Answer
Hint: Semipermeable membrane permits only some particles to undergo depending on their size, whereas the selectively permeable membrane "chooses" what passes through and it does not depend on the size.
Complete answer:
The differentiation between selectively permeable and semipermeable membrane is -
| Semipermeable membrane | Selectively permeable membrane |
| It does not allow solutes to pass through it. | It allows selected solutes to pass through it to a limited extent. |
| It acts as an ideal partition between two osmotically active solutions or between an answer and its pure solvent. | It acts as an imperfect partition with the result even plasmolyzed protoplasts get deplasmolysed automatically even kept within the same hypertonic solution. |
| It permits entry of only one solvent. | It permits entry of both solvents and to a selected extent solutes. |
| It doesn't exist within the biological word e.g. cellphane, collodion. | Almost all biological membranes are selectively permeable. |
| This type of membrane is used in dialysis maintenance of turgidity and measurement of osmotic potential. | It is useful in maintaining turgidity while retaining the ability to absorb solutes. |
| Example- egg membrane, parchment membrane, and tonoplast. | Example- plasmalemma. |
Additional Information: The plasma membrane is named as a selectively permeable membrane because it permits the movement of only certain molecules in and out of the cells. Not all molecules are liberal to diffuse. If the plasma membrane breaks down then molecules of some substances will freely move in and out of the cells.
Note:
The diffusion of water through a selectively permeable membrane is called osmosis. Other types of semipermeable
membranes are cation exchange membrane [CEM], charge mosaic membrane [CMM], bipolar membrane [BPM], anion exchange membrane [AEM], and proton exchange membrane [PEM].
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Question 4 Short Answer Questions [SA]
Q4] The cell membrane is called selectively permeable. Why ?
Answer:
Solution :
The cell membrane is a very thin layer of protein and fat. It allows only selective substances to pass through it, hence,it is called a selectively permeable membrane.
Video transcript
"Hello friends welcome leaders online cookbook solving session in desktop point at the first question the question says the cell membrane is called selectively of Liquid Fire now friends in this question. We have tell us the reason why the cell membrane is called a selectively permeable. Let's look at the self inflate first. First is the snail temperate at this of the part allow the entry and exist of the substance. The cell membrane is very thin. I'm just still nail is basically made up of protein. And act which allows the entry and exit of the substance. Don't add this process. It will allow only selective. Substance to pass through it. And as it allow only selectively substance to pass the word. It is called as selectively permeable membrane as only selectively substance are getting penetrated inside at this pair are getting the entry inside at this bite is pollock select the copy of the so this is how we approach this question. If you have any questions drop a comment below and subscribe Battle for regular updates and cue Thank you."
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Plasma membranes act not only as a barrier, but also as a gatekeeper. It must allow needed substances to enter and cell products to leave the cell, while preventing entrance of harmful material and exit of essential material. In other words, plasma membranes are selectively permeable—they allow some substances through but not others [Figure 1]. If the membrane were to lose this selectivity, the cell would no longer be able to maintain homeostasis, or to sustain itself, and it would be destroyed. Some cells require larger amounts of specific substances than other cells; they must have a way of obtaining these materials from the extracellular fluids.
This may happen passively, as certain materials move back and forth, or the cell may have special mechanisms that ensure transport. Most cells expend most of their energy, in the form of adenosine triphosphate [ATP], to create and maintain an uneven distribution of ions on the opposite sides of their membranes. The structure of the plasma membrane contributes to these functions.
Selective Permeability
Plasma membranes are asymmetric, meaning that despite the mirror image formed by the phospholipids, the side of the membrane facing the inside of the cell is not identical to the exterior of the membrane. Proteins that act as channels or pumps work in one direction. Carbohydrates, attached to lipids or proteins, are also found on the exterior surface of the plasma membrane.
These carbohydrate complexes help the cell bind substances in the extracellular fluid that the cell needs. This adds considerably to the selective nature of plasma membranes.
Recall that plasma membranes have hydrophilic and hydrophobic regions. This characteristic helps the movement of certain materials through the membrane and hinders the movement of others. Lipid-soluble material can easily slip through the hydrophobic lipid core of the membrane. Substances such as the fat-soluble vitamins A, D, E, and K readily pass through the plasma membranes in the digestive tract and other tissues. Fat-soluble drugs also gain easy entry into cells and are readily transported into the body’s tissues and organs. Molecules of oxygen and carbon dioxide have no charge and pass through by simple diffusion.
Polar substances, with the exception of water, present problems for the membrane. While some polar molecules connect easily with the outside of a cell, they cannot readily pass through the lipid core of the plasma membrane. Additionally, whereas small ions could easily slip through the spaces in the mosaic of the membrane, their charge prevents them from doing so. Ions such as sodium, potassium, calcium, and chloride must have a special means of penetrating plasma membranes. Simple sugars and amino acids also need help with transport across plasma membranes.
References
Unless otherwise noted, images on this page are licensed under CC-BY 4.0 by OpenStax.
Text adapted from: OpenStax, Concepts of Biology. OpenStax CNX. May 18, 2016 //cnx.org/contents/