Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define and give examples of competition, predation, and symbiosis.
• Explain the role of decomposers in recycling nutrients.
• Differentiate between the types of symbiotic relationships.
• Analyse how these interactions affect populations.
• Relate these concepts to real-world scenarios in South Africa.

Lesson summary

This week, we delve deeper into the fascinating world of living organisms and their environments. We've already explored basic concepts like ecosystems and food chains. Now, we'll focus on specific relationships within ecosystems, particularly competition, predation, symbiosis (mutualism, commensalism, and parasitism), and the crucial role of decomposition. Understanding these relationships is essential because it helps us appreciate the delicate balance of nature and how human activities can disrupt it. Think about the impact of poaching on lion populations (predation) or the effect of alien invasive plants competing with indigenous vegetation for resources (competition).

Lesson notes

a)

Competition: Competition occurs when two or more organisms require the same limited resources, such as food, water, sunlight (for plants), shelter, or mates. This can happen within the same species (intraspecific competition) or between different species (interspecific competition). The organism that is better adapted to obtain the resource will likely survive and reproduce, while the other may be forced to move, adapt, or even die.

Intraspecific Competition: Imagine a pride of lions competing for a single kill (zebra or wildebeest). Only the strongest and most coordinated lions will get the most food.

Interspecific Competition: Consider the case of invasive alien plant species, like the wattle (Acacia mearnsii), competing with native fynbos plants for water and sunlight in the Western Cape. The wattle grows rapidly and shades out the fynbos, reducing the biodiversity of the area. b)

Predation: Predation is a relationship where one organism (the predator) kills and eats another organism (the prey). Predators have adaptations that help them capture prey (e.g., sharp teeth, claws, speed, camouflage), while prey organisms have adaptations to avoid being eaten (e.g., camouflage, speed, poisonous spines, warning coloration).

Example: A leopard hunting an impala. The leopard uses its speed and agility to catch the impala, while the impala relies on its speed and alertness to escape. The population size of each is significantly impacted by the other. If the leopard population decreases sharply, the impala population could increase, leading to overgrazing of the vegetation. Another

Example: A spider building a web to catch insects. The web is a trap designed to ensnare unsuspecting prey. c)

Symbiosis: Symbiosis refers to close and long-term interactions between two different species. There are three main types of symbiotic relationships: Mutualism: Both species benefit from the interaction.

Example: Oxpeckers and zebras/rhinos. Oxpeckers are birds that feed on ticks and other parasites on the skin of zebras and rhinos. The oxpeckers get a food source, and the zebras/rhinos are relieved of parasites. This is mutualistic because both species benefit. Another

Example: Mycorrhizae - a symbiotic relationship between fungi and plant roots. The fungus helps the plant absorb water and nutrients from the soil, while the plant provides the fungus with sugars produced through photosynthesis.

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

Example: Cattle egrets and cattle. Cattle egrets follow cattle as they graze. As the cattle walk through the grass, they stir up insects, which the egrets then eat. The egrets benefit, while the cattle are neither helped nor harmed. Another

Example: Remora fish and sharks. Remoras attach themselves to sharks and feed on scraps of food that the shark drops. The remora benefits, and the shark is unaffected.

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

Example: Ticks and dogs. Ticks attach themselves to dogs and feed on their blood. The ticks benefit, while the dogs are harmed (they can experience itching, irritation, and transmit diseases). Another

Example: Mistletoe growing on a tree. Mistletoe is a plant that attaches to the branches of trees and extracts water and nutrients from the tree. The mistletoe benefits, while the tree is weakened. d)

Decomposition: Decomposition is the process by which dead organisms and organic matter are broken down into simpler substances. This process is carried out by decomposers, such as bacteria and fungi. Decomposers play a vital role in recycling nutrients within an ecosystem. When organisms die, the nutrients stored in their bodies are released back into the soil, where they can be used by plants to grow. Without decomposers, nutrients would remain locked up in dead organisms, and life as we know it would not be possible.

Example: A dead leaf falling to the forest floor. Fungi and bacteria break down the leaf, releasing nutrients like nitrogen and phosphorus back into the soil. These nutrients are then absorbed by the roots of nearby plants, which use them to grow.

Importance: In South African ecosystems, decomposers are crucial for maintaining soil fertility, especially in nutrient-poor soils like those found in fynbos regions. They enable the continued growth of plants, which forms the basis of the food chain. Guided Practice (With Solutions)

Question 1: Identify the type of relationship illustrated in each of the following scenarios: a) A lion hunts and eats a zebra. b) A bee collects nectar from a flower and pollinates the flower in the process. c) A tapeworm lives inside the intestine of a human, absorbing nutrients.

Solution: a)

Predation: The lion (predator) kills and eats the zebra (prey). b)

Mutualism: The bee gets food (nectar), and the flower gets pollinated, benefitting both.