PLANT STRUCTURES LEAVES FUNCTION OF LEAVES Convert light

PLANT STRUCTURES: LEAVES

FUNCTION OF LEAVES • Convert light energy into chemical energy for the plant to use (photosynthesis) • Leaves are thin and flat allowing for more surface area to absorb light energy • Epidermis is thin allowing for more light to be absorbed • Stomata on the leaves allow for gas to be exchanged easily for the process of photosynthesis • Leaf veins provide the minerals and water necessary to carry out photosynthesis

INTERNAL FEATURES Leaf Blade Layers: § Epidermis-outer layer of tissues § Cuticle: waxy protective layer on outside of epidermis. Prevents water loss on leaves, green stems, and fruits. § Leaf hairs: part of the epidermis § Palisade-tightly packed layer of parenchyma tissues filled with chloroplasts for photosynthesis § Chloroplasts: contain chlorophyll and begins the transformation of that energy into sugars

INTERNAL FEATURES Layers Cont. § Vascular bundle: xylem (transports water) and phloem (transports nutrients) tissues (leaf veins) § Spongy mesophyll: layer of parenchyma tissues that help move oxygen, carbon dioxide, and water vapor § Stomata: Openings in leaves that allow for gas exchange § Guard Cells: kidney-shaped cells that open and close the stomata

EXTERNAL FEATURES Parts of the Leaf on the Outside Include: § Leaf Blade: flattened part of the leaf § Petiole: Leaf stalk § Stipules: Leaf-like appendage at the base of leaf

LEAF TYPES Monocot § One cotyledon § Parallel venation: veins run in parallel lines Dicot § Two cotyledons § Net-veined: veins branch from main rib and subdivide (pinnate/palmate)

ADAPTATIONS FOR ENVIRONMENT • Plants that live in the water • Have stomata on the top of the leaf since this is the part exposed to the air • Conifers • Needles have adaptations that help them survive during the winter which allows trees to keep their leaves throughout the year • Deciduous • Shed leaves during the dry season to save the tree due to lack of water

TRANSPIRATION • 99% of the water that a plant absorbs is lost through evaporation. This process is called transpiration: loss of water vapor from plant parts such as the stem and leaves • The leaves have a cuticle to reduce this water loss by having a waxy covering • Stomata are the main reason most water is lost and too much water loss can cause wilting of the plant • Factors that affect transpiration • • Higher air temperatures • Light • Wind and dry air Benefits: allows for water movement, cools the plant, moves minerals through plant

GUTTATION • Many leaves have hydathodes, or openings at the tip of leaf veins. These openings can release water in liquid form (guttation) • This process typically happens at night when the stomata are closed • Sometimes guttation is misunderstood to be dew on plants in the morning

LEAF ARRANGEMENTS § Alternate: staggered arrangement along stem § Example: willow tree

LEAF ARRANGEMENTS § Opposite: Pair of leaves arranged across from each other on a stem § Example: maple tree

LEAF ARRANGEMENTS § Whorled: arranged in a ring § Example: Blackboard tree

LEAF ARRANGEMENT § Rosette: spiral cluster of leaves arranged at the base § Example: dandelion

LEAFLET ARRANGEMENT § Simple: leaf blade one continuous unit § Example: cherry, maple, elm

LEAFLET ARRANGEMENT § Compound: Several leaflets from same petiole § Palmately compound: leaflets radiate from one central point § Example: Ohio Buckeye § Double Pinnately Compound: double set of compound leaflets § Example: poison ivy

LEAF SHAPE

LEAF BASE SHAPE

MODIFIED LEAVES • Spines • Hard and pointed leaves found on desert plants used to help keep animals from eating the plant • Bracts • A leaf that is associated with a flower but not part of the flower itself

MODIFIED LEAVES • Tendrils • A leaf of a vine that is able to hold on to and attach to other objects • Carnivorous Plants • Leaves are adapted to catch insects by having hairs or sticky parts that cause the insect to stick or not be able to leave