Resource Acquisition and Transport in Vascular Plants

Resource acquisition and transport

Transport review Passive transport – no energy required, ex. diffusion Active transport – energy required Transport proteins required, ex – proton pump Uses energy from ATP to pump H+ across membrane Cotransport – coupling of the steep gradient of one solute(H+) with a solute like sucrose Drop in potential energy by H+ pays for transport of sucrose.

Water potential (potential grid problems) Osmosis – movement of water across cell membrane via aquaporins Water moves from area of high water potential to low potential Water potential includes the effects of solute concentration and physical pressure.

Transpiration Loss of water vapor from the leaves Water and minerals are transported to rest of plant via bulk flow Bulk flow is the movement of liquids in response to a pressure gradient Rate of transpiration is regulated by stomata

Stomata Pore in leaf epidermis with guard cells on each side. Water enters guard cells, following K+, turgor pressure increases, stoma opens and vise versa Stomata open and close in respond to environmental signals

Cohesion-tension hypothesis Transpiration provides the pull for the ascent of water. Water is lost due to lower water potential of the air Cohesion of water molecules via hydrogen bonds plus adhesion of water to plant cell walls form a water column.

Organic nutrient transport Girdling – removing bark form tree, accumulation of sugar Pressure flow model – 29.22 Sugar enters the sieve tubes (active transport) and creates positive pressure, phloem begins to flow Roots are a sink – provide place for sugar to be used for cellular activities (respiration) Source to sink – leaves to roots or any place that needs sugar (new leaves…)

Soil and Plant Nutrition 95% of plant’s dry weight (biomass) is carbon, hydrogen, and oxygen (carbohydrates, CO2 and water) Minerals – provide proteins and nucleic acids Essential nutrients – has role, no substitute, and a deficiency results in death. Macro and micronutrients according to concentration Beneficial nutrients – required or enhances growth

Mutualistic relationships Nitrogen-fixing bacteria – root nodules of legume plants Fix atmospheric nitrogen into a form that plants can use, plants provide food to bacteria Mycorrhizae – plant roots and fungi, plants give fungus food, fungus increases surface area for water uptake and minerals

Symbiotic relationships that are not mutualistic Parasitic plants (dodder), does not undergo photosynthesis, needs other plants for nutrients Epiphytes – grown on surface of other plants instead of soil, not parasitic, ex. orchids Carnivorous – photosynthetic but get some nitrogen and minerals from small animals