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Answers
Explanation:
The cell membrane is a phospholipid bilayer embedded in proteins which regulate the transport of molecules across to maintain homeostasis of the cell environment.The lipid soluble or nonpolar molecules can easily pass through the cell membrane, but hydrophilic or polar molecules cannot pass easily.
There are two major ways that polar molecules can be moved across a membrane viz. passive and active'
Passive diffusion : 1) simple 2) facilitated
Active diffusion ; 1) primary 2) secondary
Diffusion is the movement of molecules along the concentration gradient i.e.from higher concentration to lower concentration.
Passive simple diffusion allows small, nonpolar molecules to move down their gradient.This can be disrupted if the diffusion distance increases.
Passive facilitated diffusion occurs along the transport channels.These channels are glycoproteins with specific affinity for certain molecules.
Active transport needs energy from the cell. It usually transports molecules against the gradient.Transport that uses ATP hydrolysis as the energy source for transport is considered primary active transport. e,g, Na+_k+ pump for conduction of action potential.
The secondary active transport moves multiple molecules across the membrane powering the uphill movement of one molecule with the downhill movement of others e. g. Na+_ Ca+2 exchange.
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Explanation:
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