According to Biology in Focus: Second Edition the cell membrane is selectively permeable to allow certain substances through, but not all substances. (Campbell Biology Focus, 2014). In other words, the cell membrane’s purpose is to protect the cell from unwanted, outside substances. It is a combination of fluids comprised of lipids, proteins, and carbohydrates. The most abundant lipid found in membranes are phospholipids, which have a polar or a hydrophilic head facing out towards the hydrophilic regions and a nonpolar or hydrophobic tail that face in to the hydrophobic region. A membrane is composed of two layers of these phospholipids, the lipid bilayer, in which the tails face one another and the heads face outwards. These lipids can
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Active transport is the type of transport that does require energy, supplied from ATP, because the substance is moving from an area of low concentration to an area of high concentration. Simple diffusion is a type of passive diffusion, and as the name would suggest, this type of transport applies to substances that are most easily moved through the cell membrane. These substances include, but are not limited to: gases, small polar molecules, small lipids, cholesterol, and steroids. These substances do not need a transporter to cross the cell membrane. On the other hand, facilitated diffusion is more complicated than simple diffusion. Unlike those of simple diffusion, the substances related to facilitated diffusion do need a transporter to get across the cell membrane. Substances that need a transporter include: large polar molecules, glucose, amino acids, charged molecules, and proteins. There are two types of transporters that can be used to help diffuse a substance across the cell membrane. One of the transporters is a carrier protein. A carrier protein is used when the shape of the substance matches the shape of the carrier protein. …show more content…
The other type of transporter is a channel protein; channel proteins are used to moved charged molecules. When using a channel protein, the charge inside of the channel must be the same charge as the molecule passing through it; one charge will only interact with the same charge. For example, if the molecule passing through the protein channel is polar, the inside of the protein channel will also be polar. If the inside of the channel is polar, the outside of the channel will be non-polar. To see if facilitated diffusion is an active or passive transport, the way the molecule is moving must be observed. If the molecule is moving from an area of high concentration to an area of low concentration, then no energy is being exerted, therefore it is considered a type of passive transport. If the molecule is moving from an area of low concentration to high concentration, it is requiring energy, therefore it is an active transport. The last type of transport is bulk transport. There are certain types of substances, such as polysaccharides, large particles,
Active transport is the type of transport that does require energy, supplied from ATP, because the substance is moving from an area of low concentration to an area of high concentration. Simple diffusion is a type of passive diffusion, and as the name would suggest, this type of transport applies to substances that are most easily moved through the cell membrane. These substances include, but are not limited to: gases, small polar molecules, small lipids, cholesterol, and steroids. These substances do not need a transporter to cross the cell membrane. On the other hand, facilitated diffusion is more complicated than simple diffusion. Unlike those of simple diffusion, the substances related to facilitated diffusion do need a transporter to get across the cell membrane. Substances that need a transporter include: large polar molecules, glucose, amino acids, charged molecules, and proteins. There are two types of transporters that can be used to help diffuse a substance across the cell membrane. One of the transporters is a carrier protein. A carrier protein is used when the shape of the substance matches the shape of the carrier protein. …show more content…
The other type of transporter is a channel protein; channel proteins are used to moved charged molecules. When using a channel protein, the charge inside of the channel must be the same charge as the molecule passing through it; one charge will only interact with the same charge. For example, if the molecule passing through the protein channel is polar, the inside of the protein channel will also be polar. If the inside of the channel is polar, the outside of the channel will be non-polar. To see if facilitated diffusion is an active or passive transport, the way the molecule is moving must be observed. If the molecule is moving from an area of high concentration to an area of low concentration, then no energy is being exerted, therefore it is considered a type of passive transport. If the molecule is moving from an area of low concentration to high concentration, it is requiring energy, therefore it is an active transport. The last type of transport is bulk transport. There are certain types of substances, such as polysaccharides, large particles,