Question

What does it mean for a membrane to be selectively permeable

Answer 1

Selective permeability of membranes means the cell membrane allows certain substances through while others cannot.  

Cell membrane allows selective movement of materials in and out of the cell.

Further Explanation

• A cell membrane is an organelle whose role is to protect the cell from the outer environment. The membrane contains phospholipid bi-layer and proteins that are embedded in the bi-layer.
• Cell membranes contain receptors and channels that only allow specific molecules to pass through the cell membrane.  

Selective permeability  

• Selective permeability is one of the properties of cell membranes, such that the cell membrane only allow certain materials to pass through while others cannot.

• Movement of substances across the cell membrane may either be passive or active.
• Passive transport of molecules across cell membranes occurs without energy input while active transport of substances occurs with energy input in the form of ATP.

Examples of materials than can diffuse freely through the cell membrane

• Small uncharged molecules  
• Small non polar molecules such as CO2 and O2  
• Small uncharged polar molecules such as H2O

Examples of materials that cannot diffuse freely through the membrane

• Larger uncharged polar molecules such as glucose
• Small and larger charged molecules such as ions cannot diffuse freely through the membrane.

• However, ions and most polar molecules such as glucose that cannot diffuse through the cell membrane freely, can pass across the membrane through transporters such as trans-membrane proteins.  

Keywords: Selective permeability, transport, cell membrane

Learn more about:

• Selective permeability: brainly.com/question/3456419
• Active and passive transport: brainly.com/question/2872504
• Cellular transport: brainly.com/question/6949569

Level: High school  

Subject: Biology  

Topic: Cellular transport and physiological processes

Sub-topic: Role of cell membrane in transport

Answer 2

A membrane that is selectively permeable has the ability to allow only specific ions or molecules to traverse it with the help of passive or active transport.

Further Explanation:

When a membrane enables the passage of certain molecules and inhibits some others to cross through it, such membrane is said to be selectively permeable. Transport occurs by means of active or passive transport. In passive transport, the molecules pass the membrane through diffusion or depending on their concentration gradient without using any energy. During active transport, the transport of molecules occurs against their concentration gradient with the help of ATP (energy).

The passage of material across the membrane is determined by the molecule size or concentration of the molecule with respect to inside or outside of the membrane in question. The cell membrane contains certain protein channels that facilitate the entry or exit of various ions and are selective in nature which further contributes to the selectivity of the membrane.

The membranes are also selective to certain molecules because of the composition of the cell membrane. The membrane is generally composed of proteins and phospholipids. A phospholipid is present in the form of a bilayer. This bilayer has a hydrophobic as well as a hydrophilic part. The hydrophilic phase is water-loving and forms the head portion of the phospholipid. The tail of the phospholipid is hydrophobic in nature. The phospholipids bind together in a bilayer with the hydrophilic head facing outside while the hydrophobic tail is immersed inside the bilayer. Due to the hydrophobic center of the bilayer, the membrane allows only the hydrophobic molecules to traverse easily while the polar molecules are not able to pass through it.

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Answer Details:

Grade: Secondary School

Chapter: Membrane Permeability

Subject: Biology

Keywords:

Membrane permeability, selectively permeable, cell membrane, phospholipid bilayer, hydrophobic, hydrophilic, protein channels, polar molecules, non-polar molecules, active transport, passive transport, diffusion, concentration gradient, ATP, energy.