5 (a) Organisms can be classified by the five kingdom or three domain method - Edexcel - GCSE Biology - Question 5 - 2019 - Paper 1

In a chloroplast, oxygen is produced as a result of the process of photosynthesis, where sunlight is absorbed by chlorophyll. This process converts carbon dioxide and water into glucose and oxygen.

The three-domain system of classification has been suggested to better reflect the evolutionary relationships between organisms. This classification divides life into three domains: Bacteria, Archaea, and Eukarya, based on genetic and biochemical similarities, hence providing a clearer understanding of the fundamental differences between these groups.

To calculate the actual diameter of the cyanobacterium, we need to use the magnification factor. If the image is magnified 50000 times, we can denote the measured diameter in the image as 'd_image'. The actual diameter 'd_actual' can be calculated using the formula:

$d_{actual} = \frac{d_{image}}{50000}$

Assuming 'd_image' is measured (for example, say it is 5 cm), we convert to micrometres: 5 cm = 50000 µm. Thus,

$d_{actual} = \frac{50000 \text{ µm}}{50000} = 1 \text{ µm}$

1. Cell Wall: Bacterial cells have a rigid cell wall made of peptidoglycan, which provides structural support and shape to the cell.

2. Plasmids: These are small circular DNA molecules separate from chromosomal DNA. They can carry genes that provide advantages like antibiotic resistance.

3. Ribosomes: Bacterial cells contain ribosomes that are involved in protein synthesis, and these are smaller than those found in eukaryotic cells.

To insert the human insulin gene into a plasmid, the following steps are typically followed:

1. Isolation of the Gene: The human insulin gene is isolated using specific enzymes like restriction endonucleases that cut DNA at specific sequences.
2. Preparation of the Plasmid: The plasmid is also cut with the same restriction enzyme, creating compatible ends for the gene to be inserted.
3. Ligation: The insulin gene is then recombined with the plasmid using the enzyme DNA ligase, which seals the sugar-phosphate backbone of both DNA fragments, completing the insertion.
4. Transformation: The recombinant plasmid is then introduced into bacterial cells (for example, E. coli) through a process called transformation, where the bacteria take up the plasmid and begin expressing the insulin gene.