Unit 3: Lesson 1 - Transpiration - PDF

# Unit 3: Lesson 1 - Transpiration ## Flowering Plants - Monocot - Leaf: elongated - Veins: are parallel - Example: Corn, herbs - Dicot - Leaf: broad - Veins: are branched - Source of: wood, vegetables, nuts ## Transport System In Plants - **Xylem:** - transports H₂O...

# Unit 3: Lesson 1 - Transpiration ## Flowering Plants - Monocot - Leaf: elongated - Veins: are parallel - Example: Corn, herbs - Dicot - Leaf: broad - Veins: are branched - Source of: wood, vegetables, nuts ## Transport System In Plants - **Xylem:** - transports H₂O & minerals from roots to the leaves - **Phloem:** - transports food from leaves to all other parts of the plant. ### Xylem & Phloem are Arranged in: - vascular bundle - inside endodermis ## Distribution of Vascular Bundle in Roots, stems & leaves ### Roots: - vascular system: one vascular bundle in the center - xylem appears as a star ### Stem: - many vascular bundles - it forms a ring around the center - xylem towards the center to achieve less H₂O evaporation ### Leaves: - water moves next to the phloem sap moving next to lower surface ## Explain How Water Moves From the Soil To The Root hair / Root? - water moves from high water potential to low water potential - from the soil to low water potential in the root hair cell by osmosis. ## What are the main 2 functions of xylem? 1. Provides Strength & support for the plant. 2. Xylem is the main Structure for transplanting water for long distances. ## What are the walls of xylem made of? - walls of xylem are made of Cellulose + lignin (strong polymer, impermeable to H₂O) ## Explain How lignin is deposited in Xylem? - ring shape - spiral shape ## What is the source of wood used in furniture? - from xylem ## What would happen if lignin was not deposited on the walls? 1. walls could collapse under the water pressure. 2. water would escape through walls of vessels. 3. The plant & xylem would lose its rigidity & strength. ## Xylem: Adaptations of Xylem 1. Cells are joined end to end to form a hollow tube to transport water & minerals. 2. Ends walls joined cells would disappear (break down) to form a hollow continuous tube to transport water and minerals. 3. Lignin is a strong waterproof saccharide polymer that is impermeable to water so the cells would lose all organelles & become dead to allow free movement of water and minerals. 4. Pits: holes at the walls of xylem that allow lateral movement of water from one vessel to another. ### Transport elements of xylem - **Vessels:** - made of cells - vessel elements: joined and to end - ends break down - water movement through ends and pits - size: larger - length: longer (5-10cm) - efficiency: more efficient - **Tracheids:** - ends are closed and tapered - ends of tracheids closed - water movement through pits only - size: smaller - length: shorter - efficiency: less efficient ## Example: - Flowering plants - Conifers # Unit 3: Lesson 2 - Structure of Phloem ## What Are the Adaptations of Phloem? ### Sieve Tube: 1. Sieve tube is made of sieve tube elements/cells stacked end to end to form a continuous tube that transports organic substances. 2. Sieve plate: is perforated (have holes) to allow phloem sap to travel through the sieve plates from cell to cell. ### Companion Cells: 1. It's a living cell that contains nucleus, organelles & large number of mitochondria to provide proteins and energy ATP to sieve tubes for transporting organic substances. 2. Metabolic rate in companion cell is very high to support itself & sieve tube element cell. 3. Plasmodesmata: allowing free exchange of substances between companion cell & sieve tube. 4. Wavy cell wall to increase surface area for transport (transfer cell only). ## What is the most common solute in phloem sap? - Sugar ## Explain how the plant would convert simple sugar into complex carbohydrates? - Glucose produced in photosynthesis. - Glucose is converted to sucrose (disaccharide). - Sucrose transported to another plant cells which build complex carbohydrates Amylase & Amylo pectin & starch. ## What are the components of phloem sap? - Sugar, ions, hormones, viruses & ATP, Sucrose & Carbohydrates ## Define Sources & Sinks: ### Sources: - Any location that is a net producer of sugar ### Sinks: - A location that receives sugar ## Example: ### Sources: - Leaves ### Sinks: - Roots, stems, fruits, flowers ## What are the uses of the sugar for sinks? - Energy, Storage, Reproduction & growth ## What are the Stages of creating, moving and using sugars in plants? 1. **Loading:** (active) Sugar is transferred from sources in leaves into phloem sap. 2. **Translocation:** (passive) Phloem sap containing sugar is moved through phloem from sources to sinks. 