All questions of Living organisms for JAMB Exam

Primary mode of reproduction for viruses: Replication using host cell machinery

Viruses are unique infectious agents that are not considered living organisms. They lack the cellular machinery necessary for independent reproduction and metabolism. Instead, viruses rely on host cells to replicate and produce new viral particles. The primary mode of reproduction for viruses is replication using host cell machinery.

Explanation:

1. Introduction:
- Viruses are non-living particles that consist of genetic material (DNA or RNA) enclosed in a protein coat called a capsid.
- They cannot carry out metabolic processes or reproduce independently.
- Instead, viruses infect host cells and use their cellular machinery to replicate.

2. Replication process:
- When a virus infects a host cell, it attaches to specific receptors on the cell surface.
- The virus then injects its genetic material (DNA or RNA) into the host cell.
- Once inside the host cell, the viral genetic material takes over the cell's machinery and redirects it to produce new viral components.

3. Viral replication steps:
- The viral genetic material is replicated, producing multiple copies of the viral genome.
- Viral proteins are synthesized using the host cell's ribosomes.
- The newly synthesized viral genetic material and proteins assemble to form new viral particles.
- These new viral particles are released from the infected host cell, either by cell lysis or budding, to infect other cells and continue the infection cycle.

4. Importance of host cell machinery:
- Viruses rely on the host cell's enzymes, ribosomes, and other cellular machinery to carry out their replication process.
- They hijack the host cell's resources and redirect them towards producing new viral particles.
- The host cell may be damaged or destroyed in the process of viral replication.

5. Replication strategies:
- Different types of viruses have evolved various strategies for replication using host cell machinery.
- Some viruses directly use the host cell's enzymes and ribosomes.
- Others may modify the host cell's genetic machinery to favor viral replication.
- Viruses can also integrate their genetic material into the host cell's genome, becoming dormant until triggered to replicate.

In conclusion, the primary mode of reproduction for viruses is replication using the host cell machinery. Viruses lack independent reproduction and rely on infecting host cells to replicate and produce new viral particles. Understanding this replication process is crucial for developing antiviral strategies and treatments.

Answer:

Introduction:
In the given options, the correct example of a bacterium is Escherichia coli (E. coli). In this response, we will discuss why E. coli is an example of a bacterium and provide a brief explanation of the other options mentioned.

Explanation:
Escherichia coli (E. coli):
- Escherichia coli, commonly known as E. coli, is a gram-negative bacterium that belongs to the family Enterobacteriaceae.
- It is a rod-shaped bacterium and is a normal inhabitant of the intestinal tract of humans and animals.
- E. coli plays a crucial role in the digestion process and also helps in the production of certain vitamins.
- However, some strains of E. coli can cause infections and diseases, such as urinary tract infections, food poisoning, and diarrhea.

HIV:
- HIV (Human Immunodeficiency Virus) is not an example of a bacterium. It is a virus that attacks the immune system and causes acquired immunodeficiency syndrome (AIDS).
- HIV is transmitted through contact with certain body fluids, such as blood, semen, vaginal fluids, and breast milk.
- Unlike bacteria, viruses are not considered living organisms as they cannot reproduce or carry out metabolic activities on their own.

Hepatitis B virus:
- Hepatitis B virus is also not an example of a bacterium. It is a virus that causes hepatitis B, a liver infection.
- Hepatitis B can be transmitted through contact with infected blood, semen, vaginal fluids, and other body fluids.
- Similar to HIV, viruses cannot be classified as bacteria because they lack essential characteristics of living organisms.

Herpes simplex virus:
- Herpes simplex virus is another example of a virus, not a bacterium.
- There are two types of herpes simplex viruses: HSV-1 and HSV-2. HSV-1 is primarily responsible for oral herpes, while HSV-2 causes genital herpes.
- Herpes simplex viruses can be transmitted through direct contact with infected skin or mucous membranes.
- Again, viruses differ from bacteria in terms of their structure, replication, and other characteristics.

Conclusion:
Among the options provided, Escherichia coli (E. coli) is the correct example of a bacterium. It is a type of bacteria that is commonly found in the intestinal tract of humans and animals. The other options mentioned (HIV, Hepatitis B virus, and Herpes simplex virus) are examples of viruses and not bacteria.

Mode of Transmission for Viruses

In the context of virus transmission, it is important to understand the various ways in which viruses can spread from one person to another or from an infected source to a susceptible host.

Inhalation of Contaminated Air
- Viruses can be transmitted through the air when an infected individual coughs, sneezes, or talks, releasing respiratory droplets containing the virus.
- These droplets can be inhaled by another person in close proximity, leading to the transmission of the virus.

Direct Contact with Infected Individuals
- Direct contact with an infected person can also lead to the transmission of viruses.
- This can occur through activities such as shaking hands, kissing, or sharing personal items with an infected individual.

Ingestion of Contaminated Food or Water
- Some viruses can be transmitted through contaminated food or water.
- This can happen when food or water is contaminated with the virus, and a person ingests it, allowing the virus to enter their body.

Overall
- In conclusion, viruses can be transmitted through various means, including inhalation of contaminated air, direct contact with infected individuals, and ingestion of contaminated food or water.
- It is important to practice good hygiene, such as washing hands regularly, covering coughs and sneezes, and avoiding close contact with infected individuals, to prevent the spread of viruses.

Characteristics of Living Organisms:
Living organisms possess several key characteristics that distinguish them from non-living things. These characteristics include:

Growth and Development:
Living organisms exhibit the ability to grow and develop over time. This involves an increase in size as well as changes in shape and structure.

Cellular Organization:
Living organisms are composed of one or more cells, which are the basic units of structure and function. Cells carry out the processes necessary for life.

Metabolism and Energy Utilization:
Living organisms engage in metabolic processes to obtain energy from their environment and utilize it for various cellular functions. This energy is essential for growth, repair, and reproduction.

Explanation:
The characteristic "Inability to adapt to the environment" is NOT a characteristic of living organisms. In fact, one of the defining features of living organisms is their ability to adapt to changes in their environment in order to survive and thrive. This adaptability is crucial for the survival of species in different habitats and conditions. Living organisms possess mechanisms such as natural selection, genetic variation, and behavioral adaptations that allow them to respond to environmental challenges and changes. Therefore, the inability to adapt to the environment would go against the fundamental nature of living organisms.