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 photosynthesis when sunlight is absorbed by chlorophyll. During this process, carbon dioxide from the atmosphere and water are converted into glucose and oxygen, with chlorophyll capturing the sunlight required for this reaction.

The three domain method of classification has been suggested to provide a more accurate representation of the relationships among organisms, particularly at the molecular level. It separates organisms into three domains—Bacteria, Archaea, and Eukarya—based on differences in their genetic makeup and cellular structure, reflecting evolutionary relationships more effectively than the traditional five-kingdom system.

To calculate the actual diameter of the cyanobacterium, we can use the magnification factor. If the cyanobacterium is magnified 50000 times, and we measure the diameter in the image (let's say it measures X mm), the actual diameter is given by:

ext{Actual Diameter} = rac{ ext{Measured Diameter}}{ ext{Magnification}}

Converting mm to micrometres ( ext{µm}), where 1 mm = 1000 µm, we find:

ext{Actual Diameter in µm} = rac{X ext{ mm} imes 1000}{50000}

This formula can be used once X is determined from the figure.

Bacterial cells possess several distinct features:

1. Cell Wall: Most bacterial cells have a rigid cell wall made of peptidoglycan, which provides structural support and protection from environmental stress.
2. Nuclear Region (Nucleoid): Unlike eukaryotic cells, bacteria do not have a membrane-bound nucleus. Instead, their genetic material (DNA) is located in a nucleoid, which is an area of the cell where the circular DNA molecule resides.
3. Ribosomes: Bacterial cells contain ribosomes, which are vital for protein synthesis. These are smaller than eukaryotic ribosomes and are free-floating in the cytoplasm.

The human insulin gene can be inserted into a plasmid through a process known as genetic engineering. The steps involved include:

1. Isolation of the Insulin Gene: The specific insulin gene is identified and isolated using restriction enzymes that cut the DNA at specific sites.
2. Preparation of the Plasmid: A plasmid, which acts as a vector, is also cut with the same restriction enzymes to create complementary ends.
3. Ligation: The isolated insulin gene is then combined with the plasmid DNA using ligase enzymes, which join the two DNA fragments together, forming recombinant DNA.
4. Transformation: The recombinant plasmid is introduced into bacterial cells (a process called transformation), where it can be replicated and transcribed to produce insulin.