Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define biotic and abiotic factors with South African examples.
• Explain food chains and food webs.
• Identify the roles of producers, consumers, and decomposers.
• Describe relationships like predation, competition, and symbiosis.
• Analyse human impact on local ecosystems.

Lesson summary

Welcome to Week 6 of Natural Sciences! 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 because it helps us appreciate the delicate balance of nature and how our actions impact the South African environment. From the Kruger National Park's incredible biodiversity to the unique plant life of the Fynbos in the Western Cape, our country is a treasure trove of ecosystems that we must learn to protect.

Lesson notes

2.1 Biotic and Abiotic Factors: An ecosystem is a community of living organisms interacting with each other and with their non-living environment. The living components are called biotic factors, and the non-living components are called abiotic factors.

Biotic Factors: These are the living parts of an ecosystem.

They include: Plants: These are producers, like the grasses in the grasslands or the trees in the forests.

Animals: These are consumers, like the zebras that eat grass or the lions that eat zebras. Think of the hadeda ibis scavenging around urban areas.

Bacteria and Fungi: These are decomposers, breaking down dead organic matter. The fungi you see growing on rotting logs in the forest are examples.

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

They include: Sunlight: Provides energy for photosynthesis in plants. South Africa's abundant sunshine is vital for our plant life.

Water: Essential for all life processes. Water scarcity is a significant issue in many parts of South Africa.

Soil: Provides nutrients and support for plants. The different types of soil in South Africa support diverse plant communities.

Temperature: Affects the rate of biological processes. Temperature variations influence which organisms can survive in different regions.

Air (Oxygen and Carbon Dioxide): Oxygen is needed for respiration by animals, and carbon dioxide is needed for photosynthesis by plants. pH: The acidity or alkalinity of the soil and water can affect the types of organisms that can live there.

Example: In a South African grassland ecosystem, the grass (biotic) needs sunlight, water, and nutrients from the soil (abiotic) to grow. Zebras (biotic) eat the grass, and lions (biotic) eat the zebras. Decomposers break down dead grass, zebras, and lions, returning nutrients to the soil. 2.2 Food Chains and Food Webs: A food chain shows the flow of energy from one organism to another. It's a linear sequence.

For example: Grass → Zebra → Lion → Decomposers A food web is a more complex network of interconnected food chains. It shows all the feeding relationships in an ecosystem. Ecosystems are rarely simple food chains; they are usually complex food webs.

Example: Consider a simple food web in a South African wetland: Algae (Producer) → Tadpole (Primary Consumer) → Fish (Secondary Consumer) → Heron (Tertiary Consumer) → Bacteria (Decomposer)

Also: Water plants (Producer) -> Snails (Primary Consumer) -> Fish (Secondary Consumer) -> Heron (Tertiary Consumer) -> Bacteria (Decomposer) This example shows that fish can feed on both tadpoles and snails, and both algae and water plants contribute as producers. 2.3 Roles of Organisms in an Ecosystem: Producers: These organisms make their own food through photosynthesis. Plants are the primary producers. Examples include grass, trees, algae, and the unique Fynbos plants.

Consumers: These organisms obtain energy by eating other organisms.

Herbivores: Eat only plants (e.g., zebras, springbok, caterpillars).

Carnivores: Eat only animals (e.g., lions, eagles, snakes).

Omnivores: Eat both plants and animals (e.g., humans, baboons, some birds).

Scavengers: Eat dead animals (e.g., vultures, hyenas, hadeda ibis).

Decomposers: These organisms break down dead organic matter, returning nutrients to the soil (e.g., bacteria, fungi). They are essential for recycling nutrients in the ecosystem. 2.4 Relationships Between Organisms: Predation: One organism (the predator) kills and eats another organism (the prey) (e.g., lion hunting a zebra, a spider trapping an insect).

Competition: Organisms compete for the same resources, such as food, water, space, or sunlight (e.g., lions and hyenas competing for the same prey, different plant species competing for sunlight and nutrients).

Symbiosis: A close relationship between two different species.

Mutualism: Both species benefit (e.g., oxpeckers that eat ticks off of zebras – the oxpecker gets food, and the zebra gets rid of parasites).

Commensalism: One species benefits, and the other is neither harmed nor helped (e.g., epiphytic orchids growing on trees – the orchid gets support, and the tree is not affected).

Parasitism: One species benefits, and the other is harmed (e.g., ticks feeding on animals, a tapeworm living in a human's intestines). 2.5 Human Impact on Ecosystems: Human activities can have significant negative impacts on ecosystems.

Some examples include: Pollution: Air, water, and soil pollution can harm or kill organisms. Industrial waste, agricultural runoff, and litter all contribute to pollution. Think of plastic pollution affecting marine life along the South African coast.

Deforestation: Clearing forests for agriculture, development, or timber removes habitats and can lead to soil erosion and loss of biodiversity. The clearing of indigenous forests for agriculture is a significant problem.

Overfishing: Removing too many fish from the ocean can disrupt food webs and lead to the collapse of fish populations.