Problem 1 - Biology

Question

Which of the following is not a defining characteristic of animals? (a) heterotrophs (b) multicellular (c) eukaryotic (d) presence of a coelom (e) form a zygote that undergoes cleavage

Step-by-Step Solution

Answer

Option (d) presence of a coelom.

Step 1: Understand the Question

The question asks us to identify which option is not a defining characteristic of animals. We are given five characteristics to evaluate.

Step 2: Evaluate Each Characteristic

To determine the defining characteristics of animals, we need to know the standard traits that are common to most, if not all, animals.

Step 3: Characteristic: Heterotrophs

Animals are heterotrophs, meaning they obtain their food by consuming other organisms rather than producing their own food. This is a defining characteristic of animals.

Step 4: Characteristic: Multicellular

Animals are multicellular organisms. This means that they are composed of many cells. Multicellularity is a defining characteristic of animals.

Step 5: Characteristic: Eukaryotic

Animals are eukaryotic, meaning their cells contain a nucleus and other organelles enclosed within membranes. This is a universal trait of all animals.

Step 6: Characteristic: Presence of a Coelom

A coelom is a body cavity that some animals have, but not all. Therefore, not all animals share this trait. This is not a defining characteristic of all animals.

Step 7: Characteristic: Form a Zygote That Undergoes Cleavage

Animals typically form a zygote after fertilization, and this zygote undergoes cleavage, or a series of cell divisions. This is a common trait among animals.

Step 8: Solution Conclusion

We have identified that the presence of a coelom is not a defining characteristic of all animals. Therefore, option (d) is the correct answer.

Key Concepts

Heterotrophs

Animals are heterotrophs, which means they rely on other organisms for food. Unlike plants, which can produce their own food through photosynthesis, animals must consume other living things. This consumption could be in the form of eating plants, other animals, or sometimes both.

• Heterotrophic nutrition involves breaking down complex molecules into simpler ones that the body can use for energy.
• This method of obtaining food is crucial, as it allows animals to access energy necessary for survival, growth, and reproduction.

Understanding animals as heterotrophs helps in defining their role in ecosystems as consumers, impacting the flow of energy and nutrients through trophic levels.

Multicellular

One of the key features of animals is their multicellular structure. Multicellularity means that animals are composed of many cells, as opposed to just one. Each cell in an animal's body has specific roles, contributing to the overall functioning of the organism.

• This complexity allows for specialized functions such as movement, digestion, and respiration.
• Moreover, multicellularity facilitates larger body sizes and the development of complex body systems.

The adoption of multicellularity has enabled animals to evolve into a wide variety of forms and adapt to diverse environments.

Eukaryotic

Animals are eukaryotic organisms, which means their cells contain a well-defined nucleus and other specialized structures called organelles, all enclosed within membranes.

• These organelles perform distinct functions, like energy production, protein synthesis, and the processing of nutrients.
• The nucleus houses the animal's genetic material, orchestrating cell function and replication.

Being eukaryotic is a fundamental trait that distinguishes animals from prokaryotic organisms, like bacteria, which lack a true nucleus and membrane-bound organelles.

Coelom

Some animals possess a coelom, a fluid-filled body cavity located entirely within the mesoderm. Although not all animals have a coelom, it plays a significant role in complex organisms.

• The coelom acts as a cushion for internal organs, providing protection and structural support.
• It also allows for the independent development and movement of those organs, aiding in more efficient body function.

While a coelom is present in many animal phyla, its absence in others—like flatworms—makes it not a universal animal trait, thus distinguishing it from characteristics like multicellularity and heterotrophy.

Zygote Cleavage

In animals, reproduction typically begins with the fusion of genetic material from two parents, forming a zygote. This zygote then undergoes cleavage, a rapid series of cell divisions.

• Cleavage results in a multicellular structure called a blastula, which eventually develops into more complex structures.
• This process is essential for the growth from a single cell to a fully formed organism.

The process of zygote cleavage is a defining feature of animals, distinguishing them from other life forms that may reproduce differently, such as through budding or binary fission.