Problem 4 - Biology of Humans: Concepts, Applications, and Issues

Question

Prokaryotic cells a. rarely have a cell wall. b. are usually larger than eukaryotic cells. c. lack internal membrane-enclosed organelles. d. have linear strands of DNA within a nucleus.

Step-by-Step Solution

Answer

c. Prokaryotic cells lack internal membrane-enclosed organelles.

Step 1: Understanding Prokaryotic Cells

Prokaryotic cells are primitive cells that lack a distinct nucleus and membrane-bound organelles. These characteristics form the basis for identifying prokaryotic cells.

Step 2: Analyze Each Option

Evaluate each option given in the exercise: a. Prokaryotic cells rarely have a cell wall. b. Prokaryotic cells are usually larger than eukaryotic cells. c. Prokaryotic cells lack internal membrane-enclosed organelles. d. Prokaryotic cells have linear strands of DNA within a nucleus.

Step 3: Evaluate Option a

Prokaryotic cells usually have a cell wall, for example, bacterial cells have peptidoglycan cell walls. So option a is incorrect.

Step 4: Evaluate Option b

Prokaryotic cells are generally smaller than eukaryotic cells. Eukaryotic cells have more complex structures, which makes them larger. Thus, option b is incorrect.

Step 5: Evaluate Option c

Prokaryotic cells lack internal membrane-enclosed organelles like mitochondria, endoplasmic reticulum, etc. This statement is correct and matches the characteristics of prokaryotic cells.

Step 6: Evaluate Option d

Prokaryotic cells have a single, circular chromosome that is not enclosed within a nucleus. Thus, option d is incorrect as prokaryotic cells do not have linear strands of DNA within a nucleus.

Step 7: Conclusion

Based on the evaluation of all the options, the correct answer is c. Prokaryotic cells lack internal membrane-enclosed organelles.

Key Concepts

Cell Wall

Prokaryotic cells almost always have a cell wall. It serves as a protective layer that provides shape and rigidity. For instance, in bacteria, the cell wall is primarily composed of peptidoglycan.
This unique structure allows the cell to maintain its shape and resist internal turgor pressure. The presence of the cell wall is one of the key differences between prokaryotic cells and certain eukaryotic cells, such as animal cells, which do not have cell walls.

• The cell wall protects against mechanical stress.
• It helps prevent the cell from bursting in hypotonic environments.
• Acts as a barrier to certain substances.

This makes the cell wall crucial for the survival of many prokaryotic cells in various environments.

Prokaryotic vs. Eukaryotic Cells

Understanding the distinctions between prokaryotic and eukaryotic cells is essential. Prokaryotic cells are simpler and smaller, typically ranging from 0.1 to 5.0 micrometers in size. In contrast, eukaryotic cells are larger, usually between 10 to 100 micrometers.
Here are some key differences:

• Prokaryotic Cells: Lack a true nucleus; their genetic material is not contained within a nuclear envelope.
• Eukaryotic Cells: Have a well-defined nucleus where DNA is enclosed by a nuclear membrane.
• Prokaryotic Cells: No internal membrane-bound organelles.
• Eukaryotic Cells: Contain various organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus.

These differences lead to distinct cellular functions and complexities, with eukaryotic cells being associated with multicellular organisms like plants, animals, and fungi, while prokaryotic cells are usually single-celled organisms like bacteria and archaea.

Internal Membrane-Enclosed Organelles

A significant characteristic of prokaryotic cells is the absence of internal membrane-enclosed organelles. Organelles like mitochondria, endoplasmic reticulum, and Golgi apparatus, which are present in eukaryotic cells, do not exist in prokaryotic cells.
This simplicity means all cellular processes in prokaryotic cells occur in the cytoplasm or are associated with the cell membrane.

• Prokaryotic cells rely on the cell membrane for functions like respiration.
• The cytoplasm holds all the components necessary for basic cellular activities.

The lack of compartmentalization in prokaryotic cells leads to different metabolic pathways and simpler organization, making them highly efficient in simpler tasks.

DNA Structure

The structure of DNA is another distinguishing feature between prokaryotic and eukaryotic cells. Prokaryotic cells typically have a single, circular chromosome, whereas eukaryotic cells have multiple, linear chromosomes contained within a nucleus.
This difference affects how each cell replicates and repairs its genetic material.

• Prokaryotic DNA: Located in a region called the nucleoid, not separated by a membrane.
• Eukaryotic DNA: Found within the nucleus, enclosed by a nuclear envelope.
• Prokaryotic cells may also have plasmids, small circular DNA molecules that can carry additional genes.

The simple circular DNA structure in prokaryotes allows for rapid replication and helps these cells adapt quickly to environmental changes.