A virus is an infectious microorganism that consists of a nucleic acid, which can either be DNA or RNA, that is enclosed by a protein coat. It infects other organisms by replicating itself inside the cells of the host.

D. viruses

RNA viruses include retroviruses, which have RNA in its genetic material. On the other hand, bacteriophages either have DNA or RNA in its genetic material.

B. retroviruses

Viruses are infectious microorganisms that consist of a nucleic acid, which can either be DNA or RNA, that is enclosed by a protein coat called capsid.

They depend on the genetic information found in the living cells in order to reproduce. As soon as they enter the host cell, they take over the cell processes and replicate the genetic information in order to reproduce copies of them.

The capsid is a protein coat that envelops the genetic material of viruses. This functions to protect the nucleic acid in viruses, to allow the virus to attach to a host cell, to penetrate the cell membrane of the host cell, and to ensure the successful transfer of the genetic material between cells.

During lytic infection, the following events occur:
1. The virus binds into the surface of the host cell.
2. The virus enters the host cell and injects its DNA into the cell.
3. The virus starts to make a messenger RNA, which is later translated into proteins that chop the cell’s DNA.
4. Once the viral genes take over, the host cell begins to make copies of the nucleic acid and proteins.
5. The virus begins to reproduce and infect other cells.

During the lysogenic cycle, the bacteriophage inserts its DNA into the host cell. The term prophage refers to the DNA of the bacteriophage that is attached or integrated to the DNA of the host cell.

Vaccines are used as an effective preventive measure against most viral diseases. It introduces a weakened strain of virus into our body in order to help the immune system to develop an immunity against it.

The main difference between prokaryotes and eukaryotes is the presence of nuclei. Prokaryotic cells lack a nucleus and other membrane-bound organelles. On the other hand, eukaryotic cells have a nucleus and membrane-bound organelles.

A. lack nuclei

Binary fission is a process that is common in prokaryotes that undergo asexual reproduction. In binary fission, two identical cells are produced.

On the other hand, conjugation and endospore formation do not produce another bacterial cell. In conjugation, a hollow bridge between two bacterial cells is formed in order to exchange genetic material with each other, while endospore formation produces a thick wall which encloses the DNA of the bacteria in order to survive harsh external conditions.

A. binary fission

Prokaryotes are unicellular organisms that lack a nucleus and membrane-bound organelles.

They are either classified as Bacteria, which is the domain that contains prokaryotes with peptidoglycan in their cell walls, or Archaea, which is a domain of prokaryotes that do not contain peptidoglycan in its cell walls.

Prokaryotes are seen in a variety of shapes that include:
a. Spherical: Cocci
b. Rod-shaped: Bacilli
c. Spiral/corkscrew-shaped: Spirilla

Prokaryotes move by the following ways:
1. gliding (using slime-like secretions)
2. propelling (using flagella)

The term emerging diseases refer to the unknown diseases that are quite hard to control. Since people have no immunity to the viruses that cause these diseases, it can spread rapidly. For this reason, the occurrence of emerging diseases can be very alarming.

Here are examples of emerging diseases:
1. Zika virus – The virus is from a monkey. Eventually, it spread to humans through a mosquito bite.

2. Bourbon virus – Amblyomma americanum, which is an aggressive tick, carries the Bourbon virus that causes a fatal disease in immunocompetent adults. There is no known cure yet for this disease.

3. Zoonotic Influenza strain – The new strain, which is the avian influenza H7N2, infects humans that are in contact with infected animals, particularly birds.

According to the scientists, unicellular eukaryotes first made an appearance more than a billion years ago. These eukaryotes are now called “protists,” which is a word that means first.

B. more than 1 billion years ago

Protists are grouped into clades, wherein each clade is more related to other plants, animals, and fungi when compared to the other protists. However, these eukaryotes are not classified under the kingdoms of Plantae, Animalia, and Fungi. In this case, scientists are currently under a work in progress in classifying protists and understanding their relationship between other organisms.

C. The classification of protists is a work in progress.

The process wherein a life cycle undergoes an alternation of generations is caused by the switch between diploid and haploid phases. This event allows an exchange of genetic material between gametes and increases the genetic diversity among organisms.

D. diploid and haploid phases

According to the traditional classification, protists are classified into three groups–plantlike, animal-like, and fungus-like protists. However, this led to misinformation when the scientists discovered that the protists are nothing like plants, animals, and fungi. Protists belong to a monophyletic group, which means that these diverse organisms are not closely related to one other.

Scientists thought about a possibility that the multicellular eukaryotes emerged or evolved from a unicellular eukaryote. Since protists are unicellular eukaryotes, they can be the ancestors of the modern eukaryotes, such as plants, animals, and fungi. This was illustrated in the cladogram shown in figure 21-17. In the representation, the protists are divided into six major clades, wherein plants, animals, and fungi emerged from a protist ancestor.

Cilia and flagella are the structures used by protists for their locomotion.

The cilia, which are short finger-like structures, move in an upward waving motion that resembles the oars on a rowboat.

