Transport in Vascular Tissue Section 12.5

Transport in Vascular Tissue Learning Goal: To explore why animals eat and how much energy we need to consume. Success Criteria: I know I am succeeding when I can… explain how water, nutrients, and sugars flow throughout a plant describe the structure of the xylem and the phloem explain how transport occurs in the xylem and the phloem define sink and source cells, and explain how they influence the flow of phloem sap

Transport of Water & Nutrients Into the Roots water enters the root cells by osmosis (movement of water from high to low concentration) or enters in-between the cells nutrients enter by active transport (movement of materials from low to high concentration – requires energy) Water enters the root cells by osmosis (movement of water from high to low concentration) since water is greater in the soil than inside the plant

Transport of Water & Nutrients Cont’d… once inside the root, water and nutrients move throughout the cortex, past the endodermis into the xylem once inside the cells, the water molecules move toward the vascular cylinder, through the endodermis, and into the xylem nutrients move toward the vascular cylinder through interconnecting strands of cytoplasm of the plant cells and then are actively transported again into the xylem nutrients enter by active transport (movement of materials from low to high concentration – requires energy) because there is less nutrients in the roots than in the soil Note: the Casparian strip prevents substances from passing between the endodermal cells and forces them to pass through the cell membrane instead – keeps things flowing in the right direction

Transport of Water & Nutrients Cont’d… Up the Stem Waters moves up the xylem due to root pressure, capillary action, and transpiration root pressure: pressure created by an increase in nutrients and water in the xylem capillary action: a column of liquid is held together by weak attractive forces between molecules and rises because of attractive forces between the liquid and the sides of the tube Capillary action increases as the diameter of the tube decreases.

Transport of Water & Nutrients Cont’d… Into the Leaf transpiration: as water is evaporated from the stomata in the leaves it pulls the column of water up the xylem *Main force of water movement* Capillary action increases as the diameter of the tube decreases.

Capillary action increases as the diameter of the tube decreases.

Transport of Water & Nutrients Cont’d… as water and nutrients moves up the plant it also moves out of the xylem through the pits into the surrounding tissue so all cells in the plant body receive water and nutrients, not just those at the top of the xylem column

Transport of Sugar source: a plant cell with a high concentration of sugars (ex. a leaf cell) sink: a plant cell with a low concentration of sugars (ex. sugars converted to starch for storage or used rapidly for energy) Subject to change with the season In winter, many plants are dormant. A dormant plant does not grow and does not photosynthesize. In the spring, the plant initially depends on carbohydrates stored in its roots or stems, usually as starch. As it begins to grow, the plant breaks down the starch into sugars. As a result, root and stem cells are sources. Th e upper portions of the plant need energy to grow leaves. Th e sink cells therefore are mainly at the top of the plant, so that water and dissolved sugars (phloem sap) tend to move upward in the phloem. In summer, the leaves are photosynthesizing and the sugars they produce are stored in roots and stems. Th erefore, the source cells are now at the top of the plant, and the phloem sap moves downward.

Transport of Sugar Cont’d… From Source to Phloem after a sugar molecule is produced, it is transported from the source cell to a phloem cell by active transport (since the concentration of sugars in phloem cells is higher than the concentration in source cells) shows the transport of sugars from a source cell (a mesophyll cell) into the phloem of an angiosperm in angiosperms, companion cells transport sugars from source cells to the sieve tube elements in gymnosperms, sugars are transported from source cells directly into sieve cells, since this is the only cell type in the phloem

Transport of Sugar Cont’d… Through the Phloem the transport of substances for long distances through the phloem is called translocation shows the transport of sugars from a source cell (a mesophyll cell) into the phloem of an angiosperm in angiosperms, companion cells transport sugars from source cells to the sieve tube elements in gymnosperms, sugars are transported from source cells directly into sieve cells, since this is the only cell type in the phloem

Transport of Sugar Cont’d… From Phloem to Sink once sugar molecules reach a sink cell, they leave the phloem by passive transport (since the sink cells have a lower concentration of sugars than the phloem cells) so all cells in the plant body receive water and nutrients, not just those at the top of the xylem column

Transport in Vascular Tissue Learning Goal: To explore why animals eat and how much energy we need to consume. Success Criteria: I know I am succeeding when I can… explain how water, nutrients, and sugars flow throughout a plant describe the structure of the xylem and the phloem explain how transport occurs in the xylem and the phloem define sink and source cells, and explain how they influence the flow of phloem sap

Homework Answer 12.5 questions #1-4 & 6 on page 570