Answers · Living things and keys

Species and scientific names — answer key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. SQ1 · Practice

Model answer. c. A species is a group of organisms that can reproduce to produce fertile offspring. A horse and a donkey can mate (d), but their mule is infertile, so they are two species. Looking alike (a) or living in one place (b) is not enough.

A full answer includes

c: a species is a group of organisms that can reproduce to produce fertile offspring; mating alone, looking alike or living in one place is not enough.

Also accept

Watch for

“Two animals that can mate and have young must be the same species.” — The young must be fertile: a horse and a donkey have young, but mules are infertile.

2. SQ2 · Practice

Options as numbered on the pupil sheet: 1 — The genus: a group of closely similar species; 2 — The species within the genus; 3 — The country where it lives; 4 — The person who first described it.

Model answer. Panthera is the genus, a group of closely similar species; the tiger, Panthera tigris, is in the same genus. leo shows the species within the genus. Together, Panthera leo names the species.

A full answer includes

Panthera: the genus.
leo: the species within that genus.

Also accept

Panthera: genus; leo: species

Watch for

“The second word alone is the name of the species.” — The second part shows the species within the genus; the species is named by both words together.

3. SQ3 · Practice

Model answer. b. The genus starts with a capital letter and the species part with a small letter: Homo sapiens. In print the whole name is also in italics; by hand it is underlined.

A full answer includes

b: the genus starts with a capital letter and the species part with a small letter; in print the name is in italics, by hand it is underlined.

Also accept

Watch for

“Both words of a scientific name start with a capital letter.” — Only the genus has a capital letter; the species part starts with a small letter.

4. SQ4 · Practice

Model answer. b. Organisms are classified into groups by the features they share. The sycamore and the field maple both have leaves with lobes spreading from one point, leaves in opposite pairs, and winged fruits in joined pairs.

A full answer includes

b: organisms are classified into groups by the features they share, such as leaf shape and paired winged fruits.

Also accept

Watch for

“Organisms are grouped by where they live.” — Classification uses the features organisms share, not where they grow.

5. SQ5 · Practice

Model answer. (a) No. (b) A species is a group of organisms that can reproduce to produce fertile offspring. A horse and a donkey can produce young, but the mule is infertile: it cannot have young of its own. So horses and donkeys are two different species.

A full answer includes

(a) No, they are different species.
(b) A species is a group of organisms that can reproduce to produce fertile offspring; the horse and donkey produce a mule, which is infertile.

Also accept

(a) no; (b) a species produces fertile offspring; the mule is infertile

Watch for

“Two animals that can mate and have young must be the same species.” — The young must be fertile; a mule is not.

6. SQ6 · Practice

Model answer. a. The lion and the tiger share the genus Panthera. The cheetah is in a different genus, Acinonyx.

A full answer includes

a: the first word of a scientific name shows the genus; the lion and the tiger share Panthera.

Also accept

Watch for

“Animals that look alike must be in the same genus.” — Read the first word of each name: it shows the genus.

7. SQ7 · Practice

Model answer. Common names cause confusion: one organism can have many names in different languages, and one name can mean different organisms in different places ("sycamore" is a different tree in Britain and in North America). The binomial system is internationally agreed, so each species has one two-part name that is the same all over the world, and every scientist knows exactly which species is meant.

A full answer includes

Common names differ between countries and languages, and one name can mean different organisms (sycamore in Britain and in North America).
The binomial system is internationally agreed: each species has one scientific name, the same everywhere, so scientists know exactly which organism is meant.

Also accept

common names vary and can mean different organisms; the binomial system is internationally agreed: one name per species, the same everywhere

Watch for

“Scientific names are just Latin translations of common names.” — A scientific name is agreed internationally for each species; it does not depend on any one language's common name.

8. SQ8 · Practice

Model answer. a, c and e. Acer is the genus (a), shared with Acer pseudoplatanus (c), and the name is the same in every country (e). The word campestre on its own (b) is not the species: it means "of the fields" and is used in other genera too (genera is the plural of genus); the species is Acer campestre. Only the genus has a capital letter (d).

