The fig tree, Ficus carica, and the papaya tree, Carica papaya, produce a milky-looking fluid known as latex. The latex is released when plant tissue is wounded and it is thought to act as a defence against attack by herbivorous insects or parasitic worms. Latex is a complex mixture of substances and the exact composition of the mixture depends on the plant species. A group of enzymes that hydrolyse proteins, known as cysteine proteases, are commonly found in latex. Ficin, found in F. carica, and papain, found in C. papaya, are both cysteine protease enzymes. These enzymes have been extracted and purified for use commercially. (a) An investigation was carried out to compare the effect of temperature on the activity of ficin and papain. The results are shown in Fig. 5.1. [Figure 5.1]