Biology. Chapter 26. Plant Nutrition and Transport. Concepts and Applications 9e Starr Evers Starr. Cengage Learning 2015

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1 Biology Concepts and Applications 9e Starr Evers Starr Chapter 26 Plant Nutrition and Transport

2 26.1 Where Do Plants Get the Nutrients They Require? A plant needs sixteen elements to survive and grow Macronutrients: carbon, oxygen, hydrogen, nitrogen, phosphorous, sulfur, potassium, calcium and magnesium Micronutrients: chlorine, iron, boron, manganese, zinc, copper, and molybednum

3 Properties of Soil Carbon, oxygen, and hydrogen atoms are abundantly available in carbon dioxide and water Plants get the other elements they need when their roots take up minerals dissolved in soil water

4 Properties of Soil (cont d.) Soil consists mainly of mineral particles: Clay particles: attracts positively charged mineral ions in soil water Sand and silt: intervene between tiny particles of clay; allows roots to access oxygen

5 Properties of Soil (cont d.) Soils with the best oxygen and water penetration are loams Have roughly equal proportions of sand, silt, and clay

6 Properties of Soil (cont d.) Most plants do best in loams that contain between 10 and 20 percent humus Decomposing organic material (e.g., fallen leaves, feces) that releases nutrients and traps minerals

7 How Soils Change Soils develop over thousands of years Most form in layers, or horizons, that are distinct in color and other properties Topsoil: uppermost soil layer; most organic matter and nutrients for plant growth Grasslands typically have a deep layer of topsoil; tropical forests do not

8 How Soils Change (cont d.) O Horizon A Horizon B Horizon C Horizon Bedrock

9 How Soils Change (cont d.) Minerals, salts, and other molecules dissolve in water as it filters through soil Leaching: process by which water removes soil nutrients and carries them away Soil erosion: loss of soil under the force of wind and water

10 How Soils Change (cont d.)

11 26.2 How Do Plant Roots Absorb Water and Nutrients? Water moves from soil, through a root s epidermis and cortex, to the vascular cylinder Osmosis drives this movement; fluid in the plant typically contains more solutes than soil water Xylem distributes water and mineral ions to the rest of the plant

12 ANIMATION: Root organization To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

13 How Do Plant Roots Absorb Water and Nutrients? (cont d.) Soil water enters a root and moves through cell walls Soil water diffuses from epidermis, through the cortex, reaching the vascular cylinder A Casparian strip (waterproof band of plasma membranes) forces water to enter a vascular cylinder by passing through endodermal cells Water diffuses from cell to cell through plasmodesmata until it enters xylem

14 ANIMATION: Root functioning To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

15 How Do Plant Roots Absorb Water and Nutrients? (cont d.) Ions cannot cross the plasma membrane Mineral ions dissolved in soil water enter a cell s cytoplasm through transport proteins Once actively transported into cells, mineral ions diffuse from cell to cell through plasmodesmata until they enter xylem

16 26.3 What Mutualisms Affect Root Function? Mycorrhiza: mutually beneficial interaction between a root and a fungus Filaments of the fungus (hyphae) form a velvety cloak around roots or penetrate their cells Root cells get some scarce minerals that the fungus is better able to absorb

17 What Mutualisms Affect Root Function? (cont d.) Mutualism with nitrogen-fixing Rhizobium Roots release certain compounds into the soil that are recognized by compatible Rhizobium Roots encapsulate Rhizobium bacteria inside swellings called root nodules Rhizobium in root nodules fix nitrogen gas to ammonia for plant use Plant provides oxygen-free environment and sugars to the anaerobic Rhizobium bacteria

18 What Mutualisms Affect Root Function? (cont d.) a root nodule

19 26.4 How Does Water Move Through Xylem? Water that enters a root travels to the rest of the plant inside tubes of xylem Xylem cells deposit secondary wall material Just before the cells die, they digest away most of their primary wall Holes/pits remain in secondary walls where plasmodesmata once connected living cells In mature xylem tubes, water flows laterally through the pits, between adjacent cells

20 How Does Water Move Through Xylem? (cont d.) xylem tube pit water

21 How Does Water Move Through Xylem? (cont d.) Vessel elements: Cells that form in stacks in xylem and die when mature Their pitted walls remain to form waterconducting tubes Each tube consists of a stack of vessel elements that meet end to end at perforation plate

