File Name: explain selective permeability and why cells need to be selectively permeable key .zip
Despite differences in structure and function, all living cells in multicellular organisms have a surrounding cell membrane. As the outer layer of your skin separates your body from its environment, the cell membrane also known as the plasma membrane separates the inner contents of a cell from its exterior environment. This cell membrane provides a protective barrier around the cell and regulates which materials can pass in or out. Cholesterol is also present, which contributes to the fluidity of the membrane, and there are various proteins embedded within the membrane that have a variety of functions. The phosphate heads are thus attracted to the water molecules of both the extracellular and intracellular environments.
The hydrophobic and hydrophilic regions of plasma membranes aid the diffusion of some molecules and hinder the diffusion of others. Plasma membranes are asymmetric: the interior of the membrane is not identical to the exterior of the membrane. In fact, there is a considerable difference between the array of phospholipids and proteins between the two leaflets that form a membrane. On the interior of the membrane, some proteins serve to anchor the membrane to fibers of the cytoskeleton. There are peripheral proteins on the exterior of the membrane that bind elements of the extracellular matrix. Carbohydrates, attached to lipids or proteins, are also found on the exterior surface of the plasma membrane.
Partial Design Process These resources engage students in some of the steps in the engineering design process, but do not have them complete the full process. While some of these resources may focus heavily on the brainstorm and design steps, others may emphasize the testing and analysis phases. Although no charge or fee is required for using TeachEngineering curricular materials in your classroom, the lessons and activities often require material supplies. The expendable cost is the estimated cost of supplies needed for each group of students involved in the activity. This activity also uses some non-expendable reusable items such as beakers; see the Materials List for details. Example activity testing stations. For example, a plastic grocery store bag needs to be light and easily packaged as well as sturdy and waterproof to handle your groceries As another example, various forms of zipper plastic bags have been designed for specific purposes, such as for freezer storage to prevent freezer burn on food and for refrigerator storage more permeable.
Passive transport is a type of membrane transport that does not require energy to move substances across cell membranes. Diffusion is the net movement of material from an area of high concentration to an area with lower concentration. The difference of concentration between the two areas is often termed as the concentration gradient , and diffusion will continue until this gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to an area of lower concentration, it is described as moving solutes "down the concentration gradient" compared with active transport , which often moves material from area of low concentration to area of higher concentration, and therefore referred to as moving the material "against the concentration gradient". However, in many cases e. If there are different solutions at the two sides of the membrane with different equilibrium solubility of the drug, the difference in the degree of saturation is the driving force of passive membrane transport. Simple diffusion and osmosis are in some ways similar.
Cell membranes are not easily visualized using light microscopes. At various points, different models have attempted to explain a selectively permeable phospholipid bilayer.
All cells are enclosed by a cell membrane. This structure has two layers, and is represented in the diagram below. The extracellular environment is the area outside of the cell. Each layer has two main components, phospholipids and proteins.
One of the great wonders of the cell membrane is its ability to regulate the concentration of substances inside the cell. The phospholipids are tightly packed together, and the membrane has a hydrophobic interior. This structure causes the membrane to be selectively permeable. In the case of the cell membrane, only relatively small, nonpolar materials can move through the lipid bilayer remember, the lipid tails of the membrane are nonpolar.
Diffusion is a process of passive transport in which molecules move from an area of higher concentration to one of lower concentration. This is due to the diffusion of odor molecules through the air, from an area of high concentration the kitchen to areas of low concentration your upstairs bedroom. Diffusion is a passive process of transport.
The cell membrane plasma membrane is a thin semi-permeable membrane that surrounds the cytoplasm of a cell. Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell while keeping other substances out. It also serves as a base of attachment for the cytoskeleton in some organisms and the cell wall in others. Thus the cell membrane also serves to help support the cell and help maintain its shape. In endocytosis, lipids and proteins are removed from the cell membrane as substances are internalized. In exocytosis, vesicles containing lipids and proteins fuse with the cell membrane increasing cell size. Animal cells , plant cells , prokaryotic cells , and fungal cells have plasma membranes.
Organelles allow specialized functions within cells to be localized, contained and independently regulated. This separation is oftentimes achieved by selectively permeable membranes, which enable control of molecular transport, signaling between compartments and containment of stress-inducing factors. Here we consider the role of a number of membrane systems within the cell: the plasma membrane, that of the endoplasmic reticulum, and then focusing on the nucleus, depository for chromatin and regulatory centre of the cell. Nuclear pores allow shuttling of ions, metabolites, proteins and mRNA to and from the nucleus. The activity of transcription factors and signaling molecules is also modulated by translocation across the nuclear envelope. Regulation and response to signals and stresses, both internal and external, allow cells to maintain homeostasis within functional tissue.
General Problem: The cell membrane must simultaneously act as a barrier between "IN" and "OUT" and control specifically which substances enter and leave the cell and how quickly and efficiently they do so. Subproblems: The chemical properties of molecules that must enter and leave the cell are highly variable. Some subproblems associated with this are: a Large and small molecules or collections of molecules must be able to pass across the membrane.
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