Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define biotic and abiotic factors with examples.
• Explain interactions between biotic and abiotic factors.
• Identify feeding relationships: producers, consumers, and decomposers.
• Explain energy flow in a food chain.
• Discuss the impact of human activities on ecosystems.

Lesson summary

This week, we delve deeper into the fascinating world of living organisms and their environments. Understanding how living things interact with each other and their surroundings is crucial. South Africa boasts incredible biodiversity, from the fynbos in the Western Cape to the savanna of Kruger National Park. Learning about ecosystems helps us appreciate and protect these valuable resources for future generations. Our actions, like littering or conserving water, directly impact these environments. Knowing how ecosystems function empowers us to make informed decisions and become responsible citizens.

Lesson notes

2.1 Biotic and Abiotic Factors: An ecosystem is made up of two main components: biotic and abiotic factors.

Biotic Factors: These are the living parts of an ecosystem. Examples include plants, animals, fungi, bacteria, and other microorganisms. Biotic factors interact with each other in various ways, such as through feeding relationships (who eats whom), competition for resources (food, water, space), and cooperation (e.g., bees pollinating flowers).

Example (South Africa): In the Kruger National Park, biotic factors include elephants, lions, zebras, various tree species (e.g., Mopani), grasses, and numerous insects. The interactions between these organisms, such as lions preying on zebras, are vital for the ecosystem's balance.

Abiotic Factors: These are the non-living parts of an ecosystem. Examples include sunlight, temperature, water, soil, air, and minerals. Abiotic factors influence the distribution and survival of organisms within an ecosystem.

Example (South Africa): In the Karoo region, abiotic factors like low rainfall and high temperatures play a crucial role in determining the types of plants and animals that can survive there. Plants like succulents are adapted to store water and animals are often nocturnal to avoid the intense heat. 2.2 Interactions Between Biotic and Abiotic Factors: Biotic and abiotic factors are interconnected and constantly interact. Changes in one factor can affect the others.

Example 1: Rainfall and Plant Growth: Rainfall (abiotic) is essential for plant growth (biotic). If there is a drought, plants will struggle to survive, which in turn affects the animals that depend on those plants for food.

Example 2: Sunlight and Photosynthesis: Sunlight (abiotic) provides the energy for plants (biotic) to perform photosynthesis, the process by which they produce their own food. Without sunlight, plants cannot survive, impacting the entire food chain.

Example 3: Soil Composition and Plant Distribution: The type of soil (abiotic) influences which plants (biotic) can grow in a particular area. Sandy soils, for example, drain quickly and may only support plants adapted to dry conditions. 2.3 Feeding Relationships: Producers, Consumers, and Decomposers: Producers (Autotrophs): These organisms make their own food through photosynthesis. They are the foundation of the food chain.

Example (South Africa): Grasses in the savanna, trees in the forests, and algae in aquatic ecosystems are all producers.

Consumers (Heterotrophs): These organisms obtain their energy by eating other organisms.

Primary Consumers (Herbivores): Eat producers (plants).

Examples: Zebras, springbok, grasshoppers.

Secondary Consumers (Carnivores): Eat primary consumers (herbivores).

Examples: Lions, snakes that eat grasshoppers. Tertiary Consumers (Carnivores or Omnivores): Eat secondary consumers.

Examples: Eagles, humans (who eat both plants and animals).

Omnivores: Eat both plants and animals.

Example: Baboons Decomposers (Saprotrophs): These organisms break down dead plants and animals, returning nutrients to the soil.

Examples: Bacteria, fungi, earthworms. Decomposers play a crucial role in recycling nutrients within an ecosystem. 2.4 Food Chains and Food Webs: Food Chain: A linear sequence showing the flow of energy from one organism to another.

For example: Grass → Zebra → Lion.

Food Web: A more complex network of interconnected food chains, showing the various feeding relationships within an ecosystem.

Example (South Africa): A simple food web in the fynbos biome might include: Sun → Fynbos plants → Cape sugarbird → Snake → Eagle. 2.5 Energy Flow: Energy flows through an ecosystem from producers to consumers. When an organism eats another, it obtains some of the energy stored in that organism's body.

However, not all the energy is transferred. Some energy is lost as heat during metabolic processes. This means that the amount of energy available decreases as you move up the food chain. This is why food chains usually have only a few trophic levels (feeding levels). 2.6 Impact of Human Activities: Human activities can have significant negative impacts on ecosystems.

Pollution: Contamination of air, water, and soil with harmful substances can harm or kill organisms.

Example (South Africa): Industrial pollution in rivers can harm aquatic life and make the water unsafe for human consumption.

Deforestation: Clearing forests for agriculture or development can destroy habitats, reduce biodiversity, and contribute to climate change.

Example (South Africa): Deforestation for agriculture can lead to soil erosion and loss of valuable ecosystem services.

Overfishing: Removing fish from the ocean at a rate faster than they can reproduce can deplete fish populations and disrupt marine ecosystems.

Introduction of Invasive Species: Introducing non-native species can outcompete native species and disrupt the balance of ecosystems.