What’s the answer of “The porous cross walls between sieve tube elements”??

The xylem vessels and the phloem sieve tubes are connected end to end to transport the water and the food respectively to long distances in a plant. Their end plates are perforated to allow the easy passage of substances from one vessel and the sieve tubes.

Sieve tube cells are placed end to end in phloem The end walls may be transverse or oblique They have many small pores called sieve pits Each sieve pit is lined by a layer of callose Excessive growth of callose closes the sieve pores Due to the presence of sieve pits the end walls are commonly called sieve plates

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answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds