One of the characteristics unique to animals is a. gastrulation. b. multicellularity. c. sexual reproduction. d. flagellated sperm.

Verified step by step guidance

1. Identify the options and understand their meanings: Gastrulation is a phase early in the embryonic development of most animals, involving the formation of multiple layers of cells. Multicellularity refers to organisms that consist of more than one cell, distinguishing them from unicellular organisms. Sexual reproduction is a biological process that creates a new organism by combining the genetic material of two organisms. Flagellated sperm are sperm cells that use a whip-like structure called a flagellum to propel themselves.
2. Recognize that multicellularity and sexual reproduction are not unique to animals as they are also found in plants and fungi.
3. Understand that while flagellated sperm are common in many animals, they are also present in some plants, such as bryophytes and ferns.
4. Focus on gastrulation, which is a process that specifically occurs in animal embryonic development, leading to the formation of the embryonic layers that will develop into different tissues and organs.
5. Conclude that the correct answer is 'a. gastrulation' because it is a characteristic unique to animals, involved in their embryonic development, and not observed in other groups like plants or fungi.

Key Concepts

Gastrulation

Gastrulation is a crucial developmental process in embryology where the single-layered blastula reorganizes into a multi-layered structure called the gastrula. This process establishes the three primary germ layers: ectoderm, mesoderm, and endoderm, which later differentiate into various tissues and organs. It is a defining characteristic of animal development, distinguishing animals from other life forms.

Multicellularity

Multicellularity refers to the condition of an organism being composed of multiple cells that work together to perform various functions. While many life forms, including plants and fungi, are multicellular, this characteristic is not unique to animals. However, the complexity of cellular organization and specialization in animals is a significant aspect of their biology.

Flagellated Sperm

Flagellated sperm are a type of sperm cell characterized by the presence of a flagellum, which allows for motility. This feature is common in many animal species and is essential for sexual reproduction, as it enables sperm to swim towards the egg for fertilization. While flagellated sperm are prevalent in animals, they are also found in some protists and plants, making this characteristic not exclusive to animals.