Lesson Notes By Weeks and Term v5 - Grade 7
Living organisms and their environments (Grade 7) – Week 8 focus
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Living organisms and their environments (Grade 7) – Week 8 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Natural Sciences
Class: Grade 7
Term: Term 4
Week: 8
Theme: General lesson support
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Welcome, Grade 7 learners! This week, we delve deeper into the fascinating world of living organisms and their environments, specifically focusing on how living things interact with each other and their surroundings. Understanding these interactions is crucial because it helps us appreciate the delicate balance of nature, especially in South Africa, where our diverse ecosystems support a wealth of plant and animal life. From the fynbos of the Western Cape to the savanna of the Kruger National Park, living things are constantly interacting, competing, and cooperating to survive.
2.1 Interactions Within Ecosystems An ecosystem is a community of living organisms (plants, animals, and microorganisms) interacting with each other and with their non-living (abiotic) environment (soil, water, air, sunlight). These interactions are crucial for the survival and balance of the ecosystem. Let's look at some important types of interactions: Competition: This occurs when two or more organisms need the same resources, such as food, water, shelter, or sunlight. Resources are often limited, forcing organisms to compete.
Example:* In the Kruger National Park, lions and hyenas often compete for the same prey, such as zebras or wildebeest. The stronger or more numerous animal will have a higher chance of securing the kill. Grasses in the savanna compete for sunlight, water, and nutrients in the soil.
Predation: This is when one organism (the predator) hunts and kills another organism (the prey) for food.
Example:* A leopard (predator) hunting an impala (prey) in KwaZulu-Natal. Another example is a snake (predator) hunting a mouse (prey) in a field. The population of the predator and prey are interconnected. If the prey population decreases, the predator population will also decrease due to lack of food.
Symbiosis: This is a close and long-term interaction between two different species.
There are three main types of symbiosis: Mutualism: Both species benefit from the interaction.
Example:* Oxpeckers are birds that live on the backs of zebras, rhinos, and other large mammals. The oxpeckers eat ticks and other parasites off the animals, providing the mammals with pest control and the birds with a food source.
Commensalism: One species benefits, and the other is neither harmed nor helped.
Example:* Epiphytes, like certain orchids, grow on the branches of large trees in the rainforests of South Africa. The orchid benefits by getting access to sunlight, but the tree is not affected.
Parasitism: One species (the parasite) benefits, and the other species (the host) is harmed.
Example:* Ticks are parasites that feed on the blood of animals like dogs and cattle. The tick benefits by getting food and shelter, while the animal is harmed by the loss of blood and the potential transmission of diseases.
Saprophytism: This is a relationship where an organism (saprophyte) obtains its food from dead organic matter.
Example:* Fungi and some bacteria are saprophytes. They decompose dead leaves, fallen logs, and animal carcasses, breaking them down into simpler substances. This process releases nutrients back into the soil, which plants can then use. 2.2 Producers, Consumers, and Decomposers in Food Chains and Food Webs Producers: These are organisms that make their own food through photosynthesis. They use sunlight, water, and carbon dioxide to create glucose (sugar), which they use as energy. Producers are also called autotrophs. Plants are the primary producers in most ecosystems.
Example:* Grass in a grassland ecosystem, algae in a pond, or trees in a forest.
Consumers: These are organisms that cannot make their own food and must obtain energy by eating other organisms. They are also called heterotrophs. Consumers are divided into different categories based on what they eat: Herbivores: Eat only plants.
Example:* Springbok, zebra, and elephants are herbivores found in South African ecosystems.
Carnivores: Eat only meat (other animals).
Example:* Lions, leopards, and cheetahs are carnivores.
Omnivores: Eat both plants and animals.
Example:* Baboons and pigs are examples of omnivores.
Decomposers: These organisms break down dead organisms and waste products, releasing nutrients back into the environment. They play a crucial role in recycling nutrients.
Example:* Fungi, bacteria, and earthworms are decomposers. Food Chains vs.
Food Webs Food Chain: A food chain shows a linear sequence of organisms through which nutrients and energy pass as one organism eats another.
For example: Grass -> Zebra -> Lion.
Food Web: A food web is a more complex representation of feeding relationships within an ecosystem. It consists of interconnected food chains. Organisms often eat and are eaten by multiple species, creating a web-like structure. Food webs are more realistic because they show the complexity of interactions in an ecosystem.
Example:* Think about a grassland ecosystem. Grass is eaten by zebras and springboks. Zebras and springboks are eaten by lions and cheetahs. Lions may also eat cheetahs, and vultures might feed on the carcasses of dead animals. Fungi decompose the dead organisms, returning nutrients to the soil. This complex network of interactions forms a food web. 2.3 Energy Flow in Food Chains and Food Webs Energy flows through an ecosystem from producers to consumers. Producers capture energy from the sun and convert it into chemical energy through photosynthesis. When a consumer eats a producer, it obtains some of that energy.
However, not all the energy is transferred.