Lesson Notes By Weeks and Term v5 - Grade 9

Lesson Video

This page supports the lesson note with a companion video and a short classroom-ready summary.

For class groups and homework, share this lesson page so learners also get the summary, objectives, and full lesson context.

Performance objectives

• Define biosphere and biodiversity.
• Describe the three levels of biodiversity with South African examples.
• Explain human impacts on biodiversity.
• Discuss the importance of conservation.
• Identify specific threats to biodiversity in South Africa.

Lesson summary

The biosphere, the zone of life on Earth, and biodiversity, the variety of life within it, are critically important for all living things, including us. In South Africa, with its incredible range of ecosystems from the fynbos of the Western Cape to the savanna of the Kruger National Park, understanding the biosphere and the importance of biodiversity is crucial. Our economy, culture, and well-being are directly linked to the health of our ecosystems. For example, the fishing industry relies on healthy marine biodiversity, while tourism thrives on our unique natural landscapes.

Lesson notes

What is the Biosphere? The biosphere is the global sum of all ecosystems. It comprises the parts of Earth – land, water, and atmosphere – in which life exists. Think of it as a giant bubble encompassing all living organisms and their interactions with the physical environment. It is a closed system in terms of matter (nutrients are recycled), but an open system in terms of energy (sunlight enters, heat is released). The biosphere isn't a uniform layer; its thickness varies. It extends from the deepest ocean trenches to the highest mountain peaks, although the majority of life is concentrated in a relatively narrow zone near the Earth's surface. What is Biodiversity? Biodiversity, short for biological diversity, refers to the variety of life at all levels, from genes to ecosystems, and the ecological and evolutionary processes that sustain it. It is not just about the number of species; it also considers their relative abundance, genetic differences, and the roles they play in ecosystems. Biodiversity is not evenly distributed on Earth. Tropical regions, like parts of South Africa, generally have higher biodiversity than temperate or polar regions.

Levels of Biodiversity: Genetic Diversity: This refers to the variation of genes within a species. High genetic diversity allows a population to adapt to changing environmental conditions and resist diseases. For example, different maize varieties in South Africa have varying resistance to drought or pests, representing genetic diversity. A population with low genetic diversity is more vulnerable to extinction if a disease or environmental change occurs.

Species Diversity: This refers to the variety of different species in a given area. A community with a high species diversity is generally more stable and resilient to disturbances. For example, the Kruger National Park boasts a high species diversity, including elephants, lions, zebras, giraffes, and numerous bird and insect species. This diversity contributes to the park's stability and resilience.

Ecosystem Diversity: This refers to the variety of different ecosystems in a given region. Each ecosystem has its own unique set of organisms and environmental conditions. South Africa has a particularly rich ecosystem diversity, ranging from the fynbos biome with its unique plant species to the succulent Karoo with its arid-adapted vegetation, and the coastal ecosystems with their varied marine life.

Human Impact on Biodiversity: Human activities have a significant impact on biodiversity, often leading to its decline.

Some of the major threats include: Habitat Loss: This is arguably the biggest threat. As human populations grow, natural habitats are converted for agriculture, urban development, and infrastructure projects. For example, the expansion of agriculture and housing developments is leading to the loss of natural vegetation in many parts of South Africa, threatening endemic species.

Pollution: Pollution from industrial activities, agriculture (pesticides and fertilizers), and urban runoff contaminates air, water, and soil, harming or killing organisms. The Vaal River, for instance, has suffered from severe pollution due to sewage and industrial waste, impacting aquatic life.

Overexploitation: This refers to the unsustainable harvesting of natural resources, such as overfishing, illegal hunting (poaching), and deforestation. Poaching of rhinos for their horns is a major threat to biodiversity in South Africa.

Invasive Species: These are species that are introduced to an area outside their native range and can outcompete native species, disrupt ecosystems, and cause economic damage. The water hyacinth, an invasive aquatic plant, clogs waterways in South Africa, hindering navigation, reducing water quality, and impacting native aquatic life.

Climate Change: Climate change is altering environmental conditions, leading to changes in species distributions, increased frequency of extreme weather events, and ecosystem disruptions. Changes in rainfall patterns and temperature are impacting agricultural productivity and water availability in South Africa.

Ecosystem Services: Ecosystem services are the benefits that humans derive from ecosystems.

These include: Provisioning Services: These are tangible products obtained from ecosystems, such as food, water, timber, and medicinal plants.

Regulating Services: These are benefits obtained from the regulation of ecosystem processes, such as climate regulation, water purification, pollination, and disease control.

Supporting Services: These are fundamental ecosystem processes necessary for the production of all other ecosystem services, such as nutrient cycling, soil formation, and primary production (photosynthesis).

Cultural Services: These are non-material benefits obtained from ecosystems, such as recreation, aesthetic enjoyment, and spiritual enrichment.