Answers · Kingdoms and animal groups
The arthropods — answer key
Check meaning, not exact wording. These are teaching points, not official Cambridge marks.
1. JQ1 · Practice
Model answer. a, b and c. Every arthropod has jointed legs, an exoskeleton (a hard skeleton on the outside) and a segmented body. Many insects have wings, but spiders, woodlice and centipedes do not (d). Arthropods have no backbone (e). Six legs is an insect feature only (f).
A full answer includes
- a, b and c: jointed legs, an exoskeleton and a segmented body; many arthropods have no wings and more than six legs, and none has a backbone.
Also accept
- a, b, c
Watch for
- “All arthropods have wings.” — Many insects have wings, but spiders, woodlice and centipedes have none.
- “All arthropods have six legs.” — Six legs is an insect feature; a spider has eight and a woodlouse fourteen.
2. JQ2 · Practice
Options as numbered on the pupil sheet: 1 — Three body parts, three pairs of legs, one pair of antennae; 2 — Two body parts, four pairs of legs, no antennae; 3 — More than four pairs of legs, two pairs of antennae; 4 — A long body of many segments with legs on each, one pair of antennae.
Model answer. Insects have three body parts, three pairs of legs and one pair of antennae. Arachnids have two body parts, four pairs of legs and no antennae. Crustaceans have more than four pairs of legs and two pairs of antennae. Myriapods have a long body of many segments with legs on each, and one pair of antennae.
A full answer includes
- Insects: three body parts, three pairs of legs, one pair of antennae.
- Arachnids: two body parts, four pairs of legs, no antennae.
- Crustaceans: more than four pairs of legs, two pairs of antennae.
- Myriapods: a long body of many segments with legs on each, one pair of antennae.
Also accept
- insects: 3 parts, 3 pairs of legs, 1 pair of antennae; arachnids: 2 parts, 4 pairs, no antennae; crustaceans: more than 4 pairs, 2 pairs of antennae; myriapods: many segments with legs on each, 1 pair of antennae
Watch for
- “Arachnids have antennae.” — Spiders and scorpions have no antennae: the short feelers by a spider's mouth are pedipalps.
3. JQ3 · Practice
Model answer. b. Two body parts, four pairs of legs and no antennae are arachnid features. The two short feelers by the mouth are pedipalps, which hold food: they are not legs (c) and not antennae. An insect has three pairs of legs (a), and a myriapod has a long body of many segments (d).
A full answer includes
- b: two body parts, four pairs of legs and no antennae place it in the arachnids; the feelers are pedipalps, not legs.
Also accept
- b
Watch for
- “A spider is an insect.” — An insect has three body parts, three pairs of legs and one pair of antennae; a spider has two body parts, four pairs of legs and no antennae.
- “The feelers by its mouth are legs, so it has ten legs.” — They are pedipalps, used for holding food; the spider walks on four pairs of legs.
4. JQ4 · Practice
Model answer. An insect has three pairs of legs, all on the thorax: 6 legs. A spider has four pairs: 8 legs (the pedipalps are not legs). A woodlouse has seven pairs, one under each large plate: 14 legs.
Checked automatically
- An insect: 6 (exact value)
- Common wrong answer 3 : That is the number of pairs; the question asks for legs in total.
- A spider: 8 (exact value)
- Common wrong answer 10 : The two short feelers by the mouth are pedipalps, not legs: a spider walks on four pairs of legs.
- Common wrong answer 6 : Six legs is an insect feature; a spider is an arachnid, with four pairs of legs.
- A woodlouse: 14 (exact value)
- Common wrong answer 7 : Seven is the number of legs on one side; the woodlouse has seven pairs.
- Common wrong answer 6 : A woodlouse is not an insect: count one leg under each large plate, on both sides.
A full answer includes
- An insect: 6.
- A spider: 8.
- A woodlouse: 14.
Also accept
- insect 6; spider 8; woodlouse 14
Watch for
- “A spider has ten legs.” — The two short feelers by the mouth are pedipalps, not legs: a spider walks on four pairs.
- “A woodlouse has six legs, like an insect.” — A woodlouse is a crustacean: it has seven pairs of legs, one under each large plate.
5. JQ5 · Practice
Model answer. b. The woodlouse has more than four pairs of legs and two pairs of antennae, so it is a crustacean, a land-living relative of crabs and shrimps. Where it lives does not make it an insect (a). Myriapods have one pair of antennae (c), and arachnids have exactly four pairs of legs and no antennae (d).
A full answer includes
- b: more than four pairs of legs and two pairs of antennae are crustacean features.
Also accept
- b
Watch for
- “A woodlouse is an insect.” — An insect has three pairs of legs and one pair of antennae; a woodlouse has seven pairs of legs and two pairs of antennae.
- “Any arthropod with many legs is a myriapod.” — A myriapod has a long body of many segments and one pair of antennae; two pairs of antennae is a crustacean feature.
6. JQ6 · Practice
Model answer. Jointed legs are shared by all arthropods, so they cannot separate the groups. A spider has two body parts, an insect three. A spider has four pairs of legs, an insect three pairs. A spider has no antennae, an insect has one pair. Many insects also have wings, and a spider never does. So the spider is an arachnid.
