The Shoot System - II Leaves (1) - PDF

The Shoot System - II Leaves LEAVES Main sight of photosynthesis originate Susceptible to as extreme drying primordia in buds Sight of may be oxygen/carbo Two...

The Shoot System - II Leaves LEAVES Main sight of photosynthesis originate Susceptible to as extreme drying primordia in buds Sight of may be oxygen/carbo Two major simple or n dioxide parts compound. intake and release Functions Waste Movement Removal of water Transpirati Guttation on Photosynth esis Introductions Stalk Flattened blade Network of veins Stipules Green leaves capture light energy Stomata Introduction  Leaves may be simple or compound. Simple leaves - With a single blade Compound leaves - Blade divided into leaflets Pinnately compound leaves Bipinnately compound - Leaflets in pairs along leaf rachis (petiole) Bipinnately compound leaf - Leaflets subdivided Palmately compound leaves - All leaflets attached at same point at end of petiole. Palmately compound leaf Internal Structure of Leaves Veins Mesophy ll Epidermis Stomata Regulate Bordered gas by two exchange between guard leaf interior cells and atmosphere Regulate Inflate evaporati on of or water Deflate Leaf Arrangements and Types  Leaves are attached to stems at nodes, with stem regions between known as internodes.  Phyllotaxy - Arrangement of leaves on stem Alternate - One leaf per node Opposite - Two leaves per node Whorled - Three of more leaves at a node Alternate Whorled Opposit Leaf Venation and Types Dicots Dichotomo Monocots us venation Venati on  Leaf Venations Palmate venation Pinnate Reticulate venation venation Dichotomous venation Parallel venation Mesophyll and Veins  Most photosynthesis takes place in the mesophyll between the two epidermal layers. Palisade Mesophyll – Compactly stacked, barrel- shaped parenchyma cells, commonly in two rows – Contains most of leaf’s chloroplasts Spongy Mesophyll – Loosely arranged parenchyma cells with abundant air spaces Mesophyll and Veins  Veins (vascular bundles) are scattered throughout mesophyll. Consist of xylem and phloem tissues surrounded by bundle sheath of thicker-walled parenchyma Dicot leaf cross section  Mesophyll and Veins Monocots have some differences: Usually do not have mesophyll differentiated into palisade and spongy layers Often have bulliform cells on either side of main central vein – Bulliform cells partly collapse under dry conditions. Monocot leaf cross o Causes leaf to fold section or roll, reducing Specialized Leaves Su n Tendril lea s f Spine Shad e leaf Window leaves Specialized Leaves Prickle Thorn Flower-pot leaf sliced lengthwise Specialized Leaves – Insect Trapping Sundew Bladder of bladderwort Venus’s Flytraps Pitcher Specialized Leaves Clary’s sage Poinsettia Air Plant Autumnal Changes in Leaf Color  Chloroplasts of mature leaves contain several groups of pigments: (all of which play a role in photosynthesis)  Chlorophylls - Green  Carotenoids - Yellows  In fall, chlorophylls break down and other colors are revealed.  Water soluble anthocyanins (red (acidic) or blue (alkaline)) and betacyanins (red and restricted to certain plant families) may also be present in the vacuoles of leaf cells during the fall. Abscission  Deciduous plants drop leaves seasonally.  Abscission - Process by which leaves are shed  Occurs as a result of changes in abscission zone near base of petiole – Protective layer o Cells coated and impregnated with suberin. – Separation layer o Pectins in middle lamella of  Transport in Plants Transpiration Loss of water through its leaves Replaced by water drawn into the leaf Evaporation is the major moving force As water is lost, osmotic pressure moves water out of vascular tissue This pulls water up from the stem to the leaves Affected by heat, humidity, and wind Transport in Plants Controlling Transpiration Open the stomata – increase water loss Close the stomata – decrease water loss Transport in Plants Water Transport Active transport and root pressure Cause water to move from soil to roots Capillary action Combined with active transport and root pressure, moves materials throughout the plant  Transport in Plants Capillary Transport Capillary transport results from both cohesive and adhesive forces Water molecules attracted to one another Water is also attracted to the xylem tubes in the plant Causes water to move from roots to the stem and upward Nutrient Transport Most nutrients are pushed through plant Nutrient movement takes place in phloem Source to Sink Source – any cell that produces sugars Sink – any cell where sugars are used Pressure-flow Hypothesis  Transport in Plants Transpiration and Wilting Osmotic pressure – keeps plants semi-rigid Wilting is a result of high transpiration rates Loss of water causes a drop in osmotic pressure Loss of rigidity Conserves water  Human and Ecological Relevance of Leaves  Landscaping - Shade trees  Food - Cabbage, lettuce, celery petioles, spices  Dyes  Perfumes - Oils of orange tree, lavender  Ropes and Twine - Agave, hemp fibers  Drugs - Narcotics, tobacco, marijuana  Beverages - Tea, tequila (agave leaves)  Insecticides - Rotenone  Waxes - Carnauba and caussu waxes  Aesthetics - Floral arrangements, gardens