At the source, sucrose passes from a mesophyll cell into a phloem sieve tube via a companion cell. Describe and explain how the movement of sucrose into a phloem sieve tube from a companion cell can result in the sugar being transported to a sink.
Fig. 5.1 gives part of one route used in plant cells to make sucrose. The enzyme sucrose synthase catalyses the transfer of glucose from UDPG (uridine diphosphate glucose) to fructose. $\text{UDPG} + \text{fructose} \rightleftharpoons \text{UDP} + \text{sucrose}$ Name the kind of bond formed when sucrose is synthesised.
Explain why UDP can be described as a phosphorylated nucleotide.
Sucrose synthase works by means of an induced fit mechanism instead of a lock and key mechanism. With reference to sucrose synthase and the synthesis of sucrose, outline the difference between the induced fit mechanism and lock and key mechanism of enzyme action.
UDPG is used in some algae (photosynthetic protoctists) to make a storage substance called floridean starch. The molecular structure of floridean starch has been described as lying between amylopectin and glycogen, with little or no amylose. Describe the molecular structure of floridean starch by completing the passage. Floridean starch is a polysaccharide made of ................................ monomers. The monomers are linked by ................................ and ................................ linkages, producing a branching structure that is less highly branched than ................................. .