Passive, Active Transport

Science Revision

Passive Transport

Occurs by virtue of membrane proteins that change shape (conformational change) This shape change happens when a relevant molecule binds to it, causing the shape change.

Passive transport is a movement of biochemicals and other atomic or molecular substances across membranes. Unlike active transport, it does not require an input of chemical energy, being driven by the growth of entropy of the system.

The rate of passive transport depends on the permeability of the cell membrane, which, in turn, depends on the organization and characteristics of the membrane lipids and proteins. The four main kinds of passive transport are diffusion, facilitated diffusion, filtration and osmosis.

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Active Transport

Active transport is the movement of all types of molecules across a cell membrane against its concentration gradient (from low to high concentration). In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport.

Secondary active transport involves the use of an electrochemical gradient. Active transport uses cellular energy, unlike passive transport, which does not use cellular energy. Active transport is a good example of a process for which cells require energy. Examples of active transport include the uptake of glucose in the intestines in humans and the uptake of mineral ions into root hair cells of plants.

Active Transport enables molecules to be pumped up/or 'agaisnt' the concentration gradient. This is done by membrane protein, but requires energy to make it happen. Energy is released b the breakdown of ATP (Adenosine Tri-phosphate, producted in respiration) to ADP + P (Adenosine Tri-phosphate, plus a phosphate group)

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