because some molecules are bigger then othersand won't diffuse into the cell... hope that helps
Becuase some molecules are too big to pass through.
Simple diffusion
They pass through channels in the cell membrane.
A membrane that does not allow substances through is impermeable. One that allows some substances, but not others, is semipermeable or selectively permeable.
it allows some substances to pass through but blocks the passage of others.
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One of the characteristics of a cell membrane is that it is semi-permeable. As such, it is able to limit what can get into and out of the cell.
A selectively permeable membrane allows some substances through it and does not allow others.Allows certain substances to pass but not others
Semipermeable membrane.
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They pass through channels in the cell membrane.
A membrane that does not allow substances through is impermeable. One that allows some substances, but not others, is semipermeable or selectively permeable.
The plasma membrane acts as a selective barrier that regulates the passage of substances in and out of the cell. It helps maintain the internal balance by controlling the movement of essential molecules such as nutrients and ions into the cell, while keeping waste products and harmful substances out. This selective permeability ensures that the cell maintains the right concentrations of different molecules for proper functioning.
selectively permeable
it allows some substances to pass through but blocks the passage of others.
The phospholipid bi-layer.
it allows some substances to pass through but blocks the passage of others.
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One of the characteristics of a cell membrane is that it is semi-permeable. As such, it is able to limit what can get into and out of the cell.