Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define ecosystem, biotic, and abiotic factors.
• Describe interactions like predation, competition, and mutualism.
• Explain food chains and food webs.
• Identify producers, consumers, and decomposers.
• Analyze human impacts on ecosystems.

Lesson summary

Welcome, Grade 8 learners! This week, we delve into the fascinating world of ecosystems and the intricate interactions that occur within them. Understanding ecosystems is crucial because it helps us appreciate the delicate balance of nature around us, especially here in South Africa with its diverse and unique environments. From the Kruger National Park to the Table Mountain National Park, our country is a treasure trove of ecological interactions. By understanding these interactions, we can better protect our natural heritage and ensure a sustainable future. For example, knowing how overgrazing affects the soil in the Karoo can help farmers implement better land management practices.

Lesson notes

2.1 What is an Ecosystem? An ecosystem is a community of living organisms (plants, animals, and microbes) that interact with each other and with their non-living environment (soil, water, air, and sunlight). Think of it as a complete ecological unit. 2.2 Biotic and Abiotic Factors: Biotic Factors: These are the living components of an ecosystem.

Examples include: Plants: Grasses, trees, shrubs, algae – all producers. For example, the fynbos vegetation in the Western Cape.

Animals: Lions, elephants, zebras, snakes, insects – consumers. For example, the African wild dog.

Microorganisms: Bacteria, fungi – decomposers. These are essential for recycling nutrients.

Abiotic Factors: These are the non-living components of an ecosystem.

Examples include: Sunlight: Provides energy for producers (plants) to perform photosynthesis.

Water: Essential for all life processes.

Soil: Provides nutrients and support for plants. The type of soil can greatly influence which plants can grow. For example, nutrient-poor sandy soils support different plants than rich, clay-based soils.

Temperature: Affects the rate of biological processes. Extreme temperatures can limit the types of organisms that can survive in an ecosystem.

Air: Provides oxygen for respiration and carbon dioxide for photosynthesis.

Wind: Affects the distribution of seeds and pollen, and can influence evaporation rates.

Example: Consider a small pond ecosystem in a South African farm. Biotic factors would include the water lilies, fish, frogs, and algae. Abiotic factors would include the water itself, the sunlight, the mud at the bottom of the pond, and the temperature of the water. 2.3 Interactions Between Organisms: Organisms in an ecosystem interact with each other in various ways. These interactions can be beneficial, harmful, or neutral to the organisms involved.

Predation: One organism (the predator) kills and eats another organism (the prey).

Example: A lion (predator) hunting a zebra (prey) in the Kruger National Park. Another example would be a snake eating a mouse.

Competition: Organisms compete for the same resources, such as food, water, shelter, or mates. Competition can occur between members of the same species (intraspecific competition) or between members of different species (interspecific competition).

Example: Two species of antelope competing for grazing land. Another example is trees in a forest competing for sunlight.

Mutualism: A relationship between two species in which both benefit.

Example: Oxpeckers riding on zebras or rhinoceroses and eating ticks. The oxpeckers get food, and the zebras/rhinos get rid of parasites. Another example is the relationship between bees and flowers.

Parasitism: A relationship between two species in which one benefits (the parasite) and the other is harmed (the host).

Example: Ticks feeding on the blood of a dog. The tick benefits, while the dog is harmed. Another example includes intestinal worms inside humans.

Commensalism: A relationship between two species in which one benefits and the other is neither harmed nor helped.

Example: Birds nesting in a tree. The bird gets shelter, and the tree is unaffected. 2.4 Food Chains and Food Webs: Food Chain: A linear sequence of organisms through which nutrients and energy pass as one organism eats another. Each organism occupies a specific trophic level in the food chain.

Example: Grass → Grasshopper → Frog → Snake → Eagle Grass is the producer. Grasshopper is the primary consumer (herbivore). Frog is the secondary consumer (carnivore). Snake is the tertiary consumer (carnivore). Eagle is the quaternary consumer (carnivore).

Food Web: A more complex network of interconnected food chains, showing the feeding relationships among various organisms in an ecosystem. Food webs represent a more realistic picture of energy flow in an ecosystem because organisms often eat more than one type of food. Example of a simple South African grassland food web: Producers: Grasses, shrubs Primary Consumers (Herbivores): Zebras, wildebeest, springbok, grasshoppers Secondary Consumers (Carnivores/Omnivores): Snakes, lizards, birds Tertiary Consumers (Carnivores): Lions, cheetahs, hyenas Decomposers: Fungi, bacteria in the soil Decomposers play a vital role in breaking down dead organisms and waste products, returning nutrients to the soil for producers to use. Without decomposers, nutrients would remain locked up in dead matter, and the ecosystem would eventually collapse. 2.5 Human Impact on Ecosystems: Human activities can have a significant and often negative impact on ecosystems.

Deforestation: Clearing forests for agriculture, urban development, or timber. This leads to habitat loss, soil erosion, and climate change. Think about the impact of deforestation on indigenous forests in KwaZulu-Natal.

Pollution: Introducing harmful substances into the environment (air, water, soil). This can damage ecosystems and harm organisms.