EVERYDAY SCIENCE

Detailed explanation-1: -The uptake of glucose, for example, is carried out by a transporter that coordinately transports two Na+ and one glucose into the cell (Figure 12.31). The flow of Na+ down its electrochemical gradient provides the energy required to take up dietary glucose and to accumulate high intracellular glucose concentrations.

Detailed explanation-2: -Active transport is usually associated with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. 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.

Detailed explanation-3: -In the intestine and renal proximal tubule, glucose is transported against a concentration gradient by a secondary active transport mechanism in which glucose is cotransported with sodium ions.

Detailed explanation-4: -Glucose molecules are too big to diffuse through the plasma membrane easily, so they are moved across the membrane through gated channels. In this way glucose diffuses very quickly across a cell membrane, which is important because many cells depend on glucose for energy.

Detailed explanation-5: -The GLUTs transport glucose across the plasma membrane by means of a facilitated diffusion mechanism.