Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

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Performance objectives

• Define 'biosphere' and 'biodiversity'.
• Describe the components of the biosphere.
• Identify the three levels of biodiversity.
• Explain the importance of biodiversity.
• Discuss major threats to biodiversity in South Africa.

Lesson summary

The biosphere encompasses all living organisms on Earth and the environments they inhabit, from the deepest ocean trenches to the highest mountain peaks. Biodiversity, short for biological diversity, refers to the variety of life at all its levels, from genes to ecosystems, and the ecological and evolutionary processes that sustain it. Understanding the biosphere and biodiversity is crucial for South African learners because our country is a biodiversity hotspot, meaning it has a high concentration of unique species found nowhere else on Earth. These species are vital to our ecosystems, economy (through ecotourism and agriculture), and cultural heritage.

Lesson notes

2.1 The Biosphere: Earth's Living System The biosphere is the global ecological system integrating all living beings and their relationships, including their interaction with the elements of the lithosphere (rock), hydrosphere (water), and atmosphere (air). It is the zone of life on Earth.

Lithosphere: The Earth’s outer layer, including the crust and upper mantle. Soil, a critical component of the lithosphere, supports plant life, which forms the base of many food webs. Mining activities, however, can significantly damage ecosystems and destroy habitats, impacting biodiversity. For example, gold mining in the Witwatersrand has left a legacy of polluted water and soil.

Hydrosphere: This includes all forms of water on Earth – oceans, rivers, lakes, groundwater, and ice. Aquatic ecosystems are incredibly diverse and support a wide range of organisms, from microscopic plankton to whales. Pollution from agricultural runoff (containing fertilizers and pesticides) and industrial discharge can severely damage aquatic ecosystems, leading to loss of biodiversity. The Vaal River, a vital water source for Gauteng, faces significant pollution challenges.

Atmosphere: The layer of gases surrounding the Earth. The atmosphere provides essential gases for life (oxygen for respiration, carbon dioxide for photosynthesis) and protects us from harmful radiation.

However, increased greenhouse gas emissions from burning fossil fuels are causing climate change, leading to rising temperatures, changes in rainfall patterns, and more frequent extreme weather events, all of which threaten biodiversity.

Interaction: These components interact continuously. For example, plants in the lithosphere absorb water from the hydrosphere and carbon dioxide from the atmosphere to perform photosynthesis, releasing oxygen back into the atmosphere. Animals then consume plants, incorporating these elements into their bodies. When organisms die, decomposition returns nutrients to the soil (lithosphere) and releases carbon dioxide into the atmosphere. This is the essence of nutrient cycling within the biosphere. 2.2 Biodiversity: The Variety of Life Biodiversity encompasses the variety of life at all levels: Genetic Diversity: The variety of genes within a single species. A population with high genetic diversity is better able to adapt to changing environmental conditions and resist diseases.

Example: The different coat colors in leopards represent genetic diversity within the leopard species. Some leopards are also naturally resistant to specific diseases.

Species Diversity: The variety of different species in a given area. South Africa is home to a remarkable diversity of plant and animal species, including the iconic fynbos vegetation of the Western Cape, which is incredibly rich in endemic species (species found nowhere else).

Ecosystem Diversity: The variety of different ecosystems in a region. South Africa boasts a diverse range of ecosystems, from grasslands and savannas to forests and deserts, each supporting unique communities of organisms. The Drakensberg Mountains, for example, are a unique mountain ecosystem. 2.3 Importance of Biodiversity Biodiversity is essential for: Ecosystem Functioning: Diverse ecosystems are more resilient and better able to provide essential services such as pollination, water purification, and climate regulation. For example, a diverse range of pollinators (bees, butterflies, birds) ensures successful crop production.

Human Well-being: Biodiversity provides us with food, medicine, raw materials, and recreational opportunities. Many traditional medicines are derived from plants and animals. Ecotourism, based on South Africa’s natural beauty and wildlife, generates significant revenue and creates jobs.

Cultural Heritage: Many indigenous cultures have deep connections to the natural world and rely on biodiversity for their livelihoods and spiritual well-being. Examples include traditional healers who use indigenous plants for medicinal purposes. 2.4 Threats to Biodiversity in South Africa Habitat Destruction: The clearing of natural habitats for agriculture, urbanization, and mining is a major threat to biodiversity. Deforestation, for instance, destroys habitats for numerous species and increases soil erosion.

Invasive Species: Non-native species introduced into an ecosystem can outcompete native species for resources, leading to their decline or extinction. The water hyacinth, an invasive aquatic plant, chokes waterways and disrupts aquatic ecosystems.

Pollution: Air, water, and soil pollution can harm or kill organisms and disrupt ecosystem functioning. Plastic pollution in oceans, for instance, can be ingested by marine animals, leading to starvation and death. Acid mine drainage from old mining sites pollutes rivers and soil, harming aquatic life and vegetation.

Climate Change: Changes in temperature, rainfall patterns, and sea levels can alter ecosystems and threaten species that are unable to adapt.