22 How Does Water Move Through Xylem? (cont d.) vessel element perforation plate

23 How Does Water Move Through Xylem? (cont d.) Tracheids: Tapered cells of xylem that die when mature Their interconnected, pitted walls remain and form water-conducting tubes

24 How Does Water Move Through Xylem? (cont d.) tracheid

25 Cohesion Tension Theory Tracheids and vessel elements that compose xylem tubes are dead and cannot pump water upward against gravity The movement of water in vascular plants is driven by two features of water: Evaporation and cohesion

26 Cohesion Tension Theory (cont d.) Cohesion tension theory: water in xylem is pulled upward by air s drying power, which creates a continuous negative pressure called tension

27 Cohesion Tension Theory (cont d.) Transpiration: evaporation of water from aboveground plant parts Creates tension that pulls a cohesive column of water upward through xylem

28 ANIMATION: Transpiration To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

29 Cohesion Tension Theory (cont d.) Pits in the sides of vessels and tracheids are often bordered by pectin-containing secondary walls Pectins shrink when dry, and swell when wet

30 Cohesion Tension Theory (cont d.) When mineral-rich water flows through a pectin-bordered pit, the border swells and eventually plugs the hole Water tends to flow toward the thirstiest regions of the plant, where pectin-bordered pits are dry and open

31 26.5 How Do Land Plants Conserve Water? In land plants, at least 90 percent of water taken up by roots is lost by evaporation A waterproof cuticle helps a land plant conserve water The cuticle also restricts gas exchanges with air

32 How Do Land Plants Conserve Water? (cont d.) Stoma: an opening between a pair of guard cells (specialized cells of epidermis) When guard cells swell with water, they bend slightly forming a gap (the stoma) Open stomata allow gases and water vapor to cross the epidermis When guard cells lose water, they collapse against one another, closing the stoma

33 How Do Land Plants Conserve Water? (cont d.) guard cells closed stoma open stoma

34 How Do Land Plants Conserve Water? (cont d.) cuticle epidermis stoma guard cells

35 How Do Land Plants Conserve Water? (cont d.) Stomata open or close based on environmental cues Example: light from the sun causes guard cells to begin pumping potassium ions Water follows the ions by osmosis, plumping the guard cells, opening the stomata Carbon dioxide diffuses through the open stomata into the plant s tissues, and photosynthesis begins

36 26.6 How Do Sugars Move Through Phloem? Sieve tubes: sugar-conducting tube of phloem; consists of stacked sieve elements Sieve elements are living cells that meet end to end at sieve plates Companion cells: parenchyma cells that provide metabolic support to its partnered sieve element

37 How Do Sugars Move Through Phloem? (cont d.) phloem

38 Pressure Flow Theory Sugars are transported via sieve tubes Movement of sugars through phloem is called translocation

39 Pressure Flow Theory (cont d.) Inside sieve tubes, fluid rich in sugars flow from a source to a sink because of a pressure gradient Source: region where sugars are produced or released Sink: region where sugars are being broken down for energy

40 Pressure Flow Theory (cont d.) Pressure flow theory: A difference in turgor between sieve elements in source and sink regions pushes sugar-rich fluid through a sieve tube

41 Pressure Flow Theory (cont d.)

42 26.7 Application: Leafy Cleanup J-Field, Aberdeen Proving Ground: From World War I until the 1970s, the United States Army tested and disposed of weapons at this site Chemicals, chemical weapons, explosives, plastics, and solvents were burned in pits Lead, arsenic, mercury, and TCE contaminated the soil and groundwater

43 Application: Leafy Cleanup (cont d.) To clean up the soil and protect nearby Chesapeake Bay, the Army and the Environmental Protection Agency turned to phytoremediation The use of plants to take up and concentrate or degrade environmental contaminants

44 Application: Leafy Cleanup (cont d.) Ford Motor Company s Rouge Center: decades of steelmaking left soil contaminated with highly carcinogenic compounds Researchers developed a phytoremediation system based on native plants

45 Application: Leafy Cleanup (cont d.)

Chapter 30: Plant Nutrition & Transport

Chapter 30: Plant Nutrition & Transport Carnivorous Plants Capture animals to supplement their nutrient intake Venus flytrap lures insects with sugary bait; closes on victim Cobra lily lures insects down