leaf structure

• plant cells are organised into...

  tissues and organs
• the leaf is an ... made up of several types of ...

  organ, tissue
• cuticle description


  a waxy, waterproof layer covering the leaf
• cuticle function


  - protects plants against harsh weather, UV rays, chemical attacks, mechanical injuries and pathogen/pest infection

  - the layer being waxy and waterproof decreases water loss from translocation
• upper epidermis description


  below the cuticle and above the palisades layer
• upper epidermis function


  - prevents water loss by secreting the waxy cuticle and

  - protects the leaf by providing an extra layer between the outside and inside of the leaf

  - allows light to pass through so it can reach the palisade layer by being transparent
• palisade layer description


  layer with palisade cells packed closely together below the upper epidermis and above the spongy mesophyll
• palisade layer function


  - layer where the most photosynthesis occurs

  - contains a lot of chloroplasts to help preform photosynthesis

  - palisade cells are packed close together to maximise light absorption
• spongy mesophyll function


  - facilitates the exchange of gases essential to the process of photosynthesis by having the tissue packed loosely for efficiency

  - acts as a temporary storage for sugars and amino acids generated in the palisade layer
• spongy mesophyll description


  layer below the palisade layer and above the lower epidermis where tissue is loosely packed
• lower epidermis description


  protective layer below the spongy mesophyll containing stomata and guard cells
• lower epidermis function


  - prevents water loss with stomata and guard cells

  - regulates gas exchange with stomata and guard cells
• stomata description


  tiny openings present on the epidermis of leaves
• stomata function


  - allows carbon dioxide to enter and water/oxygen to exit (gas exchange)

  - opened and closed by guard cells
• guard cells description


  pairs of epidermal cells which surround the stomata in the lower epidermis
• guard cells function


  - help to regulate the rate of transpiration and gas exchange by opening and closing the stomata

  - triggered by mainly by light
• leaf vein description

  vascular tissue with double pipeline tubes including xylem and phloem cells in the leaf
• leaf vein function


  - carries water and minerals to the leaf

  - phloem present in the vein carries the glucose produced in the leaf during photosynthesis

  - xylem present in the vein carries water and minerals to the leaf from the roots
• phloem tube structure


  made of columns of elongated living cells with small pores in the end walls (called sieve walls) to allow cell sap to flow through
• phloem tubes function


  transports food/cell sap (mainly dissolved sugars) made in the leaves to the rest of the plant - this transport (translocation) goes in both ways
• xylem tube structure


  made up of dead cells joined end to end with no end walls between them and hole down middle - they are strengthened with a material called lignin, supporting the stem
• xylem tubes function


  takes water and mineral ions up the stem to the leaves from the roots (this goes only one way) - the movement of water out of the leaves is called transpiration steam