Difference Between Membranous and Nonmembranous Organelles

Main Difference – Membranous vs Nonmembranous Organelles

Cell membrane, cytoplasm along with its organelles, and the nucleus are the three main structures in a cell. Organelles are specialized structures, which carry out unique functions inside the cell. These structures can be categorized into two as membranous and nonmembranous organelles. Most organelles like mitochondria, plastids, endoplasmic reticulum, and Golgi apparatus are fluid-filled structures. On that account, fluid-filled organelles are membranous. Nonmembranous organelles are ribosomes, cytoskeleton, nucleolus, and centrosome. All prokaryotic organelles are nonmembranous. The main difference between membranous and nonmembranous is that membranous organelles are surrounded by single or double membranes, which are structurally similar to a cell membrane whereas nonmembranous organelles are not surrounded by any kind of a membrane.

Key Areas Covered

1. What are Membranous Organelles
      – Definition, Types, Characteristics
2. What are Nonmembranous Organelles
      – Definition, Types, Characteristics
3. What are the similarities between Membranous and Nonmembranous Organelles
      – Outline of Common Features
4. What is the difference between Membranous and Nonmembranous Organelles
      – Comparison of Key Differences

Key Terms: Membranous Organelles, Nonmembranous Organelles, Cell, Cell Membrane, Cytoplasm, Nucleus, Mitochondria, Plastids, Endoplasmic Reticulum, Golgi Apparatus, Ribosomes

What are Membranous Organelles

Membranous organelles are surrounded by the cell membrane. Nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, plastids, and lysosomes are membranous organelles. Membranous organelles are fluid-filled, and are separated from the cytoplasm. The endoplasmic reticulum is a double-membraned system that is involved in the transferring of substances from one part to the other part of the cell. Golgi apparatus is another membranous organelle that has a secretory function in the cell. Lysosomes are membranous vesicles formed from the Golgi apparatus. They contain digestive enzymes. Mitochondria are membranous organelles involved in cellular respiration. Vacuoles are membranous sacs found in plant cells; they store water and nutrients. Plastids like chloroplasts contain pigments known as chlorophyll in order to carry out photosynthesis. Chloroplast structure is shown in figure 1, which is surrounded by inner and outer membranes.

Figure 1: Chloroplast

What are Nonmembranous Organelles

Nonmembranous organelles do not contain a definite boundary for organelles. On that account, these organelles do not possess fluid-filled cavities. All organelles in prokaryotes are nonmembranous. Ribosomes, nucleoid, centrioles, cilia, flagella, and components of the cytoplasm like microtubules, microfilaments, and intermediate filaments are nonmembranous organelles.

Nucleoid is a region of the cytoplasm where the Prokaryotic genetic material is concentrated in. Ribosomes are responsible for the protein synthesis from messenger RNA (mRNA). They are composed of RNA with bound proteins. The cytoskeleton is also made up of nonmembranous organelles which provide shape and support to the cell. Centrioles are arrangements of two microtubule sets, which organize microtubules during cell division. Cilia and flagella are nonmembranous, hairlike structures involved in the movement of materials and the cell itself. Cilia are only found in eukaryotic cells. 

Figure 2: Centrioles

Similarities Between Membranous and Nonmembranous Organelles

• Both membranous and nonmembranous organelles are specialized structures that perform a unique function in the cell.
• Both membranous and nonmembranous organelles are found in eukaryotes.

Difference Between Membranous and Nonmembranous Organelles

Definition

Membranous Organelles: Membranous organelles are organelles which are surrounded by a cell membrane in order to separate out the organelles’ fluid-filled spaces.

Nonmembranous Organelles: Nonmembranous organelles are organelles which do not contain surrounding cell membranes, separating the organelle from the cytoplasm.

In Prokaryotes

Membranous Organelles: Prokaryotes lack membranous organelles.

Nonmembranous Organelles: Prokaryotic organelles are nonmembranous organelles.

Fluid-filled Organelles

Membranous Organelles: Membranous organelles comprise fluid-filled cavities inside the organelle.

Nonmembranous Organelles: Nonmembranous organelles do not comprise fluid-filled cavities inside the organelles.

Definite Boundary

Membranous Organelles: Membranous organelles comprise a defined boundary to the organelle.

Nonmembranous Organelles: Nonmembranous organelles are continuous with the cytoplasm.

Examples

Membranous Organelles: Nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, plastids, and lysosomes are membranous organelles.

Nonmembranous Organelles: Ribosomes, nucleoid, centrioles, cilia, flagella, and components of the cytoplasm like microtubules, microfilaments, and intermediate filaments are nonmembranous organelles.

Conclusion

Membranous and nonmembranous organelles are the two types of organelles found in the cell. Membranous organelles are surrounded by single or double membranes, defining a boundary to the organelle. Many of the membranous organelles comprise fluid-filled cavities inside them. Nonmembranous organelles are continuous with the contents in the cytoplasm since they are not surrounded by a membrane. Therefore, the main difference between membranous and nonmembranous organelles is the presence or absence of a definite boundary inside the cytoplasm. 

Reference:

1. “Non-membranous organelles and membranous organelles in the cytoplasm.” Science online. N.p., 18 Oct. 2016. Web. Available here. 22 June 2017. 
2. “Non-Membrane Bound Organelles: Definition & Examples.” Study.com. N.p., n.d. Web. Available here. 22 June 2017. 
3. “Nonmembranous Organelles.” CONCEPTS IN BIOLOGY. N.p., n.d. Web. Available here. 22 June 2017. 

Image Courtesy:

1. “Figure 08 01 05” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
2. “Centriole-en” By Kelvinsong – Own work (CC BY 3.0) via Commons Wikimedia