Human Impact on the Environment
Ecology and the Environment · 8 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 10% of your exam marks.
Climate change, deforestation, and biodiversity loss are growing in frequency as contemporary issues.
A pest is any organism (insect, weed, fungus) that damages crops, livestock or people. The traditional way to manage pests is to spray chemical pesticides on them, but this has several drawbacks:
- Pesticides kill non-target species (bees, ladybirds, songbirds) as well as the pests
- Pests evolve resistance (see topic 14), making the pesticide useless over time
- Pesticides can biomagnify up food chains (see topic 15)
- Chemical pesticides contaminate soil, water and the food we eat
What biological control is
Biological control is the use of a living organism to control a pest, instead of a chemical. The control organism is typically a natural predator or parasite of the pest:
- A predator that eats the pest
- A parasite or parasitoid that lives on or inside the pest, weakening or killing it
- A disease-causing microbe that infects the pest
Advantages of biological control
- No chemical pollution of soil, water or food
- Targets only the pest species if the control organism is well-chosen
- Self-sustaining once established; the predator population maintains itself
- No resistance develops in the same way as with chemicals
- Cheaper in the long run than repeated chemical sprays
Disadvantages and risks
- The control organism can become an invasive species if it has no natural predators in its new habitat
- It can attack non-target species, sometimes more so than the pest it was meant to control
- The cane toad in Australia is a famous example: introduced to control beetles, the toads ignored the beetles, multiplied uncontrollably, and now devastate native wildlife by being poisonous to anything that tries to eat them
- It can take a long time to work, so cannot deal with sudden pest outbreaks
- It does not eliminate the pest entirely; it just keeps the population low
Advantages of biological control over chemical pesticides
What comes up: "give advantages of biological control compared to using pesticides" or "explain why biological control is a long-term solution" — typically 2–3 marks.
Write: (1) biological control does not involve chemical pesticides, so there is no chemical pollution of soil or water; (2) the control organism reproduces and maintains itself, making it a long-term/self-sustaining solution; (3) unlike pesticides, the pest population cannot evolve resistance to a living predator in the same way it does to a chemical.
Watch out: the mark scheme distinguishes between a general answer ("no pollution") and a specific advantage — "long-term" is explicitly credited where "only needs to be done once / the organism will breed and reproduce" are the credited phrases. A vague "it is more natural" does not score a mark.
Integrated pest management (IPM)
Modern farming usually combines several approaches in integrated pest management:
- Biological control as the foundation
- Targeted pesticide use only when pest numbers are very high
- Crop rotation to break pest life cycles
- Pest-resistant crop varieties (sometimes from selective breeding or genetic modification)
- Physical barriers (netting, traps)
Integrated pest management uses far less chemical pesticide than traditional farming, with similar or higher yields.