What does the term 'Prokaryote' literally refer to regarding cell structure?

The term refers to organisms whose cells lack a true nucleus. Their genetic material is found directly in the cytoplasm as a single circular chromosome.

Why can prokaryotes function efficiently without mitochondria?

Their extremely small size gives them a high surface-area-to-volume ratio. This allows them to generate sufficient ATP through metabolic processes occurring on the inner surface of the cell membrane.

What is the evolutionary advantage of having a circular chromosome in prokaryotes?

Circular DNA is more resistant to degradation by certain enzymes and simplifies the process of replication in a single-celled organism with a rapid life cycle.

How does the location of genetic material differ between a prokaryote and a eukaryote?

In prokaryotes, genetic material floats freely in the cytoplasm as a circular chromosome. In eukaryotes, it is enclosed within a distinct membrane-bound nucleus.

Compare the size of prokaryotic cells to eukaryotic cells.

Prokaryotic cells are substantially smaller than eukaryotic cells. This smaller size allows them to rely on simple diffusion for internal transport without needing complex organelles.

When comparing organelles, what is uniquely missing in all prokaryotes?

Prokaryotes lack all membrane-bound organelles, such as mitochondria and chloroplasts. They perform equivalent functions using specialized regions of their cell membrane.

What is the common error regarding photosynthesis in bacteria?

Students often wrongly assume bacteria cannot photosynthesize because they lack chloroplasts. Some bacteria can photosynthesize using chlorophyll-like substances and enzymes located in the cytoplasm or membrane.

Is it correct to say all prokaryotes are pathogens? Why or why not?

No, that is incorrect. While some bacteria cause disease, many are harmless decomposers (saprobionts) or are used beneficially in processes like food production.

What mistake is often made regarding the presence of a cell wall in prokaryotes?

Students may assume only plants have cell walls. However, almost all prokaryotes (bacteria) possess a cell wall, though it is not made of cellulose.

Define the term 'Saprobiont' in the context of prokaryotic nutrition.

A saprobiont is an organism that feeds on dead organic matter. They secrete enzymes to digest complex molecules externally and then absorb the simpler resulting nutrients.

Common Features: Prokaryotic Organisms | Pearson Edexcel IGCSE Biology

1. The Nature & Variety of Living Organisms

Common Features: Prokaryotic Organisms

Summary

Prokaryotic organisms, primarily represented by bacteria, are unicellular life forms characterized by the absence of a membrane-bound nucleus and other complex organelles. They maintain genetic information in a single circular chromosome within the cytoplasm and exhibit diverse nutritional strategies, ranging from decomposition to specialized photosynthesis.

1. Definition & Core Concepts

Prokaryotes are defined as single-celled organisms that lack a distinct, membrane-bound nucleus to house their genetic material. This is the primary distinction between them and the more complex eukaryotic organisms.
All known prokaryotes are unicellular, meaning the entire organism consists of a single cell that carries out all necessary life processes independently.
Bacteria are the most prominent group within this category, varying significantly in shape, from rod-shaped Lactobacillus to spherical Pneumococcus.
They are substantially smaller in size compared to eukaryotic cells, typically requiring high-magnification microscopy to be observed clearly.

Diagram of a prokaryotic bacterial cell showing circular DNA, plasmids, and cell wall.

2. Underlying Principles of Organization

The cytoplasm serves as the site for all metabolic reactions, as prokaryotes lack specialized compartments like mitochondria or chloroplasts for energy production.
Genetic material exists as a single, circular chromosome of DNA. This chromosome is not associated with proteins in the same way eukaryotic DNA is, and it floats freely in a region of the cytoplasm.
Plasmids are small, independent loops of DNA found in many prokaryotes. They often contain genes that provide specific advantages, such as resistance to environmental stresses.
Structural integrity is provided by a rigid cell wall that surrounds the cell membrane, protecting the organism from external pressures and maintaining its characteristic shape.

3. Nutritional Methods & Techniques

Many prokaryotes are saprobionts or decomposers, meaning they obtain nutrients by breaking down dead organic matter. This process is essential for nutrient cycling in ecosystems.
Some bacteria are capable of photosynthesis despite lacking chloroplasts. They achieve this using chlorophyll-like pigments embedded in their cell membranes and specific enzymes to synthesize sugars.
Other bacteria feed on living organisms, potentially acting as pathogens. They may reside within host body cavities rather than invading cells directly to cause disease.
Specialized bacteria like Lactobacillus utilize anaerobic processes to convert sugars (such as milk lactose) into lactic acid, a technique harnessed in food production.

4. Key Distinctions: Prokaryotes vs. Eukaryotes

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions