(a) Fig. 3.1 shows the digestive system of a chicken. Fig. 3.1 (i) Label the structures marked X, Y and Z on Fig. 3.1. [3] (ii) Describe the function of str...

Labelled answer diagram:

(a)(i) The structures on the chicken digestive system diagram are: [3]

• X = Crop - the thin-walled storage pouch in the oesophagus [1]
• Y = Proventriculus (glandular stomach) [1]
• Z = Gizzard (ventriculus / muscular stomach) [1]

(a)(ii) The proventriculus (structure Y) is the glandular stomach of the chicken. It secretes hydrochloric acid and digestive enzymes (including pepsin). [1] These begin the chemical digestion of proteins in the food before it passes into the gizzard for mechanical grinding. [1] It is functionally equivalent to the acid-secreting region of a mammalian stomach.

(b) Small stones and gravel that the hen picks up act as grit inside the gizzard. [1] The thick muscular walls of the gizzard contract powerfully and grind the food against these hard particles, mechanically crushing seeds and other food items. This is essential because the hen has no teeth to chew food before swallowing it. [1]

(c) Two features of the chicken's digestive system not found in a goat (any two): [2]

1. Crop - a storage organ in the oesophagus for holding food before it reaches the stomach. Goats (ruminants) have no crop. [1]
2. Gizzard - a muscular stomach specialised for grinding food with grit. Goats rely on teeth and rumination for mechanical breakdown. [1]

Other acceptable answers: the proventriculus (a separate glandular stomach distinct from the grinding organ); two caeca (goats have one); the cloaca (a single opening for digestive, urinary, and reproductive tracts, which goats do not have).