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Questions and Answers
What is the primary function of xylem vessels in plants?
What is the primary function of xylem vessels in plants?
What is the role of companion cells in the phloem vessels?
What is the role of companion cells in the phloem vessels?
What is the main purpose of the spiral thickening in xylem vessels?
What is the main purpose of the spiral thickening in xylem vessels?
What is the main function of the sieve tube elements in the phloem vessels?
What is the main function of the sieve tube elements in the phloem vessels?
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What is the significance of the pits in the xylem vessels?
What is the significance of the pits in the xylem vessels?
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What is the role of the cambium layer in the vascular bundle?
What is the role of the cambium layer in the vascular bundle?
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How does the arrangement of xylem and phloem in the vascular bundle differ between monocots and dicots?
How does the arrangement of xylem and phloem in the vascular bundle differ between monocots and dicots?
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What is the primary role of the pericycle in the stem?
What is the primary role of the pericycle in the stem?
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How does the vascular bundle arrangement in the leaf differ from the stem?
How does the vascular bundle arrangement in the leaf differ from the stem?
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What is the significance of the sieve tube elements in the phloem vessels?
What is the significance of the sieve tube elements in the phloem vessels?
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Study Notes
Phloem Transport
- Companion cells are involved in ATP production for active loading of sucrose into sieve tubes.
- Cytoplasm of sieve tube elements and companion cells is linked through plasmodesmata, allowing communication and flow of substances such as minerals between cells.
Transpiration
- Transpiration is the process by which plants absorb water through roots, which then moves up through the plant and is released into the atmosphere as water vapor through pores in leaves.
- Carbon dioxide enters, while water and oxygen exit through a leaf's stomata.
- The transpiration stream supplies water necessary for photosynthesis, growth, and elongation, and also supplies minerals while controlling plant temperature via evaporation of water.
- Transpiration involves osmosis, where water moves from xylem to mesophyll cells, and evaporation from the surface of mesophyll cells into intercellular spaces, followed by diffusion of water vapor down a water vapor potential gradient out of the stomata.
Investigating Transpiration
- The rate of transpiration can be investigated using a potometer, where water vapor lost by the leaf is replaced by water in the capillary tube.
Sucrose Loading and Transport
- Sucrose enters the phloem through active loading, where companion cells use ATP to transport hydrogen ions, creating a diffusion gradient that causes H+ ions to diffuse back into companion cells.
- This process involves facilitated diffusion with cotransporter proteins, allowing returning H+ ions to bring sucrose molecules into companion cells, increasing sucrose concentration.
- Sucrose diffuses out of companion cells into sieve tube elements through plasmodesmata, reducing water potential and causing water to enter via osmosis, increasing hydrostatic pressure in the sieve tube.
- Water moves down the sieve tube from an area of higher pressure to an area of lower pressure, supplying assimilates such as sucrose to where they are needed.
- At the sink, sucrose is removed by diffusion or active transport, increasing water potential and causing water to leave the sieve tube by osmosis, reducing pressure in the phloem.
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Description
Test your knowledge of plant transport and transpiration processes in this quiz. Learn about sieve tube elements, companion cells, plasmodesmata, and the movement of substances in plants.
