Marine Science Honors: Chapter 4 - Unicellular Marine Organisms

How can an algal bloom be detrimental to people?

A sudden increase in the diatom population, called an algal bloom, may occur from time to time in shallow coastal waters. During several summers in the late 1980s, the coastal waters of Long Island, New York, became so clouded with algae that the waters turned brown. Marine biologists analyzed water samples and found as many as 800,000 diatoms of one particular species in 1 milliliter of water. This kind of algal bloom is called a brown tide. The brown tide devastated the scallop industry in eastern Long Island. Biologists are still investigating the causes of these mysterious algal blooms.

Explain how marine animals are dependent upon diatoms.

Almost all animals in the sea ultimately depend on diatoms as a source of food. Tiny invertebrates, such as copepods, feed on diatoms. Shellfish such as mussels, clams, oysters, and scallops consume diatoms by filtering them from the seawater. Even humans depend on diatoms to some extent, when they eat organisms that have fed on diatoms either directly or indirectly.

What adaptations do diatoms have for photosynthesis?

Diatoms, like other algae and plants, contain the green pigment chlorophyll within special structures called chloroplasts. Because diatoms have a transparent cell wall, you can see the chloroplasts inside the cell. In fact, the cell wall of a diatom is made of silica, the main ingredient of glass. Such a cell wall allows light to enter the cell. Inside the diatom, the light energy is trapped by chlorophyll in the chloroplasts. The chloroplasts lie next to the cell wall, where the intensity of light is greatest. Both the glassy cell wall and the position of the chloroplasts are adaptations that increase the rate of photosynthesis due to greater light absorption.

How do most species of bacteria obtain their nutrients?

Feeding on organic matter, bacteria exhibit the type of nutrition normally found in fungi and animals. They either create their own food (via photosynthesis and chemosynthesis) or obtain their source of nutrients from dead, organic matter.

How did Linnaeus classify organisms? Why is his system for naming organisms so useful?

In 1758, the Swedish botanist Carolus Linnaeus (1707-1778) published a book describing his system of classification, which is the grouping of organisms according to similarities in structure. The science of classification that developed from this work is called taxonomy. Linnaeus classified all living things as belonging to either of two large taxonomic categories: the animal kingdom or the plant kingdom. Linnaeus then divided the animal and plant kingdoms into smaller groups. The units he used were kingdom, phylum, class, order, family, genus, and species. The kingdom is the most inclusive group; it contains the largest variety of related organisms. The species is the smallest group; it contains only one kind of organism. According to the system developed by Linnaeus, each organism is given a two-part scientific name that consists of a genus name and a specific name. The words used for scientific names are from the Latin and Greek languages. They sometimes seem difficult to read and even harder to pronounce. Since the different species of organisms number in the millions, it is necessary for scientists around the world to have a common language to be able to identify any organism with accuracy. As you know, people in different countries have different names for organisms. This naming system prevents confusion.

Why is it important to classify organisms?

It enables people to study organisms more easily. It shows the evolutionary relationships among organisms. And it lets you make certain assumptions about organisms within a particular group.

Why are cyanobacteria placed in the kingdom Monera?

Most biologists classify cyanobacteria in the kingdom Monera with all other bacteria. Since they contain chlorophyll, cyanobacteria are able to make their own food. They are, in fact, the only moneran that is photosynthetic.

What is the evolutionary significance of the cyanobacteria?

Scientists think that the first photosynthetic organisms to inhabit Earth were the cyanobacteria. The earliest cyanobacteria produced reef-like growths called stromatolites. Like coral reefs, the mushroom-shaped stromatolites built by cyanobacteria had a framework of calcium carbonate. Fossil stromatolites more than 3 billion years old have been found.

Why are dinoflagellates classified as autotrophs and heterotrophs?

Since dinoflagellates both make and ingest food, they are considered to be autotrophs as well as heterotrophs. Diatoms, however, are strictly autotrophs.

How does the present system of classifying organisms differ from the system developed by Linnaeus?

Since the time of Linnaeus, many new organisms have been discovered, and many classification systems have been proposed. It has differed in many ways in order to include a wider variety of organisms and goes as follows: Monera: Single-celled; lack nuclear membrane (bacteria, prokaryotes*, blue-green bacteria) Protista: Mostly single-celled, some multi-celled; have nuclear membrane (algae and protozoa) Fungi: Single-celled and multi-celled; have nuclei; absorb food from living and dead organisms Plantae: Multi-celled; have nuclei; make their own food through photosynthesis Animalia: Multi-celled; have nuclei; eat other organisms

Why are dinoflagellates classified as protists?

They are single-celled organisms with two flagella; their structure (they have cell walls) and their life processes contribute to their classification as protists. They can both eat and create their own food.