Figure 16 shows a photomicrograph of two stomata in a leaf - Edexcel - GCSE Biology - Question 9 - 2023 - Paper 2

Given that the image has been magnified by 150x, the actual size can be calculated by dividing the image size by the magnification factor:

ext{Actual size} = rac{ ext{Image size}}{ ext{Magnification}} = rac{6 ext{ mm}}{150}

Calculating this gives:

$ext{Actual size} = 0.04 ext{ mm}$

In standard form, this can be represented as:

$4 imes 10^{-2} ext{ mm}$.

Denitrifying bacteria play a crucial role in the nitrogen cycle by converting nitrates (NO₃⁻) in the soil back into nitrogen gas (N₂), which is then released into the atmosphere. This process, known as denitrification, helps to:

1. Reduce excess nitrates in the soil, which can lead to nutrient pollution if left unchecked.
2. Maintain the balance of nitrogen in ecosystems, as it prevents the accumulation of nitrates that can harm plant and aquatic life.
3. Contribute to the cycling of nitrogen, making it available for plants again when conditions are suitable, thereby supporting overall ecosystem health.