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The Leaf

The Leaf. The Leaf is the Main photosynthetic organ in a plant. Controls gas exchange in plants. Controls the amount of water loss in plants when it is hot and dry by: closing their stomates . produce a thick cuticle layer. reduce the surface area of their leaves. Fig 30.10.

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The Leaf

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  1. The Leaf • The Leaf is the Main photosynthetic organ in a plant. • Controls gas exchange in plants. • Controls the amount of water loss in plants when it is hot and dry by: • closing their stomates. • produce a thick cuticle layer. • reduce the surface area of their leaves.

  2. Fig 30.10

  3. Leaf Cross Section

  4. Waxy Cuticle & Upper Epidermis Waxy cuticle Upper Epidermis • The waxy cuticleis a thin layer atop the epidermis. • Its function is to reduce/prevent water loss from the leaf. • In arid conditions (desert) this cuticle layer can be quite thick. • Upper 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. Palisade Mesophyll Layer Palisade mesophyll layer • The palisade mesophylllayer is where most of the photosynthesis occurs in the leaf. • The palisade cells contain a lot of chloroplasts to help them perform this photosynthesis. • The cells of this layer are closely packed together to maximize the absorption of light. • In the leaf cross-section we can see the palisade cells are only found in the upper part of the leaf.

  6. Spongy Mesophyll Layer • The cells in the spongy mesophyll layerare not as closely packed as the cells in the palisade mesophyll layer. • This creates air spacesinside the leaf to enable gases to move in and out. Bringing in CO2 and releasing 02 and Water Vapor • There are not as many chloroplasts in the spongy mesophyll cells as there are in the palisade mesophyll cells – but photosynthesis still occurs in the spongy mesophyll layer. Spongy mesophyll layer Air space

  7. Lower Epidermis and Stomata • Lower epidermis is the bottom layer of the leaf, and is one cell thick • May or may not contain a cuticle • Within the Lower Epidermis, there are some 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, called guard cells. • Guard cells are the only epidermis cells that contain chloroplasts. • The stoma open and close (using turgor pressure) depending upon the requirements of the plant. • It is through these stoma that water leaves the leaf, the process that powers transpiration. Guard Cell Stomata

  8. Transpiration • Process by which evaporation of water from leaf surface draws water from roots upward

  9. Stomata and Guard Cells

  10. Vein- Leaf Transport • The veins provide the transport of materials in the leaf • Carries water, minerals, and food through the leaf and rest of the plant • Has two parts • Xylem- water and mineral transport • Phloem- sugar and food transport

  11. Xylem and Phloem

  12. Exercise 4: Leaf Structure 1. ___________ Waxy cuticle 2. ___________ Epidermis 3. ______________________ Palisade mesophyll layer 4. __________ Air space 5. _____________________ Spongy mesophyll layer 6. ________ Stomata 7. __________ Epidermis

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