Plant Tissues

• • The leaf is an organ 
  • Like any organ , the leaf contains different tissues
• Here are some different Plant tissues

  • Epidermis 
  • Palisade mesophyll 
  • Spongy mesophyll 
  • Xylem vessels 
  • Phloem vessels 
  • Meristem tissue
• • This diagram shows the cross-section of a leaf 
  • In other words the leaf has been sliced from top to bottom

  
• What is the epidermis , and what is its function

  • The top and bottom of the leaf are covered with a very thin layer of cells 
  • These are called epidermal cells , and they form epidermal tissue 
  • The epidermis covers the outer surfaces of the leaf for protection 
  • The upper epidermis is transparent - this allows light to pass through to the photosynthetic cells below

  
• What is the waxy cuticle, and what is its function

  • The upper epidermis is covered with a thin layer of oily material , called the waxy cuticle 
  • The waxy cuticle reduces the evaporation of water from the surface of the leaf - this helps prevent the plant from drying out

  
• What is the stomata and guard cells, and what is their function

  • The lower epidermis has tiny pores called stomata  
  • Stomata allow carbon dioxide to enter the leaf , allow oxygen to leave the leaf and control the amount of water vapour that can pass out of the leaf -(they control the diffusion of gases in and out of the leaf)
  • On either side of the stomata are the guard cells (with chloroplasts) - they can open and close the stomata 
  • In most plants, the stomata are mainly found on the bottom surface of the leaf - this means that the sun does not shine directly on them , reducing water loss

  
• What is the palisade mesophyll, and what is its function

  • At the top of the leaf , you can find the palisade mesophyll 
  • The palisade mesophyll consists of palisade cells 
  • Palisade cells are packed full of chloroplasts (which are close to the top of the leaf to to trap maximum sunlight) 
  • Chloroplasts contain chlorophyll which absorbs the light energy needed for photosynthesis ,
  • So the palisade mesophyll is the main site for photosynthesis

  
• What is the spongy mesophyll

  • The spongy mesophyll can be found underneath the palisade mesophyll 
  • The spongy mesophyll is full of air spaces
  • These allow gases to diffuse 
  • They allow carbon dioxide to diffuse from the stomata , through the spongy mesophyll ,to the palisade cells 
  • The allow oxygen to diffuse from the palisade cells , through the spongy mesophyll to the stomata

  
• What is the function of xylem tissue / xylems vessels

  • Xylem tissue transports water through the plant , from the roots to the stem and leaves - some of the water is used for photosynthesis
  • Xylem tissues transports dissolved mineral ions - these include magnesium which is used to make chlorophyll 
  • Xylem tissue also supports the plant

  
• What is the function of phloem tissues

  • Phloem tissue transports dissolved sugar produced by photosynthesis from the leaves to the rest of the plant 
  • The sugars can be used immediately e.g. glucose is used in respiration 
  • The sugars can also be stored , for example as starch 
  • The movement of sugars and other molecules through phloem tissue is called translocation

  
• What is the function of the meristem tissue

  • Meristem tissue is found at growing tips e.g. shoots and roots 
  • Meristem tissue contain stem cells - these differentiate into different types of plant tissue (Meristem cells can produce new cells for growth)