Question

The absence of rigid cell walls in animal cells favors which one of the following mechanisms?
A. Selective permeability
B. Sodium - potassium pump for muscle contraction and nerve conduction
C. Freely permeable to chemicals
D. Both A and B

Answer 1

Hint: There are many different types of life on the planet, each with its own set of traits. At the microscopic level, however, every living thing on the planet is made up of the same fundamental, structural, and functional unit of life — the cell. Depending on the form of life, the types of cells, chemical makeup, and features change. The cell wall is one of these key features.

Complete answer:
A cell wall is a structural layer found just outside the cell membrane that surrounds various types of cells. It may be robust, flexible, and even stiff at times. It functions as a filtration mechanism as well as providing structural support and protection to the cell. Most prokaryotes (excluding mollicute bacteria), algae, fungi, and eukaryotes (including plants) have cell walls, but mammals lack them. One of their main functions is to act as pressure vessels, keeping the cell from over-expanding when water enters.
In animal cells, the cell membrane is the limiting outer membrane. The cell membrane is selectively permeable, allowing only solvent and specific solute particles to pass through. In contrast to the plant cell, which is enclosed by a cellulose cell wall, the animal cell may freely connect with the environment and external media. The cell wall's function in plants is to give rigidity and mechanical support to the cell. Certain activities of animal cells, such as muscle contraction and neurological stimulation, cannot be carried out successfully unless the animal cell is in close touch with the surrounding environment.

Thus, the answer is option D: 'Both A and B.'

Note:
The cellulose cell wall is strongly connected to the evolution of multicellularity, terrestrialization, and vascularization in photosynthetic eukaryotes (also known as plants and algae). The CesA cellulose synthase originated in Cyanobacteria and has been found in Archaeplastida since endosymbiosis; subsequent endosymbiosis events have transported it (along with arabinogalactan proteins) to brown algae and oomycetes.