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# BIOLOGY I: CHAPTER 6 ## Structure of xylem vessel related to its function **3. Hollow/Empty:** Allows large amounts of water to be transported. * **Annular:** [Diagram of an annular xylem vessel]. * **Spiral:** [Diagram of a spiral xylem vessel]. * **Pitted:** Allows lateral water movement [Dia...

# BIOLOGY I: CHAPTER 6 ## Structure of xylem vessel related to its function **3. Hollow/Empty:** Allows large amounts of water to be transported. * **Annular:** [Diagram of an annular xylem vessel]. * **Spiral:** [Diagram of a spiral xylem vessel]. * **Pitted:** Allows lateral water movement [Diagram of a pitted xylem vessel]. **4. No living content:** Minimizes resistance in water movement. **Lignification pattern:** Lignin provides structural support. * **Lignin:** Provides structural support. ## Structure of phloem related to its function **4. Sieve plate:** To retain substances temporarily. **Sieve tube:** To transport food. **5. Companion cell:** To generate ATP for loading. **6. Plasmodesmata:** To transport ions/minerals/water. **7. Sieve pore:** To allow movement of substances from one sieve tube to another. ## Xerophyte ~ plants that live in very dry/arid condition **Very day plant:** * **Swollen stem:** To maximize water storage. * **Needle-like leaf:** To minimize surface area exposed to surrounding, therefore, reducing water loss. * **Extensive root system:** To maximize water absorption. * **Sunken stomata:** To trap water vapor and maintain water potential gradient. ## Transport of H₂O from soil into xylem vessel **Key:** * **Vascular pathway:** Water moves from vacuole to vacuole of another part * **Apoplast pathway:** Water moves from cell wall to cell wall until reaching endodermis layer. * **Symplast pathway:** Water moves from cytoplasm-plasmodesmata-cytoplasm **1.** Water moves from soil into root hair through osmosis where the water will move down water potential gradient; most of the water will follow apoplast pathway. **2.** In this pathway, water will move from the cell wall of one cell to the cell wall of another cell until reaching endodermis layer which is made up of casparian strips. **3.** Water will divert the pathway into symplast pathway where the water moves from cytoplasm of one cell to the cytoplasm of another cell by using plasmodesmata. **4.** Some water will be transported by vacuolar pathway where the vacuole of one cell to the vacuole of another cell until reaching xylem vessel. ## Transport of food → translocation of food **Source:** Part of plant carrying out photosynthesis (e.g., leaf). **Sink:** Part of plant that receives photosynthetic product (e.g., root/fruit/stem/flower). **Explanation:** **1.** Photosynthesis occurs at leaf and photosynthetic products such as sucrose are formed. **2.** Protons will pump out of companion cell by using proton pump. **3.** Proton gradient established at source and proton will then cotransported together with sucrose back into the companion cell by using sucrose-proton cotransporter. **4.** Sucrose will diffuse into the sieve tube by using plasmodesmata. **5.** Water potential at the sieve tube will be lowered and water enters the sieve tube by osmosis from xylem vessel. **6.** This increases the hydrostatic pressure at the sieve tube near to the source. **7.** Sieve tube near to the sink has lower hydrostatic pressure; this results in mass flow where sucrose will move from the sieve tube near to the source to the sieve tube near to the sink. **Diagram Descriptions:** * Diagrams of xylem vessels showing different patterns (annular, spiral, pitted). * Diagrams of phloem structures (sieve plate, sieve tube, companion cell, plasmodesmata). * Diagrams showing the pathways of water transport through the root. * Diagrams showing the transport of sucrose through the phloem. * Diagrams of a cross-section of a stem showing xylem and phloem. * Diagrams of a leaf, including epidermis, stomata, guard cells.