On the other hand, flagella are relatively long structures that protrude from the cell body. They resemble a lash or a tail that moves in a whip-like manner and rotates in either clockwise or counterclockwise direction.

Yes, it is a form of reproduction. In conjugation, a hollow bridge between two cells is formed in order to exchange genetic material with each other. Prior to the exchange, two organisms undergo meiosis and produce four haploid nuclei.

Eventually, after conjugating, they reproduce using mitosis. As a result, a new life cycle begins. This is the sexual reproduction process that occurs in protists particularly in paramecia and most ciliates when they are under unfavorable environmental conditions.

Among the choices, letter A gives a false statement about fungi. Fungi are not unicellular. They are eukaryotes that contain chitin in their cell walls. They are not plants but they usually grow from the ground. They are classified as heterotrophs since they cannot carry out photosynthesis. In addition, they release enzymes that help digest their food in the external environment.

A. All fungi are unicellular.

The interaction between fungi and green algae or cyanobacteria forms a mutualistic relationship. The association between the two organisms is called a lichen. Lichens are considered pioneers species that assist in the soil formation within barren areas.

C. lichen

The vegetative part of a fungus is called mycelium. When a mycelium grows underground, it grows out a network or a mass of hyphae. The hyphae are the slender filaments that branch out to form fruiting bodies on the ground in the form of mushrooms.

The evolutionary significance of mycorrhizae, which is the symbiotic association between fungi and plants, helped in the survival of many plants and trees and in the overall health of the ecosystem. Without the help of the fungi, many plant species would not be able to gather more water and nutrients from the soil. Some species, such as orchids, are able to germinate with the help of the fungi.

HIV and cold viruses belong to a group of retroviruses that contains RNA as their genetic material.

Cold viruses infect the host cell rapidly. Once the virus enters the host cell, it interferes with the cellular process and replicates right away. Once new viruses are formed, they burst from the host cell.

Unlike cold viruses, HIV (human immunodeficiency virus) does not replicate itself right away. Once the virus enters the host cell, the genetic information is copied from RNA to DNA. Later on, the DNA is injected into the genome of the host cell. The viral genes are usually inactive at first but when they become activated, they would start to destroy the cells that fight the infections. This retroviral infection is similar to the lysogenic cycle in a bacterial infection.

During the lysogenic cycle, the bacteriophage DNA or prophage may remain in the DNA of the host cell for a long time. However, when the prophage is triggered by radiation, heat, and particular chemicals, it can be activated and it would start reproducing more copies. This allows the virus to spread in a bacterial population.

Some bacteria releases chemicals that disrupt the body’s homeostasis. One particular example is the cavity-causing bacteria that lives in the teeth. These bacteria consume sugars and convert them into acid that causes the enamel of the teeth to soften, which produces cavities eventually.

To fight this kind of bacteria, the toothpaste contains chemicals that make the enamel resistant to the acids produced by the bacteria. In this case, people who don’t brush their teeth are more prone to have cavities than those who brush their teeth regularly.

Binary fission is a process that is common in prokaryotes that undergo asexual reproduction. In binary fission, two identical cells are produced.

Unlike binary fission, conjugation and endospore formation do not produce another cell. In conjugation, a hollow bridge between two bacterial cells is formed in order to exchange genetic material with one another. On the other hand, endospore formation produces a thick wall which encloses the DNA of the bacteria in order to survive harsh external conditions.

Washing hands help dislodge bacteria and viruses in the hands without killing them. On the other hand, disinfectants are the chemicals that kill bacteria and viruses, including the good bacteria on the person’s skin.

The advantage of washing hands is its long-term effect on bacteria, viruses, and other pathogens. Not killing these organisms would reduce the possibility of them increasing their resistance to certain chemicals. On the other hand, the frequent and widespread use of disinfectants to kill bacteria, viruses, and pathogens would cause them to evolve via natural selection. This event allows them to become resistant to certain chemical solutions.

When the scientists discovered that the protists are nothing like plants, animals, and fungi, they decided to place protists in a single taxonomic category. This is similar to the way people put things that are not easy to categorize on a junk drawer.

However, some protists actually have more similarities with other plants, animals, and fungi than the other protists. For this reason, scientists are currently working on another possible angle that protists might be the ancestors of multicellular eukaryotes.

If photosynthetic organisms in the ocean are damaged or killed due to the prolonged exposure to the sun’s harmful UV rays, there would be no producers that would conduct photosynthesis. Since photosynthesis uses carbon dioxide and releases oxygen during its entire process, this event would result in the changes within the Earth’s atmosphere. It would lead to a decreasing level of oxygen and an increasing level of carbon dioxide in the atmosphere.

Penicillium, which is a fungi, releases secretion that stops the bacteria from reproducing. This event causes the bacterial colony to die. This is the fungi’s way of competing with other organisms for nutrients and resources.

The average number of bacteria colonies for each treatment are listed below:
a. Unwashed – 228.5
b. Rinsed in warm water – 205
c. Washed with soap and warm water – 18
d. Rinsed in alcohol and air-dried – 1.5

When the three treatments–rinsed with warm water, washed with soap and warm water, and rinsed in alcohol and air-dried are compared, the most effective method of killing most bacteria is the one that involves rinsing the hand in alcohol and air-drying it. During its first trial, there are only 3 bacterial colonies left, while the second trial caused all the bacteria to die.

