• 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.

Disease-Fighting Foods May Be Derived From Metal-Loving Plants

Too much metal in the soil and you have a contaminated brownfield. Too little metal in the diet and you see disease and malnutrition.

The solution to both problems may be metal-loving plants that take up large amounts of metal in their tissues, says David E. Salt, professor of plant molecular physiology at Purdue University.

There has been much scientific interest in recent years in using metal hyperaccumulating plants to clean up hazardous materials sites, a process called phytoremediation. But Salt says metal-accumulating plants have a broader potential as a way to improve people's diets or even to create foods that fight cancer.

"It's just two sides of the same coin," he says. "One of the things about metals that many people don't realize is that a lot of them are essential micronutrients that we need. They play a crucial role in certain enzymes that our bodies use to function."

Salt recently announced that he has identified and cloned the genes from a species of these plants that store metals in their tissue.

According to the World Health Organization, the lack of proper micronutrients in the diet causes health problems in many underdeveloped nations, particularly in children and pregnant women.

The metal selenium is known to be a potent anti-carcinogen, and there are wild plants that accumulate selenium naturally. If these genes could be moved into crop plants, Salt says, new foods could be created that have anti-cancer properties.

In the Western United States there is a plant known as locoweed (Astragalus bisulcatus), which accumulates selenium. The plant gets its descriptive name because livestock that eat it can become disoriented and stumble about after ingesting too much selenium. But locoweed hyperaccumulates selenium, and Salt says that it may be possible to create functional foods that have cancer-fighting properties from this plant. Although selenium supplements are available already, Salt says most of these are of little use because the human body can only absorb and use selenium if it is in certain chemical forms.

"If you go into the health food store right now, you'll see that there are many different selenium supplements. Most of those are actually sodium selenide, or sodium selenate, which is a chemical form that our bodies can't use very well. It has been shown to not be very effective," he says. "The other common supplements are yeast which has been fed selenium, and that has been shown to contain about 40 percent elemental selenium, which is completely unavailable to the human body."

Salt says the first products to market would be dried plant material that is enriched in bioavailable forms of selenium. "In the long term we'd probably like to try to engineer a vegetable crop so that we would take the selenium that's in the crops right now and move it into a more anticarcinogenic form in the foods we already eat," he says.

Adapted from: Purdue University News Release. 13^th August 2001

1. What are micronutrients? (line 14).

[two marks]

 

2. Why should children and pregnant women be particularly vulnerable to a lack of micronutrients in their diet? (lines 20-21).

[three marks]

 

3. Salt recently announced that he has identified and cloned the genes from a species of these plants that store metals in their tissue (lines 17-18). Briefly describe how the genes in question may have been cloned.

[five marks]

 

4. Suggest why wild plants need to accumulate selenium and other metals.

[two marks]

 

5. What are "bioavailable" forms of selenium? (line 45)

[one mark]

 

6. Name two other metals, other than selenium, that are required by the human body and give reasons for their importance.

[four marks]

 

7. Does engineering of Astragalus bisulcatus present any ethical problems? Give reasons for your answer.

[three marks] [Total: twenty marks]

3. Marine algae generally comprise structural and chemical defences against herbivores. These defences include the deposition of calcium carbonate and the production of secondary metabolites, both of which deter consumption by herbivores. Hay et al. (1994) tested the effect of adding calcium carbonate and secondary metabolites on herbivore feeding patterns. Commercially available calcium carbonate and natural concentrations of secondary metabolites obtained from the algae Rhipocephalus phoenix and Udotea cyathiformis were added to a powdered algal mixture in an agar base. The mixture was placed onto a fibreglass window screening material with an internal uniform grid.

1. How was the amount of algae eaten by the herbivores quantified?

[two marks]

2. Suggest one reason as to why calcification may deter herbivory.

[two marks]

3. In this experiment, which individual substance (calcium carbonate or metabolites) best deterred herbivore feeding? Justify your answer.

[three marks]

4. What do the graphs suggest about the effect of adding both calcium carbonate and metabolites to the algal mixture?

[three marks]

5. Does acid-mediated digestion occur in any of the three herbivores used in this study? Give reasons for your answer.

[three marks]

6. In a natural habitat where all the three herbivores are present, which one of the two algal species (Rhipocephalus phoenix or Udotea cyathiformis) would you expect to flourish? Give reasons for your answer.

[three marks]

7. Comment on the effect exerted by calcium carbonate on the feeding efficiency of each of the three herbivores

[four marks] [Total: twenty marks]

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

1. Mitochondria and chloroplasts are two organelles found in eukaryotic cells. Compare and contrast the structure and function of these two organelles and explain how these micro-cellular structures reveal some evidence to the probable origin of the eukaryotic cell.
2. The efficacy of many metabolic poisons is based on the disruption of enzymic activity in the affected organism. Discuss.
3. The various types of skeleton in the animal world are an adaptation to the modes of life of the organisms that possess them. Discuss.
4. Write an essay on feedback mechanisms and their role in control of biological systems.

 

 

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

5. EITHER

Evaluate the role of enzymes in genetic engineering.

OR

Give a detailed account of the role of micro-organisms in treatment of sewage.

 

Option 2: The Diversity of Eukaryotes

6. EITHER

Homologous structures present in a group of organisms can reflect evolutionary relationships and are thus used in phylogenetic classification. Difficulties may however be encountered due to adaptive radiation and convergent evolution. Discuss.

OR

Compare the reproductive structures, seed formation and seed dispersal in gymnosperms and angiosperms.

 

Option 3: Topics in Applied Botany

7. EITHER