3. **Unloading:** (active) Sugar is transferred from phloem sap into cells (for growth, reproduction, or storage) ## Sugar Sources & Active Loading: - Sources sugar cytosol - Plasmodesmata cytosol & symplast - Apoplast - Only symplast - Plasmodesmata connects sugar-producing cells in the leaf to sieve tubes. ## Sugar Would Travel by Symplast Until it Reaches Vascular Bundle: - Sugar can travel either by symplast or by apoplast ## Explain Why The Active Loading to Sieve Tube? - The concentration of sugar is the highest in phloem sap 30%. ## Define Active Loading: - Is the process of pushing the sugar into a sieve tube against the concentration gradient. ## What is the mechanism of active loading? 1. ATP is used to pump H⁺ out of the phloem by creating an H⁺ concentration gradient. (Proton ATPase) 2. Active loading uses ATP to pump H⁺ protons out of the phloem. ## ATPase Enzyme Known As "Proton Pump". - It is pumping protons against concentration (low-high) gradient. - From symplast of sieve tube and transfer cell (companion cell) to apoplast pathway. ## The Accumulation of H⁺ Ions in Apoplast Pathways Leading to Increasing Concentration. - So it starts to return back to symplast (high-low) down the concentration gradient to sieve tubes & transfer cells (companion) through protein called co transporter that release energy with the influx of H⁺. ## Energy Used to Transport Sucrose From Apoplast to Symplast to Sieve Tube & Companion Cell. ## What Would Happen if transfer Cell was Absent from Phloem? How This Would Affect the Mechanism of Active Loading? - No energy would be provided for ATPase enzyme, so no active pumping of H⁺ - No accumulation of H⁺ in source cell, so no influx of sucrose to phloem & no translocation. ## Difference Between Companion Cell & Transfer Cell: - **Companion Cell:** - **Transfer Cell:** Have wavy cell wall to increase surface area. ## The Pressure Flow Hypothesis 1. **Loading:** Active transport loads sugar into sieve tube at a source. 2. **It reduces the water potential and water flows from xylem into the sieve tube due to osmosis.** 3. **Translocation:** The entry of water into sieve tube near the source increases hydrostatic pressure pushing sap up or down depending on pressure difference. 4. **Unloading:** Sugar is unloaded to sink cells (roots, stems,...) by active transport, reducing the concentration of sugar in phloem. 5. **Water potential in sieve tube increases so it returns back to xylem by osmosis.** - This lowers the pressure in phloem. ## What are the consequences of the movement of sucrose to sieve tube at source? 1. High concentration of sugar in phloem. 2. So H₂O moves from xylem to sieve tube by osmosis. 3. The hydrostatic pressure in sieve tube becomes higher. ## Explain why there is no water movement between xylem & sieve tube in areas between source & sink? - Water potential is equal in xylem & sieve tube. ## What would happen if water was not returned from sieve tube back to xylem at Y? - The hydrostatic pressure in sieve tube would remain high. - So there would be no difference in hydrostatic pressure in sieve tube, so translocation would stop & no loading or unloading, eventually the plant would die. ## The Translocation in Sieve Tube Doesn’t Require Energy. What Is the Factor that Keeps the Flow of Sugar in Sieve Tube? - By the difference in hydrostatic pressure: phloem sap moves from high hydrostatic pressure near the source to low hydrostatic pressure near the sink. ## What Is the Role of Companion Cells in Loading/Unloading? 1. It has many mitochondria producing energy for active transport. 2. It has wavy cells to provide larger surface area for more transport. ## The Flow in sieve Tube Can be Reversed? - Sources and sinks can be reversed? - The locations of sources and sinks can change. - Example: When the plant loses its source in winter the storing parts (roots and stems) can turn into sources and loading starts to the rest of the plant. ## Once Sugar is Loaded to Sieve Tube It Can Move Up or Down in Phloem Explain? - Based on the difference in hydrostatic pressure. ## Xylem vs Phloem: | Characteristic | Xylem | Phloem | |---|---|---| | Type of tissue | Dead | Living | | Direction of movement | One direction (root → leaves) | In all directions | | Transport element | Vessels, tracheids | Sieve tube | | Type of transport | Passive | Active transport | | Source of energy | No energy needed | Companion cells (transfer) | | Pits | Present (allows lateral movement of H₂O) | No | | Sieve plate | No | Yes (perforated) | | Walls are composed of | Lignin + cellulose | Cellulose only | | Organelles | No organelles | Sieve tube - No organelles <br> Companion cells - Nucleus, ribosomes, & many mitochondria | | Process | Transpiration | Translocation |