Parts of a dichotomous key to organisms A, B, C and D are shown.  Design missing parts of the key using features visible in the following diagrams.

1.

Body with tentacles ................................................A

Body without tentacles ......................................... go to 2

2.

................................................................B

............................................................go to 3

3

.................................................................C

................................................................D

All of these organisms belong to the animal kingdom. State two structural differences between animal cells and plant cells

any visible characteristic that distinguishes between B and the rest; (eg. three pairs of legs/no legs)
characteristic that distinguishes between C and D; (eg. body divided into many segments / body not divided into many segments)
characteristic specific to C and different characteristic specific to D; (eg. C had cylinder shape and D has pores)

cell wall only in plant cells;
starch granules only in plant cells;
chloroplasts only in plant cells;
centrioles only in animal cells;
(large) vacuole in plant cells;

Despite the simplicity of 2(a), this dichotomous key question drew out some remarkable weaknesses. Too often, answers included internal or physiological characteristics as opposed to visible features of the organisms. Those candidates who did not have the proper knowledge of how to design a dichotomous key were the ones who gave a varied range of incorrect answers. Exoskeleton was accepted.   

Most candidates correctly answered question 2(b).  Some sloppy answers that gained no credit were: “Plant cells have chloroplasts.  Animal cells have mitochondria” or just “Plant cells have chloroplasts” and nothing said about animal cells.