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The Leaf The Leaf is the Main photosynthetic organ in a plant.

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Presentation on theme: "The Leaf The Leaf is the Main photosynthetic organ in a plant."— Presentation transcript:

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


5 Waxy Cuticle & Upper Epidermis
The waxy cuticle is 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.

6 Palisade Mesophyll Layer
The palisade mesophyll layer 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.

7 Spongy Mesophyll Layer
The cells in the spongy mesophyll layer are not as closely packed as the cells in the palisade mesophyll layer. This creates air spaces inside 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

8 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. Stomata Guard Cell

9 Transpiration Process by which evaporation of water from leaf surface draws water from roots upward

10 Stomata and Guard Cells

11 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

12 Xylem and Phloem

13 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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