Leaves - Ioana Dobre Leaves: Structure, Photosynthesis and...

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Ioana Dobre Leaves: Structure, Photosynthesis and Phytochemical defenses 1) Leaf and chloroplast anatomy 2) Light and dark reactions of photosynthesis 3) Chemical ecology of phytochemical defense 1) LEAF ANATOMY - There are 2 major types of leaf anatomy Normal – seen in C3 photosynthesis Kranz – seen in C4 photosynthesis in subtropical grasses and weeds *there is a 3 rd type : CAM There are 2 types of leaves: - Simple leaves : consisting of a petiole and a blade - Pinnate leaves: several leaflets make a leaf à each of these leaflets can be further subdivided à leaf anatomy presents a good tool for classification i.e taxonomic identification of plants In the cross section of lilac, a C3 plant with normal anatomy - CO2 has to go in
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Ioana Dobre - O2 and water need to come out - Mesophyll is the central section between the 2 epidermis layers where photosynthesis takes place - Groups of cells called parenchyma cells or palisade cells are found under the upper epidermis - The spongy parenchyma has space for gases necessary for photosynthesis - Veins carry sugar from the photosynthetic cells and bring water from the roots In the Xerophyte leaf: there are slight changes in anatomy -stomata is deeply embedded in cavities (controls the rate at which water comes and goes out of the leaf In the Aquatic leaf, we notice sclereids - a very special feature. These cells have thick, lignified cell walls, and their function is to provide structural support In C3 grasses (wheat) - They are the conventional photosynthetic family in the majority of plants - They have very proeminent veins
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Ioana Dobre - The bundle sheaths are not particularly well formed, and have gaps in them In C4 grasses, like sugar cane, corn, soya (+ all grasses from tropical and subtropical areas) : - There is a very strong sheath around the vein - The sheaths are quite tight and very prominent. No way anything will get into the vein - Concentric rings à this kind of anatomy was discovered by Kranz and is characteristic to C4 plants - The veins are parallel - Epidermis is not photosynthetic - Mesophyll has photosynthetic function - Bundle sheath is also photosynthetic - C4 anatomy is designed to give the plant high productivity under hot, dry conditions - Among highest productivity in the world - Stomates in scanning electron microscope - the potato stomates have a random arrangement - the maize stomates have a regular - arrangement and run parallel Photosynthetic Palisade cell anatomy - the cell wall is made of cellulose - the vacuole is huge, membrane bound, and fluid filled
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Ioana Dobre - the individual membranes are called thylakoids - each stack of them is called a granum - the thylakoids resemble flattened disks. Inside we find the thylakoid space where all
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Leaves - Ioana Dobre Leaves: Structure, Photosynthesis and...

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