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November 13, 2014 Leaf Tissues and Gas Exchange November 13, 2014 Air can only get into the cells through passive diffusion. Plant cells are specialized to maximize this diffusion rate. November 13, 2014 Dermal Tissue Guard cells allow gas exchange, they form a stomata, usually on the underside of a leaf. They do not open all the time, or they would lose too much water. Light triggers them to swell and open. When there isn't much water the guard cells close. Guard cells control transpiration. November 13, 2014 If there is high Humidity would there be more or less stomata? How about in low CO2 levels? November 13, 2014 Ground Tissue Mesophyll tissue (Between the upper and lower epidermis) 2 types of Mesophyll 1. Palisade Tissue (on top of the leaf) Long rigid rectangular cells that are exposed to the sun. Photosynthesis happens in these cells. November 13, 2014 Spongy Mesophyll loosely packed cells, with lots of space between them. This allows gas exchange. November 13, 2014 Vascular Tissue The veins on a leaf. xylem and phloem are here. November 13, 2014 Lenticels Pores on woody stems and roots which act like stomata and allow gas exchange. November 13, 2014 Pg 314 #1 to 8 November 13, 2014 Transport in Plants Cohesion and Adhesion Cohesion: Water is attracted to other Water molecules. Due to its polarity. Adhesion: Water is attracted to other substances, Attracted to the cell walls of the Xylem. November 13, 2014 Root Pressure Roots cells actively transport minerals (makes them hypotonic) Water flows into the roots and forces water up the stem. Because it moves from an area of high pressure to low pressure. Root pressure pushes water a maximum of only a few meters. November 13, 2014 Transpiration Evaporation of water from stomata and lenticels creates a transpiration pull. This pulls the adjacent water molecules up the stem. Why is there more of a pull on a hot day? November 13, 2014 Tonicity and the Plant Cell Tonicity (how much solute there is) If in a salty environment water leaves the cell, vacuoles shrink and plant appears wilted. If returned to fresh water vacuoles fill until turgid (full/ swollen) this is good because then green parts of the cell are facing the sun and more photosynthesis happens. November 13, 2014 Sugar Transport (Pressure Flow Theory) Sugar goes from a source (where its manufactured, a leaf) to a sink (where it's used or stored) Sugars are actively transported into the phloem by companion cells. then water follows, and the sugar is pushed by water pressure to the sinks, where pressure is lower. November 13, 2014 Pg 322 #1,2,3,5,7,8 November 13, 2014 Control Systems Why do stems grow up and roots grow down? 1. Phototropism Stems exhibit positive phototropism (they grow toward the light). Roots exhibit negative phototropism (they grow away from the light) November 13, 2014 2. Gravitropism Stems grow against gravity (negative gravitropism) and roots grow toward gravitational force (positive gravitropism). November 13, 2014 Pg. 328 #2,3 November 13, 2014 Pg 330 #1 to 15 and 17 I will be taking these ones in.