On the other hand, the least effective treatment is the rinsing of hand in warm water. It resulted in an average number of 205 bacteria colonies during its first and second trial.

Mutations, which are the alterations within the DNA sequence, may result in the changes within all the aspects of an organism’s life. It allows them to develop traits that are distinct from other organisms. These traits are usually passed on to the next generation. This event allows the bacterial cells to acquire a trait that can make them have immunity or resistance to infections caused by bacteriophages.

Not all organisms can utilize nitrogen gas. In this case, nitrogen-fixing bacteria helps to convert nitrogen gas into other nitrogen compounds, such as ammonia, nitrates, and nitrites, that can be utilized by plants, animals, and other organisms.

If the nitrogen-fixing bacteria are gone, many organisms would not be able to utilize the nitrogen gas in the atmosphere; hence, nitrogen cannot be recycled within the Earth. This would cause the functions of the ecosystem to fail and the death of many organisms.

According to the statement, the organism is a prokaryote that has a cell wall with peptidoglycan. This organism fits the description of all the members of kingdom Eubacteria, which falls under the domain Bacteria.

The pattern of Malaria cases that is shown on the graph has generally decreased over the years. Back in 2002, there were 15,000 reported cases of Malaria. It decreased to 6,000 cases in the year 2012.

On the other hand, the deaths caused by Malaria back in 2002 went to almost 100. There was a series of an increasing-decreasing pattern over the years. However, it finally ended with 65 deaths in 2012.

In the year 2006, there were around 12,000 Malaria cases and 90 Malaria deaths in South Africa. In this case, 0.75% of the Malaria cases were fatal.

Malaria is an infection that is caused by a Plasmodium parasite that is spread through the bite of an infected Anopheles mosquito. In this case, since South Africa has improved their mosquito control, it reduced or prevented the spreading of infection among humans. This is the reason why Malaria cases have significantly decreased over the years.

In order to classify whether an organism is a prokaryote or a protist, it is important to determine the main difference between the characteristics of these two organisms.

Prokaryotes are unicellular organisms that lack a nucleus and membrane-bound organelles. On the other hand, a protist is a unicellular eukaryote. Eukaryotes possess a nucleus and membrane-bound organelles.

After observing the two organisms under the microscope, determine if it has a nucleus and membrane-bound organelles. If the organism contains a nucleus and membrane-bound organelles in its cell, it is a eukaryote; hence, it is a protist.

On the other hand, if the organism does not have any nucleus or membrane-bound organelles in its cell, it is a prokaryote.

The interaction between fungi and blue-green algae or cyanobacteria forms a mutualistic relationship. The non-fungal partner, which contains chlorophyll, is called the photobiont. On the other hand, the fungal partner is called mycobiont. The photobiont conducts photosynthesis to manufacture carbohydrates. In other words, they prepare the food for mycobiont. In turn, the mycobiont provides shelter for the photobiont and they also absorb water and nutrients from the soil. The association between the two organisms is called a lichen. Lichens are considered pioneers species that help in the soil formation within barren areas.

Viruses consist of a nucleic acid, which can either be DNA or RNA, that is enclosed by a protein coat. Once they were able to infect the host cells, they would have the ability to reproduce, to regulate gene expression, and to undergo evolution.

Prokaryotes are unicellular organisms that lack a nucleus and membrane-bound organelles. They are either classified as Bacteria, which is the domain that contains prokaryotes with peptidoglycan in their cell walls, or Archaea, which is a domain of prokaryotes that do not contain peptidoglycan in its cell walls.

Protists are a diverse group of eukaryotes that do not fit into the other taxonomic categories. They are not an animal, a plant, or a fungus.

Fungi are eukaryotes that contain chitin in their cell walls. They are not plants but they usually grow from the ground. They are classified as heterotrophs since they cannot carry out photosynthesis. In addition, they release enzymes that help digest their food in the external environment.

The terms pathogens, emerging diseases, epidemic, and vaccines are defined below:

a. Pathogens refer to the infectious agents that cause diseases.

b, Emerging diseases refer to the unknown diseases that are quite hard to control. Since people have no immunity to the viruses that cause these diseases, it can spread rapidly.

c. An epidemic is defined as the widespread and rapid occurrence of an infectious disease in a given population.

d. Vaccines are used as an effective preventive measure against most viral diseases. It introduces a weakened strain of virus into our body in order to help the immune system to develop an immunity against it.

Diseases are an important topic in this chapter because diseases are caused by viruses, prokaryotes, protists, and fungi. The interference of these organisms in the body processes of humans has caused their homeostasis to become disrupted.

The reason why the author discussed this topic is to emphasize the evolutionary significance of the symbiotic relationship between fungi and plants. The mycorrhizae fungi are responsible for transferring carbon atoms from one tree into another. This partnership helped in the survival of many plants and trees and in the overall health of the ecosystem.