Lesson Notes By Weeks and Term v5 - Grade 12

Lesson Video

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Performance objectives

• Explain causes & consequences of deforestation.
• Describe impacts of alien invasive species.
• Analyze data on pollution.
• Evaluate sustainable resource management.
• Apply knowledge to exam questions.

Lesson summary

The Grade 12 Life Sciences curriculum dedicates significant attention to the impact of human activities on our environment. This is crucial because South Africa, like many developing nations, faces unique environmental challenges stemming from resource exploitation, population growth, and socio-economic disparities. Understanding these impacts is vital for informed citizenship and responsible decision-making that can mitigate environmental damage and promote sustainability. Our focus this week will be on consolidating our knowledge of key human impacts, refining our analytical skills for exam questions, and exploring real-world applications of environmental principles.

Lesson notes

2.1 Deforestation Definition: Deforestation refers to the clearing of forests for other land uses, such as agriculture, urbanization, and mining.

Causes in South Africa: Agriculture: Expansion of commercial farming (e.g., sugar cane, timber plantations) and subsistence farming often requires clearing forests. Small-scale farmers practicing slash-and-burn agriculture contribute locally.

Urbanization: As cities grow, forests are cleared to make way for housing, infrastructure (roads, power lines), and industrial development.

Mining: Mining activities, particularly coal and platinum mining, require large areas of land and often lead to deforestation.

Illegal logging: The illegal harvesting of timber for fuel wood, construction, and export contributes to deforestation, although less so than the other causes in South Africa compared to other countries.

Firewood: In rural areas, firewood is a primary source of energy, leading to deforestation when harvesting is unsustainable.

Consequences: Soil Erosion: Loss of tree cover exposes soil to wind and rain, leading to soil erosion. Topsoil, rich in nutrients, is washed away, reducing soil fertility and agricultural productivity. Increased sedimentation in rivers affects aquatic ecosystems.

Loss of Biodiversity: Forests are habitats for a wide range of plant and animal species. Deforestation destroys these habitats, leading to a decline in biodiversity and potential extinction of species.

Climate Change: Trees absorb carbon dioxide (CO2) from the atmosphere during photosynthesis. Deforestation releases this stored CO2 back into the atmosphere, contributing to global warming. Reduced forest cover also reduces carbon sequestration capacity.

Water Cycle Disruption: Forests play a vital role in regulating the water cycle. They help to absorb rainfall, replenish groundwater, and release water vapor back into the atmosphere. Deforestation can lead to decreased rainfall, increased runoff, and flooding.

Economic Impacts: While deforestation can create short-term economic benefits (e.g., timber sales), it can also have long-term negative economic impacts due to soil degradation, reduced agricultural productivity, and loss of ecosystem services.

Example: The clearing of indigenous forests in KwaZulu-Natal for sugarcane farming has led to significant soil erosion and loss of biodiversity in the region. 2.2 Alien Invasive Species Definition: Alien species are organisms that are introduced into an environment outside their natural range. Invasive species are alien species that cause harm to the environment, economy, or human health. Impacts on Biodiversity and Ecosystem Function: Competition: Invasive species compete with native species for resources such as food, water, and habitat. They are often more aggressive or adaptable than native species, giving them a competitive advantage.

Predation: Some invasive species are predators that prey on native species, leading to a decline in native populations.

Disease Transmission: Invasive species can introduce new diseases and parasites that native species are not resistant to.

Habitat Alteration: Invasive species can alter habitats, making them unsuitable for native species. For example, invasive plants can change soil chemistry or water availability.

Hybridization: Invasive species can hybridize with native species, leading to a loss of genetic diversity and potentially threatening the survival of native species. South African

Examples: Water Hyacinth ( Eichhornia crassipes ): This aquatic plant clogs waterways, blocking sunlight, reducing oxygen levels, and hindering navigation. It impacts aquatic ecosystems and water supplies.

Black Wattle ( Acacia mearnsii ): This tree invades grasslands and fynbos, outcompeting native vegetation, depleting water resources, and increasing fire risk.

European Starling ( Sturnus vulgaris ): This bird competes with native bird species for nesting sites and food.

Argentine Ant ( Linepithema humile ): Displaces native ant species and disrupts pollination networks.

Management Strategies: Prevention: Preventing the introduction of alien species is the most effective way to manage invasive species. This can be achieved through strict border controls and quarantine measures.

Early Detection and Rapid Response: Early detection and rapid response are crucial for controlling invasive species before they become widespread. This involves monitoring for new infestations and taking immediate action to eradicate or contain them.

Control Methods: Control methods include physical removal (e.g., hand-pulling weeds), chemical control (e.g., herbicides), and biological control (e.g., introducing natural enemies of the invasive species).

Example: The Working for Water programme is a South African government initiative that aims to control invasive alien plants and improve water security. They use a combination of manual removal, herbicide application, and biological control methods.