Accessory material in a chicken egg include the following except

Analyze the question: We need the one item that is NOT an accessory material of the egg.

Concept: A bird's egg has two kinds of parts:

• The true egg (ovum): the germinal disc (blastodisc), which holds the nucleus and cytoplasm, and the yolk, which is the food store of the ovum itself.
• Accessory materials: layers added around the ovum as it travels down the oviduct. These provide nutrition, protection, and support. They include the albumen (egg white), the shell membranes, and the shell. The chalazae are also added.

Solution:

• A. Albumen: secreted by the oviduct around the yolk, so it is accessory.
• B. Shell membrane: added in the oviduct (isthmus), so it is accessory.
• C. Shell: added in the uterus (shell gland), so it is accessory.
• D. Germinal disc: part of the ovum itself, where the female nucleus is located and where the embryo develops after fertilisation. It is not added later, so it is not accessory.

Answer: D. Germinal disc.

Tip: Think of the ovum as the "real egg" (germinal disc plus yolk) and everything added afterwards as "packaging" (albumen, membranes, shell). In "except" questions, pick the item that belongs to the ovum itself.