What organ and system protects by forming a selective barrier?

Skin and Integumentary system protects by forming a selective barrier.  

Explanation:

Multicellular organisms unlike unicellular organism have a variety of systems each having a different function. The body of multicellular organisms is covered with epidermis or skin which is known as  largest organ of the body. The skin consists of many sensory receptors and protects by enclosing muscles and other body tissues. While Integumentary system is made with skin and its various appendages like hair, feathers, nails etc. with receptors and secretary pores and protects the body from pain.

prophase: we can observe the chromosomes to coil up and condense. they become visible. nuclear membrane and envelope disintigrate.s

metaphase: chromosomes align at the center, the metaphase plate. spindle fibers attach to centromeres of the sister chromatids. they meet at kinetochores.

anaphase: sister chromatids are pulled towards each opposing centromere, set on different poles.

telophase: chromosomes are now clustered up only on either sides of the cell. nuclear membranes reform, and a new cell wall forms along the cell plate. this will lead to cytokinesis, the process that divides the cell membrane and forms the cell wall.

i am going to guess that it is co2.