A full answer includes
- Any two: body parts (spider two, insect three); legs (spider four pairs, insect three pairs); antennae (spider none, insect one pair); wings (many insects have wings, a spider never does).
Also accept
- two of: body parts 2 vs 3; legs 4 pairs vs 3 pairs; antennae none vs 1 pair; wings never vs often
Watch for
- “A spider is an insect.” — An insect has three body parts, three pairs of legs and one pair of antennae; a spider has two, four pairs and none.
- “Jointed legs make an animal an insect.” — All arthropods have jointed legs; the number of body parts, legs and antennae decides the group.
7. JQ7 · Practice
Model answer. c. A long body of many segments with legs on each, and one pair of antennae, make the millipede a myriapod, like the centipede. It does have more than four pairs of legs, but a crustacean also has two pairs of antennae (b). It has far more than three pairs of legs, so it is not an insect (a), and arachnids have no antennae (d).
A full answer includes
- c: a long body of many segments with legs on each and one pair of antennae are myriapod features.
Also accept
- c
Watch for
- “Any arthropod with more than four pairs of legs is a crustacean.” — Crustaceans have two pairs of antennae; the millipede has one pair and a long body of many segments: it is a myriapod.
- “An arthropod with antennae is an insect.” — Insects, crustaceans and myriapods all have antennae; only arachnids have none.
8. JQ8 · Practice
Options as numbered on the pupil sheet: 1 — Abdomen; 2 — Head; 3 — Thorax.
Model answer. The head is at the front, with the antennae. The thorax is the middle part and carries all six legs and the wings. The abdomen is the back part.
A full answer includes
- Head, thorax, abdomen.
Also accept
- head, thorax, abdomen
Watch for
- “The thorax is the back part of an insect.” — The thorax is the middle part, carrying all six legs and the wings; the abdomen is the back part.
9. JQ9 · Practice
Options as numbered on the pupil sheet: 1 — Insects; 2 — Arachnids; 3 — Crustaceans; 4 — Myriapods.
Model answer. The scorpion has two body parts, four pairs of legs and no antennae: an arachnid (its claws are pedipalps, like a spider's short feelers but much larger). The crab has more than four pairs of legs and two pairs of antennae: a crustacean. The centipede has a long body of many segments with legs on each and one pair of antennae: a myriapod. The butterfly and the worker ant both have three body parts, six legs and one pair of antennae: insects, even though the worker ant has no wings.
A full answer includes
- Scorpion: arachnids.
- Crab: crustaceans.
- Centipede: myriapods.
- Butterfly: insects.
- Worker ant: insects.
Also accept
- scorpion: arachnids; crab: crustaceans; centipede: myriapods; butterfly: insects; worker ant: insects
Watch for
- “An insect with no wings is not an insect.” — Wings are common in insects but not a group feature: three body parts, six legs and one pair of antennae make the worker ant an insect.
- “The scorpion's claws are a pair of legs, so it has five pairs.” — The claws are pedipalps, like a spider's short feelers but much larger: the scorpion walks on four pairs of legs, like a spider.
10. JT1 · Apply
Model answer. (a) A long body of many segments, with legs on each and one pair of antennae, makes it a myriapod. (b) Antennae alone cannot decide: insects, crustaceans and myriapods all have them, and only arachnids have none. An insect has three body parts and three pairs of legs, while this animal has 15 segments and 15 pairs of legs. (c) Count the legs: an insect always has exactly three pairs, all on its thorax.
A full answer includes
- (a) Myriapods.
- (b) Insects, crustaceans and myriapods all have antennae; only arachnids have none. An insect has three body parts and three pairs of legs; this animal has many segments with legs on each.
- (c) The legs (an insect has exactly three pairs, all on the thorax) or the body parts (an insect has three).
Also accept
- (a) myriapod; (b) insects, crustaceans and myriapods all have antennae; insects have 3 parts and 3 pairs of legs; (c) count the legs or body parts
Watch for
- “An arthropod with antennae is an insect.” — Insects, crustaceans and myriapods all have antennae; count body parts and legs as well.
11. JT2 · Apply
Model answer. (a) The first animal has three body parts, three pairs of legs and one pair of antennae: it is an insect, a real ant. The second has two body parts, four pairs of legs and no antennae: it is an arachnid, a spider that looks like an ant. (b) The narrow waist and the raised front legs make it look like an ant, but counting settles it: two body parts, not three; four pairs of legs, not three, because the waving front pair are legs; and no antennae at all. Its look and the way it moves do not decide its group.
A full answer includes
- (a) First animal: insects (it is an ant). Second animal: arachnids (it is a spider).
- (b) It has two body parts, four pairs of legs (the raised front pair are legs, not antennae) and no antennae: arachnid features. An insect has three body parts, three pairs of legs and one pair of antennae. How it looks and moves does not decide the group.
Also accept
- (a) first: insect; second: arachnid; (b) two body parts, four pairs of legs including the raised pair, no antennae; an insect has three parts, three pairs of legs and one pair of antennae; looks do not decide
Watch for
- “It looks and runs like an ant, so it is an insect.” — Look and movement do not decide the group: count body parts, legs and antennae.
- “The raised front legs are its antennae.” — They are legs, held up and waved; the spider has no antennae, and with them it has four pairs of legs.