explain selective permeability and why cells need to be selectively permeable key pdf

Explain selective permeability and why cells need to be selectively permeable key pdf

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Introduction: Compartments Within Cells

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Passive transport

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. A single substance tends to move from an area of high concentration to an area of low concentration until the concentration is equal across a space. You are familiar with diffusion of substances through the air.

Introduction: Compartments Within Cells

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.

NCBI Bookshelf. Molecular Cell Biology. New York: W. Freeman; Three-dimensional structure of a recombinant cardiac gap junction membrane channel determined by electron crystallography.

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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. Transport across a membrane can be considered from an energy story perspective; it is a process after all. For instance, at the beginning of the process a generic substance X may be either on the inside or outside of the cell. At the end of the process, the substance will be on the opposite side from which it started. At the beginning the matter in the system might be a very complicated collection of molecules inside and outside of the cell but with one molecule of X more inside the cell than out.

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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.

15.3: Membrane Transport with Selective Permeability

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.

Passive transport

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. Some examples of these are other lipids, oxygen and carbon dioxide gases, and alcohol.

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.

All cells are enclosed by a cell membrane. This structure has two layers, and is represented in the diagram below.

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