What structural adaptation in chickens allows them to lay their eggs in arid environments rather than in water?
a. Extraembryonic membranes
b. Yolk
c. Cleavage
d. Gastrulation

Verified step by step guidance

1. Understand the problem: The question is asking about a structural adaptation in chickens that allows them to lay eggs in arid environments, which means environments with little water.
2. Identify the key terms: The options provided are 'extraembryonic membranes', 'yolk', 'cleavage', and 'gastrulation'. Each of these terms relates to different aspects of egg development or embryonic development.
3. Explain 'extraembryonic membranes': These are membranes that form outside the embryo and are crucial for the development of amniotic eggs, which are adapted to terrestrial environments. They include the amnion, chorion, yolk sac, and allantois, which help in gas exchange, waste storage, and nutrient transfer.
4. Relate the adaptation to the environment: In arid environments, the ability to retain moisture and protect the embryo from desiccation is crucial. The extraembryonic membranes, particularly the amnion, create a protective, water-retaining environment for the developing embryo.
5. Conclude the reasoning: Based on the explanation, the structural adaptation that allows chickens to lay eggs in arid environments is the presence of extraembryonic membranes, as they provide the necessary protection and support for the embryo in a dry environment.

Key Concepts

Extraembryonic Membranes

Extraembryonic membranes are structures that develop outside the embryo in amniotes, including chickens, to provide protection and support. These membranes include the amnion, chorion, yolk sac, and allantois, which collectively facilitate gas exchange, waste removal, and nutrient transfer, allowing eggs to be laid in terrestrial environments without the need for water.

Yolk

The yolk is a nutrient-rich part of the egg that provides essential nourishment to the developing embryo. In chickens, the yolk contains proteins, fats, and vitamins necessary for growth, enabling the embryo to develop in a self-contained environment without external food sources, which is crucial for survival in arid conditions.

Cleavage

Cleavage is the series of rapid cell divisions that occur immediately after fertilization, leading to the formation of a multicellular embryo. In chickens, cleavage is adapted to occur within the confines of the egg, allowing the embryo to develop efficiently in a terrestrial setting, independent of water-based environments.