**Bacteriophages** are types of viruses that infect and replicate in bacterial cells– this is their specific host. These viruses differ in size, morphology, and genetic makeup[. Depending on the bacteriophage, they either kill the cell or just infect the cell and live inside it. Hence, the correct answer is **D**

D

There are three known methods by which genetic material can be transferred between bacterial cells, and they are **Conjugation**, **transformation**, and **transduction**.

**Conjugation** is the process in which a bacterial cell transfers its genetic material (DNA) to another bacterial cell through the use of pili (direct contact). During this process, a bacterium will serve as a donor of the gene, and the other will be called the recipient cell.

Bacterial cells are unicellular organisms that can be found everywhere. They are usually classified based on their basic shapes, whether they form **spherical** shape (cocci), **spiral** shape (spirilla), or **rod** shape (bacilli) and they can exist in a single cell, in pairs, in chains, and in clusters. Hence, the correct answer is **A**

A

**Binary fission** is a type of asexual reproduction that occurs in bacterial cells where the body of the parent cell divide and creates new identical offspring. In the process, the organisms first undergo DNA replication, then it will be followed by the growth of the cell, then the separation and segregation of the genetic material in preparation for the cell splitting (during this stage, a septum will not be visible in the parent cell). Lastly, the parent cell will now split and produce two daughter cells.

C

**Prokaryotes** are unicellular organisms that lack a nucleus in their cytoplasm. These organisms are identified and classified based on their shapes, substance of their cell wall, locomotion, and energy production. Hence, the correct and is **A**. Size is not used for the identification of these organisms.

A

**Food preservation** is any method that protects the food from spoilage. These methods prevent the growth of microorganisms, such as yeast or any foodborne pathogen. Some methods for food preservation are– salting of meat, freezing of food materials, sterilization of containers, and boiling. Hence, the correct answer is **D**.

D

**AIDS** is an acronym for Acquired Immunodeficiency syndrome. It is a life-threatening disease caused by a virus named **human immunodeficiency virus (HIV)** which chronically damages the immune system of the host. **Polio** is another viral disease caused by **poliovirus**. Poliovirus damages the nerves of the host organism which can lead to its paralysis. In addition, **common cold and flue** are also infections caused by the family of rhinovirus and influenza virus, respectively

Hence, the correct answer is **Diphtheria**. This infection is caused by a bacteria named ***Corynebacterium diptheriae*** which targets the mucous membranes of the host organism, specifically their throat and nose.

C

**Conjugation** is used for the exchange of genetic information between two bacterial cells. Genes move from one cell to the other. This increased genetic diversity in populations of bacteria.

C

Prokaryotes are unicellular organisms that lack a nucleus and **bacteria** are unicellular species having distinct cytoplasmic structures, and a presence of circular DNA chromosomes coated with histone-like proteins that only float in their cytoplasm. Bacterial cells do not have a true nucleus unlike the eukaryotes, rather it has a nucleoid that houses their genetic material. Hence, the correct answer is **D**

D

Based on the graph, the number of bacteria increased from 4 million to 8 million between hours 4 and 6. These hours have shown the greatest bacterial growth rate compared to the other hours.

B. Between hours 4 and 6

The decrease in the bacterial growth is a sign that the bacteria stopped reproducing and they started dying. Since there was an exponential growth that occurred, the waste products from the bacteria have accumulated in the nutrient solution and it produced toxins that are harmful to them. As a result, the accumulation of toxins led to the death of some bacteria.

D. Waste products from the bacteria accumulated in the nutrient solution