Ecosystems and Biodiversity Questions and Answers

Answer: C

The precipitation value of biodiversity is an ecosystem service value.

Forests and other vegetation regulate the water cycle: they return moisture to the air through transpiration, influence local rainfall, protect watersheds and keep rivers and springs flowing. This value is indirect. Nobody harvests or sells it, but people benefit from the service the ecosystem performs, which is what ecosystem service value covers.

Consumptive use value is the value of products used directly at home, such as fuelwood or wild food, and productive use value that of products sold in markets, such as timber. 'Essential value' is not one of the standard categories.

Answer: B

The size of the sample area is based on the species-area curve.

In phyto-sociological study the number of species recorded is plotted against increasing sample area, quadrats of growing size laid out one around another. The curve rises steeply and then levels off; the area at which it flattens, often where a 10 per cent increase in area adds no more than 10 per cent more species, is taken as the minimal area for sampling that community.

A random size would make samples incomparable. The population of a species is what the sampling measures, not what fixes the plot size. The quadrat (printed 'Quadrate') is the sampling unit itself; its size is what the curve decides.

Answer: B

The phenomenon is allelopathy.

Allelopathy is the inhibition of one plant by chemicals released by another, through root exudates, leachates from leaves, volatile compounds or decomposing litter. Juglone from black walnut and the compounds released by eucalyptus and Parthenium are familiar examples.

Allopatric describes populations or species living in separate geographical areas. An apomict is a plant that produces seed without fertilisation. Admixture means mixing, for example of genes or materials. None of them refers to chemical inhibition.

Answer: C

Directed breeding of plants and animals is artificial selection.

In artificial selection, humans choose which individuals reproduce, according to the traits they want, such as larger seeds, docility or more milk. Over generations this produced domesticated crops and livestock that differ sharply from their wild ancestors.

Foraging is collecting wild plants and hunting wild animals without controlling their reproduction. Natural selection is the same process driven by the environment rather than by human choice. Herding is the management of animal flocks, which may or may not involve deliberate breeding.

Answer: B

The interaction is synergism.

The standard example: Streptococcus faecalis converts arginine to ornithine but cannot go further, and Escherichia coli converts ornithine to putrescine but cannot use arginine. Growing together, the two make putrescine from arginine, which neither can do alone. An interaction in which two populations jointly achieve something neither manages separately, to their mutual benefit, is synergism.

Commensalism benefits only one partner and leaves the other unaffected. Amensalism is the harm of one population by a product of another, such as an antibiotic. Competition is the struggle of two populations for the same limited resource.

Answer: B

The answer is Pseudomonas carboxydovorans.

Carboxydotrophic bacteria grow aerobically on carbon monoxide as their sole source of carbon and energy, oxidising it with the enzyme CO dehydrogenase. Pseudomonas carboxydovorans, now classified as Oligotropha carboxidovorans, is the classic example.

Alcaligenes eutrophus (printed 'Alkaligenes eutrophas') is a hydrogen-oxidizing bacterium that uses H₂ for energy. Thiobacillus thiooxidans oxidizes reduced sulphur compounds, and Nitrobacter winogradskyi oxidizes nitrite to nitrate. None of them lives on CO.

Answer: B

The bacteria are Frankia spp.

Frankia is a filamentous actinomycete that forms nitrogen-fixing root nodules with a group of non-leguminous flowering plants called actinorhizal plants, among them alder (Alnus), Casuarina (printed 'Casurina'), Myrica and sea buckthorn. These plants can colonise poor soils for this reason.

Bradyrhizobium nodulates legumes such as soybean. Azotobacter vinelandii and Klebsiella fix nitrogen as free-living bacteria and form no root nodule symbiosis.

Answer: A

The prokaryote is the cyanobacteria (printed 'Cynobacteria').

Cyanobacteria carry out oxygen-producing photosynthesis like plants, and filamentous forms such as Anabaena and Nostoc develop heterocysts: thick-walled cells that lack the oxygen-evolving photosystem, so the oxygen-sensitive enzyme nitrogenase can work inside them. They are major nitrogen fixers in water and in rice paddies.

Green sulphur bacteria photosynthesize anaerobically and have no heterocysts. Frankia fixes nitrogen in vesicles and is not photosynthetic. Algae are eukaryotes, not prokaryotes.

Answer: C

The bacterium is Rhizobium NGR234.

Rhizobium sp. NGR234, isolated in Papua New Guinea, has the broadest host range known among rhizobia, nodulating plants of more than a hundred legume genera and also the non-legume Parasponia andersonii. Its breadth comes from producing a large family of different Nod factors, the signal molecules that trigger nodule formation.

Sinorhizobium meliloti nodulates mainly alfalfa and its relatives, Bradyrhizobium japonicum soybean, and Rhizobium leguminosarum peas, clover and beans. Each has a narrow host range and a small set of Nod factors.

Answer: D

The mycorrhizae are VAM, vesicular-arbuscular mycorrhizae.

The fungi of VAM (arbuscular mycorrhizae, phylum Glomeromycota) grow between the root cortex cells and penetrate their cell walls, though not the plasma membrane, forming finely branched arbuscules inside the cells. The arbuscules are where the plant's carbon is exchanged for the phosphorus and other nutrients the fungus gathers.

Ericoid mycorrhizae form hyphal coils in the roots of heaths, arbutoid mycorrhizae form a sheath and coils in Arbutus, and orchid mycorrhizae form coils called pelotons. None of them makes arbuscules.