In 1886 Ernst Hackle solved the first objection and presented three kingdom
classification system.
Fungi were placed in Kingdom plantae. Some biologists disagreed about the position of fungi in Kingdom plantae. Fungi resemble plants in many ways but are not autotrophs. They are a special form of heterotrophs and get their food by absorption. They do not have cellulose in their cell walls, rather they possess chitin.
After the clear concept for kingdom Protista, Copeland (1959) came forward with a four-kingdom system to classify the living beings. He designed a new kingdom named as Monera to place all the lower protists which include prokaryotic unicellular organisms and remaining single celled eukaryotic organisms were included in Protista.
In 1937, E-chatton suggested the terms of “Prokaryotic” to describe bacteria and “Eucaryotic” to describe animal and plant cells.
The system of classification was based on:
1. Cellular organization
2. Modes of nutrition
The levels of cellular organization, i.e., Prokaryotic, unicellular eukaryotic and multicellular eukaryotic.
Modes of Nutrition; autotrophs (plants), Ingestive heterotrophs (animals) and absorptive heterotrophs (fungi).
It includes prokaryotic organisms i.e., they are made of prokaryotic cells. Monerans are unicellular, although some types form chains, clusters, or colonies of cells. Most are heterotrophic but some perform photosynthesis.
The structure of T4 bacteriophage is different from other virus. The T4 phage belongs to the subfamily Tevenvirinae from the family Myoviridae. Under an electron microscope, the T4 phage resembles a tadpole having a head and tail. The detailed structure of the T4 bacteriophage is discussed below:
The head is made up of capsid head and nucleic acid.
The head of the T4 phage is 120 nm long and 86 nm wide having hexagonal and prism shapes. The capsid head stores and protects the genome.
T4 phage contains double-stranded DNA that contains approximately 170000 bases. The modified bases present in T4 DNA protect the genome from breakdown by bacterial restriction endonucleases.
The structure of the tail is more complicated compared to the head. It contains a tail tube, sheath, collar, whisker, spike, base plate, and tail fiber.
It is an inner non-contractile tube made up of protein. It provides the passage for the movement of DNA from head to the bacterial cell.
The tail tube is enclosed by a contractile envelope known as a sheath which is made up of tail sheath proteins. The contraction of the sheath pushes the tail tube through the outer membrane of bacteria, forming a canal for the delivery of the viral genome.
Collar and whisker are made up of fibers present near the head-to-tail interference of the page. They control the withdrawals of the long tail fibers and also helps in the attachment of tail fibers to phage particles during assembly.
It is made up of multiple protein molecules. It controls sheath contraction, host recognition, DNA ejection, and attachment.
A spike pierces the cell membrane of bacteria and makes an opening for the entrance of the tail tube.
It is like appendages. It is a thin rod-like structure used for the attachment of bacteriophage on the surface of bacteria.
