An experiment was performed on a young plant using an aphid stylet to measure the rate of transport in the phloem. The same plant was then placed in a bell jar and a chemical placed in the bell jar to absorb all the oxygen present. The rate of transport in the phloem decreased and then stopped. What is the reason for this?

TRANSPORT IN PLANTS

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Question [CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]

A	Companion cells no longer produce sufficient energy.
B	Mitochondria in the xylem vessels cease to function.
C	Photosynthesis cannot occur in the bell jar.
D	Translocation occurs only by diffusion.

Explanation:

Detailed explanation-1: -Image e: phloem sap starts to accumulate from the stylet. The droplet of phloem sap can then be analysed for traces of the isotope to determine transport rate. Aphids can be placed along the length of the plant stem to show transport along various distances.

Detailed explanation-2: -Aphids penetrate plant tissues to reach the phloem using mouth parts called stylets. If the aphid is anaesthetized and the stylet severed, phloem will continue to flow out of the stylet and both the rate of flow and the composition of the sap can be analysed.

Detailed explanation-3: -Aphids don’t suck; rather, the phloem contents are forced into the aphid (thus the phloem is under pressure) and the excess oozes out the anus (honeydew). Thus, aphid studies demonstrate that the phloem is under pressure. Further, the honeydew can be collected and we can identify its composition.

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