Stephen Hales (an English botanist) described how he carried out an investigatio

Question

Stephen Hales (an English botanist) described how he carried out an investigation in 1727. "l cut a branch (b) off an apple tree about 1 metre long, then sealed the cut end (p) and fled a piece of wet bladder over it. Then I cut off the other end of the branch at (i) and attached it glass tube (z) to it. After filling the glass tube with water, I placed the lower end in a bowl of mercury (x)." "I left the apparatus outside on a warm afternoon By 3.00 p.m. me mercury had risen over 30 cm. when the mercury reached the cut end of the stem (i) air bubbles appeared and the mercury slowly ran back into the bowl (x)." Suggest a hypothesis that was being tested in this investigation ii. Through which tissue in the stem is most water transported? iii. State two structural features of this tissue which enable it to transport water rapidly. Explain, in terms of the conesion-tension theory, why the level of mercury rose during the investigation: v. Which tissue is responsible for tong-distance transport of photosynthate and, vi. In what form is most of this fixed carbon transported

Explanation / Answer

answers:

i. Water can travel downwards / both ways in a stem / water movement through plant is passive

ii. Xylem

iii. no crosswall / continous tubes/ hollow / lignified / perforated end walls

iv. lowers water potential in leaf cells, reducing pressure in xylem , leaves transpire

v. Pholem

vi. carbon dioxide is fixed

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