Question

People belong to domain (a) eukarya; (b) archaea; (c) bacteria.

Short answer

Humans belong to the domain Eukarya.

Step-by-step solution

Understanding Biological Domains

First, it is important to know what biological domains entail. Biological domains are the highest taxonomic rank of organisms, grouping life into three broad categories based on cell structure and function: Eukarya, Archaea, and Bacteria.

Characteristics of Eukarya

The domain Eukarya consists of organisms with eukaryotic cells, which have a distinct nucleus that contains the genetic material. These organisms also have other membrane-bound organelles. Examples include animals, plants, fungi, and protists.

Characteristics of Archaea

The domain Archaea includes unicellular microorganisms. These organisms do not have a nucleus and are prokaryotes, similar to bacteria, but they have distinct biochemistry and genetic properties that differentiate them from Bacteria and Eukarya.

Characteristics of Bacteria

The domain Bacteria also consists of unicellular prokaryotic organisms that lack a nucleus. Bacteria are diverse and can be found in almost every habitat on Earth. They have a different cell wall structure compared to Archaea.

Identifying the Correct Domain for Humans

Humans are complex organisms with eukaryotic cells that contain a nucleus and other membrane-bound organelles, placing them in the domain Eukarya.

Key concepts

Eukarya Characteristics

Eukarya is one of the three main biological domains, and it comprises all organisms with eukaryotic cells. These cells are distinct because they possess a well-defined nucleus that houses the cell's genetic material. This genetic material is organized into linear chromosomes within the nucleus, allowing for complex regulation and expression of genes.
Eukaryotic cells also contain a variety of membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and, in plants, chloroplasts. These organelles perform specialized functions that contribute to the overall well-being of the organism.

• Eukaryotes include a wide range of organisms, from single-celled protists to complex multicellular forms like plants, animals, and fungi.
• This diversity among eukaryotes reflects their evolutionary adaptability and ability to thrive in various environments.

Another characteristic is that eukaryotic cells divide through mitosis, a process that ensures the correct distribution of chromosomes to daughter cells. This feature plays a critical role in growth, development, and reproduction in multicellular eukaryotes.

Archaea Characteristics

Archaea are unique single-celled microorganisms that belong to their own domain; they share some similarities with bacteria but are distinct in many significant ways. Unlike eukaryotic cells, archaeal cells are prokaryotic, lacking a true nucleus. However, Archaea possess unique genetic sequences in their ribosomal RNA, which set them apart from bacteria and eukaryotes.
This distinct biochemistry allows Archaea to inhabit some extreme environments that are typically inhospitable to most life forms, such as hot springs, salt lakes, and deep ocean vents, meriting them the name extremophiles.

• Archaeal cell membranes have a different lipid composition compared to bacteria, making them more stable and protective under extreme conditions.
• They do not possess peptidoglycan in their cell walls, a feature that is common in most bacterial cell walls, further distinguishing them from bacteria.

Despite their single-cell simplicity, Archaea play crucial roles in the environment, particularly in the nitrogen cycle and as part of the microbial communities in the human gut.

Bacteria Characteristics

Bacteria, like Archaea, are comprised of unicellular prokaryotic organisms. These cells do not contain a nucleus; instead, their genetic material is organized within a nucleoid region in the cell.
Bacteria are incredibly diverse and are found in nearly every habitat on Earth, from soil and water to living symbiotically or pathogenically within plants, animals, and humans.

• Bacterial cell walls are typically made of peptidoglycan, a unique polymer that provides structural strength and protection.
• The diversity among bacteria also translates to a wide variety of metabolic processes, allowing them to thrive in almost any environment imaginable.
• They can reproduce rapidly through a simple process called binary fission, which contributes to their adaptability and resilience.

Additionally, some bacteria have beneficial uses, contributing to food production and bioremediation, while others can cause infectious diseases, highlighting their significance in both natural ecosystems and human health.