Question

Explain the different types of Permiablity.

1) Selectively Permeable.
2) Permeable.
3) Yeh kounsa hai?? Book mein hai ni​

Answer 1

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. This is important for the cell to maintain its internal order irrespective of the changes to the environment. For example, water, ions, glucose and carbon dioxide may need to be imported or exported from the cell depending on its metabolic activity. Similarly, signaling molecules may need to enter the cell and proteins may need to be released into the extracellular matrix. The presence of a selectively permeable membrane allows the cell to exercise control over the quantum, timing and rate of movement of these molecules.

Movement across a selectively permeable membrane can occur actively or passively. For example, water molecules can move passively through small pores on the membrane. Similarly, carbon dioxide released as a byproduct of respiration quickly diffuses out of the cell. Some molecules are actively transported. For example, cells in the kidney expend energy to reabsorb all the glucose, amino acids and vitamins from the glomerular filtrate even against the concentration gradient. Failure of this process leads to the presence of glucose or the byproducts of protein metabolism in urine; a tell tale sign of diabetes.

the conversion of one molecule of ATP into ADP. This is called primary active transport, where the movement is directly coupled to the hydrolysis of a high-energy phosphate bond. A similar process is used to pump protons against their concentration gradient and this is a crucial part of both photosynthesis and cellular respiration.

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