9.2 Transport in Angiosperms

9.2.1: Root System Huge, ever growing root system increases the surface area for absorption of water and essential nutrients Surface area is also increased by the addition of root hairs Cortex cells have a structure that also facilitates the uptake of water Water can move in two routes symplastic and apoplastic

Symplastic and Apoplastic

9.2.2: Ion Uptake Minerals needed by the plants and found in soil are: N as NO3- or NH4+ K as K+ P as PO43- Ca as Ca2+ Diffusion Minerals are more concentrated in the soil than in the root When dissolved in water the minerals will diffuse into the roots Fungal Hyphae Plants work together with fungus to absorb minerals Threads of the fungus grow through the soil and absorb the minerals The threads also grow into the roots and transport the minerals into the roots These minerals would not be absorbed without the fungus Plants give the fungus sugars Mass flow of water Uptake of water which includes dissolved minerals

9.2.3: Active transport of Minerals Xylem- Stem:Tracheids & Vessel Members (see photo) Use of metabolic energy to obtain minerals in root Can occur against the concentration gradient Cytosol of the cell holds some reserves of ions Allows the cells to pull in more of these ions when available Cells tend to horde ions Highly selective – plant will choose from different forms of the same ion Ions cross into the cell through pump molecules If roots are deprived of oxygen then active transport stops The formation of the necessary metabolic energy is from respiration

Vessel Members and Tracheids are dead at maturity and are arranged end to end Thick lignified walls have pits or pores so water can move laterally

Sodium Potassium Pump

9.2.4: Plant Support Stem is used to support the leaves of the plant and to transport water, ions and organic nutrients Made up mostly of ground tissues (non-woody plants) Cells are known as parenchyma Stay rigid using cell turgor: exerting pressure on surrounding cells using a water filled vacuole Outermost layers have additional layers of thickened cellulose laid down unevenly Called collenchyma cells In woody plants Xylem tissue has cellulose thickenings that are hardened with a chemical called lignin Provides almost all the strength of the stem

9.2.5: Transpiration The loss of water vapor form the leaves and stems of a plant Water generally moves into plants through their roots and upwards through the vascular system and out of the stomata in the leaves

9.2.6: Transpiration Stream Water transport occurs in the xylem Begins as elongated cells connected end to end During development the end walls are dissolved away so long hollow tubes develop Living tissues of xylem lay down cellulose which is thickened by lignin Water lost by transpiration raises the osmotic pressure in the cells causing water uptake from surrounding cells Water comes from the xylem As water leaves the xylem more is pulled up through transpiration pull As water leaves the xylem more is pulled into the xylem at the root Water coheres to the lateral walls of the xylem maintaining a continuous column of water Much of the water pulled into the plants is lost to evaporation

9.2.7: Stomata Transpiration is regulated by the stomata Tiny pores for gas exchange Occur mostly in the leaves but sometimes found in the stem Made of 2 elongated guard cells attached to normal epidermis cells on one side Not attached to each other Open and close based on turgor pressure Open when water is absorbed by the guard cell from its neighboring epidermis cell Water is then lost through the pore Close when enough water is lost that the cell becomes flaccid Tend to be open during the day and closed at night Will close during the day if plant becomes short of water Regulates transpiration & prevents excess water loss

9.2.8: Hormone Regulation of the Stomata Abscisic acid (ABA) is a plant growth hormone that helps regulate the rate of transpiration in plants In time of physiological stress (like drought) the levels of ABA increase in the leaves Maintains stomata closure preventing excess water loss

9.2.9: Abiotic Factors and transpiration Light Stomata tend to be open in light Light can warm the leaf and raise its temperature Temperature Causes evaporation of water molecules from the surface cells of the plant Evaporation rate doubles for every 10 degree increase in temperature Wind Sweeps away water vapor causing an increase in transpiration Humid Air Decreases transpiration Soil Water -If intake of water at roots does not keep up stomata then close Carbon Dioxide -High Carbon Dioxide levels usually cause stomata to close

C4 and CAM Plants C4 ("four-carbon") plants initially attach CO 2 to PEP to form the four-carbon compound OAA (oxaloacetate) using the enzyme PEP carboxylase. This takes place in the loosely packed cells called mesophyll cells. OAA is then pumped to another set of cells, the bundle sheath cells, which surround the leaf vein. There, it releases the CO 2 for use by Rubisco. By concentrating CO 2 in the bundle sheath cells, C4 plants promote the efficient operation of the Calvin-Benson cycle and minimize photorespiration. C4 plants include corn, sugar cane, and many other tropical grasses. CAM ("crassulacean acid metabolism") plants initially attach CO 2 to PEP and form OAA. However, instead of fixing carbon during the day and pumping the OAA to other cells, CAM plants fix carbon at night and store the OAA in large vacuoles within the cell. This allows them to have their stomata open in the cool of the evening, avoiding water loss, and to use the CO 2 for the Calvin-Benson cycle during the day, when it can be driven by the sun's energy. CAM plants are more common than C4 plants and include cacti and a wide variety of other succulent plants.

9.2.10: Adaptations of Xerophytes Thick cuticle Prevents water loss through the external wall of the epidermis Hairs on the epidermis Traps moist air over the leaf Reduction in number of stomata Reduces areas where loss can occur Rolled or folded leaves Reduces area for transpiration to occur Lower epidermis is rolled inside the leaf protecting it Superficial roots Takes advantage of condensation on the soil overnight Deep and extensive roots Allows access to the deep water Reduced leaf numbers Less surface area for transpiration Low growth Limits plant exposure to wind Often show CAM photosynthesis

9.2.11: Phloem Translocation The movement of manufactured food (sugars&amino acids) Occurs in the phloem Takes sugars to new growth in young plants & to storage in older plants Amino acids are produced in the roots and transported to where they are needed for protein synthesis (usually growing parts of the plant) Chemicals sprayed on the plant also moved in this manner Phloem tissue Sieve tubes: narrow elongated cells connected end to end; no real organelles Sieve plates: end walls which have pores for material to move through Companion cells: services and maintains the sieve tubes; attached to the sieve tube by cytoplasm strands Transport requires energy Can occur in any direction