Introduction Leaf Arrangements and Types Internal Structure of Leaves Stomata Mesophyll and Veins Specialized Leaves Autumnal Changes in Leaf Color

Transcription

1 The Leaf

2 Introduction Leaf Arrangements and Types Internal Structure of Leaves Stomata Mesophyll and Veins Specialized Leaves Autumnal Changes in Leaf Color Human and Ecological Relevance of Leaves

3 Function: Photosynthesis (food production for the whole plant). Transpiration Structure Blade: Flat expanded area or lamina Petiole: stalk that connects leaf blade to stem, and transports materials. Veins: Vascular Bundles Stipules at base of petiole Leaves of flowering plants associated with leaf gaps and have axillary

4 Leaves may be simple or compound. Simple leaves: With a single blade Simple leaves Compound leaves: Blade divided into leaflets Pinnately compound leaves - Leaflets in pairs along rachis (petiole) Bipinnately compound leaf - Leaflets subdivided Palmately compound leaves - All leaflets attached at same point at end of petiole. Bipinnately compound leaf Palmately compound leaf

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6 Simple Leaf Compound Leaf

7 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 Opposite Whorled

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9 The Leaf Arrangement

10 Monocots - Primary veins parallel = Parallel venation Dicots - Primary veins divergent in various ways = netted or reticulate venation. Dichotomous venation - Veins fork evenly and progressively from base of blade. Parallel venation Reticulate venation Dichotomous venation

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12 Venation - Arrangement of veins in a leaf or leaflet blade Pinnately veined leaves - Main midvein included within enlarged midrib. Secondary veins branch from midvein. Palmately veined leaves - Several primary veins fan out from base of blade. Pinnate venation Palmate venation

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16 Three regions: Epidermis, mesophyll, veins (vascular bundles) Epidermis: Single layer of cells covering the entire surface of the leaf Devoid of chloroplasts Coated with cuticle (with cutin) Functions to protect tissues inside leaves Waste materials may accumulate in epidermal cells. Different types of glands may also be present in the epidermis.

17 Lower epidermis typically has a thinner layer of cutin and is perforated by numerous stomata. The stomata bordered by two guard cells. The guard cells originate from the same parent cell (they are sister cells), and contain chloroplasts. Their primary functions are: Regulate gas exchange between leaf interior and atmosphere Regulate evaporation of water Changes in amount of water in guard cells cause them to inflate or deflate. Inflate - Stomata open Deflate - Stomata close

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20 Most photosynthesis takes place in the mesophyll between the two epidermal layers. The mesophyll is comprised of the Palisade Mesophyll: Compactly stacked, barrelshaped parenchyma cells, commonly in two rows and contains most of leaf s chloroplasts. Spongy Mesophyll Loosely arranged parenchyma cells with abundant air spaces

21 Veins (vascular bundles) are scattered throughout mesophyll. They consist of xylem and phloem tissues surrounded by bundle sheath of thicker-walled parenchyma

22 Review: Sketch of a cross section of a dicot leaf

23 Typical Dicot Leaf

24 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 and they cause the leaf to fold or roll, reducing transpiration Monocot leaf cross section

25 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

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27 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

28 Water lily leaf with highly developed spongy parenchyma

29 Dune grass leaf with highly developed sclerenchyma

30 Tendrils Modified leaves that curl around more rigid objects, helping the plant to climb or to support weak stems. For example Garden peas Cacti o Leaf tissue replaced with sclerenchyma. o Photosynthesis occurs in stems. Tendrils

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32 SPECIALIZED LEAVES Thorns: Modified stems arising in the axils of leaves of woody plants Thorn Prickles: Outgrowths from epidermis or cortex

33 Modified leaves

34 The leaves have been completely modified into a cactuses thorns.

35 Storage leaves Succulent leaves are modified for water storage. These leaves have parenchyma cells with large vacuoles. Like in Aloe. Found in many desert plants and in some cases, the fleshy leaves also store carbohydrates like in onions.

36 Window leaves Found in succulent desert plants of Africa. In this case the leaves are buried in the ground, except for the exposed ends. The ends have a transparent, thick epidermis and transparent water storage cells underneath. These windows allow light into leaf, while buried leaves keep plant from drying out

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38 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

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40 Reproductive Leaves New plants at leaf tips. Known as the walking fern. This is not a fern, but the succulent known as Kalanchoe (crassulaceae family). Air plant - Tiny plantlets along leaf margins Air Plant

41 SPECIALIZED LEAVES Insect-Trapping Leaves Pitcher Plants: Grow in swampy areas and bogs where nitrogen and other elements are deficient in the soil. The have specialized leaves trap and digest insects. The insects trapped and digested inside cone-shaped leaves, hence the name pitcher plant. Pitcher plant

42 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. SPECIALIZED LEAVES

43 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

44 Flower-Pot Leaves Leaves develop into urnlike 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. An example is Dischidia, an epiphyte of Australia Flower-pot leaf sliced lengthwise

45 Chloroplasts of mature leaves contain several groups of pigments: Chlorophylls - Green Carotenoids Oranges and Yellows Xanthophylls: 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.

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47 Maple leaves American Beech leaves Sassafras leaves

48 Northern Red oak Pignut hickory Flowering Dogwood White Oak

49 PHOTOSYNTHESIS 1. Definition PHOTO = produced by light SYNTHESIS = manufacturing. PHOTOSYNTHESIS is the process whereby plants, algae and some bacteria, use the energy of the sun to synthesize organic compounds (sugars) from inorganic compounds (CO 2 and water).

50 Carbon Dioxide + Water+ Light CO 2 + H 2 O+Light Glucose + O2 C 6 H 12 O 6 + O 2 + H 2 O

51 3. Where?

52 Chlorophyll a is the primary photosynthetic pigment that drives photosynthesis. Other pigments such as chlorophyll b, carotenes and xanthophyll can be present. These are known as accessory pigments or antenna pigment. They absorb light at different wavelengths, extending the range of light useful for photosynthesis. Accessory pigments can collect light but the only pigment that can transform sunlight (light energy) into the chemical bonds of Glucose (chemical energy) is chlorophyll a.

53 PHOTOSYNTHESIS is one of the most important biological process on earth! Provides the oxygen we breathe Consumes much of the CO 2 Food Energy Fibers and materials

54 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

55 Introduction Leaf Arrangements and Types Internal Structure of Leaves Stomata Mesophyll and Veins Specialized Leaves Autumnal Changes in Leaf Color Human and Ecological Relevance of Leaves