Presentation on theme: "Leaves - Overview Shoot system Leaf Blade Petiole"— Presentation transcript:
1 Leaves - OverviewShootsystemLeafBladePetioleThe leaf is the main photosynthetic organ of most vascular plantsLeaves generally have a flattened blade and a stalk called the petiole,which joins the leaf to a node of the stem
2 Leaves - ComparisonsMonocots and Dicots differ in the arrangement of veins, the vascular tissue of leavesMost Dicots have branch-like veins and palmate leaf shapeMonocots have parallel leaf veins and longer, slender blades
3 Leaf Parts1. Stoma (stomata) – small pores that act as a doorway for gases involved in photosynthesis (found mainly on the underside of leaves). 2. Guard Cells – Cells that regulate the opening of the stomata. 3. Lower and upper epidermis – outer layer of a plant that serves for protection, like skin.
4 Leaf parts continued…4. Palisade layer – layer where majority of chloroplasts are found (site of photosynthesis). 5. Spongy layer – cells surrounded by air spaces; allow water, CO2 and O2 to diffuse during photosynthesis. 6. Waxy layer/cuticle – protects leaf from water loss and from feeding insects.
5 Leaves – Structure and Development Most dicots have 2 types of mesophyllPalisade mesophyllhigh photosynthesisSpongy mesophyllair spaces for gas & water exchangeMonocot leaves have 1 type of mesophyll
7 Leaves – Structure and Development Leaves are several layers thick – each with different cell types
8 Epidermis Leaves Leaf epidermis contains stomata - allow CO2 exchange Stomata flanked by two guard cells, control open vs. closedThe ground tissue in a leaf, called mesophyll, fills the middleKeyto labelsDermalGroundVascularCuticleSclerenchymafibersStomaBundle-sheathcellXylemPhloem(a) Cutaway drawing of leaf tissuesGuardcellsVeinLowerepidermisSpongymesophyllPalisadeUpperStomatalporeSurface view of a spiderwort(Tradescantia) leaf (LM)Epidermal(b)50 µm100 µmAir spacesGuard cellsCross section of a lilac(Syringa)) leaf (LM)(c)Figure Organization of primary tissues in young stems
9 Vascular TissueXylem – cells that carry water and dissolved minerals from the roots to the leaves.Phloem – cells that carry food (sugar) that is made in the leaves to all parts of the plant.Use: Collectively the vascular tissue, xylem and phloem create a vein or vascular bundle to transport material in plants.
10 Stoma Open vs. ClosedOpen – with light and when guard cells are filled with water.Closed – without light and when guard cells are lacking water (dehydrated).Why is it important to have stomata open?Closed vs. Open