Question

According to the modern concept, cell membrane is (a) solid (b) quasifluid (c) fluid (d) solidified sheath.

Short answer

The cell membrane is described as (b) quasifluid according to the modern concept.

Step-by-step solution

Understand the concept of cell membrane structure

Modern cell biology suggests that cell membranes are not rigid structures, but rather exhibit fluidity. This means that the proteins and lipids can move sideways within the layer that they are in. This characteristic is often described by the fluid mosaic model, which views the cell membrane as a mosaic of components, including phospholipids, cholesterol, proteins, and carbohydrates, which gives the membrane a fluid character.

Identify the correct option

Based on our understanding of the fluid mosaic model, we can see that the cell membrane is described as being pliable and capable of movement, rather than being solid or a solidified sheath. Therefore, the correct option would be the one that states the cell membrane possesses fluid-like properties.

Select the correct answer from the options

Given the options provided, 'quasifluid' or 'fluid' most closely aligns with the modern concept of the cell membrane as described by the fluid mosaic model. Since there is no option that simply states 'fluid', the more accurate term that is available in the options provided is 'quasifluid'. This term recognizes that while the membrane behaves like a fluid, it is not as free-flowing as a pure liquid.

Key concepts

Fluid Mosaic Model

Understanding the structure and behavior of the cell membrane is critical in cell biology, and the fluid mosaic model is a central concept in explaining its makeup.

The fluid mosaic model describes the cell membrane as a dynamic and flexible structure, akin to a fluid, where both proteins and lipids can shift and float within the layer they occupy. This movement allows the membrane to change shape and reorganize, which is essential for functions like cell growth, division, and the formation of intercellular connections.

Imagine the cell membrane as a sea of lipids, with 'islands' of proteins drifting about – this reflects the 'mosaic' of various components it comprises. In this sea, molecules such as cholesterol can be found as well, which serve to stabilize the membrane's fluidity, preventing it from becoming too rigid or too permeable.

Cell Biology

Cell biology focuses on the study of cells, their physiology, structure, and the interactions among their components. The cell membrane plays an essential role in maintaining the integrity and functionality of cells.

In the context of cell biology, the fluid mosaic model aids in explaining how cells respond to their environment and regulate the movement of substances in and out. Through processes such as endocytosis and exocytosis, cells can take up nutrients, export waste, and communicate with other cells, all of which are mediated by the fluid nature of their membranes.

• Endocytosis: Cells engulf substances from outside into vesicles within the cytoplasm.
• Exocytosis: Cells expel substances by merging vesicles with the cell membrane.

Understanding these processes at the molecular level is crucial for comprehending how diseases can affect cellular functions and for developing medical treatments.

Phospholipids

Phospholipids are the foundational molecules that form the structure of the cell membrane. They are unique in that they possess a hydrophilic (water-attracting) 'head' and two hydrophobic (water-repelling) 'tails'.

Due to their dual affinity, phospholipids naturally arrange themselves into a bilayer, creating a barrier that separates the internal contents of the cell from the external environment. This organization allows the membrane to be selectively permeable, controlling which substances can pass through.

• Hydrophilic heads: Face the aqueous environments both inside and outside the cell.
• Hydrophobic tails: Hide from water, facing each other inside the bilayer.

This structure is key to the fluid mosaic model, ensuring the membrane is sufficiently fluid for the movement and interaction of proteins and other molecules, while also providing the essential barrier function.