Fig. 2.1 shows four small animals, A, B, C and D, collected by a student from a garden and drawn to the same scale. All four are arthropods. Some of their f...
Question 1 Report
Fig. 2.1 shows four small animals, A, B, C and D, collected by a student from a garden and drawn to the same scale. All four are arthropods. Some of their features are recorded in Table 2.1.
| Animal | Number of legs | Number of body parts |
|---|---|---|
| A | ? | 3 |
| B | 8 | 2 |
| C | ? | many |
| D | 14 | 1 |
(a) Measure the length of the body of animal A along the line shown in Fig. 2.1, in mm. [1]
(b) Measure the length of the body of animal D along the line shown, in mm. [1]
(c) Complete Table 2.1 by counting the number of legs of animal A and of animal C in Fig. 2.1. [2]
(d) Use the number of legs and body parts to name the arthropod group of animal A and give a reason. [2]
(e) Name the arthropod group of animal B and give a reason. [2]
(f) Describe two features, visible in Fig. 2.1, that could be used to tell an insect from a many-legged myriapod. [2]
(g) Construct a dichotomous key that would separate animals A, B, C and D. [4]
(h) State three features shared by all arthropods. [3]
(i) Calculate how many times longer animal C is than animal A, using your measured values. Show your working. [2]
(j) Suggest one reason why a labelled biological drawing is more useful than a photograph for identifying these animals. [1]
Answer Details
Labelled answer diagram:
This question tests observation, classification of arthropods, and building a dichotomous key. First the completed feature table:
| Animal | Number of legs | Number of body parts |
|---|---|---|
| A | 6 | 3 |
| B | 8 | 2 |
| C | many (more than 15, e.g. about 30) | many |
| D | 14 | 1 |
(a) and (b) Measure the body length of animal A and of animal D along the line shown, in mm, reading each with a ruler on the printed figure [1] + [1].
(c) Counting the legs in Fig. 2.1: animal A has 6 legs; animal C has many legs (more than 15) [2], as entered in the table above.
(d) Animal A is an insect [1] because it has 6 legs and 3 body parts [1].
(e) Animal B is an arachnid [1] because it has 8 legs and 2 body parts [1].
(f) Any two distinguishing features: an insect has 3 body parts while a myriapod has many segments; an insect has 6 legs while a myriapod has many pairs; an insect may have wings and a myriapod does not [2].
(g) Dichotomous key. Each numbered couplet gives two contrasting, observable choices that lead either to an animal or to the next couplet:
| Step | Feature | Go to / Animal |
|---|---|---|
| 1a | more than 8 legs | go to 2 |
| 1b | 8 legs or fewer | go to 3 |
| 2a | long worm-like body, one pair of legs per segment | Animal C |
| 2b | flattened body with seven pairs of legs | Animal D |
| 3a | 8 legs, 2 body parts | Animal B |
| 3b | 6 legs, 3 body parts | Animal A |
Award for a workable key using contrasting observable features [2] that correctly separates all four animals [2] [4].
(h) Any three features shared by all arthropods: jointed legs (paired jointed appendages); a hard exoskeleton; a segmented body; bilateral symmetry [3].
(i) Divide the length of C by the length of A using your own measured values, for example \( \frac{\text{length of C}}{\text{length of A}} \). Method mark for dividing [1], answer mark for the number of times [1] [2].
(j) A labelled drawing can show only the key structures clearly and can be labelled, removing background clutter that a photograph would include [1].
Exam tip: a good dichotomous key uses only features you can actually see and count, such as number of legs or body parts, never colour or size, because those vary between individuals.
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