Lesson Notes By Weeks and Term v5 - Grade 8

Lesson Video

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Performance objectives

• Define ecosystem, biotic, and abiotic factors
• Explain interactions like predation and mutualism
• Describe roles like producers, consumers, and decomposers
• Construct a simple food chain and food web
• Understand the importance and threats to biodiversity in South Africa

Lesson summary

This week, we delve into the fascinating world of ecosystems and the interactions that occur within them. Understanding ecosystems is crucial because it helps us appreciate the interconnectedness of all living things and their environment. In South Africa, with its rich biodiversity from the Fynbos region to the Kruger National Park, understanding how ecosystems function is essential for conservation efforts, sustainable resource management, and addressing challenges like climate change, invasive species, and pollution which directly impact our communities and natural heritage. Think about how drought affects livestock farming, or how overfishing impacts coastal communities.

Lesson notes

2.1 What is an Ecosystem? An ecosystem is a community of interacting organisms (plants, animals, and microorganisms) and their physical environment (soil, water, air), functioning together as a unit.

Biotic Factors: These are the living components of an ecosystem, such as plants, animals, fungi, and bacteria. Examples in a South African grassland ecosystem include grasses, zebras, lions, termites, and various soil microorganisms.

Abiotic Factors: These are the non-living components of an ecosystem, such as sunlight, water, soil, temperature, and air. For example, in the Fynbos biome, abiotic factors include the sandy, nutrient-poor soil, seasonal rainfall, and frequent fires. 2.2 Types of Interactions in Ecosystems Organisms in an ecosystem interact in various ways, and these interactions play a crucial role in shaping the ecosystem.

Here are some key types of interactions: Competition: This occurs when two or more organisms require the same limited resource, such as food, water, shelter, or sunlight. For example, in the Kruger National Park, lions and hyenas compete for prey like zebras and wildebeest.

Predation: This involves one organism (the predator) killing and consuming another organism (the prey). A classic example is a leopard (predator) hunting an impala (prey) in a savanna ecosystem.

Mutualism: This is a relationship where both organisms benefit. A good example is the relationship between oxpeckers and zebras. Oxpeckers feed on ticks and other parasites on the zebra, benefiting the zebra by removing pests, and the oxpecker gets a meal.

Parasitism: This is 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 feeds on the dog's blood, benefiting the tick, but harming the dog. Another example is mistletoe growing on trees; mistletoe obtains nutrients from the tree, weakening it.

Commensalism: This is a relationship where one organism benefits, and the other is neither harmed nor helped. An example is epiphytic orchids growing on tree branches in a rainforest. The orchid benefits by getting access to sunlight, while the tree is not significantly affected. 2.3 Roles of Organisms in Ecosystems Organisms in an ecosystem can be classified based on their role in the flow of energy and nutrients: Producers (Autotrophs): These are organisms that make their own food through photosynthesis, using sunlight, water, and carbon dioxide. Plants are the primary producers in most ecosystems. In the Fynbos, examples include proteas and restios.

Consumers (Heterotrophs): These are organisms that obtain energy by consuming other organisms.

There are different types of consumers: Herbivores: Animals that eat plants. Examples include grasshoppers and springbok.

Carnivores: Animals that eat other animals. Examples include lions and eagles.

Omnivores: Animals that eat both plants and animals. Examples include baboons and many birds.

Decomposers: These are organisms that break down dead organisms and organic waste, releasing nutrients back into the ecosystem. Bacteria and fungi are the main decomposers. They play a vital role in nutrient cycling. 2.4 Food Chains and Food Webs Food Chain: A food chain is a linear sequence showing the transfer of energy from one organism to another.

For example: Grass → Grasshopper → Mouse → Snake → Eagle.

Food Web: A food web is a complex network of interconnected food chains, showing the various feeding relationships within an ecosystem. A food web provides a more realistic representation of energy flow than a single food chain. For example, in a grassland ecosystem, grasshoppers might be eaten by mice, lizards, or birds, and those animals might be eaten by snakes, hawks, or foxes. 2.5 Importance of Biodiversity and Threats Biodiversity refers to the variety of life on Earth, including the different species of plants, animals, and microorganisms, as well as the ecosystems they form. Biodiversity is crucial for healthy ecosystems because: It provides stability and resilience to environmental changes. It supports important ecosystem services such as pollination, water purification, and climate regulation. It provides resources for human use, such as food, medicine, and timber. South Africa is a biodiversity hotspot, but it faces many threats: Habitat destruction: Due to agriculture, urbanization, and mining.

Invasive species: Alien plants and animals that outcompete native species.

Pollution: From industrial activities, agriculture, and waste disposal.

Climate change: Leading to changes in rainfall patterns and increased temperatures.

Overexploitation of resources: such as overfishing and poaching.

Example: Invasive Alien Plants in the Western Cape In the Western Cape, invasive alien plants like Rooikrans (Acacia cyclops) and Port Jackson Willow (Acacia saligna) compete with native Fynbos plants for water and nutrients.