Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Define the biosphere and biodiversity.
• Explain the importance of biodiversity in South Africa.
• Identify threats to biodiversity and suggest solutions.
• Describe how living organisms are interconnected.
• Evaluate the impact of human activities on biodiversity.

Lesson summary

The biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere. Biodiversity, or biological diversity, refers to the variety of life on Earth at all its levels, from genes to ecosystems, and can encompass the evolutionary, ecological, and cultural processes that sustain life. Understanding the biosphere and biodiversity is crucial for South African learners because our country is a biodiversity hotspot. We rely on healthy ecosystems for clean water, fertile soil, and resources like timber and medicinal plants.

Lesson notes

The Biosphere: The biosphere encompasses all living organisms on Earth and their interactions with the non-living environment (atmosphere, lithosphere, and hydrosphere). Think of it as a single, interconnected ecosystem. It is not a uniform sphere, but rather a mosaic of different ecosystems, each with its own unique characteristics. The boundaries of the biosphere are not fixed; they fluctuate with changes in environmental conditions.

Example: A small pond in your backyard is a miniature ecosystem within the larger biosphere. The fish, plants, algae, and bacteria in the pond interact with each other and with the water, sunlight, and soil.

Biodiversity: Biodiversity is the variety of life at all levels: Genetic diversity: Variation in genes within a species. This is the raw material for evolution. Think of different colors of beads, representing different alleles (versions of a gene) within a population of, say, a species of Streptocarpus (Cape Primrose) flower. High genetic diversity means many different colors, enabling it to adapt to different environmental challenges.

Species diversity: The number and abundance of different species in a given area. A veld with many different types of grasses, flowers, insects, and animals has high species diversity.

Ecosystem diversity: The variety of different habitats, communities, and ecological processes in a region. The Drakensberg mountains, with its grasslands, forests, and rivers, have high ecosystem diversity.

Importance: Biodiversity provides ecosystem services (clean air, clean water, pollination), supports livelihoods, and has cultural and intrinsic value.

Ecosystem Services: These are the benefits that humans receive from ecosystems.

Examples include: Provisioning services: Food, water, timber, medicine. Think of rooibos tea harvested from the Cederberg region.

Regulating services: Climate regulation, water purification, disease control. Wetlands filter water and reduce flooding.

Supporting services: Nutrient cycling, soil formation, pollination. Bees pollinate crops.

Cultural services: Recreation, aesthetic value, spiritual value. The Kruger National Park provides opportunities for wildlife viewing and tourism.

Threats to Biodiversity: Habitat loss: Destruction or fragmentation of habitats due to agriculture, urbanization, and deforestation. Think of the clearing of fynbos for housing developments.

Invasive species: Introduction of non-native species that compete with native species for resources. Think of the water hyacinth choking rivers and dams.

Pollution: Contamination of air, water, and soil by pollutants. Acid rain harms forests and aquatic ecosystems.

Climate change: Alteration of global climate patterns, leading to changes in temperature, rainfall, and sea level. Coral bleaching is a result of warming ocean temperatures.

Overexploitation: Unsustainable harvesting of resources, such as overfishing and poaching. Rhino poaching is a serious threat to rhino populations in South Africa.

Interrelationships within the Biosphere: Living organisms are interconnected through food webs, nutrient cycles, and symbiotic relationships.

Food Webs: A network of interconnected food chains, showing the flow of energy and nutrients in an ecosystem.

Example: Grass → Grasshopper → Mouse → Snake → Eagle. The grass is a producer, the grasshopper is a primary consumer (herbivore), the mouse is a secondary consumer (carnivore/omnivore), the snake is a tertiary consumer (carnivore), and the eagle is a quaternary consumer (carnivore).

Nutrient Cycles: The movement of essential elements (carbon, nitrogen, phosphorus) through the biosphere.

Example: The carbon cycle involves photosynthesis (plants taking up CO2), respiration (organisms releasing CO2), decomposition (releasing CO2 into the soil), and combustion (burning fossil fuels releasing CO2).

Symbiotic Relationships: Close interactions between different species.

Mutualism: Both species benefit (e.g., bees and flowers).

Commensalism: One species benefits, and the other is neither harmed nor helped (e.g., epiphytes growing on trees).

Parasitism: One species benefits, and the other is harmed (e.g., ticks on dogs). Guided Practice (With Solutions)

Question 1: Define the term 'biosphere' and explain its significance to life on Earth.

Solution: The biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere, hydrosphere, and atmosphere. Its significance lies in providing the conditions necessary for life to exist. It regulates the Earth's climate, cycles essential nutrients, and provides resources like food, water, and oxygen. Without a functioning biosphere, life as we know it would not be possible. The interconnectedness within the biosphere means damage to one part can affect the whole system.

Question 2: Explain three ecosystem services provided by biodiversity in South Africa. Give specific examples for each.