Chapter 26

 95% of plant’s dry weight is CHO.  Essential nutrients of plants include:  Macronutrients- C, H, O, P, K, N, S, Ca, Mg  Micronutrients- Fe, B, Mn, Cu, Zn, Cl, Mo  Beneficial nutrients depend on the plant and are required for growth  Essential nutrients are determined through hydroponics. Minerals are added/removed from water and the effect on the plant is observed.

 Weathering and leaching help to form soil  Humus, decaying organic matter, provides nutrients to plants  Centimeter of soil takes 15 years to develop  Soil is composed of mixtures of sand, silt, and clay.

 Mixes with the top layer of soil  Allows for aeration  Soaks up water without removing air spaces and decreases runoff

 Organisms may mix, loosen, aerate, or help decompose soil

 Vertical section with horizons, parallel layers.  Topsoil- humus and living organisms  Zone of Leaching- removal of nutrients  Subsoil- accumulation of minerals and organic materials  Parent Material- weathered rock

 Wind or water carry soil to new location.  Removes 35 billion tons of topsoil annually  Deforestation, desertification, and poor farming practices increase erosion

 Utilize the same pathways  Materials pass through porous cell walls until they reach the Casparian strip  Band of suberin and lignin bordering four sides of root endodermal cells forcing water into the endodermal cells.  Water can also enter the epidermis through root hairs  Minerals are actively taken up by plants, requiring an expenditure of energy

 Root nodules- nitrogen fixing bacteria live in roots of legumes  Mycorrhizae- increases surface area for uptake  Epiphytes- specialized roots take water from the air and catch minerals from rain in special pockets at base of leaves  Parasitic plants tap into vascular system of host  Carnivorous plants obtain energy from insects

 Xylem- moves water and minerals from roots to leaves- non-living cells  Tracheids- tapered ends that overlap with adjacent cells, pits in adjacent cells allow water to pass from cell to cell  Vessel Elements- long and tubular with perforation plates. Lay end to end and from a hollow pipeline

 Phloem- transports organic nutrients to all parts of the cell  Vascular plants Sieve-tube members- conducting cells- lay end to end and connected to companion cells through plasmodesmata Companion cells- provide protein to sieve tube

 Xylem and phloem depend on the properties of water for mechanics  Osmosis, cohesion, adhesion  Root pressure- water enters root cells creating positive pressure  Guttation- drops of water are forced out of vein endings on leaves; due to root pressure; “bleeding” after injury or pruning

 Evaporation of water from leaves  90% of water from roots is lost this way Stomata open, bringing CO 2 into leaf. Mesophyll is exposed to air and dries out. Water evaporates from mesophyll to intercellular spaces. This causes transpiration. Water is replaced by veins, exerting a driving force that pulls water from the roots to the leaves. The water column must be continuous

 Pore in leaf epidermis, bordered by guard cells  Guard cells are controlled by turgor pressure.  Water enters, increased turgor pressure, stomata open  Water exits, decreased turgor pressure, stomata close Active transport of potassium causes water to diffuse into guard cells  Stomata are controlled by temperature, humidity, stress, abscisic acid, and circadian rhythm

 Phloem transports nutrients from roots to leaves and to other parts of the plant  Pressure-flow model- from source to sink