Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define ecosystem, biotic, and abiotic components.
• Explain population, community, and habitat.
• Describe feeding relationships like producers and consumers.
• Construct simple food chains and food webs.
• Explain how energy flows through an ecosystem.

Lesson summary

This week, we delve into the fascinating world of ecosystems and the complex interactions that sustain life within them. Understanding ecosystems is crucial for South African learners because our country is exceptionally rich in biodiversity, facing unique environmental challenges like water scarcity, habitat destruction, and climate change impacts. A strong grasp of ecological principles empowers us to make informed decisions about conservation, sustainable resource management, and protecting our natural heritage.

Lesson notes

2.1 What is an Ecosystem? An ecosystem is a community of living organisms (biotic factors) interacting with each other and with their non-living environment (abiotic factors). Think of it as a complex web of life and its physical surroundings.

Biotic Factors: These are the living components of an ecosystem. Examples include plants, animals, fungi, bacteria, and other microorganisms.

Abiotic Factors: These are the non-living components of an ecosystem. Examples include sunlight, water, temperature, soil, air, and minerals.

Example: A small pond near a school in Gauteng is an ecosystem. The biotic factors are the fish, frogs, insects, algae, and aquatic plants. The abiotic factors are the water, sunlight, temperature of the water, minerals in the soil at the bottom, and dissolved oxygen. 2.2 Population, Community, and Habitat Population: A group of individuals of the same species living in the same area at the same time.

Example: All the Koi fish in a specific pond in KwaZulu-Natal.

Community: All the different populations of organisms living and interacting in a specific area.

Example: The pond community includes the Koi fish population, the frog population, the insect population, and the aquatic plant populations.

Habitat: The natural environment where an organism lives; it provides the organism with food, shelter, and other resources needed for survival.

Example: The habitat of the Koi fish is the pond. The habitat of a dung beetle is a pile of animal dung.

Relationship: Populations make up communities, and communities, together with the abiotic environment, form ecosystems. An organism's habitat is where it lives within the ecosystem. 2.3 Feeding Relationships: Producers, Consumers, and Decomposers Producers (Autotrophs): These organisms make their own food through photosynthesis. They use sunlight, water, and carbon dioxide to produce glucose (sugar) and oxygen. Plants are the primary producers in most terrestrial ecosystems. Algae and phytoplankton are the primary producers in aquatic ecosystems.

Example: Grass in a field, phytoplankton in the ocean.

Consumers (Heterotrophs): These organisms cannot make their own food and must obtain energy by eating other organisms.

There are different types of consumers: Herbivores: Eat only plants. (

Example: Cows, springbok)

Carnivores: Eat only animals. (

Example: Lions, eagles)

Omnivores: Eat both plants and animals. (

Example: Pigs, humans)

Detritivores: Feed on dead organic matter (detritus). (

Example: Earthworms, dung beetles)

Decomposers: These organisms break down dead organisms and waste materials into simpler substances. They play a vital role in recycling nutrients back into the ecosystem. Bacteria and fungi are the main decomposers.

Example: Fungi growing on a dead log, bacteria breaking down leaf litter. 2.4 Food Chains and Food Webs Food Chain: A linear sequence showing the transfer of energy from one organism to another when one organism eats another. It always starts with a producer.

Example: Grass → Grasshopper → Frog → Snake → Eagle Food Web: A complex network of interconnected food chains showing the feeding relationships among various organisms in an ecosystem. It is a more realistic representation of energy flow than a simple food chain. 2.5 Energy Flow and Trophic Levels Trophic Level: Each step in a food chain or food web represents a trophic level. Producers are at the first trophic level, primary consumers (herbivores) at the second trophic level, secondary consumers (carnivores that eat herbivores) at the third trophic level, and so on.

Energy Transfer: Energy flows from one trophic level to the next when organisms consume each other.

However, only about 10% of the energy stored in one trophic level is transferred to the next trophic level. The remaining 90% is lost as heat, used for metabolic processes (like respiration and movement), or remains in undigested material. This explains why food chains usually have a limited number of trophic levels (typically 4-5).

Example: If grass captures 1000 units of energy from the sun, a grasshopper eating the grass will only get about 100 units of energy. A frog eating the grasshopper will get about 10 units of energy, and a snake eating the frog will get about 1 unit of energy. 2.6 Interactions between Organisms Competition: Occurs when two or more organisms require the same limited resource, such as food, water, shelter, or sunlight.

Example: Lions and hyenas competing for the same prey (e.g., wildebeest) in the savanna.

Predation: Occurs when one organism (the predator) kills and eats another organism (the prey).

Example: A snake eating a mouse.

Mutualism: A relationship between two organisms where both benefit.

Example: Bees pollinating flowers (the bee gets nectar, and the flower gets pollinated). Oxpeckers eating ticks off of zebras (oxpeckers get food, zebras get rid of parasites).

Parasitism: A relationship between two organisms where one benefits (the parasite) and the other is harmed (the host).