Select the wrong statement. (a) Plant cells are surrounded by a living, rigid outer layer called cell wall. (b) Plant cell wall is made up of cellulose. (c) Bacterial cell wall is made up of peptidoglycan. (d) Both prokaryotic and eukaryotic plasma membranes are composed of lipids and proteins.

The cell wall is a defining feature of plant cells. Unlike the membranes of animal cells, the cell wall is a sturdy, supportive structure that surrounds the cell membrane. It not only protects the cell but also maintains its shape and prevents it from absorbing too much water and bursting. Composed of multiple layers, the primary component of the plant cell wall is cellulose, a robust carbohydrate polymer.
This layer is not just a static barrier; it's dynamic and participates in various cellular activities such as growth, intercellular communication, and defense against pathogens. The rigidity of the cell wall contrasts with its living nature. While it is stiff and resistant, it is also permeable, allowing water, nutrients, and other substances necessary for the cell's function to pass through easily.

Cellulose is the most abundant organic polymer on the planet, and it is the main building block of plant cell walls. It consists of long chains of glucose molecules linked together, and it's the reason why plant cell walls are so strong.
When we look at cellulose under a microscope, we find a network of fibers that form a complex matrix. This matrix is not only key to supporting the structure of the plant, but also influences how the plant grows and how it withstands mechanical stresses. In our daily lives, we come across cellulose not just in the vegetables and fruits we eat, but also in paper products and textiles such as cotton, which is almost pure cellulose.

Peptidoglycan, distinctive to bacterial cell walls, is not found in plant or animal cells. It's a lattice-like structure composed of sugars and amino acids, and this composition allows it to provide strength and rigidity to bacteria, much like cellulose does for plants. However, it's also the target for many antibiotics, which work by interfering with its production, thus weakening the cell walls and leading to the elimination of the bacteria.
Understanding peptidoglycan is essential not only for microbiology but also for medicine and pharmacology. Researchers continue to study this substance to develop new antibiotics that can overcome bacterial resistance, a growing problem in healthcare.

Enveloping every cell is the plasma membrane, a crucial structure that defines the boundary of the cell while controlling the entry and exit of materials. Composed of a phospholipid bilayer, the membrane exhibits a fluid mosaic model where various proteins are embedded within the lipid layer.
These proteins are not merely structural components; they function as gates and channels for substances to move in and out of the cell, as sensors of environmental signals, and as actors in cell communication and adhesion. Additionally, the plasma membrane has cholesterol scattered within the bilayer, which contributes to both its structure and function, particularly in maintaining fluidity and stability. It's a perfect example of how the complexity of cell biology underlies the fundamental processes of life.