BIO 2137 Lecture Notes - Lecture 12: Active Transport, Sieve Tube Element, Flowering Plant
21 Jan 2021
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Lignin in cell walls provides support, impermeability to water. Xylem also contains parenchyma cells and fibers (sclerenchyma) for storage and support. Tracheids: evolved first, present in all vascular plants. Have pits (area with only thin primary cell walls - membranous) Only going to be the primary wall and that"s going to help water to flow, not only along the tube, but even between the tubes. So, and this can be important when you think about in the spring, for instance. The water column may become broken, you may have bubbles in there. And so having pits is one way that you can get around the bubbles and have a more efficient flow of water from root to leaf. Vessel elements: evolved later, present in angiosperms, and gnetophytes. Have pits and perforations (no cell walls) Transports phloem sap (water and sugars produced by photosynthesis, also, amino acids, hormones, proteins, etc. ) also transports viruses.
