic relationships, namely:

Mutualism

Commensalism

Parasitism

Symbiosis – Types

1. In mutualism, both the involved organisms benefit from each other. Example – Coral reefs are nothing but a mutualistic association between coral organisms and various types of algae residing inside them.

2. In commensalism, only one organism benefits, while the other is neither benefited nor harmed. Example – Hermit crabs use gastropod shells to protect their bodies.

3. In parasitism, one organism is benefited while the other organism is harmed. Example – Liver fluke attaches itself to the liver and makes its way to the tissue and bile.

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What other example of parasitism do you know?

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What other example of parasitism do you know?

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Hookworms consuming blood from inside an animal's intestine.

Tick that feed on the blood of dog

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Are plants the only organisms in an ecosystems that can produce their own food?

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Are plants the only organisms in an ecosystems that can produce their own food?

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There are also microorganisms that can photosynthesize

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How do animals and humans obtain energy to keep them alive?

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How do animals and humans obtain energy to keep them alive?

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Humans and other animals are not capable of making their own food. They are must eat other organisms in order to obtain their energy as well as nutrients.

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List down the organisms found in your community. Classify the organisms according to the following categories:

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Alcantara, Xaviery Blaise

Getes, Justine Grace

Juegos, Argefe

Mingollo, Terjelyn

Tiangan, Cloyd Ivan

Torcuator, Kent