Characteristics and Classification of Living Organisms: Biology 0610 (Cambridge O Level / IGCSE)

A student places a single-celled organism called an Amoeba under a microscope while it lives in a drop of pond water. The student notices a small, bubble-like structure inside the cell called a contractile vacuole.

Water constantly diffuses into the Amoeba's cytoplasm from the surrounding pond water. Over a few seconds, the contractile vacuole slowly fills with this water. It then suddenly contracts, squeezing the water out of the cell and back into the pond.

Which life process is the Amoeba carrying out when it forces this water out of its cell?

A wildlife club records the great pond snail, which has the binomial name Lymnaea stagnalis, during a stream survey.

(a) State what is meant by the term "species". [1]

(b) State the genus given in the name Lymnaea stagnalis, and describe why the binomial system is useful to scientists working in different countries. [2]

(c) Later in the survey, the club finds three unidentified freshwater snails, labelled snail 1, snail 2 and snail 3, and records the following features before returning each snail to the stream.

• Snail 1: shell coils in a flat spiral; shell has no dark bands
• Snail 2: shell coils to a pointed spire; shell has no dark bands
• Snail 3: shell coils to a pointed spire; shell has dark bands

Using only the features given, construct a dichotomous key that could be used to identify snail 1, snail 2 and snail 3. [3]

A microbiologist collects four unidentified samples from a woodland stream and records the following features under a microscope.

Sample A: a single cell with no nucleus, surrounded by a cell wall. Sample B: made of many thread-like cells woven together; each cell wall contains chitin; no chlorophyll is present; the sample is growing on, and absorbing nutrients from, a piece of decaying wood. Sample C: a single cell containing a nucleus and green chloroplasts; it swims using a single whip-like tail. Sample D: far smaller than samples A to C; consists only of a protein coat surrounding a strand of genetic material; shows no signs of activity unless it is inside a living host cell.

(a) State the kingdom to which sample A belongs. [1]

(b) State the kingdom to which sample B belongs. [1]

(c) State the kingdom to which sample C belongs. [1]

(d) Explain why sample D cannot be placed into any of the five kingdoms. [2]

Scientists compare DNA samples from three species of wild dog: the grey wolf, the coyote and the black-backed jackal. For each pair of species, they calculate the percentage similarity between the sequences of bases in their DNA. Their results are:

• Grey wolf and coyote: 96% similarity
• Grey wolf and black-backed jackal: 89% similarity
• Coyote and black-backed jackal: 88% similarity

(a) Using these results, identify which two of the three species are the most closely related. [1]

(b) Explain how the concept of DNA base sequence similarity supports your answer to (a). [2]

(c) State one aim of classification systems that this DNA evidence supports. [1]

(d) The grey wolf has the binomial name Canis lupus, and the coyote has the binomial name Canis latrans. State what this shared genus name suggests about the relationship between the two species, and link your answer to the DNA evidence given above. [2]

A field guide describes an animal found beside a mountain stream. Its skin is smooth, moist and has no scales. It lays soft, shell-less eggs in the water, and its young hatch out breathing through gills before later developing lungs and losing their gills as they mature into adults.

Which vertebrate group does this animal belong to?

A gardener plants a bean seedling in a pot of soil. Each week, for four weeks, the gardener measures the height of the seedling with a ruler. At the end of the experiment, a similar seedling grown under the same conditions is dried in an oven until its mass no longer changes, and this dry mass is compared with the dry mass of a seedling of the same age measured in week 1.

Both the height and the dry mass are found to have permanently increased over the four weeks, and neither measurement decreases again afterwards.

Which life process is being shown by the bean seedling?

The domestic cat has the binomial name Felis catus. The first word, Felis, is the genus, and the second word, catus, is the species.

Which of the following shows this binomial name written using the correct convention?

An entomologist collects four invertebrates from a garden and records the following features of each.

Specimen 1: body divided into a head, thorax and abdomen; three pairs of jointed legs, all attached to the thorax; one pair of antennae; two pairs of wings.

Specimen 2: body divided into only two regions, a cephalothorax and an abdomen; four pairs of jointed legs; no antennae.

Specimen 3: hard exoskeleton; five pairs of jointed legs; two pairs of antennae; found under a stone at the edge of a garden pond.

Specimen 4: long, thin body made up of many similar segments; most segments bear one pair of jointed legs; one pair of antennae.

(a) State the feature that all four specimens share which shows that each belongs to the arthropod group of invertebrates. [1]

(b) State the group, within the arthropod group, to which specimen 1 belongs. [1]

(c) State the group, within the arthropod group, to which specimen 2 belongs. [1]

(d) State the group, within the arthropod group, to which specimen 3 belongs. [1]

(e) State the group, within the arthropod group, to which specimen 4 belongs. [1]

A biology class compares a garden spider with a rose bush, and then examines three further plant specimens, W, X and Y, collected on a walk.

Both the spider and the rose bush are made of eukaryotic cells and are multicellular.

Specimen W: reproduces by releasing spores from structures on the underside of its fronds; produces no flowers or seeds. Specimen X: produces flowers; each seed contains one seed leaf (cotyledon); its leaves have parallel veins. Specimen Y: produces flowers; each seed contains two seed leaves (cotyledons); its leaves have a branching network of veins.

(a) State two features of the rose bush's cells that would place it in the plant kingdom rather than the animal kingdom, which the spider's cells do not have. [2]

(b) State the group, within the plant kingdom, to which specimen W belongs. [1]

(c) Explain why specimen W is placed in this group rather than with the flowering plants. [1]

(d) State the group, within the flowering plants, to which specimen X belongs. [1]

(e) State the group, within the flowering plants, to which specimen Y belongs. [1]

A humpback whale lives in the ocean, has a streamlined body shape and swims using a tail fin, features it shares with many species of fish. Early classification systems grouped whales together with fish because of these shared external features.

(a) State one feature of a humpback whale, other than its body shape or swimming ability, that instead supports classifying it in the same group as mammals such as dogs and humans. [1]

(b) Explain why grouping the whale with fish, based only on its body shape and swimming ability, can produce a misleading classification, and state what modern classification systems aim to reflect instead. [2]

(c) State the type of evidence, beyond visible physical features, that modern biologists can compare between a whale and other mammals to confirm how closely related they are. [1]