Cell Membrane and Transport

The cytoskeleton is a framework of cell membranes that work as a cover for and protect their internal organelles. This function is vital in animal cells, that lack a cell wall. The order membrane cytoskeleton (cellular networks ‘skeleton’ made of protein and is contained within the cytoplasm) and gives shape to the cell. The cytoskeleton microfilaments attached to certain proteins in the cell membrane, especially an integral part.

Passive Transport

Remember that the cell membrane is semi-permeable. This does not allow everything to pass through. Some molecules can pass easily through the membranes of your cells, while others have more difficulty. Sometimes molecules require special transport proteins help to move across cell membranes. Some molecules even need an input of energy to help them across cell membranes.
The movement of molecules across the membrane without the input of energy is known as passive transport. When energy is needed, this movement is known as active transport.

1. Diffusion
   One example of passive transport is diffusion, when molecules move from areas of high concentration (bulk) to areas of low concentration (lower number). Molecule is said to flow down their concentration gradient. Type diffusion succeed without energy input. In simple diffusion, small and uncharged molecules can diffuse freely across cell membranes. They just flow through the cell membrane. Simple diffusion does not require energy or need help transport protein. Larger other molecules or charged that diffuses across the membrane may need the help of proteins.
   Oxygen is a molecule that can freely diffuse across cell membranes. For example, the oxygen diffuses out of the air sacs in the lungs into your bloodstream because oxygen is more concentrated in the lungs than in your blood. Oxygen moves from the high concentration of oxygen in the lungs to low concentrations of oxygen in your blood stream.
2. Passive Transport uses Membrane Transport Proteins
   Sometimes, the molecules can not move through the cell membrane of their own. These molecules require special transport proteins to help them move across the membrane, a process known as diffusion facilitative. These special proteins called channel proteins or protein carrier (Figure below), and they are attached to the cell membrane. In fact, they go through the cell membrane of the cell to the outside. Protein provides the channel open drain or hallway through the cell membrane for the molecule to move across. Many protein channels allow the diffusion of ions.
3. Passive Transport
   channel proteins and carrier proteins are involved in passive transport.
   Carrier proteins bind and carry molecules across cell membranes. These proteins bind to molecules on one side of the membrane, to change shape as they carry molecules across the membrane, and store the molecules on the other side of the membrane. Although the protein is involved in both of these methods of transport, the method does not require energy. Therefore, this is the type of passive transport.

Active Transport

Active transport requires the cell to use energy-usually in the form of ATP molecules as it passes against a concentration gradient. To make this molecule goes against the current, the cell uses adenosine triphosphate (ATP) to enable the carrier protein that helps the cell membrane molecules pass through. One example is the active transport of human intestinal cells take up glucose.