Lesson Notes By Weeks and Term v5 - Grade 7

Lesson Video

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Performance objectives

• Define habitat, population, community, and ecosystem with South African examples.
• Describe how organisms interact (e.g., predation, competition).
• Explain energy flow using food chains and food webs.
• Identify non-living factors that influence life.
• Analyse the impact of human activities on ecosystems.

Lesson summary

This week, we delve into the fascinating world of living organisms and their environments, focusing specifically on how organisms interact with each other and their surroundings. Understanding these interactions is crucial for appreciating the delicate balance of nature and recognizing the impact human activities have on our ecosystems. In South Africa, this knowledge is particularly vital as we face challenges such as water scarcity, biodiversity loss, and the impact of climate change on our unique flora and fauna. Knowing how organisms depend on each other and their environment helps us make informed decisions about conservation and sustainable living.

Lesson notes

a)

Key Definitions: Habitat: A habitat is the natural home or environment of an animal, plant, or other organism. It provides the organism with everything it needs to survive, including food, water, shelter, and space.

Example: A rocky outcrop in the Drakensberg mountains is the habitat of a Drakensberg Rock Lizard.

Population: A population is a group of individuals of the same species living in a particular area at the same time.

Example: A population of Blue Cranes living in the grasslands of the Free State.

Community: A community is all the different populations of organisms that live and interact with each other in a particular area.

Example: The community in a Kruger National Park waterhole includes populations of elephants, zebras, lions, crocodiles, various bird species, and plant life.

Ecosystem: An ecosystem is a community of interacting organisms (biotic factors) and their physical environment (abiotic factors). It includes all the living things and the non-living things (like sunlight, water, soil, and air) in an area, interacting as a system.

Example: A fynbos ecosystem in the Western Cape, including the plants, animals, insects, soil, climate, and rainfall. b)

Interactions between Organisms: Predation: One organism (the predator) hunts and kills another organism (the prey) for food.

Example: A lion (predator) hunting a wildebeest (prey) in the African savanna.

Competition: Occurs when two or more organisms need the same limited resource, such as food, water, shelter, or space. This can occur between individuals of the same species (intraspecific competition) or between different species (interspecific competition).

Example: Lions and hyenas competing for the same zebra carcass on the savanna. Invasive alien plant species compete with indigenous plants for sunlight and water.

Mutualism: A relationship between two organisms of different species where both benefit.

Example: Bees pollinating flowers. The bee gets nectar for food, and the flower gets pollinated, allowing it to reproduce. Another example is the relationship between cleaner fish and larger fish; the cleaner fish eat parasites off the larger fish, providing food for the cleaner fish and keeping the larger fish healthy.

Parasitism: A relationship where one organism (the parasite) benefits at the expense of another organism (the host). The parasite lives on or in the host and obtains nutrients from it.

Example: Ticks feeding on the blood of a dog. The tick benefits, while the dog is harmed.

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

Example: Birds nesting in trees. The bird gets a safe place to build its nest, while the tree is neither helped nor harmed. c) Energy Flow in Ecosystems (Food Chains and Food Webs): Energy flows through an ecosystem in a one-way direction, starting with the sun.

Producers (Autotrophs): These are organisms that make their own food through photosynthesis, using sunlight, water, and carbon dioxide. Plants are the main producers in most ecosystems.

Example: Grass in a grassland ecosystem.

Consumers (Heterotrophs): These are organisms that cannot make their own food and must obtain energy by eating other organisms.

Primary Consumers (Herbivores): Eat producers.

Example: A zebra eating grass. Secondary Consumers (Carnivores or Omnivores): Eat primary consumers.

Example: A lion eating a zebra (carnivore). A baboon eating fruit and insects (omnivore).

Tertiary Consumers (Carnivores): Eat secondary consumers.

Example: A leopard eating a baboon.

Decomposers (Saprotrophs): These organisms break down dead plants and animals, returning nutrients to the soil.

Examples: Bacteria and fungi. They recycle nutrients, making them available for producers to use. A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another.

For example: Grass → Zebra → Lion. A food web is a more complex representation of the feeding relationships in an ecosystem, showing interconnected food chains. Food webs more accurately reflect the complex interactions between organisms in a real ecosystem. d)

Abiotic Factors: Abiotic factors are the non-living components of an ecosystem. They play a crucial role in determining which organisms can survive in a particular environment.

Examples include: Sunlight: Provides energy for photosynthesis.

Water: Essential for all living organisms.

Temperature: Affects the rate of metabolic processes.

Soil: Provides nutrients and support for plants.

Air: Provides oxygen for respiration and carbon dioxide for photosynthesis. pH: The acidity or alkalinity of the soil or water affects the availability of nutrients.

Worked example

Consider a wetland ecosystem in KwaZulu-Natal. Abiotic factors such as rainfall, temperature, and soil type influence the type of vegetation that can grow there (e.g., reeds, sedges, water lilies). This vegetation provides food and shelter for various animals, such as frogs, fish, birds, and insects. The interactions between these organisms, along with the abiotic factors, determine the overall structure and function of the wetland ecosystem.

Guided Practice (With Solutions)

Question 1: Define the terms "population" and "community" and give a South African example of each.

Solution:

Population: A group of individuals of the same species living in a particular area at the same time.

Example: A population of African Penguins on Boulders Beach.

Community: All the different populations of organisms that live and interact with each other in a particular area.

Example: The community in a pond in Kirstenbosch Botanical Garden, which includes populations of water lilies, frogs, insects, and algae.

Question 2: Describe the difference between predation and parasitism, and provide an example of each found in South Africa.