Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define ecosystem, population, community, habitat, and niche.
• Describe interactions like competition, predation, and mutualism.
• Explain the roles of producers, consumers, and decomposers.
• Understand how energy flows through a food chain.
• Identify human impacts and organism adaptations (covered in future lessons).

Lesson summary

This week, we delve into the fascinating world of ecosystems and the interactions within them. Understanding ecosystems is crucial because it helps us comprehend the interconnectedness of living things and their environment. In South Africa, where we are blessed with incredible biodiversity, from the Kruger National Park to the Fynbos region, understanding how these ecosystems function is vital for conservation and sustainable living. Our actions, whether it's polluting a river or overgrazing land, can have ripple effects throughout the entire ecosystem, impacting everything from the availability of clean water to the survival of endangered species.

Lesson notes

2.1 Basic Definitions: Ecosystem: An ecosystem is a community of living organisms (biotic factors) interacting with each other and with their non-living environment (abiotic factors). Examples of ecosystems in South Africa include the Kruger National Park (savanna ecosystem), the Table Mountain National Park (fynbos ecosystem), and a local pond.

Population: A population is a group of individuals of the same species living in the same area at the same time. For instance, a population of impala in the Kruger National Park or a population of dassies (rock hyraxes) on Table Mountain.

Community: A community consists of all the different populations that live together in a defined area. An example would be the community of organisms living in a dam, including fish, frogs, insects, plants, and microorganisms.

Habitat: The habitat is the natural home or environment of an organism. This is where an organism finds the resources it needs to survive, such as food, water, shelter, and mates. Examples include the habitat of a sugarbird being the fynbos vegetation, or the habitat of an earthworm being the soil.

Niche: The niche describes the role an organism plays in its ecosystem, including what it eats, what eats it, how it interacts with other organisms, and its impact on the environment. It’s not just where it lives, but how it lives. For example, the niche of a lion in the Kruger National Park involves hunting other animals (like zebras and wildebeest), being a top predator, and helping to control herbivore populations. 2.2 Interactions Between Organisms: Competition: This occurs when two or more organisms need the same limited resource, such as food, water, space, or sunlight. For example, different species of antelope in a savanna ecosystem may compete for grazing resources. Another example is competition for sunlight between different species of plants in a dense forest.

Predation: This is when one organism (the predator) kills and eats another organism (the prey). Examples include lions preying on zebras, snakes eating mice, and spiders catching insects in their webs.

Mutualism: A relationship where both organisms benefit. A classic example is the relationship between oxpeckers and zebras or rhinos. The oxpeckers eat ticks and other parasites off the skin of the zebra/rhino (benefiting the oxpecker by providing food), and the zebra/rhino gets rid of the parasites (benefiting the zebra/rhino). Another example is bees pollinating flowers; bees get nectar, and the flowers get pollinated.

Parasitism: A relationship where one organism (the parasite) benefits at the expense of another organism (the host). Ticks on dogs are a common example; the tick benefits by feeding on the dog's blood, while the dog is harmed. Another example is a tapeworm living inside the intestines of a human.

Commensalism: A relationship where one organism benefits, and the other is neither harmed nor helped. An example is barnacles attaching themselves to whales. The barnacles benefit by being transported to new feeding grounds, while the whale is neither helped nor harmed. Another example is birds nesting in trees; the birds get shelter, and the tree is unaffected. 2.3 Trophic Levels & Energy Flow: Ecosystems are powered by the sun. Energy flows through them in a specific way, passing from one organism to another through feeding relationships. This is often illustrated using food chains and food webs.

Producers: Producers (also known as autotrophs) are organisms that make their own food through photosynthesis. They convert sunlight, water, and carbon dioxide into energy-rich sugars. Plants, algae, and some bacteria are producers. In South Africa, examples include grass in the savanna, trees in the forest, and kelp in coastal waters.

Consumers: Consumers (also known as heterotrophs) are organisms that cannot make their own food and must obtain energy by eating other organisms.

There are different types of consumers: Herbivores: Eat only plants (e.g., zebras, springbok, caterpillars).

Carnivores: Eat only meat (e.g., lions, sharks, snakes).

Omnivores: Eat both plants and meat (e.g., humans, baboons, chickens).

Scavengers: Feed on dead animals (e.g., vultures, hyenas).

Decomposers: Decomposers break down dead organisms and waste products into simpler substances. These substances are then returned to the soil, air, and water, where they can be used by producers. Bacteria and fungi are important decomposers. Examples include bacteria in the soil breaking down dead leaves and mushrooms growing on decaying logs.

Food Chains and Food Webs: A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. A simple food chain in the South African savanna might look like this: Grass → Zebra → Lion. A food web is a more complex network of interconnected food chains. It shows the many different feeding relationships that exist within an ecosystem.