Chapter 36 By Tom Tessitore, Hannah Turk, and Allie Duca

-36.1: Land plants acquire resources both above and below ground Live above ground and below ground Algae absorbs CO2, water, and minerals from water Competition for light, water, and nutrients Taller plants have advantage Natural selection favored the production of multicellular, branching roots Natural selection favors plants capable of transporting nutrients, water, and minerals over a long distance Plant success depends on photosynthesis Many mechanisms have been developed to acquire light, CO2, and water

Arrangement and size of leaves on a stem = phyllotaxy Determined by the shoot apical meristem and specific species Most angiosperms have alternate phyllotaxy (spiral around stem) Each leaf max light and reduces shading by other leaves (lower) Features reduce self-shading increase light absorbed Leaf area index: the ratio of the total upper leaf surface of a single plant divided by the surface area of the land it’s growing on Higher than 7 is not helpful  Add more leaves means respire not photosynthesize  Programmed cell death, leaves and branches shed = self-pruning  Leaf orientation affects light capture

Variation in shoot architecture because plants have finite amount of energy for it Allows to grow tall and prevent shading by other plants Natural selection  shoots to optimize light absorption Vary in stem thickness The stronger the plant, the stronger the root system Taproot = anchored tall plant Fibrous root systems do not anchor tall as strongly Mycorrhizae = specialized mutualistic assosiations between roots and fungi The elongation, branching, and mycorrhizae help roots obtain water and minerals

-36.2: Transport occurs by short-distance diffusion or active transport and by long-distance bulk flow Diffusion and active transport of solutes Diffusion is the spontaneous movement down concentration gradients Diffusion if facilitated by aquaporins Transport proteins help diffusion across membranes Proton pumps generate an H+ gradient used to transport solutes Diffusion of water (osmosis) Osmosis = spontaneous movement of free water down its concentration gradient Water flows across membranes from regions with higher water potential to regions with lower water potential

Solutes decrease When plants lose water the become flaccid Greater solute becomes turgid Wilts with loss of water Protoplast shrinks and pulls away from cell wall = plasmolysis External solution has lower water potential and water diffuses out of cell

3 major pathways of transport: the apoplastic-moving in the spaces between cells Symplastic-moving through the cells themselves transmembrane routes-a combination of both apoplastic and symplastic routes  cytoplasmic channels = plasmodesmata  bulk flow due to pressure differences at opposite ends

36.3- Water and minerals transported from roots to shoots Absorption of water and minerals by root cells most of the water and mineral absorption occurs at the roots epidermal cells are permeable to water root hairs are a type of epidermal cells that account for much of the absorption of water by roots the soil solution the root hairs absorb consists of water and mineral ions although soil solution usually has a low mineral concentration, active transport helps roots obtain essential minerals

Transport of water and minerals into the Xylem Water cannot be transported to the rest of the plant until they enter the xylem of the stele, or vascular cylinder. Endodermis- the innermost layer of cells in the root cortex, surrounds the stele and functions as the last checkpoint for the passage of minerals into the vascular tissue. Casparian Strip- a “dead-end” that blocks minerals from reaching the stele. It forces water and minerals that are passing moving to cross the plasma membrane.

Bulk Flow Driven by Negative Pressure in the Xylem Transpiration lowers water potential in the leaf by producing negative pressure (tension) Low water potential draws from the xylem Xylem Sap- the water and dissolved minerals in the xylem At night- root cells continue pumping mineral ions into the xylem of the stele. Root pressure- a push of xylem sap. Guttation- water pushed out of leaves; happens when more water enter the leaves than is transpired.

Material can be moved: Upward by positive pressure from below Downward by Negative Pressure above. Transpirational pull depends on Adhesion Cohesion Surface Tension Cohesion and adhesion help transportation by bulk flow Cohesion is due to hydrogen bonding- can pull xylem sap without the water breaking Adhesion is also due to hydrogen bonds- bonds to hydrophilic cell walls to slow the force of gravity.

Xylem sap ascent by bulk flow: a review Transpiration maintains movement of xylem sap against gravity The water potential gradient is essentially a pressure gradient. Plants do not use energy to lift xylem by bulk flow.

36.4- Stomata help regulate the rate of transpiration. Plants control loss of water from their leaves using stomata Stomata open and close using guard cells Potassium ions are transported through the plasma and vascular membranes and causes the guard cells to become more turgid when the water enters when it becomes more turgid, it opens when the potassium ions leave, it closes generally stomata open during the night and close during the day Plants know that it is dawn because: 1. Light 2. Carbon Dioxide 3. an internal clock some plants called xerophytes are adapted to regions of little moisture. CAM plants photosynthesize differently than other plants.

36.5-Transportation of Sugars –Transpiration only pulls water from the roots up Instead, sugar moves from a sugar source to a sugar sink –Sugar source-a plant organ that makes sugar (Ex:a fully developed leaf) –Sugar sink-organ that consumes sugar (Ex:growing roots, fruit) Sugar sinks use nearest sugar source Sugar moves both apoplasticly and symplasticly into the phloem Building up of sap at a sugar source gives it the pressure to move quickly to sugar sinks

36.6-The Dynamic Symplast –Plasmodesmata were once thought to be rigid –In fact, they are actually fluid and changing Plants are able to dilate plasmodesmata to allow proteins to pass through Viruses make proteins that cause the plasmodesmata to open, allowing the viruses to move from cell to cell

–The symplast allows proteins and RNA molecules to coordianate development between cells It also allows electric signals to pass through it, triggering different systems –These include change in gene transcription, respiration, photosynthesis, and hormone levels –This allows the phloem to act as a pseudo- nerve