Biodiversity, practice questions

C, Kingdom is the broadest group in the taxonomic hierarchy; species is the narrowest.

B, The first part, Oryza, is the genus; the second, lower-case part, sativa, is the species name.

B, A dichotomous key presents paired either/or statements about observable features that narrow the identification step by step.

C, Variation between individuals of the same species is genetic diversity.

B, The count of different species sharing one habitat is species diversity.

B, More species and genes give an ecosystem more ways to cope with disturbance, so it is less likely to collapse.

B, Decomposer bacteria and fungi break down dead organisms and return nutrients to the environment.

B, A bacterium is a living cell that reproduces independently, while a virus can only reproduce inside a host cell.

B, A virus lacks cytoplasm and independent metabolism, and depends entirely on a host cell to reproduce.

B, A wide range of habitats within a relatively small land area supports an unusually high number of species.

• (a) Kingdom, phylum, class, order, family, genus, species.
• (b) Species is the most specific level because it contains only organisms that can interbreed to produce fertile offspring.
• (c) The name is written Panthera tigris, in italics.
• One rule applied is that the genus name begins with a capital letter.
• A second rule is that the species name is entirely in lower case.
• Each level from kingdom to species narrows the group, with kingdom being the broadest and species the narrowest.

• (a) The coral reef shows greater species diversity because it supports a wider variety of fish, coral and other organisms living together, while the single-species mangrove planting supports far fewer species.
• (b) High biodiversity gives an ecosystem more alternative feeding relationships and genetic variation.
• This means the loss of one species or a disease affecting one gene variant is less likely to disrupt the whole system.
• An ecosystem with low biodiversity depends more heavily on fewer species, so losing one can cause a larger disruption.
• (c) The comparison in part (a) is at the level of species diversity.
• Species diversity is measured by the number of different species living together within one habitat.

• (a) A bacterium is a complete cell with cytoplasm and a cell membrane, while a virus has no cytoplasm and is not a cell.
• A bacterium contains its own genetic material free in the cytoplasm, while a virus's genetic material is enclosed only in a protein coat.
• (b) A virus has no organelles and cannot carry out metabolism on its own, so it lacks the machinery needed to make copies of itself.
• It must invade a living host cell and use that cell's own machinery to reproduce.
• (c) One beneficial role is decomposition, in which bacteria break down dead organisms and waste, releasing nutrients back into the environment.
• Another accepted example is the use of bacteria or yeast in food production, such as fermentation.

Organisms are grouped by shared features into kingdoms and smaller groups down to species. The full hierarchy runs kingdom, phylum, class, order, family, genus and species, with species being the smallest and most specific group and kingdom the broadest. Learning this order makes it far easier to answer questions that ask you to name the group immediately above or below a given level.

Each species has a two-part scientific name: genus (capitalised) then species, written in italics. This worldwide naming system avoids the confusion caused by different common names for the same organism in different languages or regions. Getting the capitalisation, word order or italics wrong is treated as an error even if the underlying organism is identified correctly.

A tool that identifies an organism through a series of paired either/or questions about its features. Following the matching statement at each step narrows the possibilities until only one organism's identity remains. A well-built key should never require more than a small number of paired steps to reach a single, unambiguous answer.

Genetic diversity within a species, species diversity within a habitat, and ecosystem diversity across regions. These three levels are often tested together, each needing a distinct, correctly labelled example rather than a general description. A common exam trap is describing species diversity when the question is actually asking about genetic diversity, or vice versa.

Bacteria, fungi and protozoa are microscopic organisms with important roles such as decomposition and nutrient recycling. Some microorganisms are also pathogens, meaning they cause disease in humans, animals or plants. Not all microorganisms are harmful; many, including most bacteria and fungi found in soil, play a beneficial role in an ecosystem.

Viruses are not cells; they can only reproduce inside a host cell, so they sit on the boundary of living and non-living. A virus is made of genetic material surrounded by a protein coat, with no cytoplasm of its own. Because a virus depends entirely on a host cell to multiply, most classification systems place it outside the five kingdoms altogether.

High biodiversity makes an ecosystem more stable, because a wider variety of species and genes gives it more ways to cope with disease, changing conditions, or the loss of a single species. Low biodiversity leaves an ecosystem more vulnerable to collapse from a single disturbance. This is why conservation programmes usually aim to protect several species together, not just one flagship species.

Moving from kingdom to species narrows the group at every step: humans, for example, belong to the kingdom Animalia, the phylum Chordata, the class Mammalia, and finally the genus Homo and species sapiens. Placing a familiar organism at each level is a common exam task. The same logic applies to any organism, from a rice plant to a housefly, not only to humans.

Bacteria are single-celled living organisms with their own cytoplasm and genetic material that can reproduce independently by simple cell division; viruses have neither cytoplasm nor the ability to reproduce without a host cell. This difference is the most commonly tested contrast in this content standard. A useful memory aid is that bacteria are always alive, while a virus is only ever 'active' inside another living cell.

Malaysia's tropical rainforests support an unusually high number of species relative to its land area, which is why it is described as megadiverse. Conserving this biodiversity is examined as a matter of maintaining ecosystem stability and genetic resources, not simply as an environmental slogan. Habitats such as lowland rainforest, mangrove forest and coral reef each contribute a different set of species to this total.