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 an ecosystem and its components.
• Describe interactions like competition and predation.
• Explain how energy flows through food chains and webs.
• Analyze human impact on local ecosystems.
• Construct a simple South African food web.

Lesson summary

This week, we delve into the fascinating world of ecosystems and the intricate interactions that occur within them. An ecosystem is a community of living organisms (plants, animals, and microorganisms) that interact with each other and with their physical environment (soil, water, air, sunlight). Understanding ecosystems is crucial, especially in South Africa, because our lives are directly connected to the health and balance of these natural systems.

Lesson notes

2.1 Ecosystems: A Definition An ecosystem is a community of living organisms (biotic factors) interacting with each other and their non-living physical environment (abiotic factors).

Biotic factors: These are the living things within an ecosystem, including plants (producers), animals (consumers), fungi, and bacteria (decomposers).

Abiotic factors: These are the non-living components, such as sunlight, water, air (gases like oxygen and carbon dioxide), soil (minerals and nutrients), temperature, and climate.

Example: A pond ecosystem includes biotic factors like fish, frogs, water lilies, algae, and bacteria. Abiotic factors include the water itself, sunlight, dissolved oxygen, and the minerals in the pond sediment. 2.2 Interactions between Organisms: Organisms in an ecosystem interact in various ways: Competition: When two or more organisms require the same limited resources, such as food, water, shelter, or sunlight.

Example:* Lions and hyenas compete for the same prey (e.g., zebras, wildebeest) on the African savanna.

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

Example:* A snake preying on a mouse. A leopard preying on an impala.

Mutualism: A relationship where both organisms benefit.

Example:* Bees pollinating flowers. The bee gets nectar (food), and the flower gets its pollen spread. In South Africa, oxpeckers eat ticks off of cattle, benefiting both the bird (food) and the cattle (tick removal).

Parasitism: A relationship where one organism (the parasite) benefits at the expense of the other organism (the host).

Example:* Ticks feeding on a dog. The tick benefits, and the dog is harmed (loss of blood, irritation). Tapeworms living in the intestines of animals.

Commensalism: A relationship where one organism benefits, and the other is neither harmed nor helped.

Example:* Epiphytes (like orchids) growing on trees. The orchid gets support and sunlight, and the tree is neither helped nor harmed. Remora fish attaching to sharks; the remora gets food scraps, while the shark is unaffected. 2.3 Energy Flow: Food Chains and Food Webs Energy flows through an ecosystem, typically originating from the sun. This flow is often depicted using food chains and food webs.

Food Chain: A linear sequence showing the transfer of energy from one organism to another. Each organism occupies a trophic level. The first trophic level is always occupied by producers (plants) that make their own food through photosynthesis.

The subsequent levels are consumers: herbivores (plant eaters), carnivores (meat eaters), and omnivores (eat both plants and animals).

Example:* Grass → Zebra → Lion. The grass (producer) is eaten by the zebra (herbivore), which is eaten by the lion (carnivore).

Food Web: A complex network of interconnected food chains representing the feeding relationships in an ecosystem. Food webs are more realistic than food chains because organisms often eat a variety of things.

Example:* Consider a South African savanna food web. Grass is eaten by zebras, wildebeest, and springbok. Zebras and wildebeest are eaten by lions and hyenas. Springbok are eaten by cheetahs and leopards. Vultures scavenge on the carcasses of dead animals. This interconnected web shows the complex flow of energy within the ecosystem. Decomposers play a crucial role by breaking down dead organisms and waste, returning nutrients to the soil, which are then used by producers. They are often not explicitly shown on a food web diagram but are always present. 2.4 Human Impact on Ecosystems Human activities can have significant and often negative impacts on ecosystems. These impacts can disrupt the delicate balance of the environment and lead to various problems: Pollution: Air pollution from factories and vehicles, water pollution from sewage and industrial waste, and soil pollution from pesticides and fertilizers can all harm organisms and disrupt ecosystems. Think about the pollution from mining activities affecting water sources and soil quality.

Deforestation: Clearing forests for agriculture, housing, or logging removes habitats, reduces biodiversity, and can lead to soil erosion. In South Africa, deforestation for agriculture is a major concern in some areas.

Overfishing: Removing fish from the ocean at a rate faster than they can reproduce can lead to the collapse of fish populations and disrupt marine ecosystems.

Introduction of Invasive Species: Non-native species introduced to an ecosystem can outcompete native species, disrupt food webs, and cause ecological damage.

Example: The water hyacinth, an invasive plant in many South African waterways, chokes out native plants and reduces oxygen levels in the water.

Climate Change: Increased greenhouse gas emissions are leading to global warming, which is causing changes in temperature, rainfall patterns, and sea levels, impacting ecosystems worldwide.

Example: Rising sea levels threaten coastal ecosystems and communities.