NEET BIOLOGY

Detailed explanation-1: -Diffusion occurs when molecules move from an area of high concentration to an area of low concentration. Diffusion does not require energy because the molecules move down their concentration gradient (from areas of high to low concentration).

Detailed explanation-2: -The mechanism by which sugars are transported through the phloem, from sources to sinks, is called pressure flow. At the sources (usually the leaves), sugar molecules are moved into the sieve elements (phloem cells) through active transport.

Detailed explanation-3: -In some plants sugars travel through cell walls from mesophyll cells to cell walls of companion cells and some sieve cells. Sugar is then actively transported into the phloem by a sucrose transport protein (Apoplast Pathway).

Detailed explanation-4: -Active transport is used to load organic compounds into phloem sieve tubes at the source. High concentrations of solutes in the phloem at the source lead to water uptake by osmosis. Incompressibility of water allows transport along hydrostatic pressure gradients.

Detailed explanation-5: -Phloem transport is called active because phloem loading at the source and unloading at the sink are both done by active transport.