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Magazine Chapter 3: Problem 5
Unlike eukaryotic cells, prokaryotic cells ________________ . a. have no plasma membrane b. have RNA but not DNA c. have no nucleus d. a and \(c\)
Short Answer
Expert verified
Option c: Prokaryotic cells have no nucleus.
Step by step solution
01
Understand the Characteristics of Prokaryotic Cells
Prokaryotic cells are a fundamental type of cell that lacks a membrane-bound nucleus. Their genetic material, unlike eukaryotic cells, is not enclosed in a nuclear membrane.
02
Evaluate Option A
Consider whether prokaryotic cells have a plasma membrane. All cells, including prokaryotic cells, have a plasma membrane that protects and encloses their contents.
03
Evaluate Option B
Check if prokaryotic cells have RNA but not DNA. Prokaryotic cells have both DNA and RNA, just like eukaryotic cells, although their DNA is organized differently.
04
Evaluate Option C
Consider the existence of a nucleus in prokaryotic cells. Prokaryotic cells do not have a true nucleus; their genetic material is not surrounded by a nuclear membrane.
05
Evaluate Option D
Option D combines statement a and c. Since option a is incorrect (prokaryotes do have a plasma membrane) and option c is correct, option D is not correct because one of its components is false.
06
Determine the Correct Answer
Since option c is the only correct statement regarding prokaryotic cells, which lack a nucleus, it stands as the accurate choice.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cell Structure
Prokaryotic cells have a simple yet efficient structure that allows them to thrive in a variety of environments. Unlike eukaryotic cells, prokaryotic cells do not have membrane-bound organelles. Their internal structure is more rudimentary compared to the complexity observed in eukaryotic cells. This simplicity is a key feature:
- Lack of Membrane-Bound Nucleus: Genetic material is found freely in the cytoplasm, organized in a region called the nucleoid.
- Small Size: Generally range from 0.1 to 5.0 micrometers, facilitating rapid growth and reproduction.
- Shapes: Can be spherical (cocci), rod-shaped (bacilli), or spiral (spirilla).
Nucleus
A defining characteristic of prokaryotic cells is the absence of a true nucleus. In contrast to eukaryotic cells, which enclose their DNA within a nuclear membrane, prokaryotic DNA is not separated from the rest of the cell by a membrane. This results in several distinct features:
- Nucleoid: The region in the cytoplasm where DNA is concentrated. It lacks a surrounding membrane, setting it apart from the nucleus in eukaryotic cells.
- Circular DNA: Prokaryotic cells typically have a single, circular chromosome as opposed to the multiple linear chromosomes found in eukaryotes.
- Plasmids: Small, circular DNA molecules that may be present and carry additional genes beneficial for survival, such as antibiotic resistance.
Plasma Membrane
Prokaryotic cells are surrounded by a plasma membrane, a crucial structure that maintains the integrity and homeostasis of the cell. This semi-permeable membrane plays several key roles:
- Barrier Function: Separates the interior of the cell from the external environment, protecting the cell from unwanted substances.
- Transport: The plasma membrane controls the entry and exit of nutrients, ions, and waste, essential for sustaining cell functions.
- Sensory Receptors: Contains proteins that sense environmental changes, enabling the cell to respond accordingly.
Genetic Material
In prokaryotic cells, genetic material is present in a unique and efficient form that serves the organism's simple structure and rapid reproductive needs. Here are the main characteristics:
- DNA Structure: Prokaryotic cells typically contain a single circular DNA strand located in the nucleoid region.
- Genome Size: Generally smaller and more compact than eukaryotic genomes due to fewer non-coding regions.
- Binary Fission: Prokaryotic cells reproduce through a process called binary fission, where the DNA is duplicated and the cell divides into two identical cells.
