Everything from the 4 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
Humans have increased food production by using agricultural machinery to farm larger areas efficiently, chemical fertilisers to improve yields, insecticides to improve quality and yield, herbicides to reduce competition with weeds and selective breeding to improve production by crop plants and livestock. Large-scale monocultures and intensive livestock production give high yields at low cost, but reduce biodiversity, spread disease and pollute the environment.
Insecticides kill insects; herbicides kill weeds (plants). Both are pesticides. Do not mix them up, and remember fertilisers supply mineral ions, not "food" for the plant: plants make their own food by photosynthesis.
"Higher profit" on its own is a weak answer. Say why: higher yield per hectare, less labour per tonne, or less energy wasted by the animals.
Biodiversity is the number of different species that live in an area. Habitats are destroyed to provide land for housing, crop plants and livestock, to extract natural resources and by freshwater and marine pollution. By altering food chains and food webs, humans can have a negative impact on habitats. Deforestation reduces biodiversity, can cause extinction, and leads to loss of soil, flooding and an increase of carbon dioxide in the atmosphere.
Biodiversity is the number of different species, not the number of individual organisms. A field of a million wheat plants has very low biodiversity.
Do not write that deforestation "reduces oxygen so animals suffocate". The expected effects are lower biodiversity, extinction, soil loss, flooding and more carbon dioxide.
Untreated sewage and excess fertiliser entering rivers and lakes cause algae to grow rapidly and then oxygen levels to fall, killing fish and other animals. Extended: this process is eutrophication: more nitrate and other ions, more growth of producers, more decomposition after they die, more aerobic respiration by decomposers, less dissolved oxygen and death of organisms that need it. Non-biodegradable plastics are not broken down by decomposers, so they harm animals on land and in water for many years. Extra carbon dioxide and methane cause the enhanced greenhouse effect and climate change.
Fish do not die because the algae "use up the oxygen". In the light algae produce oxygen. The oxygen is used up by the huge numbers of decomposers respiring aerobically as they break down the dead producers.
Breaking into tiny pieces is not the same as being decomposed. Microplastics are still plastic: no decomposer has broken them down.
The greenhouse effect itself is natural and necessary. The problem is the enhanced greenhouse effect caused by extra gases. Also, it is not the same as the hole in the ozone layer.
A sustainable resource is one which is produced as rapidly as it is removed from the environment, so that it does not run out. Forests and fish stocks can be conserved and managed sustainably. Organisms become endangered or extinct through climate change, habitat destruction, hunting, overharvesting, pollution and introduced species. They can be conserved by monitoring and protecting species and habitats, education, captive breeding programmes and seed banks.
A larger mesh size lets young, small fish escape, so they survive to reproduce. It does not mean catching bigger fish to make more money.
Increasing the number of animals does not restore genetic variation on its own. New alleles must come from unrelated animals, for example by AI or IVF with animals from other populations.