Figure 4 shows the structures in a leaf - Edexcel - GCSE Biology - Question 4 - 2019 - Paper 1

The process being shown in Figure 5 is A: aseptic technique. This is a method used to prevent contamination from harmful microorganisms during laboratory experiments.

The scientist worked near a Bunsen burner to create an aseptic environment. The heat from the Bunsen burner helps to sterilize the air, reducing the risk of contamination from airborne microorganisms.

To calculate the area, we use the formula for the area of a circle, given by:

$A = ext{πr}^2$

Substituting the value of radius (r = 12 mm) and π = 3.14:

$A = 3.14 imes 12^2 = 3.14 imes 144 = 452.16 ext{ mm}^2$

Thus, the area of inhibition for chemical A is 452.16 mm².

Two variables the scientist needed to control include:

1. The volume of the bacterial solution used for inoculation, to ensure equal exposure to both chemicals.
2. The size of the filter paper discs soaked in the chemicals, to ensure that each disc releases the same amount of active compound.

One advantage of producing genetically modified crop plants that produce toxic chemicals is that it can lead to reduced pesticide usage. This not only lowers the cost of crop production but also minimizes the environmental impact associated with chemical pesticides, promoting safer agricultural practices.