植物中的水與糖運輸 - Lecture 10/11: Water & Sugar Transport in Plants?

回顧問題不定期更新 Study Questions are Made by Prof. Cruz & Prof. Moore from Oberlin College & Conservatory

Lecture 10: Water Flow Through Plants

1. Does solute transport in xylem require energy? Explain.

2. Would you expect to find heavy metal ions (i.e. a non-nutrient ion) like aluminum in the leaf? Why or why not?

3. Why are plasmodesmata important in water flow through the root?

4. Imagine that while looking at a cross section of a leaf under a microscope, you observe a thick coating of hairs on the leaf and sunken stomata. Does this plant live in a wet or dry environment? Explain how you know.

5. Would you expect the rate of transpiration from a plant to increase or decrease on a cool, rainy day, compared to normal environmental conditions? How does a cool, rainy day affect the rate of water flow through the xylem? Explain your answer, making sure to include how a cool, rainy day affects the tension on the meniscus.

6. Does the likelihood of cavitation within the xylem increase or decrease on hot, sunny day, compared to normal environmental conditions? Explain.

Lecture 11: Sugar Transport through Phloem

1. Where does the water in phloem sap come from?

2. Why are sieve tube elements near sugar sources turgid? Now, think about the pressure-flow hypothesis. Why might sieve plates be important for the pressure gradient in sieve tubes?

3. How does active transport of sugars from the sieve tube elements into the companion cells at sugar sinks help to maintain a pressure gradient in the phloem?

4. Does water transport require energy? Does sugar transport require energy?

5. Why are all mesophyll cells located very close to leaf veins?

6. How are sieve tubes similar to and different from vessels?

7. Think about the cost of bulk flow through a tube. Does it make sense that a sugary fluid like phloem sap could NOT be transported through sieve tubes (remember that phloem sap requires high pressure to move) as easily as water flows through xylem? Explain.

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