A student collected five small animals from a freshwater pond and labelled them P to T. The photograph shows the five specimens, and the table below records...
Question 1 Report
A student collected five small animals from a freshwater pond and labelled them P to T. The photograph shows the five specimens, and the table below records four external features for each one: the number of legs, and whether wings, antennae and a shell are present or absent. Four of the animals have jointed legs, while the other has a soft body protected by a shell. The student wants to build a dichotomous key so that other pupils can identify each animal from a series of paired choices.
| Animal | Number of legs | Wings | Antennae | Shell |
|---|---|---|---|---|
| P | 6 | present | present | absent |
| Q | 8 | absent | absent | absent |
| R | 0 | absent | absent | present |
| S | 14 | absent | present | absent |
| T | 6 | absent | present | absent |
(a) State how many of the five animals are arthropods. [1]
(b) State the feature, shown in the table, that shows animal R is not an arthropod. [1]
(c) Name the arthropod group to which animal Q belongs and give the feature you used to decide. [2]
(d) Construct a dichotomous key that separates animals P, Q, S and T using the features in the table. [4]
(e) Explain why the colour of an animal is a poor feature to use in a dichotomous key. [2]
(f) Describe how the body length of one of these animals could be measured accurately. [3]
Answer Details
This question tests classification of arthropods and the construction of a dichotomous key from a table of features.
(a) How many are arthropods [1] Four (P, Q, S and T) - they all have jointed legs.
(b) Feature showing R is not an arthropod [1] R has no (jointed) legs / has a shell / has a soft body. Arthropods must have jointed legs, which R lacks.
(c) Arthropod group of Q, with reason [2] Q is an arachnid (1); because it has four pairs of legs (eight legs) (1). Arachnids have 8 legs, insects 6.
(d) Dichotomous key for P, Q, S and T [4] A key uses paired, opposite statements that split the group step by step:
- Six legs .......... go to 2
More than six legs .......... go to 3 - Wings present .......... P
Wings absent .......... T - Eight legs .......... Q
Fourteen legs .......... S
Award 1 mark for using paired opposite statements and 1 mark each for correctly separating P, Q, S and T (max 4).
(e) Why colour is a poor key feature [2] The colour of an animal can vary between individuals or change with age, diet or surroundings (1); so it is not a reliable or constant feature for identification (1). A good key uses fixed, easily observed features.
(f) Measuring body length accurately [3] Place the animal against a ruler marked in millimetres (1); straighten the body and measure in a straight line from one end to the other, reading at eye level to avoid parallax (1); repeat and take an average to improve accuracy (1).
Download The App On Google Playstore
Everything you need to excel in your exams
