Two major categories. BIOLOGY 189 Fundamentals of Life Sciences. Spring 2004 Plant Structure and Function. Plant Structure and Function

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1 BIOLOGY 189 Fundamentals of Life Sciences Spring 2004 Plant Structure and Function Examination #1 Class Average: 33/60 for 55% 4 Chapters March 5, 2004 next Friday Plant Structure and Function Primary focus: Angiosperms Dominant plant species for ~100 M years Over 250,000 species today Represent most of the plant-derived food sources Two major categories Defined Defined by number of first leaves (cotyledon) appearing on plant embryo One leaf = monocotyledon Two leaves = dicotyledon

2 Monocotyledons Also called Monocots Monocotyledons Examples: palm trees, orchids, bamboo, grain plants and grasses Dicotyledons Also called Dicots Examples: majority of angiosperms, deciduous trees, flowers, vegetables

3 Internal plant cell structure Water filled Maintains firmness of cell Not all cells have two plant walls Chloroplast plant specific energy producing organelle Cell wall Communication channels Structure maximizes interception of light Organizes Biochemistry of photosynthesis Plasmodesmata Granum Transfer water, nutrients and other small molecules

4 Basic structure - Roots and Shoots Root systems - many forms, specialized function Roots Anchor Transport minerals and water Store food Large tap root sugar beets, carrots (food storage for plant) Runners method of plant reproduction (new shoots can arise from a runner) Sometimes when very large, called tubers (potatoes)

5 Rhizomes store food and give rise to new plants Basic structure - Roots and Shoots Shoots Stems support and fluid transport Leaves for photosynthesis Flowers (on some) reproduction Important Leaf Structures Stomata and Guard Cells Stomata (singular = stoma) Pores in leaf Allow CO 2 in, O 2 out Release H 2 O

6 Guard Cells Regulate opening/closing of stomata Open sunlight, H 2 O Close nighttime, lack of moisture 3-dimensional conformation rules K + gradient, osmotic movement of water into guard cells open stomata Water loss, guard cells shrink close stomata Cactus spines (protection) Tendrils (aid climbing plants) Extra large petioles (e.g. celery water and food storage) Modified shoots Parenchyma cell Most common Basic cell types Has only a thin Primary Wall (no secondary wall) Primary functions: food storage, photosynthesis, aerobic respiration AND Divide and differentiation into other plant cell types repair and rejuvenation Collenchyma cells Basic cell types Single-layered layered walls, thick uneven material Function: structural support at growth areas Sclerenchyma cells Rigid secondary wall made of lignin (woody structure) Function: structural support and protection at non-growth areas In mature plants, most sclerenchyma are dead

7 Xylem and Phloem Xylem water conducting cells made of dead tissues, also provide structural support Phloem nutrient conducting cells made of live tissues Tracheids and vessel elements 2-layered walls Cell-specific chains all tracheids or all vessel elements overlapping ends Most of these cells are dead in mature plants, so tubes are hollow Xylem Sieve tube members Single-layered, layered, thin cell walls Cells are alive in mature plants lose nuclei, ribosomes and other organelles Sieve tube plate communication junction Phloem Companion cells Connected to sieve tube members by plasmodesmata Produce proteins for the STM Phloem

8 Plant Nutrition and Transport Growth from air AND soil AND sunlight 95% of weight from air- derived CO 2 Soil provides, water and minerals and oxygen Sunlight allows all to be used for energy Root cells control soil delivered materials Root hairs expand surface area Plasma membrane permeability controls what is absorbed All substances are in aqueous solution when absorbed Defying gravity?? How fluids move Transpiration and Root Pressure Two routes Root pressure the push Inorganic ions are pumped into the xylem creating a concentration gradient. Osmosis brings in water Increased volume pushes up through the xylem and into the plant body

9 Transpiration the pull Dry external air and moist internal plant cell Fick s law says?? Stoma close when moisture in leaves is less than plant body (preservation) another diffusion gradient leaves leaves pull fluid up from plant body Nutrients move from production source to storage reservoir Production - sugar source photosynthetic production or chemical breakdown of starches Usually leaves, except in spring when storage vessels (like tubers and roots) become sources Storage sugar sink Growing roots, shoot tips, fruits, nonphotosynthetic stems, tap roots, tubers Mediated via Pressure-flow Mechanism Osmotic pressure and density gradients Flow is always from the source to the sink, regardless of location in the plant