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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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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.
waxy cuticle upper epidermis
Waxy Cuticle & Upper Epidermis

Waxy cuticle

Upper Epidermis

  • 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.
  • 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.
palisade mesophyll layer
Palisade Mesophyll Layer

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.
spongy mesophyll layer
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 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

lower epidermis and stomata
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

transpiration
Transpiration
  • Process by which evaporation of water from leaf surface draws water from roots upward
vein leaf transport
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
exercise 4 leaf structure
Exercise 4: Leaf Structure

1. ___________

Waxy cuticle

2. ___________

Epidermis

3. ______________________

Palisade mesophyll layer

4. __________

Air space

5. _____________________

Spongy mesophyll layer

6. ________

Stomata

7. __________

Epidermis