A full answer includes

a, c and e: Acer is the genus, shared with Acer pseudoplatanus, and the name is the same everywhere; the species is named by both words together, and only the genus has a capital letter.

Also accept

a, c, e

Watch for

“The second word alone is the name of the species.” — campestre is used in the names of plants in other genera too; the species is named by both words together.
“Both words of a scientific name start with a capital letter.” — Only the genus has a capital letter.

9. SQ9 · Practice

Model answer. W and X differ only at the 4th base (G and C): 1 difference. W and Y differ at the 2nd, 4th, 6th, 8th and 10th bases: 5 differences. X and Y differ at the 2nd, 6th, 8th and 10th bases: 4 differences.

Checked automatically

Differences between W and X: 1 (exact value)
- Common wrong answer 9 : That is the number of places that are the same; count the differences.
Differences between W and Y: 5 (exact value)
- Common wrong answer 4 : Check the 4th base: W has G and Y has C.
Differences between X and Y: 4 (exact value)
- Common wrong answer 5 : Check the 4th base: X and Y both have C there.

A full answer includes

W and X: 1.
W and Y: 5.
X and Y: 4.

Also accept

W–X 1; W–Y 5; X–Y 4

Watch for

“Count the bases that are the same.” — Count the places where the two bases are different.

10. ST1 · Apply

Model answer. (a) All three share the genus Panthera, so they share many features and are classified close together, but each is a different species. The names alone cannot tell which two are most closely related. (b) The lion and the leopard: their base sequences differ in only 2 places, compared with 5 for each of them with the tiger. Sequences change slowly over many generations, so the pair with the most similar sequences shares the most recent common ancestor.

A full answer includes

(a) All three are in the same genus, Panthera, so they share many features; each is a different species.
(b) The lion and the leopard: their sequences have the fewest differences (2), so they have had the least time to change since their common ancestor.

Also accept

(a) same genus Panthera, different species; (b) lion and leopard: fewest differences, so most recent common ancestor

Watch for

“Organisms that look alike are always closely related.” — The DNA base sequences are a better guide than looks: the fewer differences, the more recent the common ancestor.
“The more differences, the more closely related.” — More differences means more time since the common ancestor, so a more distant relationship.

11. ST2 · Apply

Model answer. (a) It is more closely related to the field maple, because both are in the genus Acer: they share many features, such as lobed leaves in opposite pairs and paired winged fruits. The oak is in a different genus, Quercus. (b) Classification aims to reflect evolutionary relationships, so the two maples should share a more recent common ancestor. Their DNA base sequences would be more similar, with fewer differences, than either compared with the oak.

A full answer includes

(a) The field maple: it shares the genus Acer, so the two share many features and are classified in the same group.
(b) Acer palmatum and the field maple would have more similar base sequences (fewer differences) than either has with the oak, because they share a more recent common ancestor.

Also accept

(a) field maple: same genus Acer, shared features; (b) the two Acer species have more similar base sequences than either has with the oak (more recent common ancestor)

Watch for

“Trees with similar names in English must be closely related.” — Use the scientific name: the genus shows the group of closely similar species.

12. ST3 · Apply

Model answer. (a) Yes. (b) A species is a group of organisms that can reproduce to produce fertile offspring. The mixed puppies grow up and have puppies of their own, so they are fertile, and Chihuahuas and Great Danes belong to one species, however different they look. A horse and a donkey can also have young, but the mule is infertile, so horses and donkeys are two species, even though they look more alike than a Chihuahua and a Great Dane.

A full answer includes

(a) Yes, they are the same species (dogs).
(b) A species is a group of organisms that can reproduce to produce fertile offspring; the mixed puppies are fertile, however different the parents look. A horse and a donkey produce mules, which are infertile, so they are two species.

Also accept

(a) same species; (b) their offspring are fertile, which is what makes one species, not looks; horse and donkey: mule infertile, so two species

Watch for

“Organisms that look very different must be different species.” — Look at the offspring, not the parents: fertile offspring means one species.
“Two animals that can mate and have young must be the same species.” — The young must be fertile: the horse and the donkey have young, but mules are infertile.