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Ch 7 Part 2

Ch 7 Part 2. Specialized Leaves. Shade Leaves Receive less total light than sun leaves Compared to sun leaves, shade leaves: Tend to be larger Tend to be thinner Have fewer well-defined mesophyll layers and fewer chloroplasts Have fewer hairs. Specialized Leaves. Leaves of Arid Regions

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Ch 7 Part 2

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  1. Ch 7 Part 2

  2. Specialized Leaves • Shade Leaves • Receive less total light than sun leaves • Compared to sun leaves, shade leaves: • Tend to be larger • Tend to be thinner • Have fewer well-defined mesophyll layers and fewer chloroplasts • Have fewer hairs

  3. Specialized Leaves • Leaves of Arid Regions • Arid regions have limited availability of water, wide temperature ranges, and high light intensities. • Leaves reduce loss of water by: • Thick, leathery leaves • Fewer stomata or sunken stomata • Succulent, water-retaining leaves, or no leaves • Dense, hairy coverings • Leaves of Aquatic Areas • Less xylem and phloem • Mesophyll not differentiated into palisade and spongy layers. • Large air spaces

  4. Specialized Leaves • Tendrils • Modified leaves that curl around more rigid objects, helping the plant to climb or to support weak stems • Garden peas Tendrils • Spines • Modified leaves that reduce leaf surface and water loss, and protect from herbivory. • Cacti • Leaf tissue replaced with sclerenchyma. • Photosynthesis occurs in stems. Spine

  5. Specialized Leaves • Thorns - Modified stems arising in the axils of leaves of woody plants Thorn • Prickles- Outgrowths from epidermis or cortex

  6. Specialized Leaves • Storage leaves • Succulent leaves are modified for water storage. • Have parenchyma cells with large vacuoles • Many desert plants • Fleshy leaves store carbohydrates. • Onions, lily

  7. Specialized Leaves • Flower-Pot Leaves • Leaves develop into urn-like pouches that become home of ant colonies. • Ants carry in soil and add nitrogenous wastes that provide good growing medium for the plant’s own roots. • Dischidia, an epiphyte of Australia Flower-pot leaf sliced lengthwise

  8. Specialized Leaves • Window leaves • In succulent desert plants of Africa • Leaves buried in ground, except for exposed end. • End has transparent, thick epidermis and transparent water storage cells underneath. • Allows light into leaf, while buried leaves keep plant from drying out

  9. Specialized Leaves • Reproductive Leaves • Walking fern - New plants at leaf tips • Air plant - Tiny plantlets along leaf margins Air Plant

  10. Specialized Leaves • Floral Leaves (bracts) • At bases of flowers or flower stalks • Poinsettia - Flowers do not have petals, instead brightly colored bracts surround flowers. • Clary’s sage - Colorful bracts are at top of flowering stalks above flowers. Poinsettia Clary’s sage

  11. Specialized Leaves • Insect-Trapping Leaves • Grow in swampy areas and bogs • Nitrogen and other elements are deficient in soil. • Specialized leaves trap and digest insects. • Pitcher Plants • Insects trapped and digested inside cone-shaped leaves. Pitcher plant

  12. Specialized Leaves • Insect-Trapping Leaves • Sundews • Have round to oval leaves covered with glandular hairs that have a sticky fluid of digestive enzymes at tip • Venus’s Flytraps • Only in North Carolina and South Carolina • Blade halves trap insects.

  13. Specialized Leaves • Insect-Trapping Leaves • Bladderworts • Submerged or floating in shallow water • Tiny bladders on leaves have trap doors that trap insects inside bladders. Bladder of bladderwort

  14. Autumnal Changes in Leaf Color • Chloroplasts of mature leaves contain several groups of pigments: • Chlorophylls - Green • Carotenoids - Yellows • In fall, chlorophylls break down and other colors are revealed. • Water soluble anthocyanins (red or blue) and betacyanins (red) may also be present in the vacuole.

  15. 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 • Cells coated and impregnated with suberin. • Separation layer • Pectins in middle lamella of cells are broken down by enzymes.

  16. 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

  17. Review • Introduction • Leaf Arrangements and Types • Internal Structure of Leaves • Stomata • Mesophyll and Veins • Specialized Leaves • Autumnal Changes in Leaf Color • Abscission • Human and Ecological Relevance of Leaves

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