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

To find the actual size of the guard cell, divide the measured length by the magnification factor:

$ext{Actual Size} = \frac{6 ext{ mm}}{150}$

Calculating this gives:

$\text{Actual Size} = 0.04 ext{ mm}$

Expressing this in standard form:

$0.04 ext{ mm} = 4.0 imes 10^{-2} ext{ mm}$

Denitrifying bacteria play a crucial role in the nitrogen cycle by converting nitrates (NO₃⁻) in the soil back into nitrogen gas (N₂), which is released into the atmosphere. This process is essential for maintaining the nitrogen balance in ecosystems.

These bacteria help in reducing the concentration of nitrates in the soil, which can be harmful in high amounts. They typically thrive in anaerobic conditions, such as in waterlogged soils. By returning nitrogen back to the atmosphere, denitrifying bacteria contribute to the natural cycling of nutrients, ensuring that nitrogen remains available for various biological processes.