This document explains human influences on ecosystems for CAIE IGCSE Biology, focusing on how human activity impacts biodiversity, resources, and sustainability. It begins with food supply, where agricultural machinery, fertilisers, pesticides, selective breeding, and large-scale monoculture increase yield but reduce biodiversity and raise risks of pest resistance. Intensive livestock farming improves efficiency but causes welfare issues, disease spread, and pollution. Habitat destruction through deforestation and land use reduces biodiversity, increases CO₂ levels, contributes to global warming, causes soil erosion, and flooding. Pollution is covered in detail: pesticides disrupt food chains through bioaccumulation, plastics choke animals and pollute waters, while greenhouse gases like CO₂ and methane intensify climate change. Eutrophication is explained as nutrient enrichment from fertilisers and detergents leading to algal blooms, oxygen depletion, and aquatic life death. The section on conservation highlights sustainable use of resources such as forests and fish stocks, alongside recycling of water, paper, plastic, and metals. Methods to protect endangered species include education, captive breeding, seed banks, and habitat preservation. Advanced techniques like artificial insemination and in vitro fertilisation (IVF) in breeding programmes are also described. This resource equips students to understand human impacts on ecosystems and conservation strategies.