Deck 6: Multicellular Primary Producers: Seaweeds and Plants

Question 1

Some biologists place the seaweeds in the kingdom Plantae; others consider seaweeds to be protists. Assume that a better arrangement is to group the green, brown, and red algae in their own kingdom, which we will call Macrophyta. Characterize the new kingdom by first giving its unique characteristics and then differentiate it from the protists and the true plants. Be sure to consider major exceptions or overlaps.

Answer 1

Producers are extremely important part of the ecosystem. They help in producing oxygen in the marine environment. These organisms help in sustaining the growth and development of other marine organisms. Producers in the marine system can either be unicellular or multicellular.
Kingdom Protista is the group of organisms containing those organisms that could not be placed in either kingdom Animalia or kingdom Plantae. It is extremely beneficial to include the different algae in a separate group. There are several specific characteristics of these organisms as mentioned below:
•These organisms are eukaryotic and mostly multicellular, while some of the organisms in this kingdom are unicellular. Protists are mainly eukaryotic and unicellular organisms. Plants are eukaryotic and multicellular organisms.
•This newly formed kingdom includes organisms that are mostly autotrophic, while the organisms in kingdom Protista are heterotrophic in nature. Plants are autotrophic in nature.
•The new Algae kingdom does not include well differentiated body parts. On the other hand, plants have specialized tissues such as roots, shoots, and leaves for performing specific tasks.
•Some of the exceptions are specialized parasites such as Plasmodium, Trichomonas (protozoa), Cuscuta and Rafflesia (plants).

Question 2

The actual color can vary among some species of red and brown algae. A particular species is collected and is described as "dark redbrown." How could we tell if this alga is a member of the Rhodophyta or of the Phaeophyta?

Answer 2

One possibility is to examine the reproductive structures of the alga because they differ in the two groups. This difference is particularly noteworthy in Rhodophyta, where the life history includes a third generation that produces carpospores, a feature absent in Phaeophyta. There is no alternation of generations in Rhodophyta, whereas it is absent in Phaeophyta (see fig. 6.11). The type of photosynthetic, or accessory, pigments, which can be chemically analyzed, is different in both groups: Rhodophyta contains phycobilins, which are absent in Phaeophyta (see table 6.1).

Question 3

Only very few flowering plants have invaded the oceans, but those that have are very successful. What are some possible reasons for the small number of marine flowering plants? How do those that have taken the step manage to thrive in some environments?

Answer 3

Producers are extremely important part of the ecosystem. They help in producing oxygen in the marine environment. These organisms help in sustaining the growth and development of other marine organisms. Producers in the marine system can either be unicellular or multicellular.
Most of the terrestrial plants are unable to grow in the marine environment. This inability is caused due to difficulty in overcoming the high osmotic demand of the plant present in hypertonic solution. Another difficulty faced by the terrestrial plants is the inability of the organism to fertilize. Fertility in plants is possible following the process of pollination. Most of the plants require insects for pollination. Since the marine environment do not have many insects, therefore it is difficult to fertilize under such conditions. The already established seaweeds would pose sufficient competition to the plants, thus rendering their growth in the marine environment.