21.2 The Vascular System TEKS 4B, 5B, 10B, 10C The student is expected to: 4B investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules; 5B examine specialized cells, including roots, stems, and leaves of plants...; 10B describe the interactions that occur among systems that perform the functions of transport, reproduction, and response in plants; 10C analyze the levels of organization in biological systems and relate the levels to each other and to the whole system

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C KEY CONCEPT The vascular system allows for the transport of water, minerals, and sugars.

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C Water and dissolved minerals move through xylem. Xylem contains specialized cells. –vessel elements are short and wide –tracheid cells are long and narrow –xylem cells die at maturity vessel element tracheid

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C –Plants passively transport water through the xylem. –Cohesion is the tendency of water molecules to bond with each other. The cohesion-tension theory explains water movement. –Adhesion is the tendency of water molecules to bond with other substances.

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C –absorption occurs at roots Water travels from roots to the top of trees. –cohesion and adhesion in xylem –transpiration at leaves

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C –water vapor exits leaf stomata –helps pull water to the top branches Transpiration is the loss of water vapor through leaves.

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C Phloem carries sugars from photosynthesis throughout the plant. Phloem contains specialized cells. –sieve tube elements have holes at ends –companion cells help sieve tube elements –unlike xylem, phloem tissue is alive

21.2 The Vascular System TEKS 4B, 5B, 10B, 10C –plants actively transport sugar from the source –sugar flows to the sink due to pressure differences sugars phloemxylem water Sugars move from their source, such as photosynthesizing leaves, into the phloem. 1 The sugars move into the sink, such as root or fruit, where the are stored. 3 Water moves from the xylem into the phloem by osmosis, due to the higher concentration of the sugars in the phloem. The water flow helps move sugars through the phloem. 2 The Pressure-flow model explains sugar movement.