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

How do bacteria contribute to the recycling of nutrients in ecosystems?

1. They produce energy directly from sunlight

2. They live in the soil and produce a variety of enzymes

3. They absorb DOM without breaking it down

4. They filter the air and remove pollutants

The correct answer is: They live in the soil and produce a variety of enzymes

Bacteria play a critical role in nutrient recycling within ecosystems, particularly because they are adept at breaking down organic matter. By living in the soil, bacteria produce a variety of enzymes that help decompose complex organic materials such as dead plants and animals, as well as waste products from living organisms. These enzymes facilitate the breakdown of proteins, carbohydrates, and lipids into simpler compounds, which can then be absorbed by plants and other organisms. This process not only contributes to the recycling of essential nutrients like nitrogen, phosphorus, and potassium but also helps improve soil structure and fertility. As bacteria decompose organic matter, they convert it into forms that are more easily taken up by plants, thus maintaining the balance of ecosystems. The other choices do not accurately represent how bacteria contribute to nutrient recycling. For example, while some bacteria can absorb dissolved organic matter (DOM), they do tend to break it down rather than simply absorbing it without any further transformation. Bacteria do not directly produce energy from sunlight like plants do through photosynthesis, nor do they primarily filter the air or remove pollutants as a main function within nutrient cycling. Therefore, the role of bacteria in producing enzymes to aid in the decomposition of organic matter is a key aspect of their contribution to nutrient recycling.