Problem 4 - Campbell Biology Concepts & Connections

Question

A new organism has been discovered. Tests have revealed that it is unicellular, is autotrophic, and has a cell wall that contains peptidoglycan. Based on this evidence, it should be classified as a(n) a. alga. b. archaean. c. protist. d. bacterium.

Step-by-Step Solution

Answer

d. bacterium

Step 1: Identify the organism's characteristics

The organism is described as unicellular, autotrophic, and having a cell wall that contains peptidoglycan.

Step 2: Understand key characteristics of each option

a. Algae can be unicellular or multicellular, usually lack peptidoglycan in their cell walls.b. Archaea are unicellular but their cell walls do not contain peptidoglycan.c. Protists are mostly unicellular, some autotrophic, but they do not have peptidoglycan in their cell walls.d. Bacteria are unicellular, can be autotrophic, and their cell walls contain peptidoglycan.

Step 3: Match the organism's characteristics to the options

Compare the organism's characteristics to each option. The organism is unicellular, autotrophic, and has peptidoglycan in its cell wall. This matches the description of a bacterium.

Step 4: Determine the correct classification

Based on the comparison, the correct classification is bacterium.

Key Concepts

Unicellular Organisms

Unicellular organisms consist of only one cell. This single cell performs all the functions needed for life, such as reproduction, metabolism, and response to the environment.
Common examples include bacteria, archaea, and many protists.
The simplicity of their structure doesn't imply that they are primitive; rather, they are incredibly efficient and adaptable.
These organisms can thrive in a variety of environments, from boiling hot springs to deep ocean trenches.
Their simplicity allows them to reproduce quickly, often within hours, which ensures their survival in changing environments.

Autotrophic

Autotrophic organisms can produce their own food from inorganic substances. They do this primarily through photosynthesis or chemosynthesis.
Photosynthetic autotrophs, like green plants and some bacteria, capture light energy to convert carbon dioxide and water into sugars and oxygen.
Chemosynthetic autotrophs, found mainly in extreme environments like deep-sea vents, derive energy from chemical reactions, often using sulfur or methane.
The ability to create their own food sustains them without the need for other organic compounds, making these organisms foundational in many ecosystems.

Peptidoglycan

Peptidoglycan is a crucial component of the cell wall in many bacteria. It provides structural strength to the bacterial cell and protects it from bursting due to osmotic pressure.
Peptidoglycan is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane.
It's the target for many antibiotics, such as penicillin, which disrupts its synthesis, leading to cell death.
The presence of peptidoglycan in cell walls is a key differentiator between bacteria and other organisms like archaea, which lack this component in their cell walls.

Bacteria Classification

Bacteria are incredibly diverse microorganisms that can be classified based on various characteristics. One key method is based on their cell wall composition, particularly the presence of peptidoglycan.
Bacteria can be gram-positive, with thick layers of peptidoglycan that retain the crystal violet stain used in Gram staining.
Alternatively, they can be gram-negative, with thinner peptidoglycan layers that don't retain the stain but have an additional outer membrane.
Classification can also be based on their metabolism, such as autotrophic, like the newly discovered organism, or heterotrophic, which rely on consuming organic matter.
Additional classifications include shape (cocci, bacilli, spirilla) and habitat (thermophilic, halophilic, etc.).