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What are the 4 layers of a leaf?

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  1. Leaves are thin, flat organs responsible for photosynthesis in the plants
  2. The internal structure of the leaf shows three main parts, they are epidermis with stomata, mesophyll cells and vascular system.
  3. The epidermis is the outermost layer of the leaf.
  4. It covers the upper and lower surfaces of the leaf, thus, forming two epidermal layers: the upper epidermis and the lower epidermis.

4 layers of a leaf:

Palisade level:

  1. It consists of one or more layers of cylindrical cells that are perpendicular to the plane of the leaf along their long axis.
  2. The cells are filled with chloroplasts and most of the photosynthesis is in the leaves.

Upper epidermis:

  1. This is a layer of cells with few or no chloroplasts.
  2. The cells are very transparent and absorb most of the light which is allowed to pass through the inner cells.
  3. The upper surface is covered with a wax-like, waterproof cuticle, which helps to reduce water loss from the leaves.

Sponge layer:

  1. Below the palisade layer, its cells are irregular in shape and pack loosely.
  2. Although they contain few chloroplasts, their main function appears to be a temporary accumulation of sugars and amino acids synthesized in the palisade layer.
  3. During the day, these cells deliver oxygen and water vapor to the air around them.
  4. The air spaces are connected to each other and eventually open outwards through holes called stomata.

Lower epidermis:

  1. Typically, most stomata are located in the lower epidermis.
  2. Although most cells of the lower epidermis resemble cells of the upper epidermis, each stoma is surrounded by two sausage-shaped cells called guard cells.
  3. These differ from other cells of the lower epidermis not only in their shape but also in having chloroplasts.

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