Biology: Module 3 On your Own Q&A

You might say that diatoms are the most important form of algae in creation. Why?

Diatoms are responsible for the majority of photosynthesis on earth. Without this photosynthesis, the earth's oxygen supply would quickly dwindle, killing off everything. Thus, diatoms are pretty important!

Construct a biological key for separation of organisms in kingdom Protista into phyla. You can assume that any organism for which you use the key is already known to be in kingdom Protista. You can also assume that if an organism is completely autotrophic it belongs in subkingdom Algae, but if it is at all heterotrophic it belongs in subkingdom Protozoa. With those assumptions, you should be able to use the characteristics in Figure 3.1 to construct the questions for the key.

Biological Key for separating members of kingdom Protista into phyla: 1. Organism is completely autotrophic........................................subkingdom Algae...............2 Organism is heterotrophic ..........................................................subkingdom Protozoa..........6 2. Single-celled ................................................................................................3 Multicellular .....................................................................................................5 3. Cell wall made of silicon dioxide ..................................................................phylum Chrysophyta Cell wall made of cellulose or is atypical .......................................................4 4. Marine habitat ................................................................................................phylum Pyrrophyta Fresh water habitat ............................................................................................phylum Chlorophyta 5.* Cell wall made of cellulose and alginic acid .................................................phylum Phaeophyta Cell wall made just of cellulose ..........................................................................phylum Rhodophyta 6. Possesses a means of locomotion ...............................................................7 Possesses no means of locomotion ...................................................................phylum Sporozoa 7. Uses pseudopods for locomotion ...................................................................phylum Sarcodina Does not use pseudopods for locomotion ........................................................8 8. Uses cilia for locomotion ................................................................................phylum Ciliophora Uses flagella for locomotion ...............................................................................phylum Mastigophora *This key could ask whether habitat is warm water or cold water. That would separate the two phyla as well

If an organism is in phylum Chlorophyta, it must have a chloroplast. Why?

Chloroplasts hold the chlorophyll that is a part of photosynthesis. Since all members of phylum Chlorophyta have chlorophyll, they must also have chloroplasts to hold it.

According to most biologists, an organism must always perform photosynthesis or chemosynthesis to be considered autotrophic. Why do these biologists say that the euglena is not autotrophic?

Euglenas can obtain food either autotrophically (by photosynthesis) or heterotrophically, depending on environmental conditions. Thus, it does not always perform photosynthesis.

One way that people fight the spread of malaria is to significantly reduce the population of mosquitoes in their vicinity. Why does this work?

Mosquitoes carry the Plasmodium and spread it by biting humans. Control the mosquito population, and the spread of the disease is controlled as well.

A biologist studies a group of bacteria (all one species) and a group of paramecia (all one species). She notices that while the bacteria all seem to be almost exact duplicates of each other, there is a great deal of variation among the paramecia. Why?

Paramecia can engage in a form of conjugation that allows DNA to be mixed between organisms. As a result, the offspring formed will not be an exact duplicate of the parents, because the parents have mutually exchanged DNA. When bacteria conjugate, DNA transfer is one-way and the recipient ends up looking like the donor.

A paramecium cannot conjugate. What organelle is not functioning properly?

Since conjugation occurs via the oral groove, that organelle must not be functioning properly in the paramecium.

A euglena is in dim light. There is a bright spot of light not too far away, but the euglena does not move towards it. Instead, it seems to wander aimlessly. What organelle is not functioning properly in the euglena?

Since it is wandering around, its flagellum is working fine. Since it can't find the light, however, its eyespot must not be working. NOTE: Even if the photosynthetic mechanism of the euglena is destroyed, it will continue to seek light as long as the eyespot is working.

Suppose you were observing an amoeba under the microscope and it suddenly exploded. What organelle was probably not working properly in the amoeba?

Since the contractile vacuoles control pressure in the cell by collecting and removing excess water, those organelles must not have been working in that poor amoeba.

Of the three genera of green algae discussed above, which would you consider the most complex?

Spirogyra are the most complex because they exist as colonies. Thus, to a very limited degree, the cells work together. The other two exist as individual cells. Any time you get a group of individuals to work together (even to a very small degree), you are adding complexity to the picture.

What is the difference between cysts (such as those formed by amoebae and ciliates) and spores?

Spores are formed as a natural part of an organism's life. An organism that produces spores will always produce spores as a part of its life cycle. Cysts, on the other hand, are formed only when life-threatening conditions occur. If no life-threatening conditions occur over the course of an organism's lifetime, it will never form a cyst.

A biologist is studying an amoeba and sees a vacuole with several small solid objects in it. Most likely, what kind of vacuole is it?

The biologist must be looking at a food vacuole. A contractile vacuole should contain water. The solid objects in this vacuole are most likely partly-digested food.

In the book of Exodus (chapter 7), God caused several plagues to befall Egypt. In the first plague, all of the rivers turned to blood, the fish died, and the Egyptians could not drink from the rivers. Some have said that algae offer a natural explanation for this miracle. What algae are they referring to and why do they think this? Why is this not a good explanation?

They refer to the Gymnodinium brevis, because it causes red tide. Since the water in a red tide turns red, it might appear to be blood. Also, red tides are toxic to humans, so people cannot drink the water in a red tide. This is not a good explanation, however, because the Bible does not say that the waters looked like blood; it says they turned into blood. Also, the water in containers also turned into blood. It would be hard to explain how a red tide could occur in a container of water that was once clear. It is very dangerous to look for naturalistic explanations for clearly supernatural events!

A biologist has a sample of what looks to be a marine plant. He thinks, however, that it might be an unknown species of brown algae. To test this, he takes part of the "plant," dries it, crushes it into a powder, and mixes it with a solution. The solution thickens. Is this evidence that the organism is a plant or an alga? Why?

This is evidence that the organism is an alga. Since the water thickens, the plant most likely contains alginic acid, a substance that is in the cell walls of brown algae.

In a later section of this module, you will learn about members of genus Plasmodium, which can live in people. These microorganisms get food and shelter from the people they inhabit, but they cause malaria, which can be deadly. Is this an example of symbiosis? If so, what kind?

This is symbiosis, because the organism from genus Plasmodium benefits. It is also parasitism, since the person that the microorganism inhabits is harmed.

Suppose you could analyze a water sample for the presence of any chemical. If you were given two samples, one that contained members of phylum Chlorophyta and another that contained members of phylum Chrysophyta, how could you determine which was which?

You would look for the presence of cellulose or silicon dioxide. The sample that contained members of phylum Chlorophyta would have cellulose, while the sample with members of phylum Chrysophyta would contain silicon dioxide. You might also look for oil, as diatoms store their excess food as oil. You cannot look for chlorophyll, as both diatoms and members of phylum Chlorophyta have chlorophyll, since they both perform photosynthesis.