Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define and give examples of 'biotic' and 'abiotic' factors.
• Describe interactions like predation, competition, and symbiosis.
• Explain the roles of producers, consumers, and decomposers.
• Understand how changes in abiotic factors impact ecosystems.

Lesson summary

This week, we delve deeper into understanding the intricate relationships between living organisms and their environment. This is particularly important in South Africa, a country blessed with incredible biodiversity, but also facing environmental challenges like habitat loss, pollution, and the impact of climate change. Understanding these relationships allows us to appreciate the delicate balance of nature and encourages responsible actions to protect our environment for future generations. Think about the Knysna forest, the Kruger National Park, or even the small ecosystems in your own backyard - they all rely on the interactions we will be exploring.

Lesson notes

2.1 Biotic and Abiotic Factors: An ecosystem consists of two major components: biotic and abiotic factors. Biotic factors are all the living organisms in an ecosystem. This includes plants, animals, fungi, bacteria, and all other living things. In a South African grassland, biotic factors include grasses, zebras, wildebeest, lions, vultures, and various insects and microorganisms in the soil. Abiotic factors are the non-living parts of an ecosystem. These include sunlight, temperature, water, soil, air, minerals, and humidity. The amount of sunlight reaching the fynbos region, the average rainfall in the Drakensberg mountains, and the type of soil in the Karoo are all examples of abiotic factors.

Example: Consider a puddle of water after a rainstorm in a schoolyard.

Biotic: Algae, mosquito larvae, small insects.

Abiotic: Water, sunlight, temperature, minerals dissolved in the water, the surface on which the water sits. 2.2 Interactions between Living Organisms: Living organisms interact with each other in various ways, which can be beneficial, harmful, or neutral.

Some important interactions include: Predation: One organism (the predator) kills and eats another organism (the prey). This is a vital way of controlling population size. For example, a leopard (predator) hunting an impala (prey) in Kruger National Park. The leopard benefits by obtaining food, while the impala is harmed.

Competition: When two or more organisms require the same limited resources (food, water, space, sunlight), they compete. This can occur between individuals of the same species (intraspecific competition) or between different species (interspecific competition). For example, lions and hyenas compete for the same prey animals.

Symbiosis: This is a close and long-term interaction between two different species.

There are three main types of symbiosis: Mutualism: Both species benefit.

Example: Oxpeckers (birds) feed on ticks and other parasites on rhinos. The oxpeckers get food, and the rhinos get rid of parasites.

Commensalism: One species benefits, and the other is neither harmed nor helped.

Example: Epiphytes (plants) like orchids growing on the branches of trees in a rainforest. The orchid benefits from the support and access to sunlight, while the tree is neither harmed nor helped.

Parasitism: One species (the parasite) benefits, and the other species (the host) is harmed.

Example: Ticks feeding on the blood of a dog. The tick benefits, and the dog is harmed. 2.3 Food Chains and Food Webs: Food Chain: A linear sequence showing the transfer of energy from one organism to another through feeding. It always starts with a producer.

Food Web: A complex network of interconnected food chains showing all the feeding relationships in an ecosystem.

Producers: These are organisms that make their own food through photosynthesis (using sunlight, water, and carbon dioxide). Plants are the main producers in most ecosystems. In South Africa, examples include grass in the savanna, trees in the forests, and algae in the oceans.

Consumers: These are organisms that obtain energy by eating other organisms.

There are different types of consumers: Herbivores: Eat only plants.

Examples: Zebras, springbok, caterpillars.

Carnivores: Eat only animals.

Examples: Lions, eagles, snakes.

Omnivores: Eat both plants and animals.

Examples: Baboons, humans, pigs.

Decomposers: These are organisms that break down dead plants and animals and release nutrients back into the soil.

Examples: Bacteria, fungi, earthworms. Decomposers are essential for recycling nutrients in the ecosystem. Example of a simple food chain in a South African savanna: Grass (Producer) → Zebra (Herbivore) → Lion (Carnivore) → Vultures (Scavengers) → Bacteria (Decomposers) 2.4 Impact of Abiotic Factors: Changes in abiotic factors can significantly impact the populations of organisms in an ecosystem.

Rainfall: A prolonged drought can lead to a decline in plant growth, which in turn affects the populations of herbivores and carnivores that depend on those plants. In areas like the Karoo, rainfall is a limiting factor for plant growth and therefore, the entire food web.

Temperature: Extreme temperatures (both hot and cold) can be harmful to many organisms. For example, frost can kill sensitive plants, and heat waves can cause animals to suffer from heatstroke. Climate change, leading to increased temperatures and altered rainfall patterns, poses a serious threat to South African biodiversity.

Sunlight: Sunlight is essential for photosynthesis. Reduced sunlight can limit plant growth and affect the entire food chain. This is especially important in aquatic ecosystems, where the depth of sunlight penetration affects the distribution of photosynthetic organisms.

Example: Suppose a severe drought hits the Eastern Cape.

This could lead to: Death of many plants due to lack of water. Starvation of herbivores like cattle and sheep.