Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define ecosystem, habitat, population, and community.
• Explain the difference between biotic and abiotic factors.
• Describe feeding relationships and create a food chain.
• Understand how organisms compete for resources.
• Explain the importance of biodiversity.

Lesson summary

This week, we delve deeper into the fascinating world of living organisms and their environments, focusing on how living things interact with each other and their surroundings. Understanding these interactions is crucial for appreciating the delicate balance of nature, especially in South Africa, where our rich biodiversity faces numerous challenges, from habitat loss to climate change. By learning about ecosystems and the roles organisms play within them, you'll be better equipped to understand and contribute to the conservation of our precious natural heritage.

Lesson notes

2. 1.

Basic Ecological Concepts Ecosystem: An ecosystem is a community of living organisms (biotic factors) interacting with each other and with their non-living (abiotic) environment. An ecosystem can be as small as a puddle or as large as an ocean. In South Africa, examples include the fynbos ecosystem of the Western Cape, the savanna ecosystems of Kruger National Park, and the coral reef ecosystems off the KwaZulu-Natal coast. These areas teem with life, interacting in complex ways.

Habitat: A habitat is the natural home or environment of an organism. It provides the organism with the resources it needs to survive, such as food, water, shelter, and space. Examples include a dassie living amongst rocks on Table Mountain, a fish living in a river, or a bird nesting in a tree.

Population: A population is a group of individuals of the same species living in a particular area at a particular time. For instance, all the zebras in a specific section of Kruger National Park form a population. All the baobab trees in a certain area constitute another population.

Community: A community consists of all the different populations of living organisms that live and interact in a particular area. For example, the community in a pond might include fish, frogs, insects, plants, and microorganisms. 2.

2. Biotic and Abiotic Factors Biotic Factors: These are the living components of an ecosystem.

Examples include: Plants (e.g., grass, trees, flowers) Animals (e.g., lions, elephants, birds, insects) Bacteria and fungi (decomposers)

Abiotic Factors: These are the non-living components of an ecosystem.

Examples include: Sunlight (essential for photosynthesis) Water (necessary for all life processes) Soil (provides nutrients for plants and habitat for many organisms) Temperature (affects the rate of biological processes) Air (provides oxygen and carbon dioxide) Rainfall (affects the availability of water)

Example: Consider a small stream in the Drakensberg. The biotic factors include the trout, the algae growing on the rocks, the insects living in the water, and the plants along the banks. The abiotic factors include the water, the rocks, the sunlight, the temperature of the water, and the oxygen dissolved in the water. 2.

3. Feeding Relationships 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 ecosystems. Examples in South Africa include grass in the savanna, fynbos shrubs in the Western Cape, and algae in rivers and oceans.

Consumers (Heterotrophs): These organisms cannot make their own food and must obtain energy by consuming other organisms. Consumers are classified based on what they eat: Herbivores:* Eat only plants (e.g., springbok, elephants, caterpillars)

Carnivores:* Eat only animals (e.g., lions, snakes, eagles)

Omnivores:* Eat both plants and animals (e.g., baboons, pigs, humans)

Decomposers: These organisms break down dead plants and animals, returning nutrients to the soil. Examples include bacteria, fungi, and earthworms. Decomposers play a vital role in recycling nutrients in the ecosystem.

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 → Zebra → Lion. The arrow indicates the direction of energy flow.

Food Web: A food web is a more complex diagram showing the interconnected food chains in an ecosystem. It illustrates the multiple feeding relationships between different organisms. Example Food Chain (South African Savanna): Sun → Grass → Impala → Cheetah → Decomposers In this chain, the sun provides energy to the grass (producer). The impala (herbivore, primary consumer) eats the grass. The cheetah (carnivore, secondary consumer) eats the impala. When the cheetah dies, decomposers break down its body, returning nutrients to the soil, which helps the grass grow.

Example Food Web (Simplified): Imagine a field with grass, rabbits, snakes, and eagles. The grass is eaten by the rabbits. The rabbits are eaten by the snakes. The snakes are eaten by the eagles. The grass is also eaten by some insects. The insects are eaten by the snakes and by some birds. When any of these organisms die, decomposers break them down. This creates a web of interconnected feeding relationships. 2.

4. Competition for Resources Organisms in an ecosystem compete for limited resources such as: Food: Animals compete for food sources, such as grazing areas for herbivores or prey for carnivores.

Water: Water is essential for all living things. In dry areas, competition for water can be intense.

Shelter: Organisms need shelter to protect themselves from predators and the elements.

Sunlight: Plants compete for sunlight to carry out photosynthesis.

Space: Organisms need space to grow, reproduce, and find resources.