OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What can be a consequence of increasing the use of herbicides on GM crops?

1. Reduced crop productivity

2. Development of resistant weed species

3. Enhanced soil quality

4. Increased biodiversity

The correct answer is: Development of resistant weed species

Choosing "Development of resistant weed species" is correct because the repeated use of herbicides, especially non-selective ones or those with the same action mechanism, can lead to certain weed species developing resistance. This happens through natural selection: those weeds that have genetic variations allowing them to survive the herbicide will reproduce, passing on those resistant traits to their offspring. Over time, this can create a population of weeds that are difficult to control, leading farmers to use even more herbicides or different types, escalating the problem. In contrast, reduced crop productivity typically stems from various factors, but is not directly a consequence of increasing herbicide use. Enhanced soil quality is generally negatively impacted by excessive herbicide usage, which can reduce soil microbial diversity and health. Similarly, increased biodiversity is usually adversely affected since herbicides can kill unintended plants and organisms in the ecosystem, leading to a reduction in overall biodiversity.