• Answer ALL questions in Section A and any TWO questions from Section B. These two sections are based on the core area of the syllabus. Answer ONE question from Section C. This section is based on the optional parts of the syllabus. Write all your answers in the separate booklet provided.

1. Read the extract below carefully and afterward, from the information given and from your knowledge of biology, answer the questions that follow. The numerals in the left-hand margin are line numbers.

Sewage May Spur Growth Of Harmful Algal Blooms

In nature, there's no accounting for taste. New research shows that a common type of marine alga may prefer urea, an organic nitrogen compound found in urine and in agricultural and urban runoff, over inorganic fare that occurs naturally in the ocean. When excess nutrients cross their paths, these single-celled organisms, called dinoflagellates, can grow into potentially toxic blankets of algae commonly known as red tides.

The new findings, published in the current issue of Aquatic Microbial Ecology, suggest that urea in urban and agricultural runoff may play a greater role than previously thought in triggering or sustaining harmful algal blooms found growing off California's coastline.

"The particular bloom we looked at, which extended from the upper Baja peninsula in Mexico to the Monterey Bay, occurred after heavy urban runoff events in the southern California region," said Raphael Kudela, assistant professor of ocean sciences at the University of California, Santa Cruz. "Our data suggests it was probably triggered by the increased concentration of urea introduced to the ocean by urban runoff," Kudela said.

Kudela and coauthor William Cochlan examined the physiology and ecology of the bloom, which occurred in 1995 and was the largest and most widespread red tide found off California's coast since 1902. Though marine scientists usually monitor marine ecosystems for high concentrations of common inorganic nutrients known to spur harmful algal blooms, urea is generally ignored, the researchers said.

Previous studies have shown that urea can nourish the growth of dinoflagellates under laboratory conditions. The new study shows for the first time, however, that the naturally occurring red-tide dinoflagellate responsible for the 1995 bloom -known scientifically as Lingulodinium polyedrum- can use organic urea as a nutrient source and even prefers it over traditionally measured inorganic forms of nitrogen.

"Although urea as a source of pollution is generally ignored by state and federal environmental agencies, research shows that urea represents an average of one-third of the total nitrogen uptake supporting growth of phytoplankton in regions where red tides can occur," Cochlan said. "In some estuarine areas, such as the Chesapeake Bay, urea can represent 60 percent of the nitrogen uptake at certain times of the year."

While most blooms are not harmful, a small number of phytoplankton species can produce potent neurotoxins when they form into a bloom, sometimes poisoning or killing higher life forms such as zooplankton, shellfish, fish, birds, marine mammals, and even humans as the toxin is transferred up the food chain.

Although Lingulodinium polyedrum has been reported to produce yessotoxin, a compound related to the class of poisons that cause paralytic shellfish poisoning, the researchers found no evidence that the 1995 bloom was toxic. However, large algal blooms of any type pose an additional risk by lowering the available oxygen in the surrounding water when they decay, causing small marine animals, such as zooplankton and fish, to suffocate.

According to Kudela, these harmful bloom events are becoming more common off the California coastline. In addition to the dinoflagellate Lingulodinium polyedrum, the diatom species Pseudo-nitzschia australis also plagues California's coastal waters in deadly bloom form. Pseudo-nitzschia was recently identified as the culprit when more than 400 sea lions died and many more suffered from domoic acid poisoning on California's Central Coast in 1998. "However, there's no evidence that Pseudo-nitzschia responds to urea," Kudela noted.

1. Name two forms of inorganic nitrogen that would be expected to occur in ocean water (line 30).

[two marks]

 

2. Why would phytoplankton require a source of nitrogen ?

[two marks]

 

3. What is an "algal bloom" ? (line 10)

[one mark]

 

4. Why should urban runoff be expected to contain urea ? (lines 2-3)

[two marks]

 

5. What is a neurotoxin ? (line 39)

[one mark]

 

6. In what ways may toxins be transmitted through a food chain ? (line 41)

[three marks]

 

7. Why may scientists have ignored urea as a possible source of nutrients ? (lines 22 through 24)

[one mark]

8. "In some estuarine areas, such as the Chesapeake Bay, urea can represent 60 percent of the nitrogen uptake at certain times of the year." (lines 35 - 36). At what times of year would you expect to find elevated concentrations of urea in seawater ? Justify your answer.

[three marks]

 

10. Why should the decay of large algal blooms (lines 45 through 48) cause depletion of dissolved oxygen ?

[three marks]

 

11. Suggest a reason as to why bloom events are becoming more frequent (line 50).

[two marks]

[total: twenty marks]

3. The shore crab Carcinus maenas feeds on the bivalve mussel Mytilus edulis by breaking open the shell using its chelae (claws), and consuming the fleshy parts found within. In a study carried out by Townsend & Hughes (1981), crabs were fed on different sizes of mussel. The results are recorded graphically in Figure 1 (following page).

1. To which phyla do Carcinus maenas and Mytilus edulis belong?

[two marks]

 

2. Which size range of mussels give the highest return in terms of profitability?

[three marks]

 

3. Suggest a method by which the food energy value may be measured

[three marks]

 

4. What is the drawback of consuming the smallest mussels?

[three marks]

 

5. What is the drawback of consuming the largest mussels ?

[three marks]

 

6. What trend is shown by mussel size class 1 in graph (b) ?

[three marks]

 

7. Explain the trend referred to in Question 2.7.

[three marks] [total: twenty marks]

(Answer any two questions from this section; your answers should take the form of essays. Each question carries twenty marks).

3. Proteins are the working molecules within the cell. Discuss
4. Diffusion over the general body surface is not sufficient to meet the oxygen demands of multicellular organisms. Review the various strategies developed by aquatic and terrestrial organisms to obtain this metabolite in adequate concentrations.
5. Ectothermal organisms cannot control their body temperature. Discuss.
6. Write a comparative account of circulatory systems in animals. The account should focus on the functional adaptability of the various systems in relation to the environment in which these organisms are found.

 

SECTION C

(Answer one question only from this section; your answer should take the form of an essay. Each question carries twenty marks).

OPTION 1: Biotechnology

7. EITHER

The Human Genome Project is a topic of much contention in modern day biotechnology. Evaluate the positive and negative aspects of this project.

OR

Evaluate the role of transgenic organisms in present day biotechnology

 

OPTION 2: The Diversity of Eukaryotes

8. EITHER

‘The structural complexity of vascular plants is essentially an adaptation to the constraints imposed by a terrestrial existence.’ Discuss.

OR

‘A reduced nervous system is typical of sessile organisms.’ Discuss this statement, giving examples from different animal phyla.

 

Option 3: Topics in Applied Botany

9. EITHER