McqMate
| Q. |
Which of the following statements about phloem transport is correct? |
| A. | phloem transport occurs unidirectionally |
| B. | gravity influences phloem transport |
| C. | Ca+ is the most abundantcation in phloem sap |
| D. | sugar is transported in phloem as nonreducing sugar |
| Answer» D. sugar is transported in phloem as nonreducing sugar | |
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Explanation: According to most textbooks, only non-reducing carbohydrate species such as sucrose, sugar alcohols, and raffinose family sugars function as phloem translocates. In non- reducing sugar, the hydroxyl group on the anomeric carbon, the number one car-bon, is tied up which means that they are less reactive and more chemically stable. Exclusive transport of non-reducing sugars probably reflects packaging of carbohydrate in a chemical form which protects it from being metabolized. |
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