Translocation is the movement of dissolved substances, such as sucrose and amino acids, from parts of the plant where the substances are made to other parts of the plant where they’re needed. Translocation takes place in the phloem - transport vessels made up of two types of cell, sieve tube elements and companion cells. The parts of the plant which make these substances are referred to as sources (e.g. the leaves) and the parts of the plant which store or use the substances are called sinks (examples include bulbs and roots). When sucrose reaches a sink, it is converted into starch for carbohydrate storage. This maintains a concentration gradient between the source and the sink, so that more sucrose moves into the source. Translocation is an active process, so if respiration is reduced or inhibited (e.g. using a respiratory toxin), translocation will be impaired.