Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Define key ecological terms like ecosystem, population, and community.
• Describe different interactions like competition, predation, and mutualism.
• Give examples of interactions using South African organisms.
• Explain how changes in one part of an ecosystem affect others.

Lesson summary

This week, we're diving into the fascinating world of ecosystems and how different living things interact within them. Understanding ecosystems is crucial, especially in South Africa, because our country boasts incredible biodiversity and faces unique environmental challenges like water scarcity and the impact of invasive species. We'll learn how these interactions affect the health and stability of our environment, and ultimately, our own well-being. From the grasslands of the Free State to the coastal regions of KwaZulu-Natal, these principles apply everywhere. Thinking about ecosystems also helps us to appreciate the natural heritage we need to protect for future generations.

Lesson notes

2. 1.

Defining Ecosystems: 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 fynbos biome, the savanna biome, freshwater ecosystems like rivers and dams, and even smaller ecosystems like a termite mound.

Biotic factors: These are the living components, such as plants (producers), animals (consumers), and decomposers (bacteria and fungi).

Abiotic factors: These are the non-living components, such as sunlight, water, soil, temperature, and air. A population is a group of individuals of the same species living in the same area at the same time. For example, a population of springbok in the Karoo. A community is a group of different populations living and interacting in the same area. For example, the plant community in a fynbos ecosystem might include proteas, ericas, and restios, along with various animal populations. A habitat is the natural environment where an organism lives. It provides the organism with food, water, shelter, and other resources. For example, the habitat of a Cape sugarbird is the fynbos biome. A niche is the role an organism plays in its ecosystem, including its feeding habits, interactions with other organisms, and its impact on the environment. For example, the niche of a honey badger includes being a predator of snakes and insects, as well as being a disperser of seeds. 2.

2. Types of Interactions in Ecosystems: These interactions determine how energy and nutrients flow through an ecosystem and influence the population sizes of different species.

Competition: This occurs when two or more organisms require the same limited resources, such as food, water, shelter, or sunlight. For example, lions and hyenas compete for prey like zebras and wildebeest in the savanna. Plants also compete for sunlight, water, and nutrients in the soil.

Example: Black wildebeest and Blue wildebeest both graze on similar grasses in the grasslands. This is an example of interspecific competition (competition between different species).

Predation: This is when one organism (the predator) kills and eats another organism (the prey). For example, a leopard preying on an impala, or a spider catching a fly.

Example:* A Secretary Bird preying on snakes in the grassland. The Secretary Bird is the predator, and the snake is the prey.

Parasitism: This is when one organism (the parasite) benefits by living on or in another organism (the host) and harming it. The parasite obtains its nutrients from the host. For example, ticks living on cattle, or intestinal worms in humans.

Example:* Ticks on a cow. The tick benefits by feeding on the cow's blood, while the cow is harmed by blood loss and potential disease transmission.

Mutualism: This is a relationship where both organisms benefit. For example, bees pollinating flowers. The bees get nectar for food, and the flowers get pollinated, allowing them to reproduce.

Example:* Oxpeckers and zebras/rhinos. The oxpeckers eat ticks and other parasites off the zebra/rhino, benefiting from a food source. The zebra/rhino benefits by having the parasites removed.

Commensalism: This is a relationship where one organism benefits, and the other is neither harmed nor helped. For example, barnacles attaching to whales. The barnacles get a free ride and access to food in the water, while the whale is not affected.

Example:* Cattle egrets following grazing cattle. The egrets feed on insects stirred up by the cattle as they graze. The egrets benefit, while the cattle are neither harmed nor helped. 2.

3. Food Webs and Trophic Levels: A food chain is a linear sequence showing how energy and nutrients are transferred from one organism to another when one organism eats another.

For example: Grass -> Zebra -> Lion. A food web is a more complex diagram showing the interconnected food chains in an ecosystem. It represents the feeding relationships among all the organisms in the community. Trophic levels represent the different feeding positions in a food chain or food web.

Producers: These are organisms that make their own food through photosynthesis, such as plants. They are at the first trophic level.

Primary consumers: These are herbivores that eat producers, such as zebras and springbok. They are at the second trophic level.

Secondary consumers: These are carnivores that eat primary consumers, such as lions and leopards. They are at the third trophic level.

Tertiary consumers: These are carnivores that eat secondary consumers, such as eagles that eat snakes. They are at the fourth trophic level (and often the top).

Decomposers: These are organisms that break down dead plants and animals and return nutrients to the soil, such as bacteria and fungi. They play a vital role in recycling nutrients. Changes at any trophic level can have cascading effects on other levels.