X section of a leaf - PowerPoint PPT Presentation

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X section of a leaf

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  1. Plant cell types rise by mitosis from a meristem. A meristem may be defined as a region of localized mitosis.

  2. X section of a leaf

  3. Key Words Waxy cuticle Waterproof layer atop the epidermis Stoma Pores that allow gaseous exchange Found in the spongy mesophyll layer, enable gases to reach the leaf cells Air spaces One-cell thick outer layer of cells that prevent water loss from the leaf Epidermis Contain numerous chloroplasts and are densely packed Palisade mesophyll cell Loosely packed cells that do not contain as many chloroplasts as palisade cells Spongy mesophyll cell

  4. Waxy Cuticle & Epidermis Waxy cuticle Epidermis The waxy cuticle is a thin layer atop the epidermis. Its function is to reduce the water lost from the leaf. In arid conditions this cuticle layer can be quite thick. Epidermis cells contain no chloroplasts – not true of the stoma cells. They form layers on the upper and lower surfaces of the leaf. Their function is to prevent water getting out and stopping unwanted substances/organisms getting in.

  5. Stomata There are holes found in leaves called stoma. These holes allows gases to diffuse in and out of the leaves. The stoma are formed by two highly specialized epidermis cells. These cells, called guard cells, are the only epidermis cells that contain chloroplasts. The stoma open and close depending upon the requirements of the plant. It is through these stoma that water leaves the leaf, the process that powers transpiration. Stomata

  6. Palisade Mesophyll Layer The palisade mesophyll layer is where most of the photosynthesis occurs in the leaf. Palisade mesophyll layer The palisade cells contain a lot of chloroplasts to help them perform this photosynthesis. The palisade cells are closely packed together to maximize light absorption. In the leaf cross-section we can see the palisade cells are only found in the upper part of the leaf.

  7. Cells of the mesophyll make up the bulk of internal leaf tissue and are the major site of photosynthesis in a plant by virtue of containing large populations of chloroplast organelles. The differentiation of the mesophyll and its coordinated expansion is important to leaf function because light interception by chloroplasts and gas exchange in the internal airspaces of the leaf are crucial to optimize rates of photosynthesis.

  8. A Thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. The word "thylakoid" is derived from the Greek thylakos, meaning "sac". Thylakoids consists of a thylakoid membrane surrounding a thylakoidlumen. Chloroplast thylakoids frequently form stacks of disks referred to as "grana" (singular: granum). "Grana" is Latin for "stacks of coins". Grana are connected by intergrana or stromathylakoids, which join granum stacks together as a single functional compartment.

  9. 1. outer membrane2. intermembrane space3. inner membrane (1+2+3: envelope)4. stroma (aqueous fluid)5. thylakoid lumen (inside of thylakoid)6. thylakoid membrane7. granum (stack of thylakoids)8. thylakoid (lamella)9. starch10. ribosome11. plastidial DNA12. plastoglobule (drop of lipids)

  10. Photosynthesis Chloroplasts are organelles of plant cells that contain a green substance called chlorophyll. Scientists believe chlorophyll absorbs light energy and this energy is then used to make food. The raw materials of photosynthesis are carbon dioxide and water. The waste product of this reaction is oxygen. The carbon dioxide required is absorbed through the stoma in the leaves – this is how the oxygen is also removed. The water required is absorbed by the roots. The word equation for this reaction is... The chemical equation for this reaction is... 6H2O + 6CO2 C6H12O6 + 6O2

  11. The thylakoid membrane is the site of the light-dependent reactions of photosynthesis with the photosynthetic pigments embedded directly in the membrane.

  12. Thylakoid membranes contain integral membrane proteins which play an important role in light harvesting and the light-dependent reactions of photosynthesis. There are four major protein complexes in the thylakoid membrane: • Photosystems I and II • Cytochrome b6f complex • ATP synthase

  13. The thylakoids are the site of the light-dependent reactions of photosynthesis. These include light-driven water oxidation and oxygen evolution, the pumping of protons across the thylakoid membranes coupled with the electron transport chain of the photosystems and cytochrome b6f complex, and ATP synthesis by the ATP synthase utilizing the generated proton gradient.

  14. Chlorophyll molecule