The blastula in birds consists of a cap of cells, the Blank______, atop the yolk.Multiple choice question.blastodiscblastocoelblastomereblastocyst

To answer this multiple-choice question effectively, let's break down the terms provided and their relevance in the context of embryology, specifically relating to birds.

1. Understanding the Options

• Blastodisc: This is the term used to describe the disc of cells that forms on top of the yolk in the eggs of birds and reptiles. It is what eventually develops into the embryo.

• Blastocoel: This refers to the fluid-filled cavity within the blastula. In birds, it is not specifically a term that describes the cellular structure atop the yolk.

• Blastomere: This is a term for the individual cells formed by the cleavage of the zygote. They make up the blastodisc.

• Blastocyst: This term refers to a structure formed in the early development of mammals, not birds. It contains an inner cell mass that later develops into the embryo.

2. Analyzing the Question

From the description of the blastula in birds, we know that the structure that sits on top of the yolk is a cap of cells. Given the definition of the blastodisc and the descriptions of the other terms, we can identify the correct answer.

3. Final Answer

The correct term to fill in the blank is blastodisc.

Answer: blastodisc