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

The figure shows an aseptic technique, which is a method used to prevent contamination by unwanted microorganisms during experimentation.

Working near a Bunsen burner creates an updraft of heat that reduces the risk of contamination by airborne microorganisms. The heat helps to ensure a sterile environment when handling cultures.

The area of a circle is calculated using the formula:

A = rac{22}{7} r^2 (approximating π as 3.14)

For chemical A, with a radius of 12 mm:

$A = 3.14 imes 12^2$

Calculating this gives:

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

1. The temperature of the agar plates should be controlled to ensure consistent growth conditions.

2. The type and amount of bacteria should be kept constant across both experiments to ensure a fair comparison.

One advantage of genetically modified crop plants is that they can be engineered to produce toxic chemicals that deter pests, reducing the need for chemical pesticides and promoting safer agricultural practices.